Disrupted social development enhances the motivation for cocaine in rats

Early social experiences are of major importance 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 long-lasting behavioural impairments and increase the vulnerability for psychiatric disorders, such as drug addiction. 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. Rats were socially isolated from postnatal days 21 to 42 followed by re-socialization until adulthood. Cocaine self-administration 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. Early social isolation resulted in an enhanced acquisition of self-administration of a low dose (0.083 mg/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. 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.