Cellular activation in limbic brain systems during social play behaviour in rats.

Positive social interactions during the juvenile and adolescent phases of life are essential for proper social and cognitive development in mammals, including humans. During this developmental period, there is a marked increase in peer-peer interactions, signified by the abundance of social play behaviour. Despite its importance for behavioural development, our knowledge of the neural underpinnings of social play behaviour is limited. Therefore, the purpose of this study was to map the neural circuits involved in social play behaviour in rats. This was achieved by examining cellular activity after social play using the immediate early gene c-Fos as a marker. After a session of social play behaviour, pronounced increases in c-Fos expression were observed in the medial prefrontal cortex, medial and ventral orbitofrontal cortex, dorsal striatum, nucleus accumbens core and shell, lateral amygdala, several thalamic nuclei, dorsal raphe and the pedunculopontine tegmental nucleus. Importantly, the cellular activity patterns after social play were topographically organized in this network, as indicated by play-specific correlations in c-Fos activity between regions with known direct connections. These correlations suggest involvement in social play behaviour of the projections from the medial prefrontal cortex to the striatum, and of amygdala and monoaminergic inputs to frontal cortex and striatum. The analyses presented here outline a topographically organized neural network implicated in processes such as reward, motivation and cognitive control over behaviour, which mediates social play behaviour in rats.