Previous research has shown that the toxicities of single S (-) enantiomers levobupivacaine and ropivacaine to the cardiovascular and central nervous systems are weaker than a racemic mixture of S (-) and R (+) enantiomers such as bupivacaine. In this study, we investigated effects of levobupivacaine, ropivacaine, bupivacaine and R (+) bupivacaine on excitatory synaptic inputs to spinal dorsal horn neurons evoked by dorsal root stimulation, and on action potentials (APs) in dorsal root ganglion (DRG) neurons generated by the dorsal root stimulation. In the spinal dorsal horn, levobupivacaine reversibly suppressed the amplitude of monosynaptic Aδ and C fiber-evoked EPSCs. However, Aβ fiber-evoked EPSCs were slightly inhibited in amplitude at the same concentration. On the other hand, bupivacaine equally suppressed those of the three fiber-evoked EPSCs. These local anesthetics did not change the frequency and amplitude of miniature EPSCs. In DRG neurons, APs were reversibly inhibited in amplitude by the local anesthetics. Half-maximum inhibitory concentrations (IC₅₀) of bupivacaine and R (+) bupivacaine were almost equal on Aβ , Aδ and C neurons. On the other hand, IC₅₀ of levobupivacaine and ropivacaine on Aδ and C neurons were lower than that on Aβ neurons. The present results suggest that pure S (-) enantiomers especially levobupivacaine effectively inhibits noxious transmission to the spinal dorsal horn by the blockade of AP conduction through C and Aδ fibers. [J Physiol Sci. 2006;56 Suppl:S180]

View full abstract

BACKGROUND For millenniums, medicinal herbs have been used to alleviate pain because pain control is human eternal issue. We have also tested various herb extracts in search of active ingredients capable of relieving pain, particularly when it is heat-induced. Simultaneously as pain perception is very complex and widely varies among individuals, we have originally developed an experimental protocol to be able to induce equivalent pain intensity. METHODS A double-blind, placebo controlled, cross-over study was performed on volunteers to compare the pain felt when a heated copper coin was placed on their skin 10 minutes after the application of green tea extract, that have never been tested, or placebo transdermally. The degree of pain that each volunteer felt was then measured on a Visual Analogue Scale <VAS >. RESULTS Heat-induced pain was significantly reduced by the application of green tea extract. Particularly, the pain suppressive effect was more visible with increasing pain though green tea extract never cause numbness at the applied area. CONCLUSION Our results suggested that green tea extract has original functions to ease heat-induced pain, even when applied for a short period prior to the painful experience. The extract can be broadly and safely used in the pain-control or aesthetic business, differently from local anesthesia. [J Physiol Sci. 2006;56 Suppl:S181]

View full abstract

<Objectives> The aim of present study is to elucidate the underlying neuronal mechanism of the change in trigeminal nociceptive transmission with advancing age. <Methods> The adult (8-12 months old) and aged (30-12 months old) rats were injected with 10 mM capsaicin into the right whisker pat under adequate anesthesia. In addition, other adult and aged rats were injected capsaicin into the right whisker pat at 20 min after the naloxone administration (1.2 mg/kg, i.v.) in order to study the involvement of descending modulation system on trigeminal nociception in aged rats. They were perfused at 5 min after capsaicin injection. The whole brain was removed, and then 30 μm thick serial sections were made. We analyzed the change in pERK-LI expression in the medulla and the upper spinal cord of adult and aged rats. <Results> A large number of pERK-LI cells were expressed in the superficial laminae of the ipsilateral trigeminal subnucleus caudalis (Vc) and C1 of the spinal cord in each rats. A few pERK-LI cells were observed in the paratrigeminal nucleus bilaterally in the adult and aged rats. The expression pattern of pERK-LI cells in Vc/C1 was not difference between adult and aged rats. After the naloxone administration, the number of pERK LI cells in the ipsilateral Vc/C1 in the adult rats was significantly larger than that of aged rats. <Conclusions> These findings suggest that the advancing age may lead to the dysfunction of descending pain modulation system as well as ascending system, resulting in the abnormal pain sensation in aged rats. [J Physiol Sci. 2006;56 Suppl:S181]

View full abstract

Clinically, it is known that the incidence of chronic pain is much lower in children than in adults. This low-incidence may disclose some important factors to develop chronic pain in the adulthood. In this study, we examined whether chronic pain would be induced in child rats, using a chronic pain animal model we previously developed. Lipopolysaccharide (LPS: 2 mg/kg) and 6% hypertonic saline were injected into the unilateral gastrocnemius muscle of rats. The treatments were done in 3-week-old rats (T-3w) and 9-week-old rats (T-adult). We measured changes in the pain behaviors (von Frey test: VFT) at the bilateral plantar surface, the circumference of the calves, and the body weights. Non-treated age-matched control group was also measured. Pain behavior increased and lasted over 10 weeks in T-adult. On the contrary, in T-3w, pain behaviors did not last and decayed after post-treated two weeks. The responses to LPS were smaller in T-3w than in T-adult. In the normal condition, sensitivity to VFT was higher in 3-week-old rats than in 9-week-old rats. In child rats, it was indicated that chronic pain was hard to occur. It is suggested that the developments of nervous and immune systems may be important in onset and maintenance of chronic pain. [J Physiol Sci. 2006;56 Suppl:S181]

View full abstract

Some clinical reports demonstrate that zinc deficiency brings about taste disturbance. But there are very few reports about behavioral responses in zinc deficient animals. In the present study, therefore, we investigated whether or not zinc deficient rats could discriminate qualities of four basic taste stimuli by using the conditioned taste aversion paradigm. As the zinc deficient animals, male Wistar rats fed zinc deficient diet during 5 weeks after the weaning period were used. When these rats were subjected to aversive conditioned to one of the basic taste stimuli, any animals could acquire the conditioned taste aversion, and they never generalized to other stimuli. This result suggests that zinc deficient rats have the ability of the discrimination of the taste qualities. [J Physiol Sci. 2006;56 Suppl:S181]

View full abstract

Frog taste discs consist of morphologically and physiologically diverse types of cells. Recently, Suwabe and Kitada have demonstrated the properties of voltage-gated inward currents of type Ib, type II and type III cells in frog taste discs. However, little is known about the properties of outward currents of these cells. To investigate the properties of outward currents of morphologically identified cells, patch clamp technique was used to make recordings from taste cells in vertical slices of taste disc. Cell types were identified by staining with Alexa Fluor 488 hydrazide in a pipette. We recorded voltage-gated potassium outward currents from all recorded type Ib, II and III cells under the sodium-free Ringer perfusion. Peak amplitudes of outward currents of type Ib and III cells were significantly larger than that of type II cells. Outward currents were composed of delayed rectifier current, transient potassium currents and calcium activated potassium currents. Type Ib and II cells exhibited delayed rectifying potassium currents and transient potassium currents. Type III cells exhibited all three types of outward potassium currents. Calcium activated potassium currents of type III cells were sensitive to apamin and charybdotoxin. These observations demonstrate that the properties of potassium currents are different among cell types and suggest that the roles in taste reception and transduction of each cell types may differ. [J Physiol Sci. 2006;56 Suppl:S182]

View full abstract

Application of bitter substances and some salts to the tongue elicits phasic taste responses in the frog glossopharyngeal nerve. However, it is not known whether there are multiple taste receptor sites in the phasic components. In the present study, cross-adaptation was carried out by varying concentrations of bitter substances (quinine-HCl, caffeine, theophylline and denatonium) and salts (NaCl and choline Cl) in a wide range. The peak magnitude of the integrated responses of the glossopharyngeal nerve to taste stimuli in the frog (Rana catesbeiana) were measured. The response to caffeine after quinine was decreased with increasing concentrations of quinine applied first and reached the spontaneous level, while that to theophylline and denatonium after quinine was decreased to 60-70% of the original level. Responses to NaCl and choline Cl were scarcely affected after adaptation of quinine. The results obtained suggest that quinine and caffeine stimulate the same receptor site and that theophylline and denatonium stimulate receptor sites that are different from the receptor site responsible for quinine response although there exist receptor sites stimulated commonly by bitter substances. It is also suggested that quinine and salts such as NaCl and choline Cl stimulate different receptor sites. [J Physiol Sci. 2006;56 Suppl:S182]

