An initial analgesia followed by hyperalgesia to phasic noxious stimuli occurs after ingestion of sucrose ad libitum. However, the mechanism underlying hyperalgesia is not known. The present study was designed to explore the role of VMH in the mediation of the hyperalgesic effect of sucrose ingestion. Adult male albino rats received sucrose solution (20% p.o.) in addition to laboratory food pellets and tap water ad libitum. Their behavioural responses to various phasic and tonic noxious stimuli were recorded after 6, 12 and 48 h during pre and post-sucrose fed states in both the control and VMH lesion groups of rats. Sucrose feeding to control rats significantly reduced the tail flick latency (TFL) and threshold of vocalization during stimulus (SV) and after discharge (VA) indicating hyperalgesia, while the threshold of tail flick remained unaffected. The average pain rating during the formalin test (tonic pain) decreased significantly indicating analgesia. VMH lesion decreased the latency (mean ± SD) for tail flick (11.26 ± 4.65 from 15.61 ± 5.12 s), threshold (median) for tail flick (0.04 from 0.08 mA), vocalization during stimulus (0.05 from 0.1 mA) and vocalization after discharge (0.15 from 0.2 mA), while the tonic pain rating increased, thereby suggesting a hyperalgesic state. However, sucrose feeding to lesioned rats neither potentiated nor attenuated their hyperalgesia. The results suggest that sucrose feeding for 6–48 h ad libitum produces hyperalgesia to phasic noxious and analgesia to tonic noxious stimuli, while VMH lesion produces hyperalgesia to both phasic and tonic noxious stimuli. Secondly, sucrose ingestion by VMH lesion rats does not affect their responses to pain, suggesting the possible role of VMH in the mediation of sucrose-fed nociceptive responses.

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We attempted to fit heart rate (HR) changes induced by constant exercise loads of different intensities to an exponential hyperbolic sine curve by the least-squares method, and we compared the results with the fitting of the changes to exponential curves. Seven healthy male volunteers performed three different intensities of constant-load exercise on a bicycle ergometer. The exponential hyperbolic sine function adequately fitted the HR responses induced by all three different intensities of loads: low (30 W: correlation coefficient, r = 0.68 ± 0.13, mean ± SD), moderate (75 W: r = 0.93 ± 0.07) and high (125 W: r = 0.97 ± 0.02). The first-order exponential curve fitted only the moderate load response. Although the second-order exponential equation fitted the HR response for both the moderate and high loads, the equation did not fit the low-load response (r = 0.43 ± 0.26). In low-load exercise, the sum of the power of the residuals for the exponential hyperbolic sine curve fitting was significantly smaller than that for the first- or second-order exponential curve fitting. In conclusion, the exponential hyperbolic sine function is useful for quantitative analyses of the HR response to exercise loads of various intensities.

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The cross-sectional areas and succinate dehydrogenase activities of different types of fibers in different regions of the plantaris and tibialis anterior muscles in 10-week-old male rats were determined using quantitative histochemistry. The muscle fibers were classified as type I, type IIA, or type IIB according to their adenosine triphosphatase activities. There were no regional differences in either the mean cross-sectional area or the mean succinate dehydrogenase activity of type IIA fibers in both muscles. In contrast, type IIB fibers in the deep region of both muscles had smaller cross-sectional areas and higher succinate dehydrogenase activities than those in the superficial and middle regions. These data suggest the presence of regional differences in the cross-sectional area and succinate dehydrogenase activity of type IIB fibers in the muscle.

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Gastric H⁺,K⁺-ATPase consists of α- and β-subunits. The catalytic α-subunit contains a very unique structure consisting of lysine and glycine clusters, KKK(or KKKK)AG(G/R)GGGK-(K/R)K, in the amino-terminal cytoplasmic region. This structure is well conserved in all gastric H⁺,K⁺-ATPases from different animal species, and was postulated to be the site controlling the access of cations (or proton) to its binding site. In this report, we studied the role of this unique structure by expressing several H⁺,K⁺-ATPase mutants of the α-subunit together with the wild-type β-subunit in HEK-293 cells. Even after replacing all the positively-charged amino acid residues (six lysines and one arginine) in the cluster with alanine or removing all the glycine residues in the cluster, the mutants preserved the H⁺,K⁺-ATPase activity, and showed similar affinity for ATP and K⁺ as well as similar pH profiles as those of wild-type H⁺,K⁺-ATPase, indicating that the cluster is not indispensable for H⁺,K⁺-ATPase activity and not directly involved in determination of the affinity for cation (proton).

