NEURONAL NICOTINIC RECEPTORS - FUNCTION, MODULATION AND STRUCTURE

In the present paper; we discuss the diversity of nicotinic receptors (nAChRs) expressed in hippocampal neurons and their functional propert ies. Three distinct types of whole-cell currents can be identified in hippocampal neurons by brief application of nicotinic agonists. These currents, which are referred to as types IA, II and III, were distingu ished pharmacologically on the basis of their differential sensitiviti es to various nicotinic agonists and antagonists, and functionally on the basis of their rectification properties and rundown. Most of the h ippocampal neurons show type IA current in response to nicotinic agoni sts, and the single channels that account for these currents in additi on to having a very short open time and a high conductance, have a hig h Ca2+ permeability and inactivate very fast. Based on the comparison of the properties of the nicotinic currents elicited in hippocampal ne urons with those elicited by activation of nAChRs transiently expresse d in oocytes, we have concluded that type IA currents may be subserved by alpha 7-bearing nAChRs, type II currents by alpha 4 beta 2 nAChRs, and type III currents by alpha 3 beta 4 nAChRs. Indeed in-situ hybrid ization shows that mRNAs coding for alpha 7, alpha 4 and beta 2 nAChR subunits are present in hippocampal neurons. These findings altogether have given new insights for the studies of neurophysiological process es and neuropathological conditions in which neuronal nAChRs may be im plicated.