Identification of the nicotinic receptor subtypes expressed on dopaminergic terminals in the rat striatum

Neuronal nicotinic acetylcholine receptors (nAChRs) expressed on mesostriatal dopaminergic neurons are thought to mediate several behavioral effects of nicotine, including locomotion, habit learning, and reinforcement. Using immunoprecipitation and ligand-binding techniques, we have shown that both alpha6beta2* and alpha4(nonalpha6)beta2* nAChRs are expressed in the caudate-putamen and that only alpha6* nAChRs can bind alpha-conotoxin MII and methyllycaconitine with affinities of 1.3 and 40 nm, respectively. Further studies performed on 6-hydroxydopamine-lesioned striatum led to the identification of nAChR subtypes selectively expressed on dopaminergic terminals [alpha4alpha5beta2, alpha4alpha6beta2(beta3), and alpha6beta2(beta3)], nondopaminergic neuronal structures (alpha2alpha4beta2), or both structures (alpha4beta2). The identification of the nAChRs expressed on striatal dopaminergic terminals opens up the possibility of developing selective nAChR ligands active on dopaminergic systems and associated diseases, such as Parkinson's disease.