RESUMO
Risk-taking behavior is a vital aspect mediating the formation of social structure in animals. Here, we utilized the visible burrow system (VBS), a model in which rats form dominance hierarchies, to test the hypothesis that dominant rats in the VBS are natural risk takers and display an increased motivational state after VBS exposure. In particular, we predicted that dominant rats would have attenuated anxiety-like behavior and augmented acquisition of operant responding for food reward relative to subordinate and controls. We further hypothesized that these behaviors would correlate with elevated mesocortical orexin signaling. Prior to burrow exposure, male Long-Evans rats were tested on the elevated plus maze (EPM), and subsequently exposed to the VBS for seven consecutive days. At the conclusion of burrow exposure body weight and plasma corticosterone were used to confirm social rank within each colony. Interestingly, rats that went on to become dominant in the VBS spent significantly more time in the open arms of the EPM prior to burrow exposure and displayed increased operant responding for food reward. This effect was present over a range of reinforcement schedules and also persisted for up to 1 month following VBS exposure. Moreover, dominant rats displayed increased orexin receptor mRNA in the medial prefrontal cortex (mPFC) relative to subordinate and control rats. These data support previous findings from our group and are consistent with the hypothesis that risk-taking behavior may precede dominance formation in social hierarchies.
