Expression profiles of JunB and c-Fos proteins in the rat circadian system

The immediate-early genes c-Fos and JunB are implicated in light signaling within the suprachiasmatic nucleus (SCN), the mammalian circadian clock. Li ght induces phase-dependent expression of c-Fos and JunB within the retinor ecipient SCN. In the absence of light, rhythmic expression of these genes h as been observed in the dorsal region of the SCN with peak expression obser ved near dawn. The present study examined the pattern of induction of c-Fos and JunB in the SCN and intergeniculate leaflet (IGL) of rats housed in co nstant conditions, under light-dark cycles, or in dark-adapted light-stimul ated animals. In contrast with previous studies, no evidence of expression of c-Fos and JunB was observed within the dorsal SCN, regardless of circadi an time. Strain differences could account for the absence of rhythmic JunB expression, whereas the use of a monoclonal anti-c-Fos antibody in the pres ent study may account for the absence of dorsal SCN c-Fos staining. The pro file of light-induced c-Fos and JunB expression was consistent with previou s observations. In the SCN, light-induced expression of c-Fos and JunB was phase dependent, whereas in the IGL light-induced both c-Fos and JunB regar dless of circadian time. (C) 2000 Elsevier Science B.V. All rights reserved .