View full abstract

We have shown that distilled water (DW) applied to the pharyngolaryngeal region is effective for elicitation of swallowing reflex, but NaCl solutions reduced the effect of DW. However, little is known about role of taste in swallowing reflex in humans. In the present study, we examined how taste stimulation of the tongue is involved in swallowing reflex in humans. Each subject was instructed to repeat swallowing as fast as possible. In dry swallowing without a supply of fluid, the time between the first and 6th swallowing (the dry swallowing test time) was measured. Then, taste solutions were delivered to the anterior tongue through a fine tube at a slow rate (0.2 ml/min). In taste stimulation, the intervals between two consecutive swallowings in a test (swallowing intervals) were measured. The effect of Na salts taste stimulation on swallowing reflex appeared only in subjects who showed long dry swallowing test time (>60 sec). That is, swallowing intervals induced by 0.15 M NaCl and 0.15 M Na acetate were much shorter than those by DW, 0.15 M KCl and olive oil. While, the effect of Na salts taste stimulation on swallowing reflex did not appear in subjects who showed short dry swallowing test time (<55 sec). The present study suggests that salty taste is effective for swallowing initiated voluntarily. Since the effect of Na salts appeared only when swallowing intervals are long, it is also suggested that excitation of sodium-taste receptors affects swallowing center in brain stem slowly. [J Physiol Sci. 2006;56 Suppl:S182]

View full abstract

In the present study, we investigated whether oral capsaicin affects the taste-evoked neuronal activities in the brainstem gustatory centers, the nucleus of the solitary tract of the medulla (NTS) and parabrachial nucleus of the pons (PBN), in the rat by using c-fos immunohistochemistry. Taste stimuli used were as follows: 0.2 M NaCl, 2 mM quinine-HCl, 0.2 M NaCl mixed with 330 μM capsaicin, and 2 mM quinine-HCl mixed with 330 μM capsaicin. Rats were chronically implanted with oral cannula and presented with these test stimuli for 10 minutes (500 μl/min). Application of either NaCl or quinine alone induced significant Fos-like immunoreacitivity (FLI) both in the waist and lateral areas of PBN. It has been reported that the neurons are responsive to NaCl or quinine in the waist and lateral areas, respectively. Combined application of capsaicin with NaCl or quinine, however, significantly reduced FLI in the waist area in PBN compared with FLI induced by NaCl or quinine by itself, whereas addition of capsaicin did not affect FLI in the lateral area of PBN. Furthermore, combined application of capsaicin with quinine reduced FLI in the gustatory portion of NTS compared with the FLI evoked by quinine alone. These results suggest that Capsaicin affects neuronal activity in subnuclei of the PBN differentially. These inhibitory effects of capsaicin on taste neuron can correlate with capsaicin-induced suppression of taste perception in humans. [J Physiol Sci. 2006;56 Suppl:S182]

View full abstract

It is reported that T1r2/T1r3 heterodimer plays a role as a sweet taste receptor. Mice lacking T1r3 showed no preference for artificial sweeteners and had diminished but not abolished behavioral and nerve responses to sugars, suggesting that T1r3-independent sweetener binding site also exist in taste cells in mice. However, the numbers and functions of ligand binding sites on T1r2/T1r3 (and/or other sweet receptor) remain largely unknown. In this study, in order to predict the number of sweetener binding site in human, we measured sensitivity thresholds to various sweet taste substances [sucrose, glucose, fructose, saccharin, aspartame, acesulfame-K, glycine, D-phenylalanine, D-tryptophan and L-proline] in human subjects and examined the qualitative similarities among these sweeteners by using a hierarchical cluster analysis. We also used Gymnemic acid and γ-cyclodextrin, which selectively inhibits sweet responses and reduces the inhibitory action of it in human. The ten sweet compounds were classified into five groups [(1) sucrose, glcose and fructose, (2) saccharin, aspartame, acesulfame-K and glycine, (3) D- phenylalanine, (4) D- tryptophan, (5) L- proline]. Four and two single nucleotide polymorphisms with amino acid substitution were detected in T1r2 and T1r3, respectively. These results suggest that there may be at least five different binding sites in human sweet receptor system. The individual differences in sweet sensitivities may be due to these single nucleotide polymorphisms. [J Physiol Sci. 2006;56 Suppl:S183]

View full abstract

We investigated if the changes in gustatory and olfactory thresholds (G-th and O-th) in the process of chemotherapy affect food intake in patients with hematopoietic tumor. 32 patients were studied after obtaining informed consent. Measurements of G-th and O-th, the amount of food intake (AFI) and questionnaires were carried out before the initiation of chemotherapy (before), on the third day (3rd) and on the seventh day (7th) during chemotherapy, and 2 weeks after the termination of chemotherapy (after). AFI was remarkably decreased at 3rd and was recovered at after. The patients, who experienced alterations of gustatory and olfactory sensations, were increased in number at 3rd. The% change of G-th for salt and bitter as basis by that at before was significantly elevated at 3rd, whereas that for sweet was significantly decreased at after (P<0.05). The% change of O-th for detection was significantly decreased at 7th ; however, O-th for recognition was significantly increased in female (P<0.05). Multiple regression analysis revealed that the increase in G-th for salt significantly decreased AFI and that the decrease in O-th for detection of β-phenyl ethyl alcohol significantly decreased AFI. The averaged O-th for recognition reciprocally correlated with AFI in female patients (r = -0.34, P<0.05). Alterations in G-th and O-th in the process of chemotherapy affected AFI in the patients with hematopoietic tumor. [J Physiol Sci. 2006;56 Suppl:S183]

View full abstract

Previous electrophysiological studies have shown that the chorda tympani nerve contains two types of NaCl-responsive fibers. One, N-type fiber, narrowly responds to NaCl and the NaCl response is strongly inhibited by amiloride, a blocker of the epithelial sodium channel (ENaC). The other type (E- or H-type) has broad responsiveness to electrolytes and shows almost no amiloride sensitivity. These fibers may receive input from amiloride sensitive and insensitive taste receptor cells. In this study, we examined NaCl responses of mouse fungiform taste cells in isolated taste bud and amiloride sensitivity of them. In our experiments, taste stimuli were applied only to the pore side of an isolated taste bud, and responses of one single cell of the bud to the stimuli were recorded from its basolateral side of the membrane as increase in firing frequency. The response to apical NaCl stimulation was recorded in some fungiform taste cells. These responses were concentration dependent. Amiloride mixed with apical NaCl solution inhibited NaCl responses in some taste cells [amiloride sensitive (AS) cells] but not in others [amiloride insensitive (AI) cells]. AI cells responded to other electrolytes such as KCl and HCl. These results suggest the existence of at least two types of NaCl sensitive cells, AS and AI cells. N- or E-type fiber may selectively innervate AS or AI cells respectively. [J Physiol Sci. 2006;56 Suppl:S183]

