Stress, prolactin and hypothalamic dopaminergic neurons.

Most of what is known about dopamine (DA)-containing neurons in the brain has been learned from studies on the nigrostriatal system, although it is misleading to consider a neuron in this system as a "model" for other DA neurons in the brain. In this presentation the properties of nigrostriatal DA neurons are compared with those hypothalamic DA neurons that comprise the tuberoinfundibular system. These latter neurons, which have cell bodies in the arcuate nucleus and short axons which terminate in the median eminence, function to inhibit the release of prolactin from the anterior pituitary. The activities of the nigrostriatal and tuberoinfundibular DA neurons were estimated biochemically by measuring the rates of synthesis (accumulation of DOPA after the administration of a decarboxylase inhibitor, NSD 1015), turnover (decline of DA after the administration of a tyrosine hydroxylase inhibitor, alpha-methyltyrosine) and metabolism (concentrations of dihydroxyphenylacetic acid) of DA in regions of the brain that contain the terminals of these neurons (striatum and median eminence, respectively). Tuberoinfundibular DA neurons differ from nigrostriatal DA neurons in that the former neurons: (1) are not directly regulated by DA receptor-mediated mechanisms, (2) are stimulated by prolactin, (3) exhibit a sexual difference with activity being 2-3 times greater in females and (4) are inhibited by afferent neuronal circuits that are activated by suckling and restraint stress.