DISTRIBUTION OF THE ALPHA-2, ALPHA-3, AND ALPHA-5 NICOTINIC ACETYLCHOLINE-RECEPTOR SUBUNITS IN THE CHICK BRAIN

Nicotinic acetylcholine receptors (nAChRs) are ionotropic receptors co mprised of alpha and beta and subunits. These receptors are widely dis tributed in the central nervous system, and previous studies have reve aled specific patterns of localization for some nAChR subunits in the vertebrate brain. In the present study we used immunohistochemical met hods and monoclonal antibodies to localize the alpha 2, alpha 3, and a lpha 5 nAChR subunits in the chick mesencephalon and diencephalon. We observed a differential distribution of these three subunits in the ch ick brain, and showed that the somata and neuropil of many central str uctures contain the alpha 5 nAChR subunit. The alpha 2 and alpha 3 sub units, on the other hand, exhibited a more restricted distribution tha n alpha 5 and other subunits previously studied, namely alpha 7, alpha 8 and beta 2. The patterns of distribution of the different nAChR sub units suggest that neurons in many brain structures may contain severa l subtypes of nAChRs and that in a few regions one particular subtype may determine the cholinergic nicotinic responses.