Social interaction prevents the development of depressive-like behavior post nerve injury in mice: a potential role for oxytocin.

OBJECTIVE To examine the salubrious role of social interaction in modulating the development of allodynia (increased sensitivity to typically innocuous physical stimuli) and depressive-like behavior post peripheral nerve injury in mice. The determination of potential mechanisms that mediate social influences on the behavioral and physiological response to peripheral nerve injury. METHODS Mice were pair housed or socially isolated for 2 weeks before spared nerve injury (SNI). Animals were cannulated; socially isolated animals were centrally treated with oxytocin; and socially paired animals were centrally treated with an oxytocin receptor antagonist. Animals were subsequently monitored for the development of mechanical allodynia and depressive-like behavior, and tissue was collected for analysis of the central levels of the cytokine interleukin 1 beta (IL-1beta). RESULTS Depressive-like behavior was assessed via the Porsolt forced swim test, developed only among socially isolated mice with nerve injury. Socially isolated mice with nerve injury also were the only experimental group to exhibit increased frontal cortex IL-1beta gene expression on day 7 post injury. Moreover, central treatment of socially isolated mice with oxytocin, a neuropeptide associated with social bonding, attenuated the effects of SNI on depressive-like behavior and reduced frontal cortex IL-1beta protein levels in socially isolated animals. Conversely, pair-housed animals treated with a selective oxytocin receptor antagonist developed depressive-like behavior equivalent to that of socially isolated animals and displayed increased IL-1beta protein levels within the frontal cortex. CONCLUSION These data suggest that social interaction significantly alters the affective and neuroinflammatory responses to SNI through a mechanism that could involve oxytocin.