CONCURRENT DECREASE OF VASOPRESSIN AND PROTEIN-KINASE-C-ALPHA IMMUNOREACTIVITY DURING THE LIGHT PHASE IN THE VOLE SUPRACHIASMATIC NUCLEUS

Vasopressin (AVP) is a major neuropeptide in the suprachiasmatic nucle us, the mammalian hypothalamic circadian pacemaker. Protein kinase C a lpha is a putatively coupled intracellular messenger. Mean numbers of AVP- and protein kinase C alpha- immunoreactive neurons were determine d in the suprachiasmatic nucleus of common voles, entrained to a 12:12 h light-dark (LD) cycle, at the beginning of the light period (zeitge ber time zero) and 6 h later (zeitgeber time six). At zeitgeber time z ero, mean numbers of AVP- and protein kinase C alpha- immunoreactive n eurons were 2194 and 9897, respectively. Both numbers decreased signif icantly with about 40% at zeitgeber time six. This concurrent decrease was most pronounced in the dorsomedial aspect of the suprachiasmatic nucleus. These findings are consistent with the findings of a peak of AVP release in rats during the early light phase. (C) 1998 Published b y Elsevier Science Ireland Ltd. All rights reserved