Isolation rearing impairs wound healing and is associated with increased locomotion and decreased immediate early gene expression in the medial prefrontal cortex of juvenile rats

In addition to its maladaptive effects on psychiatric function, psychosocial deprivation impairs recovery from physical illness. Previously, we found that psychosocial deprivation, modeled by isolation rearing, depressed immediate early gene (IEG) expression in the medial prefrontal cortex (mPFC) and increased locomotion in the open field test [Levine JB, Youngs RM, et al. (2007) Isolation rearing and hyperlocomotion are associated with reduced immediate early gene expression levels in the medial prefrontal cortex. Neuroscience 145(1):42–55]. In the present study, we examined whether similar changes in behavior and gene expression are associated with the maladaptive effects of psychosocial deprivation on physical injury healing. After weaning, anesthetized rats were subjected to a 20% total body surface area third degree burn injury and were subsequently either group or isolation reared. After 4 weeks of either isolation or group rearing (a period that encompasses post-wearing and early adolescence), rats were killed, and their healing and gene expression in the mPFC were assessed. Locomotion in the open field test was examined at 3 weeks post–burn injury. We found that: 1) gross wound healing was significantly impaired in isolation-reared rats compared with group-reared rats, 2) locomotion was increased and IEG expression was suppressed for isolation-reared rats during burn injury healing, 3) the decreased activity in the open field and increased IEG expression was greater for burn injury healing group-reared rats than for uninjured group-reared rats, 4) the degree of hyperactivity and IEG suppression was relatively similar between isolation-reared rats during burn injury compared with uninjured isolation-reared rats. Thus, in the mPFC, behavioral hyperactivity to novelty (the open field test) along with IEG suppression may constitute a detectable biomarker of isolation rearing during traumatic physical injury. Implications of the findings for understanding, assessing, and treating the maladaptive effects of psychosocial deprivation on physical healing during childhood are discussed.