This chapter discusses the microscopic visualization of cholinergic receptors in the rat and human brain. The cholinergic receptors are well represented in the human brain with highly diversified regional distributions. Both nicotinic and muscarinic receptors are families of several different receptor proteins. The chapter reviews the advances of the distribution of the cholinergic receptors in the human brain. The pharmacological and autoradiographical techniques are used to examine the anatomical and microscopical localization of cholinergic receptors and their alterations in the human brain. The heterogeneity of these receptors is much larger than previously suspected. Both nicotinic receptor (nAChRs) and muscarinic cholinergic receptors (mAChRs) are involved in several diseases of the central nervous system (CNS). These results strongly support an involvement of the different cholinergic receptors in the function of specific brain areas. It is necessary to establish the cellular localization of these receptors in the human brain. For that, the development of more selective ligands, of probes for the visualization of the messenger RNA (mRNA) coding for the different receptor subtypes and of antibodies, specific for the different receptor proteins, are necessary. All these tools should provide the ways to clarify the distribution, localization, and modification of cholinergic receptors at the cellular level.
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