Neural basis for social defeat and entrapment

Two models used in the study of stress are restraint and social defeat. During restraint, entrapment is clear and intense, while in the social defeat both defeat and entrapment play a role in stress generation. Although the neural basis for both stress models have been addressed, detailed comparison between them has not been studied and could reveal a dissociation between the neural circuit of entrapment and defeat. The aim of this work was to compare Fos, an indicator of neuronal activation, expression in the hypothalamus of male rats exposed to restraint (10 min) or social defeat (5 min exposure to a dominant conspecific). Results showed a partial overlap in neuronal activation between experimental groups. Restraint triggered intense activation of neurons in the paraventricular nucleus and moderate upregulation of Fos in the anterior part of the anterior nucleus, the juxtadorsomedial region of the lateral hypothalamic area (LHA) and the dorsomedial part of the dorsal premammillary nucleus (PMDdm). While social defeat activated the same areas as restraint, additional Fos expression was observed in the hypothalamic reproductive circuit and the subfornical region of the LHA. Taking into account the afferent information that these hypothalamic sites receive, it is fair to speculate that while the anterior part of the anterior nucleus and the juxtadorsomedial region of the LHA are involved in the entrapment circuit, social defeat may be organized by the reproductive circuit and the subfornical region of the LHA. The PMDdm, in turn, integrates information from both defeat and entrapment circuits, and seems critical to influence the behavioral outcome.