SOCIAL STRESS IN HAMSTERS - DEFEAT ACTIVATES SPECIFIC NEUROCIRCUITS WITHIN THE BRAIN

During an agonistic encounter, subordinate male hamsters display defen sive and submissive postures and show increased secretion of glucocort icoids, whereas dominant males do not. To determine whether specific n euronal pathways are activated during the behavioral and neuroendocrin e responses of subordinate males, expression of c-fos mRNA within the brains of subordinate males was compared with the pattern in dominant males after fighting. After 1 week of handling, pairs of hamsters were either swapped between cages (handled control males), or were allowed to interact for 30 min [dominant (DOM) males and subordinate (SUB) ma les]. A second group of control animals that received no handling or s ocial stimulation (unhandled control males) were also included. After testing, all animals were killed by decapitation, their brains were re moved for c-fos in situ hybridization, and trunk blood was collected f or analysis of plasma cortisol and corticosterone levels. Exposure of males to their partner's cage for 30 min resulted in increased express ion of c-fos mRNA in multiple brain regions. In addition, fighting inc reased c-fos expression in the medial amygdaloid nucleus of both DOM a nd SUB males as well as having more selective effects. In DOM males, c -fos expression was elevated within the supraoptic nucleus of the hypo thalamus. In SUB males, c-fos expression increased within a multitude of brain areas, including cingulate cortex, lateral septum, bed nucleu s of the stria terminalis, medial preoptic area, several hypothalamic nuclei, central amygdaloid nucleus, amygdalohippocampal area, dorsal p eriaqueductal gray, dorsal raphe, cuneiform nucleus, and locus coerule us. These findings are discussed in relation to neurocircuits associat ed with behavioral arousal and stress.