Little information is currently available on the localization of noradrenergic systems in the human CNS. We used quantitative autoradiography with [125I] iodopindolol to examine beta-adrenergic receptors in postmortem human brain. The concentration of beta-receptors was highest in all subfields of the hippocampus, followed by cerebellum, and then thalamic nuclei, basal ganglia, midbrain, and cerebral cortex. Low levels were found in white matter and hypothalamus. This distribution differed from the distribution of beta-receptors reported in membrane homogenates of human brain and also from the distribution of beta-receptors in rat brain determined by autoradiography. The similarities and differences between the distribution of beta-receptors in the human and rat brains may have implications regarding the role of norepinephrine in the CNS of these two species.
1-Methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) causes parkinsonism in humans and other species. We found [3H] MPTP binding sites that were saturable, specific, and of high affinity. In autoradiographic studies, the highest binding densities of [3H] MPTP occurred in the hypothalamus, interpeduncular nucleus, and ependymal lining of the ventricles. High to moderate binding was seen in the dentate gyrus, caudate, putamen, substantia nigra, and cingulate cortex. The distribution of [3H] MPTP binding correlated with the distribution of [3H] pargyline binding to MAO. Human substantia nigra contains more MPTP binding sites than rat substantia nigra, and this may explain the sensitivity of humans to the neurotoxic effects of MPTP.
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