Distribution of Ca2+-dependent protein kinase C isoforms in the suprachiasmatic nucleus of the diurnal murid rodent, Arvicanthis niloticus

The suprachiasmatic nuclei (SCN) contain the major 'biological clock' in mammals that controls most circadian rhythms expressed by these animals. The functional importance of protein phosphorylation and intracellular Ca2+ in the mammalian circadian pacemaker is becoming increasingly apparent. Here we report the immunocytochemical localization of the four Ca2+-dependent protein kinase C (PKC) isoforms (alpha, beta I, beta II, gamma) within the SCN of the diurnal murid rodent, Arvicanthis niloticus, and the nocturnal golden hamster. In the SCN of A. niloticus, PKC a was the most abundant of the four isoforms. Cells containing PKC a were homogeneously distributed throughout the SCN. PKC beta I cells were sparsely distributed in the perimeter of the SCN and were absent in its central area. PKCII and -gamma were not found in the SCN of A. niloticus. In the SCN of the golden hamster, PKC alpha cells were most heavily concentrated in the dorsomedial region, though some were also present laterally and ventrally. The distribution of arginine-vasopressin (AVP) cells in the SCN overlapped with that of PKC in both species. Species differences in the location of the Ca2+-dependent PKC isoforms suggest differences in function such as the relaying of photic or non-photic information to the clock mechanism, or the synchronization of AVP neurons and their subsequent output signals. (C) 1999 Elsevier Science B.V. All rights reserved.