Social effects on AVT and CRF systems

Using the reactive scope model to redefine the concept of social stress in fishes

The term 'social stress' has traditionally referred to physiological stress responses induced by the behaviour of conspecifics, particularly aggression or agonistic behaviours. Here, we review the physiological consequences of social status in fishes using the reactive scope model (RSM) to explain the divergent physiological phenotypes of dominant and subordinate fish. The RSM plots levels of different physiological mediators (e.g. behaviour, glucocorticoid hormones) over time, using them to define functional ranges that differ in their consequences for the animal. We discuss differences in growth, reproduction and tolerance of environmental challenges, all of which are suppressed in subordinate individuals, and focus on the underlying mechanisms that give rise to these phenotypes. Repeated and/or continual activation of the hypothalamic-pituitary-interrenal (HPI) axis in subordinate fish can lead to prolonged elevation of cortisol, a key physiological mediator. In turn, this increases physiological 'wear and tear' in these individuals, lowering their reactive scope (i.e. the physiological range of a healthy animal) and increasing their susceptibility to homeostatic overload. That is, they experience social stress and, ultimately, their capacity to cope with environmental challenges is limited. By contrast, reactive scope is maintained in dominant individuals, and hence they are better able to tolerate environmental challenges. Redefining social stress in terms of the RSM allows us to overcome the ambiguities and limitations associated with the concept of stress.

Comparing the ontogeny, neurobiology, and function of social play in hamsters and rats

Syrian hamsters show complex social play behavior and provide a valuable animal model for delineating the neurobiological mechanisms and functions of social play. In this review, we compare social play behavior of hamsters and rats and underlying neurobiological mechanisms. Juvenile rats play by competing for opportunities to pin one another and attack their partner's neck. A broad set of cortical, limbic, and striatal regions regulate the display of social play in rats. In hamsters, social play is characterized by attacks to the head in early puberty, which gradually transitions to the flanks in late puberty. The transition from juvenile social play to adult hamster aggression corresponds with engagement of neural ensembles controlling aggression. Play deprivation in rats and hamsters alters dendritic morphology in mPFC neurons and impairs flexible, context-dependent behavior in adulthood, which suggests these animals may have converged on a similar function for social play. Overall, dissecting the neurobiology of social play in hamsters and rats can provide a valuable comparative approach for evaluating the function of social play.