FOS PROTEIN EXPRESSION IN THE CIRCADIAN CLOCK IS NOT ASSOCIATED WITH PHASE-SHIFTS INDUCED BY A NONPHOTIC STIMULUS, TRIAZOLAM

Recent studies have shown that light-induced phase shifts of the circa dian rhythm of locomotor activity are associated with c-fos expression in the suprachiasmatic nucleus (SCN) and intergeniculate leaflet (IGL ) of the lateral geniculate nucleus of rodents. In order to determine whether c-Sos expression is necessary for the phase shifting effects o f a non-photic stimulus, we assessed Fos-like immunoreactivity (Fos-li r) in the SCN and IGL at various times after an injection of the short -acting benzodiazepine, triazolam, at circadian time (CT) 6; i.e. at a time when triazolam induces an acute increase in locomotor activity a nd maximal phase advances in the circadian rhythm of locomotor activit y. Specific Fos-lir staining was not observed in the SCN or IGL region s of any animals treated with triazolam or vehicle at any time point e xamined. These results indicate that exposure to an activity-inducing stimulus at circadian times when this stimulus induces phase shifts do es not induce Fos protein synthesis in the SCN or IGL regions.