View full abstract

The effect of amiloride on responses of the chorda tympani (CT) nerve to NaCl differs among mouse strains. For example, in C57BL mice, amiloride suppresses NaCl responses to about 50% of control, whereas no clear amiloride inhibition was observed in 129 mice. The 129 inbred strain, however, has a number of substrains derived mainly from two major parent stocks, 129/J and 129/SvJ. Recently, 129X1/SvJ (formerly 129/SvJ) mice are reported to differ from the 129P3/J (formerly 129/J) strain by 25% of sequence length polymorphisms. In the current study, therefore, we examined possible substrain difference between 129P3/J and 129X1/SvJ in the amiloride sensitivity of the CT response. The results suggest that amiloride is effective in 129X1/SvJ mice. CT responses to 0.3 M NaCl were significantly suppressed by amiloride at the concentration of 10 µM or more, and the inhibition reached the maximum (about 50% of control to 0.03-0.3 M NaCl) at 100 µM. In contrast, no such amiloride inhibition was evident in 129P3/J mice. These results suggest that amiloride-sensitivity of NaCl responses differ among 129 substrains. [J Physiol Sci. 2006;56 Suppl:S183]

View full abstract

TRPM5, a member of the transient receptor potential channel(TRP), is related with taste cell responses to sweet,umami and bitter compounds. Activation of TRPM5 occurs downstream activation of G-protein-coupled taste receptors and is proposed to generate a depolarizing potential in taste receptor cells. Mice with a partial deletion of the TRPM5 protein, which retained intact the amino terminal portion, have been shown to be unresponsive to bitter, sweet, umami tastes. To avoid any confounding effects of this amino terminal fragment, we generated knockout mice null for TRPM5 protein. In previous study, this TRPM5 knockout mice showed reduced, but not abolished, responses to quinine hydrochloride in both nerve recording and two-bottle preference test. In this study, in order to examine behavioral responses to quinine hydrochloride in TRPM5 knockout mice in further detail, we used a short-term (10s) lick test for measurement of consumption of its solutions. TRPM5 knockout mice showed significantly reduced responses to 0.1-10 mM quinine hydrochloride, but not abolished at high concentrations (3.0,10mM) of it, although no such difference was evident in response to DW. These results may be almost consistent with previous nerve recording and two-bottle preference test, suggesting that there may be TRPM5-dependent and independent pathways in signal transduction mechanism for quinine hydrochloride.. [J Physiol Sci. 2006;56 Suppl:S184]

View full abstract

TRPV2, a member of the transient receptor potential family, has been isolated as capsaicin-receptor homolog and is thought to respond to noxious heat. Here we show that TRPV2 mRNA is expressed in GAP43-positive immature and OMP-positive mature olfactory sensory neurons. Intensive TRPV2 immunostaining was observed at the olfactory axon bundles in olfactory mucosa. TRPV2-positive labeling was preferentially found in the olfactory nerve layer in the olfactory bulb. Furthermore, we demonstrated that cell bodies of olfactory sensory neurons settled in cell layer expressing TRPV2 mRNA are insulin-like growth factor (IGF)-I receptor-immunopositive. The increase in intracellular calcium levels in olfactory neurons isolated from adult olfactory mucosa was found to be induced by the application of IGF-I, and was not observed in the presence of SKF96365, an inhibitor of TRPV2. In embryonic stages, TRPV2 immunoreactivity was observed on axon bundles of developing olfactory neurons in the nasal region starting from 12.5 days of gestation and through fetal development. Observations in this study indicate that TRPV2 localizes to growing olfactory axons and contributes to the elevation of intracellular calcium levels in olfactory neurons in response to IGF-I. [J Physiol Sci. 2006;56 Suppl:S184]

View full abstract

The olfactory epithelium is innervated by efferent neurites and the olfactory receptor cells express muscarinic receptors. These observations raise the possibility that acetylcholine could affect odor responses of the olfactory receptor cells. Here we investigated the effect of acetylcholine on newt olfactory receptor cells, using the whole-cell version of the patch-clamp technique. Under current clamp condition, bath-applied 100 μM carbachol, an agonist of acetylcholine receptor, lowered spike threshold from 5.3 ± 0.6 pA to 3.8 ± 0.5 pA. Furthermore, the maximum spike frequency was increased from 9.1 ± 1.4 spikes/s to 11.0 ± 1.3 spikes/s by carbachol. These results suggest carbachol directly modulates spike generation in ORCs. Under voltage clamp, condition carbachol increased the peak amplitude of a voltage-gated T-type calcium current by 39% and sodium current by 32%. However, carbachol did not change the amplitude of an L-type calcium current or a delayed rectifier potassium current significantly. An antagonist of muscarinic acetylcholine receptor, atropine, blocked the enhancement by carbachol of sodium current, suggesting that carbachol modulates sodium current via the muscarinic receptor. Because T-type calcium current is known to lower the threshold in olfactory receptor cells, we suggest that acetylcholine, which is released from efferent fibers, may enhance odorant sensitivity by lowering the threshold of spike generation in olfactory receptor cells. [J Physiol Sci. 2006;56 Suppl:S184]

View full abstract

Pheromones are detected by the vomeronasal organ, but precise natures of detection at the cellular level are poorly understood. To characterize cellular aspects of receptivity to pheromones, we investigated responsiveness of the vomeronasal neuron (VRN) to pheromone–containing materials in the cell culture. As previously reported, VRNs in culture form a spherical structure with a central cavity, referred to as a vomeronasal pocket (VNP). We also reported the maturation of each VRN in the VNP was induced by co-culture with dissociated accessory olfactory bulb (AOB) neurons. Using this co-culture system, we applied charged compounds in mouse urine iontophoretically into the cavity of VNP using microelectrode and analyzed VNP response by a Ca²⁺ imaging method with or without cultured AOB cells. When urine compounds were ejected into the VNP co-cultured with AOB cells with a current of 1-2 μA, subpopulation of VRNs clearly showed long-lasting Ca²⁺ increases. Such Ca²⁺ increases were not observed without AOB neurons and injections of a current below 5 μA alone had no effect. Moreover, a western blotting analysis showed the expression of some putative pheromone receptors in the VNP was induced and increased with days in co-culture. These results indicate that VRNs result in expressing pheromone receptors and then acquire responsiveness to compounds in urine by interacting with AOB neurons in co-culture. [J Physiol Sci. 2006;56 Suppl:S184]

View full abstract

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels contribute to physiological functions such as regulating cell excitability, eliciting rhythmic activities and so on. Four subtypes (HCN1-4) have ever been identified. We previously cloned HCN4, which shows the slowest activation kinetics and the profound modulation by cAMP. To investigate the physiological roles of HCN4, we have generated a transgenic (Tg) mouse, in which tetracycline repressor protein (TetR) is expressed under the control of HCN4 promoter. This mouse was crossbred with another Tg mouse, in which GFP expression is regulated by TetR. Thus generated Tg mouse expressed GFP in HCN4-expressing cells. We observed on this Tg mouse that GFP fluorescence and HCN4 immunoreactivity (HCN4-IR) were colocalized in the cerebrum, the sino-atrial node, the taste buds and the retina; all of which were previously confirmed to express HCN4. The olfactory receptor neurons (ORN) expressed GFP, where only HCN current (Ih) had been formerly reported, however, its physiological roles remain unknown. HCN4-IR was detected in the olfactory knobs, the soma and the axon bundles of the ORN. We have further performed immunohistochemistry to determine the expression patterns of the other HCN subtypes in the ORN. Also electrophysiological studies are in progress to analyze the physiological properties of HCN channels in the ORN. [J Physiol Sci. 2006;56 Suppl:S185]

