Effects of alpha-methyl-p-tyrosine on monoamines and catecholamine receptors in rat cerebral cortex and neostriatum.

The effects of inhibiting the synthesis of catecholamines using alpha-methyl-p-tyrosine (alpha-MPT) were investigated in four cortical regions (cingulate, somatosensory, visual and entorhinal-piriform) as well as in the neostriatum (caudate-putamen). After acute (48 hours) treatments with alpha-MPT the endogenous NA levels were significantly reduced in all regions examined. The DA contents were also decreased in regions known to possess a dense dopaminergic innervation (neostriatum, cingulate and entorhinal-piriform cortices) but not in the somatosensory and visual areas, where DA is normally present in small amounts. Serotonin and 5-HIAA levels were either unaffected or increased. After such catecholamine synthesis inhibitions, there were no changes in the binding parameters (Bmax and Kd) of [3H]prazosin (alpha 1-receptors), [3H]idazoxan (alpha 2-receptors), [3H]dihydroalprenolol (total beta receptors) in the cerebral cortex nor in [3H]SCH23390 sites (dopamine D1 receptors) in both cerebral cortex and neostriatum. The results indicate that acute catecholamine depletions but with conservation of the fibers do not produce receptor modifications.