[Stimulatory control by oxytocin (or an analog peptide) of the pituitary intermediate lobe in rabbits. Inhibitory role of serotonin].

The peculiar innervation of the intermediate lobe (IL) in Leporidae obviously corresponds to a regulation mechanism different from that known in other mammals. Physiological observations on IL superfused in vitro show, in addition to the previously reported absence of dopaminergic inhibitory control, the existence of an oxytocinergic-like control involved in the stimulation and not in the inhibition of alpha MSH release by the rabbit IL. Serotonine has inhibitory effects and may play a modulatory role. However, the strong stimulation of alpha MSH release obtained with K+ at a depolarizing concentration (8K) suggests that the presence of any powerful inhibitory axonal system in the rabbit IL is rather unlikely.