Evidence for Opiate Receptors on Pituicytes

A hypothalamo-neurohypophyseal enkephalinergic pathway has been described and the pars nervosa of the rat pituitary contains enkephalin-like material which may coexist in vasopressin and oxytocin terminals. At the level of the pars nervosa itself, stereospecific opiate receptors with properties very similar to those of brain receptors have been described, and opiates have been shown to inhibit the release of both vasopressin and oxytocin. The location of the opiate receptors involved has been presumed to be pre-terminal on the neurosecretory fibres. Using an autoradiographic technique to visualize opiate receptors, however, we now report that destruction of the neurosecretory fibres following pituitary stalk section does not result in a significant change in the neural lobe opiate receptor population. This suggests that the opiate receptors within the neural lobe may be present on pituicytes rather than on neurosecretory fibres.