The brain at play: neural substrates of social play behaviour in adolescent rats

The period between weaning and sexual maturity (i.e. childhood and adolescence in humans, roughly equivalent to the juvenile and adolescent stages in rodents) has received widespread attention because of its importance for behavioural development, and conversely, because of the emergence of certain psychiatric disorders during this period. During adolescence, substantial changes occur in brain and behaviour. In particular, there are profound changes in social behaviour, including increased complexity of the social repertoire and a remarkable increase in peer-peer interactions. For a large part, these peer-peer interactions take the form of social play behaviour. Social play behaviour is one of the earliest forms of non-mother directed social behaviour in mammals, although it can also be observed in other species, e.g. reptiles, invertebrates, and avian species. Social play behaviour during adolescence is thought to be important for proper social and cognitive development. Indeed, abnormalities in play behaviour have been observed in childhood psychiatric disorders such as autism and attention deficit/hyperactivity disorder. In addition, childhood social trauma may have long-lasting repercussions, that last well into adulthood. Therefore, in view of its importance for behavioural development, and its relevance for child and adolescent psychiatry, it is essential to identify the neural substrates underlying social play behaviour, which was the aim of this thesis. Several neuronal networks and neurotransmitters systems were investigated. This thesis indicates that the neuronal networks and neurotransmitters involved include those important for cognition, emotion, and motivation. Together with previous studies, the results from this thesis serve as to further delineate a potential ‘play’ network in the rat brain. This ‘play’ network plausibly consists of several cortical and subcortical systems that work together to establish the appropriate behavioural components of social play behaviour. Key regions in this network are the prefrontal cortex, striatum, thalamus, habenula, VTA, and amygdala, as well as the monoamine neurotransmitter systems. As a result, this ‘play’ network establishes the proper behavioural acts in response to social and environmental cues to ensure that the appropriate behaviour is expressed considering the temporal and contextual setting, i.e. proper expression of social play behaviour. Therefore, the studies described in this thesis provide new clues considering the neural underpinnings of social play behaviour.