Neuroreceptor Changes in the Putamen of Alcohol Abusers

Abstract

The purpose of this study was to determine if alcohol abuse affects muscarink cholinergic and benzodiazepine receptors in histologi-cally normal brains obtained at autopsy in a general hospital population. Patients were excluded from this study if they had clinical brain (including Wernicke's) disease, died in coma, had liver disease, significant brain atrophy, or dementia severe enough to require institutionalization. We found that muscarinic cholinergic synaptic receptor density determined with [³H]quinuclidinyl benzilate was decreased by 40% in homogenates of the putamen of 27 alcohol abusers compared with 37 matched nonalcoholic controls. In contrast, receptor densities and affinities of benzodiazepine receptors determined with [³H]flunitrazepam were not significantly different in the two groups. Age and death-autopsy time interval had no significant effects on either wet tissue protein concentrations, yields of protein after centrifugation, or receptor binding. The contributions of age and time interval were each less than 3% of the total variance of protein concentrations and receptor binding. When patients who had received cholinergic, anticholinergic, or benzodiazepine medications before death were excluded or included we observed no significant effects on the final results. Pneumonia, known to be associated with acute hypoxia, and chronic obstructive pulmonary disease, known to be associated with chronic hypoxia, were approximately equally distributed between the two groups and had no significant effects on the results reported here. It is significant that the loss of muscarinic and the sparing of benzodiazepine receptors in the putamen occurs in histologically normal brains in the absence of significant atrophy and gross dementia. It implies that these changes are early in the development of alcoholic encephalopathy. We have previously reponed a decrease of muscarinic and benzodiazepine receptor binding in the frontal cortex and a decrease of muscarinic but not benzodiazepine receptors in the temporal cortex of alcohol abusers. Taken together, these findings suggest that alcohol neurotoxicity does not simply result in a random loss of neurons and/or their associated synapses with their receptors. Instead, different types of receptors are specifically affected or spared, depending upon their location in different brain regions. This suggests the involvement of region- and receptor-specific mechanisms in alcohol toxicity, which then probably results in specific patterns of altered behavior.