r-bPiDI, an α6β2* Nicotinic Receptor Antagonist, Decreases Nicotine-Evoked Dopamine Release and Nicotine Reinforcement

α6β2* nicotinic acetylcholine receptors (nAChRs) expressed by dopaminergic neurons mediate nicotine-evoked dopamine (DA) release and nicotine reinforcement. α6β2* antagonists inhibit these effects of nicotine, such that α6β2* receptors serve as therapeutic targets for nicotine addiction. The present research assessed the neuropharmacology of 1,10-bis(3-methyl-5,6-dihydropyridin-1(2H)-yl)decane (r-bPiDI), a novel small-molecule, tertiary amino analog of its parent compound, N,N-decane-1,10-diyl-bis-3-picolinium diiodide (bPiDI). bPiDI was previously shown to inhibit both nicotine-evoked DA release and the reinforcing effects of nicotine. In the current study, r-bPiDI inhibition of [³H]nicotine and [³H]methyllycaconitine binding sites was evaluated to assess interaction with the recognition binding sites on α4β2* and α7* nAChRs, respectively. Further, r-bPiDI inhibition of nicotine-evoked DA release in vitro in the absence and presence of α-conotoxin MII and following chronic in vivo nicotine administration were determined. The ability of r-bPiDI to decrease nicotine self-administration and food-maintained responding was also assessed. Results show that r-bPiDI did not inhibit [³H]nicotine or [³H]methyllycaconitine binding, but potently (IC₅₀ = 37.5 nM) inhibited nicotine-evoked DA release from superfused striatal slices obtained from either drug naïve rats or from those repeatedly treated with nicotine. r-bPiDI inhibition of nicotine-evoked DA release was not different in the absence or presence of α-conotoxin MII, indicating that r-bPiDI acts as a potent, selective α6β2* nAChR antagonist. Acute systemic administration of r-bPiDI specifically decreased nicotine self-administration by 75 %, and did not alter food-maintained responding, demonstrating greater specificity relative to bPiDI and bPiDDB, as well as the tertiary amino analog r-bPiDDB. The current work describes the discovery of r-bPiDI, a tertiary amino, α-conotoxin MII-like small molecule that acts as a potent and selective antagonist at α6β2* nAChRs to specifically decrease nicotine self-administration in rats, thus, establishing r-bPiDI as a lead compound for development as a treatment for nicotine addiction.