Differential sensitivity of hypothalamic dopaminergic and noradrenergic neurones to pharmacological manipulation

The effects of apomorphine (Apo), haloperidol (Hal), reserpine, phenyoxybenzamine, oxotremorine and scopolamine on hypothalamic caatecholamines and metabolites were assessed. All these drugs, except Apo, significantly changed the hypothalamic concentration of 3-methoxy-4-hydroxyphenylglycol (MHPG), thus suggesting parallel changes in noradrenaline (NA) metabolism and turnover. Hal increased MHPG, an effect which was reversed by Apo pretreatment. Oxotremorine and scopolamine respectively increased and decreased MHPG, reserpine decreased NA and increased MHPG. Phenoxybenzamine increased MHPG without altering NA concentrations. Dopamine and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were not changed by Apo and Hal, but were influenced by the other drugs. These results indicate that NA in the hypothalamus is influenced by both cholinergic and dopaminergic events occurring in the brain and that dopaminergic neurones in this organ are different in their biochemical and pharmacological characteristics from neurones present in other central and peripheral systems.