A novel nicotinic acetylcholine receptor subtype in basal forebrain cholinergic neurons with high sensitivity to amyloid peptides

Nicotinic acetylcholine receptors (nAChRs) containing α7 subunits are thought to assemble as homomers. α7-nAChR function has been implicated in learning and memory, and alterations of α7-nAChR have been found in patients with Alzheimer's disease (AD). Here we report findings consistent with a novel, naturally occurring nAChR subtype in rodent, basal forebrain cholinergic neurons. In these cells, α7 subunits are coexpressed, colocalize, and coassemble with β2 subunit(s). Compared with homomeric α7-nAChRs from ventral tegmental area neurons, functional, presumably heteromeric α7β;2-nAChRs on cholinergic neurons freshly dissociated from medial septum/diagonal band (MS/DB) exhibit relatively slow kinetics of whole-cell current responses to nicotinic agonists and are more sensitive to the β;2 subunit-containing nAChR-selective antagonist, dihydro-β- erythroidine (DHβE). Interestingly, presumed, heteromeric α7β2-nAChRs are highly sensitive to functional inhibition by pathologically relevant concentrations of oligomeric, but not monomeric or fibrillar, forms of amyloid β_1-42 (Aβ_1-42). Slow whole-cell current kinetics, sensitivity to DHβE, and specific antagonism by oligomeric Aβ_1-42 also are characteristics of heteromeric α7β2-nAChRs, but not of homomeric α7-nAChRs, heterologously expressed in Xenopus oocytes. Moreover, choline-induced currents have faster kinetics and less sensitivity to Aβ when elicited from MS/DB neurons derived from nAChR β2 subunit knock-out mice rather than from wild-type mice. The presence of novel, functional, heteromeric α7β2-nAChRs on basal forebrain cholinergic neurons and their high sensitivity to blockade by low concentrations of oligomeric Aβ_1-42 suggests possible mechanisms for deficits in cholinergic signaling that could occur early in the etiopathogenesis of AD and might be targeted by disease therapies.