Tyrosine hydroxylase-immunoreactive neurons are decreased in number in the cerebral cortex of Parkinson's disease.

Tyrosine hydroxylase (TH)-immunoreactive (IR) neurons and their relationship with Lewy bodies were investigated in Parkinson's disease. Using anti-TH and/or anti-ubiquitin antibodies, we evaluated the cerebral cortices included superior frontal gyrus, precentral gyrus, postcentral gyrus, inferior temporal gyrus, cuneus, cingulate gyrus, short and long gyri of insula, and parahippocampal gyrus from 18 autopsy cases of Parkinson's disease and 16 controls. The appearance of TH-IR neurons in cerebral cortices was suggestive of non-pyramidal interneurons. The mean number of TH-IR neurons and the density of TH-IR fibers in Parkinson's disease were decreased in comparison with the controls. The cognitive impairment in Parkinson's disease has been accounted for by the lesions of the basal nucleus of Meynert, the locus ceruleus, and the cortical Lewy bodies in the cerebral cortex. In addition to these lesions, the global loss of non-pyramidal TH-IR cortical neurons and TH-IR fibers would induce the dysfunction of higher-order control of the neocortex and the limbic system in Parkinson's disease. Double-immunostaining with anti-TH and anti-ubiquitin antibodies did not show the TH-IR neuron with cortical Lewy body in the cerebral cortices of Parkinson's disease. In the cerebral cortices of Parkinson's disease, TH-IR non-pyramidal neurons in which cortical Lewy body is not formed decreased in number.