Dopamine/Neuroleptic Receptors in Basal Hypothalamus and Pituitary

In order to determine whether the basal hypothalamus or the pituitary (or both) is the likely locus of action of the tuberoinfundibular (TI) dopamine neurons, these regions were examined for dopamine and neuroleptic receptors. High affinity receptors for haloperidol and dopamine were found in the rat pituitary while none were detected in rat basal hypothalamus. The relative ability of two neuroleptics, chlorpromazine and haloperidol, to displace (3H)haloperidol from the receptor in monkey pituitary is similar to that for rat striatum. The lack of receptors capable of binding (3H)haloperidol or (3H)dopamine in the basal hypothalamus strongly suggests that the TI neurons do not produce postsynaptic effects in this region. The pituitary receptors for (3H)haloperidol and (3H)dopamine have the characteristics of a functional system. The presence of neuroleptic/dopamine receptors in the pituitary and lack of such receptors in the basal hypothalamus supports the hypothesis that dopamine may act directly as a prolactin release inhibiting factor (PIF) rather than releasing PIF from adjacent nerve terminals in the median eminence.