View full abstract

It is generally believed that the main olfactory system processes common odors and the vomeronasal system is involved mainly in the detection of pheromones. The accessory olfactory bulb (AOB) is the first relay station in the vomeronasal system. To investigate how pheromonal information is processed in the rat AOB, we obtained high resolution mapping of pheromone-induced activation by optical imaging of intrinsic signals. Urine collected from male or female rats were used as test substances. Application of volatile components in the male urine (2-5%) with a syringe mainly activated the anterior AOB (aAOB), whereas female urine-induced activation was observed in both the aAOB and caudal part of the AOB in the male rats. In the female rats, urine-induced activation occurred mostly in the aAOB. Application of non-volatile urine components was performed by putting the nostrils contact with filter paper moistened with urine (3-5%). Either male or female urine induced mainly activation in the posterior AOB (pAOB) and to a lesser extent in the aAOB. In contrast, urinary responses were also observed in a few of glomeruli of the main olfactory bulb. The threshold for urine-induced activation in the glomeruli, however, was approximately 50%, which was higher than that obtained in the AOB (1%). These results provide the evidence that the aAOB is activated by volatile components in male or female urine, whereas the pAOB is activated by non-volatile components. [J Physiol Sci. 2006;56 Suppl:S185]

View full abstract

The processing of spectral and temporal information in the core fields of the left and right auditory cortices of the guinea pig was investigated using optical imaging with a voltage-sensitive dye (RH795). 23 guinea pigs were anesthetized with ketamine (80mg/kg) and xylazine (40mg/kg). In order to compare the tonotopical organization between the left and the right auditory cortex, optical imaging patterns to tone stimulation at 2, 4, 8, 16 kHz were recorded from core auditory fields (primary (AI), dorsocaudal (DC) fields) of both sides and tonotopy maps were made. In the same animal, the tonotopic organization of AI and DC of one side was more clear than the other side. In 65% animals, the distance between 2kHz and 16kHz isofrequency bands in the left AI was longer than that of the right AI, whereas that of left DC was shorter than that of the right DC. To compare the temporal properties, click or noise trains were presented at different repetition rates (4-20 Hz). Repetition rate transfer functions (RRTF) in field AI were low-pass showing a sharp drop-off in evoked activity per click or noise above 10 Hz but RRTFs in field DC were band-pass with the peak of 8 or 10 Hz. The cut-off frequencies of RRTF in the left cortex were the same as those in the right cortex but the slopes of the RRTF in the left cortex were sharper. We discuss the functional difference between the left and right auditory cortices of guinea pigs. [J Physiol Sci. 2006;56 Suppl:S185]

View full abstract

We have developed an optical recording system to detect neural activity for a long time from 1020 sites of the cerebral cortex. But its signal-to-noise (S/N) ratio was insufficient for analyzing the neural response from single sweep recordings. Since there is no way to remove shot noise, to improve the S/N ratio for detecting the neural activity without averaging, we had to increase the excitation light intensity and enlarge signal size. For this purpose, we introduced a new illumination device using optic fiber bundle. Light from a halogen-tungsten lamp was rendered quasi-monochromatic by a band pass filter, converged to an optic fiber bundle and illuminated the preparation, which had been stained with a voltage-sensitive dye (RH414) in advance. A tandem lens system formed a magnified real image of the preparation, and the fluorescent light intensity was detected with a photodiode array. Neural responses to the electrical foot stimulation were monitored optically in the rat somatosensory cortex with this improved system. Among a large artifact derived from pulsation, we could detect neural response in a single sweep. Furthermore, with using digital subtraction, aligned at ECG, of a control record without stimulation, we succeeded in greatly reducing the pulsation artifact leaving the optical signal related to neural activity fairly intact. In this way, we could apparently detect cortical neural responses in vivo with a sufficient S/N ratio for analyses on the basis of single sweep recordings. [J Physiol Sci. 2006;56 Suppl:S185]

View full abstract

Mammalian inferior colliculus(IC) is an integrative auditory processing center of the midbrain. IC has complex neural circuits and is majorly devided into two regions: central nucleus (CIC, tonotopic region) and dorsal and external cortices (non-tonotopic region). By the focal injection of neuronal tracers into IC and GAD immunohistochemical technique, we investivated the characteristics of the local circuits of IC. The results show that the left and right ICs have characteristic connections; 1) the left and right CIC-CIC, cortices-cortices have strong connections(about 70% of total connections). 2) the CIC-CIC connections are symmetric and they are majorly excitatory (98%). We further analyzed the characteristics of the labeled local circuits by in vivo and in vitro electrophysiological techniques. [J Physiol Sci. 2006;56 Suppl:S186]

View full abstract

A large positive potential in the endolymph, named the endocochlear potential (EP) has been considered to occur at cochlear stria vascularis and this DC potential is essential for the transduction of sound by hair cells. In this study, we examined the effect of the intracellular Ca²⁺ concentration ([Ca]_i) in the endolymphatic surface cells on EP by using conventional and Ca²⁺-sensitive microelectrodes. 1) A large increase in the Ca²⁺ concentration in the endolymph up to 10⁻³ M with a decrease in EP from +70 mV to +20 mV was induced by transient asphyxia (100 sec). 2) The application of 300 μM EGTA-tetraacetoxymethyl ester (EGTA-AM) with 10 mM EGTA-containing solution or 3 μM nifedipine to the endolymph produced a slight increase in EP and suppressed significantly an initial decrease in EP induced by transient asphyxia. 3) The administration of 10 μM Bay K 8644, an activator of L-type Ca²⁺ channels, to the endolymph produced a gradual decrease in EP. 4) Perilymphatic administration of 1 mM EGTA-AM or 30 μM nifedipine caused no significant suppression of the asphyxia-induced decrease in EP. These results suggest that transient asphyxia-induced decrease in the EP is triggered by an increase in [Ca]_i with the activation of L-type Ca²⁺ channel in endolymphatic surface cells. [J Physiol Sci. 2006;56 Suppl:S186]

View full abstract

Interaural time difference (ITD) is an essential cue for the sound source localization along the horizontal axis. In birds, ITDs are first calculated in neurons of nucleus laminaris (NL) by detecting the coincidence of binaural synaptic inputs. Previously, we recorded neurophonic-potentials (NPs) in NL of anesthetized chicken, and pharmacologically demonstrated that NPs originated from EPSCs and action potentials in NL. Because of the robust NPs, recording single unit from NL is difficult. However, occasionally recorded NL unit activities showed the same properties as NPs in the sensitivity to frequency and ITD of stimulus sound. Plot of NL activity against ITDs (ITD tuning curve) has peaks and troughs alternately, corresponding to the favorable and unfavorable ITDs. In the high- and middle-best frequency (BF) neurons, the increase of sound intensity shifted the whole ITD tuning curve upward, but in the low-BF neurons, the troughs of ITD tuning curve was depressed compared to the peaks, creating a large contrast between peaks and troughs. This proposes the effect of inhibitory input from superior olivary nucleus (SON). For testing this hypothesis, we lesioned SON electrolytically, and recorded well-isolated and stable single-unit activities with a loose patch technique. After lesioning SON, the whole ITD tuning curve shifted upward even in the low BF neuron when sound intensity was increased. This might support the idea that inhibitory input from SON improves coincidence detection in NL. [J Physiol Sci. 2006;56 Suppl:S186]

View full abstract

Recent our histochemical study has shown that the sensory nerves travel in both the sympathetic and parasympathetic nerve routes supplying to the submandibular gland in the rat. In the present study we analyze afferent neural activities in the peripheral cut ends of the sympathetic and parasympathetic nerve branches innervating the submandibular gland in urethane-anesthetized rats. The following results were obtained: 1) The afferent activity could be recorded from both sympathetic and parasympathetic routes; 2) both afferents had no spontaneous activities, but responded to mechanical pressure applied onto the gland; 3) when back pressure was applied from the main excretory duct by infusion of saline, both afferents showed tonic impulse discharges at pressure of higher than 100 mmHg; 4) the threshold pressure was little lower than the maximal secretory pressure measured by electrical stimulation of the parasympathetic secretory nerve (the chorda tympani); 5) there is no differences in the threshold pressures between afferents in the sympathetic and parasympathetic nerve routes; 6) when Bradykinin was infused from the duct, the afferent nerve discharged vigorously. Previous histochemical studies show that substance P and CGRP-containing nerves considered as possible afferent fibers were identified frequently around small ducts and blood vessels. We speculate that the afferent activity may relate to monitoring of excessive pressure of the fluid secretion and blood flow, or to pain due to salivary stone. [J Physiol Sci. 2006;56 Suppl:S186]

