Interaction of nicotine and social reward in group-reared male adolescent rats.

Adolescents exhibit great sensitivity to nicotine and social interaction; accordingly, when both stimuli are presented together, they interact to enhance the incentive value of the context in which they occur. Noteworthy, most studies assessing the interaction between nicotine and social reward have used isolated-reared rats. Adolescent isolation is an adverse condition that impacts brain development and behavior, so it is not known if the interaction also occurs in rats without social deprivation. The present study used a conditioned place preference model (CPP) to examine the interaction between nicotine and social reward in group-reared male adolescent rats. At weaning, Wistar rats were randomly assigned to four groups: vehicle, vehicle and a social partner, nicotine (0.1 mg/Kg s.c.), and nicotine and a social partner. Conditioning trials occurred on eight consecutive days followed by a test session in which the preference change was assessed. Besides the establishment of CPP, we examined the effects of nicotine on (1) social behaviors during CPP trials and (2) tyrosine hydroxylase (TH) and oxytocin (OT) as markers of changes in the neuronal mechanisms for reward and social affiliation. Similar to previous results, the joint presentation of nicotine and social reward induced CPP, whereas either nicotine or social interaction presented alone did not. This finding coincided with an increase in TH levels observed after nicotine administration only in socially conditioned rats. The interaction between nicotine and social reward is not related to the effects of nicotine on social investigation or social play.

Post-weaning social isolation increases the incentive value of nicotine-related contexts and decreases the accumulation of ΔFosB in nucleus accumbens in adolescent rats.

Adolescent social conditions profoundly affect vulnerability to drug abuse. Preclinical studies have shown that preventing social interactions during adolescence increases the rewarding effects of drugs like alcohol, cocaine, or amphetamines, however, little data exist regarding the impact of social isolation on nicotine effects. The current study evaluated the effects of differential rearing conditions during adolescence (isolation or group rearing) on (1) conditioned place preference induced by low nicotine doses (0.1 or 0.3 mg/kg) and (2) sensitization to the locomotor effects of nicotine after sub-chronic administration (3) and accumulation of ΔFosB in nucleus accumbens (NAc). Results showed that nicotine induced place preference in isolated and grouped rats, but the effect was more persistent for the rats reared in isolation. Isolated reared rats also exhibited lower levels of ΔFosB accumulation in NAc. No differences were found in the behavioral sensitization to nicotine effects between rearing conditions. The results suggest that isolation engenders a more robust incentive value of nicotine-related contexts. This effect could be related to the basal expression of ΔFosB: lower levels of this transcription factor seem to impair the motivation of isolated reared rats and increase their vulnerability to the effects of drugs like nicotine.