Bifeprunox: a partial agonist at dopamine D2 and serotonin1A receptors, influences nicotine-seeking behaviour in response to drug-associated stimuli in rats

Environmental stimuli repeatedly associated with the self-administered drugs may acquire motivational importance. Because dopamine (DA) D-2/D-3 partial agonists and D-3 antagonists interfere with the ability of drug-associated cues to induce drug-seeking behaviour, the present study investigated whether bifeprunox, 7-[4-([1,1'biphenyl]-3-ylmethyl)-1-piperazinyl]-2(3H)-benzoxazolone mesylate), a high-affinity partial agonist of the D-2 subfamily of DA receptors and of serotonin(1A) receptors, influences reinstatement of drug-associated cue-induced nicotine-seeking behaviour. The study also explored whether bifeprunox reduced motivated behaviour by evaluating its effects on reinstatement induced by stimuli conditioned to sucrose. To verify whether bifeprunox interferes with the primary reinforcing properties of either drug or sucrose, we compared its effects on nicotine self-administration and on sucrose-reinforced behaviour. Different groups of experimentally naive, food-restricted Wistar rats were trained to associate a discriminative stimulus with response-contingent availability of nicotine or sucrose and tested for reinstatement after extinction of nicotine or sucrose-reinforced behaviour. Bifeprunox (4-16 mu g/kg, s.c.) dose-dependently attenuated the response-reinstating effects of nicotine-associated cues. Higher doses (64-250 mu g/kg, s.c.) reduced spontaneous locomotor activity and suppressed operant responding induced by sucrose-associated cues and by the primary reinforcing properties of nicotine or sucrose. Provided they can be extrapolated to abstinent human addicts, these results suggest the potential therapeutic use of partial DA D2 receptor agonist to prevent cue-controlled nicotine-seeking and relapse. The profile of action of high doses of bifeprunox remains to be examined for potential sedation or anhedonia effects.