Quipazine and light have similar effects on c-fos induction in the rat suprachiasmatic nucleus

The effects of the serotonin agonist, quipazine, on the induction of c-fos in the suprachiasmatic nucleus of the rat was examined at different times of the 24 h cycle. Quipazine administered at night induced Fos production in a dose dependent manner (1, 3, 10, 30 μmol/kg) in the ventrolateral portion of the suprachiasmatic nucleus at ZT18. Administration of the highest dose at other times resulted in c-fos induction at ZT15 but not at other times of the day or subjective day examined (CT6 and ZT12). When compared to the effects of light pulses (2 lux/1 min), quipazine only caused c-fos induction at times when light caused induction. Our results support a role of serotonergic pathways in the transmission or modulation of photic information from the retina to the suprachiasmatic nucleus of the rat.