View full abstract

Epithelial tight junction forms the barrier with ion moving pathway. Paracellular ion permeability is modified by expression pattern of claudins, a component of tight junction, but the mechanism of its regulation and physiological implication is unknown. In renal epithelial A6 cells, hypotonicity induces Na⁺ transport via the transcellular pathway. However, the effect of hypotonicity on paracellular ion permeability is unknown. To study the effect of hypotonicity on paracellular ion permeability, we measured currents in A6 cells. Basolateral but not apical hypotonicity markedly increased the paracellular conductance (Gp) and current (Ip) from apical to basolateral side, indicating that the basolateral hypotonicity increases the paracellular permeability to more Na⁺ than Cl⁺. Furthermore, replacement of NaCl with sucrose in the basolateral solution did not increase Gp or Ip. Furthermore, under the condition that Na⁺ replacement with NMDG, basolateral hypotonicity increased Gp but not Ip. Under the condition that Cl⁺ replacement with gluconate, basolateral hypotonicity did not increase Gp or Ip. These observations indicate that basolateral hypotonicity and paracellular Cl⁺ movement increase paracellular permeability and induce more conductance for Na⁺ than Cl⁺ and NMDG. Based on these observations, we conclude that the hypotonicity-induced changes of paracellular ion conductances stimulate Na⁺ reabsorption in the renal A6 cells via not only transcellular but also paracellular pathway. [J Physiol Sci. 2006;56 Suppl:S187]

View full abstract

Saccade accuracy, a prerequisite for efficient collection of visual information, is maintained by an adaptive mechanism that modifies saccade amplitude. Previous studies show that adapting saccade amplitude induces correlated changes in neuronal activity in the cerebellar fastigial oculomotor region (FOR). In the present study we recorded the activity of saccade-related inhibitory burst neurons, IBNs, which may relay FOR signals to motoneurons. We examined if IBN activity changed during adaptation and could contribute to it. We tested 44 IBNs during amplitude-decreasing adaptation of contraversive (off-direction) saccades. Thirty-seven IBNs fired, at least occasionally, for off-direction saccades. The remaining 7 exhibited no spikes for off-direction saccades. We used intrasaccadic target steps to adapt the gain of saccades to 10° target steps in the off-direction. Many IBNs which exhibited off-direction spikes showed an increasing number of spikes (23/37), a shortening burst lag (13/37) or both (12/37) as adaptation progressed. IBNs with no off-direction spikes showed no spike activity after adaptation. These results suggest that the adaptation-related changes in IBN activity decrease the size of contraversive saccades by decreasing the size of the burst in motoneurons. [J Physiol Sci. 2006;56 Suppl:S187]

View full abstract

To examine coordinate frames for FEF pursuit signals, we first compared preferred directions during head-fixed upright position and static 40° roll tilt. Preferred directions of 30 pursuit neurons were shifted minimally during static tilt, indicating that their coordinate frames are not world-centered. In the head-fixed condition, head-centered- and body-centered- coordinates are not dissociated. To dissociate them, the monkeys were allowed to rotate the heads horizontally on the upright stationary body for pursuit of a reward feeder and laser spot. Responding neurons during gaze (eye-in-space)-pursuit were tested for eye-pursuit of the spot while the feeder was stationary and head-pursuit of the feeder while the spot was stationary. Majority (61%) of 99 responsive neurons fired strongly for both eye- and head-pursuit even when gaze was stationary; the modulation during gaze-pursuit was linear sum of modulation during eye- and head-pursuit. Modulation during VOR cancellation induced by passive whole body rotation was not correlated with eye-pursuit modulation. These results suggest that these cells fired for body-centered coordinates. Minority (24%) was modulated during gaze- and eye- pursuit similarly but minimally during head-pursuit when gaze was stationary; modulation during VOR cancellation was correlated well with eye-pursuit modulation, suggesting that these cells fired for head-centered coordinates. Our results suggest that both body-centered and head-centered coordinates are present in FEF for processing eye-, head-, and gaze-pursuit signals. [J Physiol Sci. 2006;56 Suppl:S187]

View full abstract

The convergence eye movement is known as a disjunctive eye movement in which, typically, both eyes adduct symmetrically in the same time. But asymmetrical convergence also found in the natural condition. These asymmetrical convergence may reflect asymmetries of central control of convergence eye movement. The lateral suprasylvian (LS) areas are extrastriate cortices which receive visual information from V1. The LS has contralateral dominant receptive fields. The cat has convergence-related areas in the LS of both hemispheres. From the short latency regions of convergence-related area, symmetrical convergence was evoked but from convergence eye movements evoked from the long latency regions were asymmetrical. The convergence-related areas have neurons respond to approaching movement of a visual target. Cats (n=7) were trained to start convergence by an alarm signal (buzzer sound or combination of buzz and blinking of LED), preceding target movement by 4s. After training, ocular convergence was elicited by the alarm signal before target movement (predictive open-loop convergence) in 60% of trials. In two cats, we used training with obliquely approaching target. After training, asymmetrical anticipatory eye movements were observed. Based on these findings, related LS neuronal activities and results from lesion study, we will discuss the role of LS in asymmetry of anticipatory and visually-evoked convergence eye movement. [J Physiol Sci. 2006;56 Suppl:S188]

View full abstract

N-methyl-D-aspartate (NMDA) receptors are implicated in synaptic plasticity and learning in the hippocampus. In the cerebellar cortex, NMDA receptors are expressed in glanule cells and inhibitory interneurons, and the NMDA receptor dependent plasticity has been reported. However, physiological role of such synaptic plasticity remains to be investigated. Here we examined the role of NMDA receptors in the adaptive modification of optokinetic response (OKR adaptaion) as a model of cerebellar-dependent motor learning in mice. OKR adaptation was induced by sustained sinusoidal oscillation (0.4Hz, 6deg peak-to-peak) of a vertically striped screen around a mouse. The mutant mice deficient in NR2A/NR2C subunit failed to show the adaptive increase of OKR gain. Further, iontophoretic application of NMDA receptor antagonist (D-AP5) into the flocculus (the cerebellar cortical region implicated in the control of OKR) in wild type mice, suppressed the adaptive increase in the OKR gain. These results suggest that NMDA receptor dependent mechanisms in the cerebellar cortex are involved in motor learning. [J Physiol Sci. 2006;56 Suppl:S188]

View full abstract

On pointing or reaching movements, a target is usually in the peripheral visual field and a hand reaches toward the target after eyes moved to foveate the target. It has been suggested that a position of a remembered target for these hand movements is remapped in gaze-centered coordinates during eye movements. To investigate this remapping mechanism, we asked subjects to point a remembered target with eye-fixations. The subjects remembered a target with gazing at an initial fixation point (FP1) and moved their eyes to a second fixation point (FP2) after the target had been turned off, and pointed to the remembered target with gazing at the FP2. The following three task conditions were used: 1) the single fixation condition (SF), the FP2 appeared at the same position of the FP1 and a target was presented at the peripheral visual field; 2) the center of visual field condition (CVF), the FP2 appeared at the different position from the FP1 and a target was presented at the FP1; 3) the peripheral visual field condition (PVF), the FP2 appeared at the different position from the FP1 and a target was presented at the peripheral visual field. We assumed that the subjects calculated a sum of a FP1-target vector and a FP2-FP1 vector as a FP2-target vector (i.e., a gaze-centered remembered target position) and they had to estimate the target-FP1 and FP1-FP2 vector. The rates of miss-estimation of these vectors determined by results of the SF and CVF condition well explained results of the PVF condition. This study provides a plausible model of localization of a remembered target. [J Physiol Sci. 2006;56 Suppl:S188]

