Uptake of 5-hydroxytryptamine by gonadotrophs of the bat's pituitary: A combined immunocytochemical radioautographic analysis.

Serotonergic mechanisms were examined in the bat pituitary. A seasonal fluctuation in the concentration of serotonin in the pituitary was found; the concentration rose just prior to hibernation, fell during hibernation, and transiently rose at the time of arousal from hibernation. This pattern is consistent with serotonin being stored within a cell that becomes inactive while bats hibernate. The uptake of 3H-serotonin was examined utilizing electron microscopic radioautography and the simultaneous light microscopic radioautographic localization of 3H-serotonin and the immunocytochemical localization of adenohypophyseal peptides. Uptake of 3H-serotonin was found to be a saturable process, inhibited by fluoxetine, but neither mimicked nor inhibited by norepinephrine. Cells responsible for uptake of 3H-serotonin contained luteinizing hormone immunoreactivity and were identified as gonadotrophs. The seasonal fluctuation and the presence of a specific serotonin uptake mechanism suggests that serotonin plays a role in the function of the adenohypophysis.