Localization of dopamine and norepinephrine in the medial basal hypothalamus of the rat

To clarify the spatial localization of dopamine (DA) and norepinephrine (NE) in the basal hypothalamus of the rat, superficial, intermediate or deep portions of the basal hypothalamus were assayed for these amines. Superficial basal hypothalamic specimens (av. wt. 0.45 mg) comprising mainly the median eminence (ME) had the highest concentrations of DA (>10 μg/g tissue). The intermediate and deep specimens, which included increasing amounts of tissue adjacent to and deep to the ME, had lower concentrations (5 and 3 μg/g, respectively). In contrast, the concentrations of NE did not differ in the three preparations and averaged 2 μg/g. The concentration of epinephrine, a substance which can interfere with the assay for NE, was less than 0.1 μg/g. These results indicate that DA in the basal hypothalamus is concentrated in the ME, and confirm previously published histochemical and pharmacological studies indicating that DA is the predominant catecholamine in this region.