A calcium-regulating hormone 1α,25-dihydroxyvitamin D₃ (1,25-[OH]₂D₃) has been known to rapidly stimulate the transcellular active calcium transport in the chick duodenum. However, its effects on the solvent drag–induced paracellular calcium transport, which normally contributes ~70% of the total active calcium transport, and the underlying mechanism were unknown. The present study aimed to investigate the rapid nongenomic actions of physiological concentrations of 1,25-(OH)₂D₃, i.e., 1, 10, and 100 nmol/l, on the duodenal calcium absorption in female rats. Quantitative real-time PCR revealed strong expressions of the classical vitamin D receptor (VDR) and the membrane-associated rapid response steroid binding receptors (MARRS) in both small and large intestines. By using the Ussing chamber technique, we found that duodenal epithelia acutely exposed to 10 and 100 nmol/l 1,25-(OH)₂D₃ rapidly increased the solvent drag–induced calcium transport, but not the transcellular calcium transport, in a dose-response manner. On the other hand, 3-day daily injections of 1,25-(OH)₂D₃ enhanced the transcellular active duodenal calcium transport. The 1,25-(OH)₂D₃–stimulated solvent drag–induced transport was abolished by the phosphatidylinositol 3-kinase (PI3K) inhibitors, 200 nmol/l wortmannin and 75 μmol/l LY294002, as well as PKC (1 μmol/l GF109203X) and MEK inhibitors (10 μmol/l U0126). Although 100 nmol/l 1,25-(OH)₂D₃ did not alter the transepithelial mannitol flux, indicating no widening of the tight junction, it decreased the transepithelial resistance and increased both sodium and chloride permeability through the paracellular channel. We conclude that 1,25-(OH)₂D₃ uses the nongenomic signaling pathways involving PI3K, PKC, and MEK to rapidly enhance the solvent drag–induced calcium transport, partly by altering the charge-selective property of the duodenal epithelium at least for the pathways involving PI3K and MEK.

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Recently, electroacupuncture (EA) has been gaining more and more attention as a treatment for epilepsy. However, concrete evidence is needed to better understand its antiepileptic effect and the mechanism underlying this effect. The present study was designed to assess the effect of EA stimulation of hindlimb on the incidence of behavioral seizures (spontaneous recurrent seizures, [SRS]) and electroencephalogram (EEG) seizures, and the extent of supragranular mossy fiber sprouting (MFS) using the lithium-pilocarpine rat model of epilepsy. Sham EA at the same point without electrical stimulation was set as the control. EA and the sham EA were performed bilaterally (at the symmetrical Zusanli acupoints on both hind legs) 30 times every two days. The numbers of behavioral seizures and EEG seizures were then analyzed to evaluate the antiepileptic effect. After confirmation of the antiepileptic effect, MFS in the dentate gyrus (DG) supragranular layer was investigated by Timm’s staining. The results showed that the EA stimulation of hindlimb significantly reduced the behavioral seizures, EEG seizures, and supragranular MFS; however, the sham EA without electrical stimulation showed no significant effect on seizures or supragranular MFS. The findings indicate that EA stimulation of hindlimb possesses an antiepileptic effect, which is probably related to its suppressive effect on aberrant MFS in DG.

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Gonadotropin-releasing hormone (GnRH) neurons represent the final output neurons in the central control of reproduction. γ-Amino butyric acid (GABA), one of the major regulators of GnRH neurons, depolarizes GnRH neurons isolated from adult rats via GABA_A receptors. The presence of GABA_A receptors in GnRH neurons has also been demonstrated morphologically. Furthermore, the pineal hormone melatonin is involved in the regulation of reproductive function, including the timing of the luteinizing hormone surge. The suprachiasmatic nucleus and the GABAergic system in the medial preoptic area are considered as possible sites of the action of melatonin. Until now, however, a direct action of melatonin on GnRH neurons has not been reported. Therefore we examined the effect of melatonin on GABA_A receptor currents in GnRH neurons isolated from GnRH-EGFP transgenic rats by means of perforated patch-clamp experiments. The GABA_A receptor currents were modulated by melatonin in a sex-specific manner. In GnRH neurons from adult males, melatonin augmented these currents in 67% of the neurons examined, but attenuated the currents in only 19% of them. These modulations were blocked by the melatonin receptor antagonist luzindole, suggesting an involvement of melatonin receptors. The modulation by melatonin was not observed in GnRH neurons isolated from infantile rats. These findings indicate that GABA affects the excitability of GnRH neurons in adult rats through GABA_A receptors, and that melatonin modifies this excitability via melatonin receptors in a sex-specific manner.

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The purpose of this study was to examine the validity of using ultrasonography for detecting the force generated by the psoas major muscle, a muscle positioned in the deep trunk. We measured the displacement of central tendon on B-mode ultrasound images of two different longitudinal sections of the muscle during passive hip flexion-extension and isometric hip flexion at varied hip angles. In both tasks, the values of tendon displacement obtained independently from each section coincided well, indicating that tendon displacement took place along a straight trajectory, i.e., close to the nodal line between two scanned planes. It was strongly correlated with both the hip angle (R² = 0.98) and the hip-flexion torque (R² = 0.83). In the second set of experiment, we measured the tendon displacement during dynamic movements with the combination of ultrasonography and VICON-based motion analysis. From the tendon displacement during dynamic thigh lifting and walking, the force generated by the muscle could be estimated by extracting the force-related component. These results indicate that ultrasonography of the psoas major muscle can measure the displacement of its central tendon accompanied with either length change of the muscle or the elongation of tendon. Although much attention has to be paid to the limitations of this methodology, ultrasonography may be useful for detecting the force generation of the muscle during a variety of dynamic movements.

