Yoshikazu Suzuki

Molecular analysis of avian circadian clock genes.

Unlike mammals, avian circadian rhythms are regulated by a multiple oscillatory system consisting of the retina, the pineal and the suprachiasmatic nucleus in the hypothalamus. To understand avian circadian system, we have cloned Clock and Period homologs (qClock, qPer2 and qPer3) and characterized these genes in Japanese quail. Overall, qCLOCK, qPER2 and qPER3 showed approximately 79%, approximately 46% and approximately 33% amino acid identity to mCLOCK, mPER2, mPER3, respectively. Clock was mapped to quail chromosome 4 and chicken chromosome 4q1.6-q2.1. Per2 and Per3 genes were both localized to microchromosomes. qClock mRNA was expressed throughout the day, while qPer2 and qPer3 showed robust circadian oscillation in the eye and the pineal gland. All three genes were expressed in various tissues. In addition, qPer2 mRNA was induced by light, but neither qClock nor qPer3 was induced. These results can explain the molecular basis for circadian entrainment in Japanese quail and also provide new avenues for molecular understanding of avian circadian clock and photoperiodism.

The relationship between ocular melatonin and dopamine rhythms in the pigeon: effects of melatonin inhibition on dopamine release

Our previous study has shown that the phases of circadian rhythms of ocular melatonin and dopamine are always opposite and intraocular melatonin injection suppresses dopamine release. Therefore, it is possible that dopamine rhythms result from inhibitory action of melatonin. We have examined this possibility in the following experiments. In the first experiment effects of continuous light on melatonin and dopamine release were examined. The data indicated that continuous light exposure resulted in loss of circadian rhythmicity of melatonin and dopamine by suppressing melatonin and enhancing dopamine levels throughout the day. To further examine the effects of light in the second experiment, 2 h light pulse was applied during the night, then temporal changes of melatonin and dopamine release were studied. The light pulse rapidly suppressed melatonin release, whereas it rapidly increased dopamine release. These changes occurred within 30 min in both melatonin and dopamine. However, the recovery after the cessation of the light stimulus was slower in melatonin than dopamine. In the third experiment it was tested if dopamine release was increased by lowering melatonin release with an intraocular injection of the D2 agonist, quinpirol. Although quinpirol strongly inhibited melatonin release independently of the time of injection, dopamine did not always increase by the inhibition of melatonin. These results indicate that ocular dopamine rhythms are not simply produced by melatonin inhibitory action.

Effects of L-carnitine on action potential of canine papillary muscle during hypoxic perfusion

Under hypoxic (95% N2 + 5% CO2) perfusion, electrophysiological effects of L-carnitine on canine papillary muscles were studied using standard microelectrode techniques. During hypoxic perfusion for 60 min, resting membrane potential (RMP), action potential amplitude (APA) and maximum upstroke velocity of phase 0 were decreased, and action potential duration (APD) and effective refractory period (ERP) were shortened. Application of L-carnitine 25 mM under hypoxic perfusion increased RMP and APA and prolonged APD and ERP significantly. As effects of L-carnitine during hypoxic perfusion might be that of hypertonicity, effects of sucrose of the same tonicity as L-carnitine were studied under hypoxia. Sucrose did not cause significant changes on various parameters of action potential compared with hypoxic perfusion. It was suggested that the increase in RMP, and the prolongation of APD and ERP might be caused by an increase in intracellular ATP content. The findings in this study could be an explanation of possible antiarrhythmic effects of L-carnitine.

Changes of Plasma Levels of TRH and Its Target Hormones by Two Hour Constant Intravenous Infusion of TRH Tartrate in Man

Constant iv infusion of TRH tartrate for 2 hours was administered to normal men in a dosage of 0.5 (n=4), 1.0 (n=2) and 2 (n=4) mg/120 minutes. Measurements at every 15 minutes were performed for plasma levels of TRH, TSH, Thyroxine (T4) and Triiodothyronine (T3) by radioimmunoassay. Plasma levels of TRH increased promptly and stayed at the same levels until the end of the infusion. The Mean Clearance Rate (MRC), Half-life and Volume of Distribution of TRH were respectively, 4.62 +/- 0.53 L/min. (M +/- SE), 17.8 +/- 3.8 minutes and 112 +/- 15 L in the 0.5 mg administered group and 6.38 +/- 2.50 L/min., 9.0 +/- 1.4 minutes and 82 +/- 30 L in the 2 mg administered group. Plasma levels of TRH increased in two phases, and increments of plasma TSH were dose dependable to the dosage of TRH. Plasma levels of T4 increased gradually in the course of TRH infusion and stayed at high levels even in the withdrawal phase of TRH. Plasma levels of T3 increased markedly during and after the TRH infusion in the 0.5 mg administered group, while increments of plasma T3 were minute in the 2 mg administered group. From the above data, it is suggested that the amount of TRH production in man, which is much more than has previously been reported, may indicate the existence of an extrahypothalamic synthesis of TRH in man.