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.