Winning agonistic encounters increases testosterone and androgen receptor expression in Syrian hamsters

Abstract

Winning aggressive disputes is one of several experiences that can alter responses to future stressful events. We have previously tested dominant and subordinate male Syrian hamsters in a conditioned defeat model and found that dominant individuals show less change in behavior following social defeat stress compared to subordinates and controls, indicating a reduced conditioned defeat response. Resistance to the effects of social defeat in dominants is experience-dependent and requires the maintenance of dominance relationships for 14 days. For this study we investigated whether winning aggressive interactions increases plasma testosterone and whether repeatedly winning increases androgen receptor expression. First, male hamsters were paired in daily 10-min aggressive encounters and blood samples were collected immediately before and 15-min and 30-min after the formation of dominance relationships. Dominants showed an increase in plasma testosterone at 15-min post-interaction compared to their pre-interaction baseline, whereas subordinates and controls showed no change in plasma testosterone. Secondly, we investigated whether 14 days of dominant social status increased androgen or estrogen alpha-receptor immunoreactivity in brain regions that regulate the conditioned defeat response. Dominants showed more androgen, but not estrogen alpha, receptor immuno-positive cells in the dorsal medial amygdala (dMeA) and ventral lateral septum (vLS) compared to subordinates and controls. Finally, we showed that one day of dominant social status was insufficient to increase androgen receptor immunoreactivity compared to subordinates. These results suggest that elevated testosterone signaling at androgen receptors in the dMeA and vLS might contribute to the reduced conditioned defeat response exhibited by dominant hamsters.

Dopamine D2 receptors in the dorsomedial prefrontal cortex modulate social hierarchy in male mice

“…Consistent with previous studies ( Zielinski and Vandenbergh 1993 ; Clinard et al 2016 ), we found higher basal serum T levels in dominant individuals ( Figure 2A ), which could partly explain their more competitive in the tube test. For CORT, our results were inconclusive, despite a trend for subordinate individuals to have higher CORT levels than dominant ones ( Figure 2B ).…”

Dominance relationships in Syrian hamsters modulate neuroendocrine and behavioral responses to social stress

“…While dominant hamsters show a reduced CD response compared to subordinates and animals without social status, they do not differ from SSCs in extinction of stress-induced plasma cortisol and transcription of CRH mRNA. In contrast, dominant hamsters do differ from subordinates in stress-induced neural activity within the vmPFC, medial amygdala (MeA), and lateral portions of the ventromedial hypothalamus (Morrison et al, 2014), as well as the density of androgen receptors in the MeA (Clinard, Barnes, Adler, & Cooper, 2016). The vmPFC is a key neural substrate regulating status-dependent differences in stress-related behavior because pharmacological inhibition of the vmPFC reinstates a robust CD response in dominant hamsters (Morrison et al, 2013).…”

The challenge hypothesis revisited: Focus on reproductive experience and neural mechanisms

“…We explore a subset of brain areas that may contribute to different aspects of territory formation and maintenance including the nucleus accumbens, hippocampus and bed nucleus of the stria terminalis. A number of other brain regions express androgen receptors and are associated with aggression are not included in this review such as the medial amygdala (Clinard et al, 2016) and ventromedial hypothalamus (Falkner et al, 2016). Most work on amygdala and hypothalamic modulation of aggression focuses primarily on intensity of aggression rather than other aspects of territoriality (Kruk et al, 1998;Yamaguchi and Lin, 2018).…”