Nicotine enhances responding for conditioned reinforcement via α4β2 nicotinic acetylcholine receptors in the ventral tegmental area, but not the nucleus accumbens or the prefrontal cortex

Abstract

Nicotine enhances the conditioned reinforcing properties of reward-paired cues. We investigated the role of the ventral tegmental area (VTA), nucleus accumbens (NAcc), and prelimbic (PrL) and infralimbic (IL) cortices in mediating this enhancement. Male Long-Evans rats were implanted with bilateral guide cannulae aimed at either the VTA, NAcc, PrL or IL cortex. Next, rats underwent 12 sessions of Pavlovian conditioning. Each session consisted of 30 trials wherein a 5 s conditioned stimulus (CS) was paired with water (0.05 ml). Tests of responding for conditioned reinforcement were conducted during which presentation of the CS, now acting as a conditioned reinforcer (CRf), was contingent upon pressing one of two levers (CRf lever). Pressing the other lever had no consequences (NCRf lever). To determine if nicotinic acetylcholine receptors (nAChRs) in the VTA, NAcc, PrL cortex, or IL cortex mediate nicotine-enhanced responding for a CRf, the α4β2 nAChR antagonist Dihydro-Beta-Erythroidine (DHβE; 10 nmol/0.5 μL) was infused into the respective areas prior to a systemic nicotine injection (0.2 mg/kg; SC). DHβE infused into the VTA, NAcc, or IL cortex, but not PrL cortex, attenuated nicotine-enhanced responding for a CRf. Next, to confirm that nAChRs in the VTA, NAcc, or IL cortex mediate this enhancement, nicotine (8, 16, or 32 nmol/0.5 μL) was infused into the respective areas. Nicotine infused into the VTA, but not NAcc or IL cortex, enhanced responding for a CRf. These findings suggest that nicotine primarily acts on α4β2 nAChRs in the VTA to potentiate the conditioned reinforcing properties of reward-related cues.