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Type 2 diabetes is associated with many circulatory manifestations, including alteration in endothelial function and hypertension. In this study we investigate the morphology and contractile response as well as the endothelial function of resistance arteries from the spontaneously diabetic Goto-Kakizaki (GK) rat, a model of lean type 2 diabetes expressing glucose intolerance. METHODS: Isolated mesenteric small arteries were investigated under isometric conditions in a wire myograph system using noradrenaline (NA) and the endothelium-dependent vasorelaxant acetylcholine (ACh). Media thickness was measured and media lumen ratio calculated. RESULTS: No apparent morphological difference was noted between the arteries from GK rats and control Wistar (CW) rats. When exposed to the maximal NA concentration used (30 μM), arteries from GK rats developed significantly more tension than arteries from CW rats. In the presence of indomethacin (a specific blocker of the COX synthase) and of L-NAME (an inhibitor of eNOS), the response to NA was still significantly greater in GK rat arteries. Under control conditions, arteries from both groups showed intact relaxation to ACh. After incubation with indomethacin and L-NAME, both groups showed a non-NO nonprostaglandin-dependent relaxation to ACh. This relaxation could be blocked by a combination of apamin and charybdotoxin. CONCLUSION: This study shows that mesenteric small arteries from the diabetic GK rat have increased contractile response to NA, along with a normal endothelial function and unaltered morphology.

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The mechanisms of the protective effect conferred by heat shock preconditioning (HS) are currently unknown. The purpose of this study was to determine the effect of HS on muscle injury after downhill running and to address the mechanism of the effect. Female Wistar rats were assigned to three groups: HS, downhill running (E), and downhill running after heat shock preconditioning (HS + E). The HS and HS + E rats were placed in a heat chamber for 60 min (ambient temperature 42 ± 1.0°C) 48 h before downhill running. Reactive oxygen species (ROS) scavenging activity was determined by electron spin resonance (ESR), and heat shock protein 72 (HSP72) mRNA expression was measured in rat quadriceps femoris. Leukocyte infiltration and degenerated muscle fibers were determined histopathologically. ROS scavenging activity significantly increased at 3 days after HS (151 ± 18%) and HSP72 mRNA expression increased immediately after HS (1750 ± 1914%). No decrease in ROS scavenging activity was observed in the HS + E rats at 2 days after exercise compared with the E rats (102 ± 9% vs. 79 ± 5%). Degenerated muscle fibers in HS + E rats were significantly less than in E rats at 2, 3, and 7 days after exercise (0.8 ± 1.0 vs. 2.8 ± 1.6, 0.8 ± 1.0 vs. 1.8 ± 1.6, 0 vs. 0.3 ± 0.6, respectively). These data demonstrated that HS can reduce muscle injury after downhill running, and this effect may be mediated by increased ROS scavenging activity. Furthermore, HS may protect the antioxidant defense system in skeletal muscle by enhancing the adaptive HSP72 mRNA response.

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This study examined the effects of a different number of eccentric contractions (ECs) on histological characteristics, surface electromyogram (EMG) parameters (integral EMG, iEMG; muscle fiber conduction velocity, MFCV; and action potential waveform), and isometric peak torque using the rat EC model. Male Wistar rats (n = 40) were anesthetized, and ECs were initiated in the tibialis anterior muscle via electrical stimulation while the muscle was being stretched by electromotor. The rats were grouped according to the number of ECs (EC1, EC5, EC10, EC20, EC30, EC40, and EC100). Three days after the ECs, surface EMG signals and isometric peak torque were measured during evoked twitch contractions via electrical stimulation of the peroneal nerve. The muscle damage was evaluated from hematoxylin-eosin (HE) stained cross sections as a relative number of damaged fibers to intact fibers. Intense histological muscle damage (approximately 50% to 70% of the fiber), loss of isometric peak torque, disturbance of action potential waveform, and depression of iEMG (approximately −60% to −70%) were observed at EC20, EC30, EC40, and EC100. On the other hand, the MFCV did not change in any EC group. Although muscle damage and pathological surface EMG signals were not found at EC10, isometric peak torque was reduced significantly. In conclusion, the extent of histological muscle damage is not proportionally related to the number of ECs. Muscle damage was reflected by iEMG and action potential waveforms, but not by MFCV, which remained unaffected even though approximately 50% to 70% of the fiber demonstrated injury.

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This study was performed to examine whether electroacupuncture potentiates the neostigmine-induced antiallodynia in neuropathic pain rats. Although intrathecal neostigmine (0.05, 0.1, and 0.3 μg) dose-dependently relieved cold allodynia, 0.3 μg neostigmine caused side effects. The coapplication of 0.1 μg neostigmine and electroacupuncture, however, produced potent antiallodynia, which was parallel to the effect of 0.3 μg neostigmine, without side effects. These results indicate that electroacupuncture can enhance the antiallodynic action of intrathecal neostigmine.

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In the article "Effects of Dendroaspis Natriuretic Peptide on Calcium-Activated Potassium Current and Its Mechanism" by Guo et al. published in Volume 58, Number 1, pp. 1-6, 2008, of the Journal of Physiological Sciences, Central Laboratory, Zhongshan Affiliated Hospital of Dalian University should have been included as first author's affiliated laboratory. All authors and their affiliations are shown here. [Corrected PDF]

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