No triazolam-induced expression of Fos protein in raphe nuclei of the male Syrian hamster.

While the visual projections to the suprachiasmatic nuclei (SCN) play a role in mediating the effects of light on circadian rhythms, the functional significance of the serotonergic projection from the raphe nuclei (RN) to the SCN is uncertain. Because previous results indicated that RN would appear to be a likely site for triazolam (Tz)-induced phase shifts, we used the expression of Fos-protein as a marker of Tz-induced neuronal activation. Immunocytochemistry was used to visualize the presence of Fos-like protein. Tz-induced Fos-labeled nuclei were found in superior colliculi, Edinger-Westphal nuclei (EW) and dorsal tegmental nuclei (DTg), but not in the RN. The SCN showed only occasionally labeled nuclei in all experimental groups, whereas there was no Tz-induced Fos-immunoreactivity in the intergeniculate leaflet (IGL). The present data not necessarily exclude the implication of the RN in the phase shifting effect of Tz. The phase shift could still be accomplished using a different set of immediate early genes (IEG), or without an IEG response. Alternatively, as will be discussed, other pathways could mediate the phase shifting effect of Tz.