Muscarinic and nicotinic cholinergic binding sites in alzheimer's disease cerebral cortex

The total population of muscarinic receptors and a subpopulation of muscarinic receptors with high affinity for agonists were measured with [³H]quinuclidinyl benzilate and [³H]acetylcholine, respectively, in homogenates of cerebral cortex from control and Alzheimer's disease brains. No significant differences between control and Alzheimer's diseased cortex were found in either the total population of receptors or the subpopulation with high affinity for agonists in either the frontal or temporal poles. Nicotinic cholinergic receptors labeled by [³H]acetylcholine were measured in homogenates and by autoradiography in the same brain areas. In contrast to muscarinic sites, binding to nicotinic sites was markedly decreased in Alzheimer's disease cortex. Autoradiography of [³H]acetylcholine binding to nicotinic sites indicated that in control cortex these sites are more concentrated in laminae IV–VI than in the superficial laminae, and that in Alzheimer's disease there is loss of these sites in all cortical laminae.