Abstract
Many physiological functions show circadian rhythms controlled by suprachiasmatic nucleus (SCN) in mammals. From the SCN, ca. 24 hr rhythmicity accompanying the time of day information (phase) is conveyed to the other area of the brain and peripheral organs. Arg-vasopressin (AVP) containing neuron is one of the output neuron from the SCN. VIP and glutamate increased AVP release from the SCN, meanwhile suppressed by GABA (via GABAa receptor) and melatonin (MT2 receptor). The rPer2 mRNA products (CCG protein) promote the rBmal1 mRNA increase, which concerns the AVP mRNA transcription. In the SCN, before and after the 8-hr advance of the LD cycle, AVP mRNA and AVP peptide in the SCN remain coupled with time. After the light pulse (800 lux, 15 min at ZT 22), AVP mRNA increased in the SCN, but not in the paraventricular nucleus (PVN). Following the melatonin injection (1 mg/kg, i.p.), AVP content in the SCN decreased at both light and dark period, while no changes were observed in the PVN. In the SCN, rPer2 mRNA increased at both light and dark period. In the PVN, rPer2 decreased and increased at light and dark period, respectively. While in the pineal gland, rPer2 mRNA increased at 180 min after the melatonin injection. The melatonin-AVP reciprocal system indicates that PVN is temporally coupled with the SCN clock activity. The AVP and melatonin on the locomotor activity and body temperature rhythms are interesting theme. Body temperature decrease caused by the melatonin application (i.p.) during the night is considered to be a decrease of AVP in the SCN. Functional significance of AVP in the SCN would be discussed. [J Physiol Sci. 2006;56 Suppl:S55]
