Dj. Earnest et Ja. Olschowka, CIRCADIAN REGULATION OF C-FOS EXPRESSION IN THE SUPRACHIASMATIC PACEMAKER BY LIGHT, Journal of biological rhythms, 8, 1993, pp. 190000065-190000071
The primary objective of this research was to examine expression of th
e immediate-early gene c-fos within the suprachiasmatic nucleus (SCN)
for evidence of circadian regulation by photic stimuli. In vivo and in
vitro analyses demonstrate that photic signals have an inductive effe
ct on c-fos expression in the SCN, but only at critical times when lig
ht is capable of phase-shifting circadian rhythms. This evidence for c
orrelative relations between the effects of light signals in inducing
c-fos gene expression in the SCN and modulating the circadian period o
f the SCN pacemaker suggests that immediate-early genes may be compone
nts of the signal transduction cascade by which light entrains circadi
an rhythms. In addition, dual-immunostaining methods were utilized to
examine neurochemical identity of SCN cells that exhibit this circadia
n induction of c-fos expression in response to light. Within the ventr
olateral SCN, the photic induction of Fos expression occurred in neuro
ns expressing gastrin-releasing peptide (GRP), but not in those contai
ning vasoactive intestinal polypeptide (VIP). This finding suggests th
at SCN neurons containing GRP may be involved in the transduction of p
hotic signals mediating circadian entrainment.