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In a previous study, we showed that the protein kinase C (PKC) activator 4β-phorbol 12-myristate 13-acetate (PMA) inhibited the γ-aminobutyric acid (GABA)–gated currents in Xenopus oocytes expressing human ρ1 GABA_C receptors. To investigate whether the inhibition of currents was due to a decrease in efficacy or in the potency of ρ1 GABA_C receptor, concentration-response curves for GABA were compared before and after PMA treatment. The EC₅₀ concentrations of GABA obtained during the maximally inhibited period were not statistically different from the concentrations obtained before PMA treatment (1.74 ± 0.33 and 1.45 ± 0.28 μM, respectively). These results indicate that the inhibition depends on a change in number or conductance of active receptor channels, but not on a change in affinity for GABA. To allow histochemical detection of ρ1 GABA_C receptors, we constructed a receptor tagged at the C-terminal position with human c-myc epitope. Electrophysiologically, the tagged receptors showed almost the same sensitivities for GABA and PMA as those of wild-type ρ1 GABA_C receptors. Immunohistochemistry with anti-myc antibody detected a dense concentration of tagged receptors at the surface area of Xenopus oocytes. Transient exposure to PMA reduced the density of immunofluorescence at the surface area and increased it in the subsurface area. These results suggest that the stimulation of protein kinase C leads to internalization of ρ1 GABA_C receptors expressed in Xenopus oocytes.

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To identify the characteristics of the oscillator located in the pineal organ, we examined the effects of temperature and light on melatonin secretion rhythm using pineal organs in cultures. At 20°C, the melatonin rhythm was obvious: low secretion during the daytime and high during the nighttime. When the temperature was lowered from 20 to 10°C, the melatonin rhythm disappeared. When the temperature was returned from 10 to 20°C, the rhythm quickly reappeared. The plasma melatonin level was measured in living lampreys kept at 7°C to establish the melatonin profile at low temperature in vivo: secretion was not significantly different between daytime and nighttime. Under continuous light conditions, the melatonin elevation normally seen during the subjective night became obscure after 72 h. When the LD cycle was shifted by 6 h (phase-advanced or phase-delayed), the melatonin rhythm shifted to remain in the same phase relation to the LD cycle. This re-synchronization took several LD cycles. The results indicate that, in cultures, the melatonin secretion rhythm in the pineal organ of the lamprey is both light- and temperature-sensitive, and that in vivo, the melatonin rhythm is not the critical factor maintaining the locomotor activity rhythm of the lamprey. The role of the pineal organ and melatonin in the circadian organization of the lamprey is discussed.

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We recently found a specific strain of rats (OLETF rats) in which CCK-A receptor gene expression is lacking because of a genetic abnormality. As delayed gastric emptying has been reported in this strain, we examined its mechanism. A liquid gastric load containing phenol red was administered using an orogastric tube into the stomach in OLETF and control (LETO) rats. The stomach was removed 0, 15, 30 and 45 min after meal ingestion and the content of phenol red was measured to estimate the rate of gastric emptying. Pretreatment of reserpine enhanced gastric emptying in both strains. A tenfold dose of reserpine was required in OLETF rats to induce a similar effect to LETO rats. The plasma noradrenalin level was significantly higher in OLETF than LETO rats. When the smooth muscle of the stomach was isolated and contraction in vitro was examined, the smooth muscle functions were not deteriorated in OLETF rats. The thickness of muscle determined by hematoxylin-eosin staining was not different between strains. It is suggested that the delayed gastric emptying in OLETF rats may be due to increased sympathetic nerve function.

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The pulmonary ventilation–O₂ uptake (VE-VO₂) relationship during incremental exercise has two inflection points: one at a lower VO₂, termed the ventilatory threshold (VT); and another at a higher VO₂, the respiratory compensation point (RCP). The individuality of RCP was studied in relation to those of the chemosensitivities of the central and peripheral chemoreceptors, which were assessed by resting estimates of hypercapnic ventilatory response (HCVR) and hypoxic ventilatory response (HVR), respectively, and the rate of lactic acid increase during exercise, which was estimated as a slope difference (δslope) between a lower slope of VCO₂-VO₂ relationship (VCO₂: CO₂ output) obtained at work rates below VT and a higher slope at work rates between VT and RCP. Twenty-two male and sixteen female subjects underwent a 1 min incremental exercise test until exhaustion, in which VT, RCP and δslope were determined. All measures were normalized for body surface area. In the males, the individual difference in RCP was inversely correlated with those of HVR and δslope (p < 0.05), and in the females, similar tendencies persisted, while the correlation did not reach statistically significant levels (0.05 < p < 0.1). There was no significant correlation between RCP and HCVR in either sex. A multiple linear regression analysis showed that 40 to 50% of the variance of RCP was accounted for by those of HVR and δslope, both of which were related linearly and additively to RCP, this relation being manifested in the males but not in the females without consideration of the menstrual cycle. These results suggest that the individuality of RCP depends partly on the chemosensitivity of the carotid bodies and the rate of lactic acid increase during incremental exercise.

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A novel inverted triple grease-gap chamber for electrophysiological studies and photometric detection of calcium release in skeletal muscle fibers is described. The chamber allows the construction of grease seals displaying high electrical resistance and mechanical stability. The fiber mounting procedure is fast, simple and not skill demanding, and the preparation is highly stable and reliable. Electrophysiological and photometric data are presented to illustrate the chamber performance.

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NMR micro-images of the kidney and liver were measured at 9.4 T in intact mouse, schistosoma Mansoni–infected mouse, and lupus nephritis in an MRL/lpr mouse. High-field NMR imaging has the advantages of sensitivity, spatial resolution, and tissue contrasts based on longitudinal and transverse relaxations, magnetic susceptibility differences and blood flow.

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