Cholinergic receptors: dual roles in transduction and plasticity

The regional distributions and possible functions of nicotinic acetylcholine receptors (nAChRs) in the developing and adult auditory rat brain are reviewed. The predominant nAChR in the auditory brainstem is the alpha 7 homomeric receptor. alpha 7 mRNA and protein are expressed in selected regions of the cochlear nucleus (CN), inferior colliculus (IC), medial superior olive, lateral superior olive, ventral nucleus of the lateral lemniscus and superior paraolivary nucleus. Peak expression of mRNA and protein occurs by the second postnatal week in most auditory brainstem areas. In contrast, the alpha 3 and beta 4 nicotinic subunits are expressed in the embryo and early in postnatal development in the CN and IC, but not other brainstem nuclei. Of particular interest is the octopus cell region of the posteroventral cochlear nucleus (PVCN). alpha 3 and beta 4 are down-regulated in the octopus cell region about postnatal day 10, which is the age that alpha 7 is at peak expression. NAChRs play important roles in transduction and in regulating intracellular calcium. The ability of the alpha 7 receptor to synchronize synaptic activity and stabilize synapses makes it a prime candidate as a mechanism underlying homeostatic plasticity in the auditory system. (C) 2000 Elsevier Science B.V. All rights reserved.