Disrupted social development enhances the motivation for cocaine in rats

for behavioural development. In particular, social play behaviour during post-weaning development is thought to facilitate the attainment of social, emotional and cognitive capacities. Conversely, social insults during development can cause longlasting behavioural impairments and increase the vulnerability for psychiatric disorders, such as drug addiction. Objectives The aim of this study was to investigate whether a lack of social experiences during the juvenile and early adolescent stage, when social play behaviour is highly abundant, alters cocaine self-administration in rats. Methods Rats were socially isolated from postnatal days 21 to 42 followed by re-socialization until adulthood. Cocaine selfadministration was then assessed under a fixed ratio and progressive ratio schedule of reinforcement. Next, cue, cocaine and stress-induced reinstatement of cocaine seeking was determined following extinction of self-administration. Results Early social isolation resulted in an enhanced acquisition of self-administration of a low dose (0.083mg/infusion) of cocaine, but the sensitivity to cocaine reinforcement, assessed using a dose–response analysis, was not altered in isolated rats. Moreover, isolated rats displayed an increased motivation for cocaine under a progressive ratio schedule of reinforcement. Extinction and reinstatement of cocaine seeking was not affected by early social isolation. Conclusions Early social isolation causes a long-lasting increase in the motivation to self-administer cocaine. Thus, aberrations in post-weaning social development, such as the absence of social play, enhance the vulnerability for drug addiction later in life