The last decade has revealed an astounding degree of physiological and structural diversity in neurotransmitter-activated receptors. In particular, mo lecular studies of the acetylcholine-gated receptors in vertebrate muscle cells and Torpedo electrocytes gave birth to a new era of research on a relat ed subfamily of nicotinic receptors (nAChRs) expressed by central and periph eral neurons. This review focuses on the nAChR subtypes expressed by neurons, viewed mainly from a physiological perspect ive. It is intended to complement several excellent recent reviews on muscle-type A ChRs (42, 45, 56) and on the anatomical distribution, biochemistry, and molecular biology of neuronal nAChRs (35, 61, 66, 95).

The work summarized in this review has helped answer a long-standing question: How can t he well-known behavioral, cognit ive, and addictive effects of nicotine be reconci led with the paucity of evidence for CNS s ynapses where the trans mission is mediated by nicotinic receptors? The identificat ion of a large family of neuronal nAChR subu nit genes and an array of functionally distinct nAChRs has given a basis for the diverse effects of nicot ine. Perhaps