Complete hypothalamic deafferentations were made in male rats with a modified Haläsz knife to isolate tuberoinfundibular dopaminergic neurons from the rest of the brain. A radioenzymatic procedure was employed to quantify dopamine and norepinephrine concentrations in various regions of the hypothalamus. Dopamine concentrations were unaltered while norepinephrine concentrations were reduced 50% in the median eminence and hypothalamic island 16-33 days after surgery. Basal serum prolactin concentrations were unaltered in these rats but were elevated 16 hours after the injection of haloperidol and 1 hour after α-methyltyrosine. The isolation of tuberoinfundibular neurons from the rest of the brain did not alter the ability of haloperidol to increase the rate of α-methyltyrosine-induced decline of dopamine in the median eminence. These results indicate that the haloperidol-induced, prolactin-mediated increase of dopamine turnover in the median eminence results from a direct action of this hormone on neurons within the medial basal hypothalamus.
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