Change in protein kinase C activity on day 5 of decidualization in pseudopregnant rats.

Administration of fluoxetine(10 mg/kg i.p.)caused a significantly greater increase in extracellular5-HT levels in hypothalamus of rats adapted to a reverse light period(lights off 9:00 am-9:00 pm)thanthose adapted to the regular cycle(lights off 6:00 pm-6:00 am).Sequential administration of theantagonist 5-HT(subscript 1A)/β-adrenergic receptors(-)-pindolol at 0.1,0.3,1,and 3 mg/kg s.c.significantlyenhanced the fluoxetine-induced elevation of 5-HT levels in both groups of rats.(-)-Pindolol at 0.1 mg/kg potentiated the fluoxetine-induced elevation in 5-HT levels significantly higher in rats adapted to thereverse light cycle than in those accustomed to the regular light cycle.The greater effects of fluoxetineand the subsequent administration of(-)-pindolol in the reverse cycle group may relate to the differencein activity of 5-HT neurons in the dorsal raphe of conscious animals adapted to the two light periods.