Hypothalamic enkephalin neurones may regulate the neurohypophysis [13]

WE have previously reported that significant amounts of immunoreactive (ir)-Leu⁵-enkephalin were present in extracts of the neurointermediate lobe of the rat pituitary¹. Negligible amounts of the pentapeptide were detected in the anterior lobe. In these assays, the concentration of Leu⁵-enkephalin in the neurointermediate lobe was higher than in the globus pallidus, the brain region reported to contain the densest enkephalinergic innervation². The high content of (ir)-Leu-enkephalin in the neurointermediate lobe of the pituitary led us to further investigation of its distribution and possible function. We report here that (ir)-enkephalins in the pituitary are concentrated in nerve fibres projecting from the hypothalamus to the pars nervosa and that this pathway may be involved in the regulation of neurohypophysial neurosecretion.