View full abstract

Repetitive exposures to the acceleration of the target velocity for a brief period immediately after the onsets of the eye movements adaptively modify the velocity of smooth pursuit. After we located monkey frontal pursuit areas by unit recording and microstimulation, we injected GABA_A-receptor agonist muscimol locally. Inactivation of frontal pursuit areas reduced velocities of smooth pursuit in both ipsi and contra -versive directions to the inactivated frontal eye field by 70%, and significantly depressed the adaptation of smooth pursuit velocity dependent on the sites of inactivation. These results suggest that the frontal pursuit areas are involved in the adaptation of smooth pursuit. [J Physiol Sci. 2006;56 Suppl:S188]

View full abstract

An important structure in the neural circuitry for saccadic gaze shift control is the midbrain's superior colliculus (SC). It has been proposed that the SC intermediate layer lies within a gaze feedback loop and generates an error signal specifying gaze position-error (GPE), the distance between target and current gaze positions. We investigated previously this feedback hypothesis, in cat, by briefly stopping head motion during large gaze saccades made in the dark. Firing frequency of a cell gradually increased to a maximum that just preceded the optimal gaze saccade encoded by the cell's position in the caudal SC. In "brake" trials, we demonstrated that the activity-level just preceding a brake-induced gaze plateau continued steadily during the plateau and waned to zero only near the end of the corrective saccade. In the present experiments, we tested descending axonal projections of the SC neurons on the motor map to the brain stem, using antidromic mapping technique. Stimulus currents were usually restricted to less than 30μ A. Some neurons were antidromically activated by the dorsal part of the midbrain and the reticular formation. The neural activity-level continued during the brake-induced gaze plateau. Discharge pattern reflected gaze trajectory perturbations. The data suggest that the cat's tecto-reticular cell probably lies in a gaze feedback loop. [J Physiol Sci. 2006;56 Suppl:S189]

View full abstract

To investigate the effects of thickening agents, which may reduce the risk of aspiration, on the swallowing threshold during food mastication, the physical properties of bolus immediately prior to swallowing during mastication of test food containing a thickening agent (xanthan gum) were measured in healthy ten adult participants (mean age 31 yrs). Two kinds of test food (test food C, boiled Koya-dofu as a control and test food X, boiled Koya-dofu containing 1% xanthan gum) were prepared. Each test food has a cubic shape (15×15×15mm). Physical properties of test food and the test food bolus collected from the oral cavity immediately prior to swallowing were measured by method of the texture profile analysis (double bite test). Texture parameters (hardness, adhesiveness, cohesiveness, gumminess) were obtained from the stress strain curve. The number of chewing strokes until swallowing during mastication of the X was significantly smaller than that during mastication of the C. Hardness, cohesiveness and gumminess of both the C and X boluses were significantly decreased during mastication. Adhesiveness of the X bolus was also significantly (p<0.05) decreased during mastication, but the adhesiveness of the C bolus was significantly (p<0.01) increased. Adhesiveness of the X bolus immediately prior to swallowing was significantly (p<0.001) higher than that of the C bolus. These results suggest that the decrease in adhesiveness of bolus may be a main factor in initiating the swallowing during mastication of solid food containing the thickening agent. [J Physiol Sci. 2006;56 Suppl:S189]

View full abstract

Effects of mastication on the jaw-opening reflex (JOR) were studied in awake rabbits. The JOR was evoked by unilateral low-intensity electrical stimulation of the inferior alveolar nerve either chewing or non-chewing side before (control) and during mastication. The entire masticatory sequence (from food intake to just before swallow) was divided into three functionally different masticatory periods (preparatory, rhythmic-chewing and preswallow periods) based on the jaw movements and the related activity pattern of the jaw muscles, and each chewing cycle in each period was further divided into jaw-closing and jaw-opening phases. Then amplitude of the JOR was compared 1) among the masticatory periods and 2) between the stimulation sides (i.e. chewing or non-chewing sides). Overall, the JOR was suppressed during mastication. Although the suppressive effect on the JOR did not differ between the stimulation sides, considerable differences were noted in the suppressive effect among the masticatory periods. During rhythmic-chewing and preswallow periods, the JOR was strongly suppressed in the jaw-closing phase (8 to 20% of the control), but the suppressive effect was phasically weakened (30 to 61% of the control) in the late part of the jaw-opening phase. On the other hand, such phase-dependent fluctuation in the suppressive effect was not observed during the preparatory period. The findings suggest that neural mechanisms modulating the JOR during the preparatory period may be different from other masticatory periods. [J Physiol Sci. 2006;56 Suppl:S189]

View full abstract

We examined whether the electrical stimulation of the superior laryngeal nerve (SLN) induces swallowing in an isolated brainstem preparation. We used in vitro brainstem preparations isolated either with or without the oro-facial and neck structure from 0-4 day-old Wistar rats. Neural activities were monitored from XII nerves as well as C4 ventral roots (C4 vr) with suction electrodes. Tongue EMG was monitored with wire electrodes. Movements of the peripheral structure were observed with a CCD camera system. Electrical stimulation of the SLN was applied through a suction electrode. In the preparation with peripheral structure, SLN stimulation induced the swallowing-like movements of the tongue and the larynx, involving the elevation of the tongue tip and anterior movement of the larynx. They corresponded to the tongue EMG with no concurrent activity in C4 vr, and were distinct from the spontaneous inspiratory activities in a burst shape. In the preparation without peripheral structure, SLN stimulation induced the short latency XII bursts whose shape was indistinguishable from the tongue EMG in the preparation with peripheral structure. The results demonstrate that the electrical stimulation of the SLN induces fictive swallowing in an isolated brainstem preparation as in vivo preparations. These preparations will be useful for the investigation of mechanisms underlying the central pattern generation of swallowing. [J Physiol Sci. 2006;56 Suppl:S189]

View full abstract

Nucleus prepositus hypoglossi (NPH) is involved in the velocity-position integration for horizontal eye movements. To clarify which types of neurons compose the NPH, we investigated membrane properties, such as afterhyperpolarization (AHP), responses to hyperpolarizing currents, and firing patterns, of NPH neurons using whole-cell patch clamp technique in rat brainstem slices. AHPs were classified into three types: AHP without a slow component, AHP with a slow component, and AHP with a slow component and an afterdepolarization. Responses to hyperpolarizing current pulses were classified into three types: time-dependent inward rectification, time-independent inward rectification, and no inward rectification. Firing patterns were classified into continuous-spiking neurons that exhibited repetitive firings with relatively constant interspike intervals (ISIs), late-spiking neurons that exhibited a delay in the generation of the first spike, and neurons exhibiting an extremely low firing rate. Continuous-spiking neurons were further divided into two types according to whether the first ISI was markedly longer than the second. Neurons exhibiting the long first ISI were designated as FIL neurons. Application of 100μM apamin abolished the long ISI of FIL neurons, suggesting that the long ISI is attributed to activation of SK-type Ca²⁺ activated K⁺ conductances. All these results suggest that the NPH consists of heterogeneous neuronal population with various membrane properties and these neurons contribute to the neural integrator. [J Physiol Sci. 2006;56 Suppl:S190]

