Social Stress in Hamsters: Defeat Activates Specific Neurocircuits within the Brain

Abstract

During an agonistic encounter, subordinate male hamsters display defensive and submissive postures and show increased secretion of glucocorticoids, whereas dominant males do not. To determine whether specific neuronal pathways are activated during the behavioral and neuroendocrine 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) males]. A second group of control animals that received no handling or social stimulation (unhandled control males) were also included. After testing, all animals were killed by decapitation, their brains were removed for c-fos in situ hybridization, and trunk blood was collected for analysis of plasma cortisol and corticosterone levels. Exposure of males to their partner's cage for 30 min resulted in increased expression of c-fos mRNA in multiple brain regions. In addition, fighting increased c-fos expression in the medial amygdaloid nucleus of both DOM and SUB males as well as having more selective effects. In DOM males, c-fos expression was elevated within the supraoptic nucleus of the hypothalamus. In SUB males, c-fos expression increased within a multitude of brain areas, including cingulate cortex, lateral septum, bed nucleus of the stria terminalis, medial preoptic area, several hypothalamic nuclei, central amygdaloid nucleus, amygdalohippocampal area, dorsal periaqueductal gray, dorsal raphe, cuneiform nucleus, and locus coeruleus. These findings are discussed in relation to neurocircuits associated with behavioral arousal and stress.

Stress-Induced c-Fos Expression is Differentially Modulated by Dexamethasone, Diazepam and Imipramine

“…The boundaries of the brain areas were identified using adjacent Nissl-stained sections. A template or outline was developed for each brain nucleus or subnucleus based on the shape and the size of the region (Kollack-Walker et al, 1997). The location and relative size of each template are illustrated in Figure 2.…”

Predator threat induces behavioral inhibition, pituitary-adrenal activation and changes in amygdala CRF-binding protein gene expression

“…Furthermore, psychosocial stressors are known to precipitate stress-induced psychopathology (Dunner et al, 1979;Hammen et al, 1992). Therefore, when performing preclinical studies to understand mechanisms relevant to human psychopathology, it is important to use species-specific psychosocial stressors (Albeck et al, 1997;Kollack-Walker et al, 1997;Blanchard et al, 1998). Exposure of rats to a natural predator such as a ferret represents a potent form of psychosocial stress.…”

Social defeat, a paradigm of depression in rats that elicits 22-kHz vocalizations, preferentially activates the cholinergic signaling pathway in the periaqueductal gray

“…Dramatic increases in transcriptional activity in the PAG during dominant/submissive encounters have been observed. In hamsters, agonistic encounters between dominant and submissive animals produce increased fos-immunolabeled neurons in the dorsolateral columns of the PAG in the subordinate animals [40]. In addition, recent studies in the rat demonstrated that excitation of the lateral PAG produced largely defensive responses, including emission of 22-kHz distress ultrasonic vocalizations (USVs).…”