Dopamine D3 receptor ligands block nicotine-induced conditioned place preferences through a mechanism that does not involve discriminative-stimulus or antidepressant-like effects

Abstract

Environmental stimuli previously paired with drug taking appear to play a critical role in nicotine dependence. Converging anatomical, pharmacological, and behavioral evidence implicates dopamine D3 receptors (D3Rs) in the mechanisms underlying stimulus-controlled drug-seeking behavior. This study assessed the effects of BP 897, a D3R partial agonist and ST 198, a D3R antagonist, on nicotine-induced conditioned place preferences (CPPs), used as a measure of drug-seeking behavior, on food-maintained responding and on discrimination performance under a two-lever-choice nicotine discrimination procedure. BP 897 and ST 198 both blocked the expression of nicotine-induced CPP at doses selective for D3R. They had no effect on locomotor activity in the CPP apparatus and no significant effect on nicotine discrimination performance or food-maintained responding under the discrimination procedure. Involvement of antidepressant actions in the effects of BP 897 and ST 198 on CPP is unlikely, since we found no effect of D3R blockade with BP 897 or genetic depletion of D3Rs in a forced swimming test, used as a behavioral test for antidepressant activity. This suggests that D3R ligands reduce the motivational effects of nicotine by a mechanism distinct from those of nicotine replacement therapy and bupropion, the two currently used aids for smoking cessation in humans. These findings support the use of D3R ligands as aids for smoking cessation and indicate that their effects would be selective for those rewarding or reinforcing effects of nicotine that contribute to the maintenance of tobacco-smoking behavior, without affecting subjective responses to nicotine or producing any antidepressant-like effects.