Developmental regulation of multiple nicotinic AChR channel subtypes in embryonic chick habenula neurons: contributions of both the α2 and α4 subunit genes

Habenula neurons from both early and late stage embryonic chickens express multiple subtypes of nicotinic acetylcholine receptor channels (nAChRs). The channel subtypes expressed by habenula neurons are similar in functional properties, but apparently distinct in subunit composition, from their peripheral counterparts in autonomic ganglia. Early in development, nicotine activates four classes of neuronal bungarotoxin (nBGT)-sensitive channels (approx. conductance=15, 30, 50, 60pS) that are intermingled on the surface of habenula neuronal somata. In neurons removed from older animals, nAChR channel activity has increased 4- to 40-fold and channel subtypes have become spatially segregated from one another. Analysis of the profile of nAChR subunit gene expression by polymerase chain reaction indicates that several of the α-type subunit genes, including α2,3,4,5,7, and α8, as well as both β2 and β4, are expressed. Treatment of the neurons with subunit specific antisense oligonucleotides reveals that the α2 and α4 (but not α3) subunits contribute to the functional profile of native nAChRs expressed by habenula neurons. Consideration of the functional properties and apparent subunit composition of autonomic ganglion nAChRs in the chick suggests that habenula neurons may utilize a very distinct set of subunit combinations to produce an array of nAChR channel subtypes similar in both conductance and pharmacological profile to those expressed by sympathetic neurons. © 1994 Springer Verlag.