View full abstract

I have previously reported that the subjects who did not move their head at all during chewing could always increase the maximum bite force (BF) by supporting their head. The purpose of this study is to investigate the functional role of lateral and dorsal neck muscles on the bite force production by the electromyographic (EMG) method. Fifteen adult volunteers participated in this study. The EMGs of the masticatory (MAS), the lateral neck (SCM) and the dorsal neck (TPZ) muscles were recorded with a pair of surface electrode. A bite stick with a strain-gauge transducer was used to measure the BF. The subject was asked to produce and maintain the BF at about 40% level of the voluntary maximum BF. There were close relationships between the BF and the EMGs of the MAS and the SCM. The dorsal head flexion elicited by contracting the TPZ decreases the BF as well as the EMGs of the MAS and the SCM. The tap stimulus to the muscle belly of the TPZ also decreases the BF. These results suggest that the lateral neck muscles as well as the masticatory muscles play an important role in the bite force production, and that the dorsal neck muscles, which function as the head stabilizer in the upright posture, control the above bite force producing muscles. [J Physiol Sci. 2006;56 Suppl:S190]

View full abstract

We studied pERK expression in the trigeminal spinal nucleus caudalis (Vc) of the rats with TMJ inflammation, in order to elucidate the underlying neuronal mechanism of the trigeminal chronic pain. CFA was injected in the TMJ under pentobarbital anesthesia (50 mg/kg, i.p.). Two weeks after CFA injection, passive jaw opening (JO) was applied to the TMJ inflamed rats for 5-30 min (JO distance: 4, 6 and 15 mm). The pERK expression was studied in the medulla and upper cervical spinal cord after JO. The face temperature was significantly increased 2-3 days after CFA injection and returned to the preoperative level 7 days after that. The pERK-like immunoreactive (LI) cells were observed in the dorsal portion of the trigeminal spinal nucleus caudalis (Vc) of the TMJ inflamed rats after JO. On the other hand, we could not observe any pERK-LI cells in naive rats after 4, 6 and 15 mm JO. The number of pERK-LI cells was increased following increase in the JO duration (5, 15 and 30 min) and JO distance (4, 6 and 15 mm). The increment ratio of pERK-LI cells in Vc was significantly larger in 15 mm JO group than 4 and 6 mm JO groups following different JO duration. These findings suggest that the hyperexcitability of nociceptive neurons in the dorsal portion of the Vc would be involved in the TMJ chronic pain following TMJ inflammation through the activation of the intracellular ERK cascade. [J Physiol Sci. 2006;56 Suppl:S190]

View full abstract

For arm movements, it is suggested that indirect corticomotoneuronal pathways, which are partly mediated by C3-C4 propriospinal neurons (PNs), have important roles as well as direct pathways. The purposes of the present study were to establish a procedure to quantify functions of PNs, and to examine left-right differences of the pathways by using the procedure. Surface electromyograms were recorded from the right or left biceps (Bi) muscle of right-handed normal human subjects (n=11), who all gave informed consent. During weak tonic voluntary contraction of the muscles, 1) electric stimulation of the ipsilateral ulnar nerve (wrist) alone, 2) transcranial magnetic stimulation (TMS) of the contralateral primary motor cortex alone, and 3) combined stimulation of both were delivered in pseudo-random order. Interstimulus intervals for the combined stimulation were set to 8.0-9.0ms (ulnar stimulation ahead). When appropriate stimulus strengths were selected, TMS-induced potentials in Bi were facilitated by combined ulnar stimulation. However, the facilitation was disappeared when strengthening ulnar stimulation and/or TMS. These were the case on both sides of all subjects, though appropriate stimulus strengths were variable among the subjects. When comparing the maximum facilitations on both sides, they tended to be stronger on the dominant (right) side. We conclude that the current procedure is valuable to quantify functions of PNs, though stimulus condition and handedness have to be considered. [J Physiol Sci. 2006;56 Suppl:S190]

View full abstract

To understand the functional difference between dominant and non-dominant limbs in human upright standing, we analyzed electromyographic (EMG) activities while subjects stood on rocking platforms with various sizes. EMG activities were recorded from muscles of ankle and knee joints of both limbs. Subjects were instructed to stand on the rocking platforms so that they rocked in the saggital plane. Movements of the platforms, equivalent to fore and back movements of the subjects, were recorded by a force plate (center of pressure, COP). Mean EMG amplitudes of ankle extensors (m. triceps surae, GS) and flexor (m. tibialis anterior, TA) were higher in the non-dominant side than in the dominant side. Nevertheless mean EMG amplitudes of knee joint muscles were rather complicated; some muscles of the dominant side could show lower amplitude than those of the non-dominant side. As the radius of the rocking platform decreased, the ratio of mean EMG amplitudes of dominant and non-dominant muscle pairs (dominant-ratio) increased, and the correlation coefficient of these muscle pairs increased. Cross correlation analysis of the COP and EMG changes showed that non-dominant side muscles strongly correlated with the COP when subjects stood on the rocking platform with the largest radius. It was supposed that in a condition where subjects easily kept standing, non-dominant limb muscles were primarily used to control the COP, but dominant and non-dominant muscle pairs were used synchronously when it was difficult to keep standing. [J Physiol Sci. 2006;56 Suppl:S191]

View full abstract

Dopaminergic (DAergic) system in the medial prefrontal cortex (mPFC) is involved in cognition, memory, and behavioral control. Although the dysfunction of the DAergic system is suggested to cause several mood disorder and schizophrenia, the neural mechanisms for behavioral control through the interaction between the mPFC and the basal ganglia remain to be unclear. To elucidate this issue, we examined the effects of blockade of DAergic transmission in the mPFC of C57/BL6J mice during methamphetamine (METH)-induced hyperlocomotion. When mice received intra-mPFC infusions of muscimol, a GABA_A receptor agonist, METH-induced hyperlocomotion was significantly reduced. Infusions of SCH23390, a D1 DA receptor antagonist, and sulpiride, a D2 DA receptor antagonist, also decreased their locomotion. Although METH induced c-fos expression in the subthalamic nucleus (STN), these drugs infused into the mPFC significantly suppressed METH-induced STN activation. These results indicate that DAergic transmission in the mPFC during DA-induced locomotion facilitates their behavioral activity through the activation of the STN, implying that the mPFC-STN pathway contributes to DA-induced behavioral activation. [J Physiol Sci. 2006;56 Suppl:S191]

View full abstract

This study aimed to investigate characteristics of fore- and hindlimb locomotor movements evoked by stimulation to the midbrain in decerebrate rabbits. Under halothane anesthesia, adult rabbits (NZW, 2-3 kg) were surgically decerebrated at the precollicular-postmammillary level. The head was then fixed in a stereotaxic apparatus, and the body was supported by rubber belts. To evoke locomotion, 50-Hz stimuli (10-100 μA, 0.2 ms duration, 5-10 sec) were applied to the midbrain cuneiform nucleus, which corresponds to the mesencephalic locomotor region in cats, with Wood's-metal-filled glass microelectrodes. When the midbrain was stimulated, the left and right hindlimbs consistently exhibited nonalternating, rhythmic hopping movements. Even after the spinal hemisection at the lower thoracic level, the stimuli still evoked in phase rhythmic movements of bilateral hindlimbs. In contrast, left and right forelimbs basically displayed alternating locomotor movements when the midbrain was stimulated. In particular, after complete transection of the lower thoracic cord, the stimuli evoked purely reciprocal movements of bilateral forelimbs at any stimulus intensity. Despite such differences in fore- and hindlimb movement patterns, locomotor cycle frequency of fore- and hindlimbs was usually equal when the full hindlimb hopping was evoked. These findings suggest that spinal neuronal circuits involved in the generation of fore- and hindlimb locomotor patterns are tightly coupled, although they are constituted in a different manner. [J Physiol Sci. 2006;56 Suppl:S191]

