Disrupted social development enhances the motivation for cocaine in rats
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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.
KeywordsSocial isolation Adolescence Cocaine Self-administration Motivation Reinforcement Extinction Reinstatement
This study was supported by the National Institute on Drug Abuse Grant R01 DA022628 (L.J.M.J.V.). We thank Yavin Shaham, Taco de Vries and Chris Pierce for advice on the design of the extinction-reinstatement experiment and Mark H. Broekhoven for technical assistance.
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