Loss of muscarinic cholinergic receptors from the temporal cortex of alcohol abusers.

It is currently controversial whether all the brain damage in alcohol abusers in the result of thiamine deficiency (Wernicke-Korsakoff's disease) or whether, in addition, alcohol abuse may affect the brain by other mechanisms as well. The purpose of this study was to determine if alcohol abuse affects muscarinic cholinergic and benzodiazepine receptors in histologically normal brains obtained at autopsy in a general hospital population. Patients were excluded from this study if they had clinical brain diseases (including Wernicke's disease), died in coma, or had liver disease, significant brain atrophy, or dementia severe enough to require institutionalization. We found that muscarinic cholinergic synaptic receptor density determined with [3H] quinuclidinly benzilate was decreased by 40% in homogenates of the tempeoral cortex of 26 alcohol abusers compared with 26 matched nonalcoholic controls. The affinities of the muscarinic receptors were not significantly different between the two groups. 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 2% of the total variance of protein concentrations and receptor binding. When patients were excluded or included who had received cholinergic, anticholinergic, or benzodiazepine medications before death, no significant effects on the final results were observed. Pneumonia, known to be associated with acute hypoxia, and chronic obstructive pulmonary disease, known to be associated with chronic hypoxia, where approximately equally distributed between the two groups and had no significant effects on the results reported here. The loss of muscarinic and the sparing of benzodiazepine receptors occurs in the temporal cortex of histologically normal brains in the absence of significant atrophy and of gross dementia. This means that these changes are early in the development of an alcohol encephalopathy. We have previously reported a decrease in both muscarinic and benzodiazepine receptor binding in the frontal cortex and a decreasing 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, depending upon their location in different brain regions, are specifically affected or spared. This suggests the involvement of region- and receptor-specific mechanisms in chronic alcohol toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)