View full abstract

In our previous study, temporal activity of single neurons of the primary motor cortex (MI) was correlated with kinematics or dynamics variables of arm movements using a multiple linear regression analysis. The present study extended the analysis to the dorsocaudal premotor cortex (PMdc) and compared the results with those of MI. As explanation variables, we used the following four types of variables sets (or models); 1) kinematics variables represented in Cartesian coordinates (model Kc), 2) those in joint coordinates (model Kj), 3) dynamics variables in Cartesian coordinates (model Dc) and 4) those in joint coordinates (model Dj). The analysis was applied to 189 MI and 52 PMdc units that responded to passive movements of the shoulder and/or elbow joints or maneuver manipulations of the muscles controlling these joints. Each unit was classified into one of the four types according to the model that best fitted the unit. About 85% neurons belonged to either of the dynamics types (i.e., type Dc or Dj) with predominance of type Dj, and the ratio of each type of neurons was similar in MI and PMdc. Moreover, activity of about 80% of the neurons preceded the arm movements, and this was observed commonly for MI and PMdc neurons. These results suggest that MI and PMdc neurons receiving proprioceptive information share similar roles in the execution of manual reaching movement. [J Physiol Sci. 2006;56 Suppl:S191]

View full abstract

The STN is a target for ‘deep brain’ stimulation (DBS) in the treatment of Parkinson's disease. DBS effects are likely to be a mixture of multiple effects, affecting both axons and somata within the STN. We here report on experiments studying one key component of the overall response to DBS, i.e., the effect of stimulation on the activity of neurons within the STN. Two monkeys received two chronic recording chambers each. The two chambers were directed at the same STN. One of them was used to carry out electrical stimulation of the STN with a microelectrode (using monophasic stimulation at 1/s, pulse width 50 µs, amplitude ∼ 300 µA), and the other to simultaneously record the neuronal activity in STN with standard extracellular single-unit recording techniques. Peristimulus histograms were calculated to determine the latency and duration of stimulation-evoked responses. In most cases, STN neurons responded to the nearby stimulation with a cessation of activity, typically starting immediately after the stimulation and lasting for 37.2 ± 20.7 ms (n = 161). In some neurons, the inhibition was followed by an excitation. The results suggest that electrical stimulation of the STN has prominent and complex effects on the neuronal activity within the STN. Given the high frequency of therapeutic DBS (130 Hz), it is unlikely that the excitatory effects will manifest themselves. The inhibitory responses may result from activation of GPe axons which then would inhibit STN neurons. [J Physiol Sci. 2006;56 Suppl:S192]

View full abstract

The pig hippocampus has a highly laminated dentate hilus, which clearly resemble to that of primates. However, few studies have been performed to investigate its neural activities. Therefore, in this study we examined local field potentials (LFPs) in the hippocampus of male Landrace piglets under general anesthesia. The anesthesia was maintained by halothane (1-2%) or by intravenous administration of urethane and chloralose with the minimal level of halothane (0.5%). A few spike-shaped waves in the LFPs were found in the hippocampus of the five piglets anesthetized with halothane. In contrast, spike-shaped waves in the LFPs were observed frequently in the three animals anesthetized with urethane and chloralose. Thus, the present study indicates that more spiking activities can be obtained in the hippocampus of the piglets anesthetized by with urethane-chloralose than by halothane. This suggests that the hippocampal neurons are more excitable in the piglets anesthetized with urethane and chloralose than with halothane only. [J Physiol Sci. 2006;56 Suppl:S192]

View full abstract

To investigate whether local field potential (LFP) levels may change in association with the learning stage, we analyzed LFPs from rat hippocampus (Hip) and prefrontal cortex (PFC) during operant discrimination reversal trainings. Rats were trained with initial discrimination task using light and sound (one for S+ and another for S-) as the discrimination stimuli until a stable discriminative performance was achieved. Then the rats received the reversal training. In this training, responses to S+ signal increased within 2-4 training sessions (early learning phase), whereas those to S- decreased at the late phase (4-8th sessions). LFP gamma-band powers showed an increase during training, which was significantly attenuated at the first training session in the Hip, and in the late learning phase in the PFC. These results suggest that LFP gamma-band powers change during the learning stage in the Hip and PFC differently. First exposure to the reversal training may depress Hip gamma-band activity. The depression of PFC gamma-band activity may relate to inhibitory control in the late learning phase. [J Physiol Sci. 2006;56 Suppl:S192]

View full abstract

Long-term potentiation (LTP) and long-term depression (LTD) are both forms of synaptic plasticity, which have been studied extensively in rodents. However, information about LTP and LTD in the primate brain is limited, especially when using in vivo models. This limitation is primarily due to difficulties in the precise implantation of electrodes within deep telencephalic structures of the primate brain. Using MRI and local field potentials to guide the implantation procedure, we inserted a stimulation electrode in the perforant pathway and a recording electrode in the dentate gyrus of the monkey. Correct implantation was confirmed by the appearance of evoked potentials in the dentate gyrus following stimulation of the perforant pathway. Evoked potentials changed systematically according to the depth of the electrodes. The effects of high-frequency stimulation (HFS; 100, 200 or 400 Hz) or low-frequency stimulation (LFS; 1, 2 or 5 Hz) on evoked potentials were tested in an awake condition. We used HFS or LFS parameters that have been demonstrated to produce LTP or LTD in rodents. In the monkey, however, we found that only the HFS with the highest frequency induced LTP, while all LFS levels failed to induce LTD. These data suggest that 1) the present animal model is suitable for testing long-term synaptic plasticity in the primate brain, and 2) the primate hippocampus is more resistant to the induction of long-term synaptic plasticity than the rodent hippocampus. [J Physiol Sci. 2006;56 Suppl:S193]

View full abstract

Present experiments were undertaken to explore the effects of exercise on dentate gyrus (DG) neurogenesis and the ability of learning and memory in hippocampus-lesioned adult rats. Hippocampus lesion was produced by intrahippocampal microinjection of kainic acid (KA). Bromodeoxyuridine (BrdU) was used to label dividing cells. Y maze test was used to evaluate the ability to learning and memory. Exercise was conducted in the form of forced running in a motor-driven running wheel. The speed of wheel revolution was regulated at 3 kinds of intensity: lightly running, moderately running, or heavily running. Hippocampus lesion could increase the number of BrdU-labeled DG cells, moderately running after lesion could further enhance the number of BrdU-labeled cells and decrease the error number (EN) in Y maze test, while neither lightly running, nor heavily running had such effects. There was a negative correlation between the number of DG BrdU-labeled cells and the EN in the Y maze test after running. The results suggested that moderate exercise could enhance the DG neurogenesis and ameliorate the ability to learning and memory in hippocampus-lesioned rats. [J Physiol Sci. 2006;56 Suppl:S193]

View full abstract

To investigate the effect of forced running on neurogenesis in the hippocampal dentate gyrus ( DG ) of adult rats, 5-bromo-2-deoxyuridine ( BrdU ), the thymidine analog, that can be incorporated into the DNA during the S phase of cell cycle, was applied to mark cell proliferation. Neuroepthelial stem cell protein (nestin) expression was used to identify neural stem cell/precursor cells. The BrdU- and nestin-positive cells were examined by immunocytochemical technique. The ability of spatial learning and memory was evaluated by Y maze and Morris water maze tests to explore the functional role of the newly born cells in DG after running. It was found that the number of BrdU- and nestin-positive cells in the dentate gyrus in running groups was significantly increased as compared to that of control group. The effect of forced running on neurogenesis was intensity-dependent. In addition, an improvement of spatial learning ability was observed after forced running in Y maze, as well as in Morris water maze tests. These findings demonstrated that forced running could enhance neurogenesis in the hippocampal dentate gyrus of adult rats and facilitate acquisition of a hippocampus-related spatial learning task. [J Physiol Sci. 2006;56 Suppl:S193]

View full abstract