FIG. 2.

Primary nAChR subtypes in the mammalian CNS. The α6α4β2β3 and α6β2β3 nAChRs have a relatively restricted distribution in the CNS, including the nigrostriatal system. By contrast the α4β2 nAChRs, which exists in two unique conformations, and the α4α5β2 nAChR are widely present throughout the brain, including the nigrostriatal pathway. The homomeric α7 nAChR also exhibits an extensive distribution in the mammalian CNS, although this subtype is not densely expressed in the rat and monkey nigrostriatal system.