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 circadian 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-fos expression is necessary for the phase shifting effects of a non-photic stimulus, we assessed Fos-like immunoreactivity (Fos-lir) 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 and maximal phase advances in the circadian rhythm of locomotor activity. Specific Fos-lir staining was not observed in the SCN or IGL regions of any animals treated with triazolam or vehicle at any time point examined. These results indicate that exposure to an activity-inducing stimulus at circadian times when this stimulus induces phase shifts does not induce Fos protein synthesis in the SCN or IGL regions.