Effects of dominance status on conditioned defeat and expression of 5-HT1A and 5-HT2A receptors

Abstract

Past experience can alter how individuals respond to stressful events. The brain serotonin system is a key factor modulating stress-related behavior and may contribute to individual variation in coping styles. In this study we investigated whether dominant and subordinate hamsters respond differently to social defeat and whether their behavioral responses are associated with changes in 5-HT1A and 5-HT2A receptor immunoreactivity in several limbic brain regions. We paired weight-matched hamsters in daily aggressive encounters for two weeks so that they formed a stable dominance relationship. We also included controls that were exposed to an empty cage each day for two weeks. Twenty-four hours after the final pairing or empty cage exposure, subjects were socially defeated in 3, 5-min encounters with a more aggressive hamster. Twenty-four hours after social defeat, animals were tested for conditioned defeat in a 5-min social interaction test with a non-aggressive intruder. We collected brains following conditioned defeat testing and performed immunohistochemistry for 5-HT1A and 5-HT2A receptors. We found that dominants showed less submissive and defensive behavior at conditioned defeat testing compared to both subordinates and controls. Additionally, both dominants and subordinates had an increased number of 5-HT1A immunopositive cells in the basolateral amygdala compared to controls. Subordinates also had more 5-HT1A immunopositive cells in the dorsal medial amygdala than did controls. Finally, dominants had fewer 5-HT1A immunopositive cells in the paraventricular nucleus of the hypothalamus compared to controls. Our results indicate that dominant social status results in a blunted conditioned defeat response and a distinct pattern of 5-HT1A receptor expression, which may contribute to resistance to conditioned defeat.

Serotonin and stress coping

“…In one study, dominant and subordinate hamsters previously subjected to social defeat exhibited different behavior during social confrontation (dominant showing less submissive/passive behavior). Higher 5-HT1A immunopositive cells in the dorsal medial amygdala of subordinates were evident, while dominants had fewer 5-HT1A immunopositive cells in the paraventricular nucleus of the hypothalamus, pointing to distinct patterns of 5-HT1A receptor expression in relation to coping attitudes [94]. From these studies a major role of 5-HT1A receptors in coping behavior in experimental animals stands out clearly.…”

Mouse Model ofOPRM1(A118G) Polymorphism Increases Sociability and Dominance and Confers Resilience to Social Defeat

“…5a). Dominant rodents within a hierarchy do not express SD behavior and exhibit increased social interaction (Morrison et al, 2011(Morrison et al, , 2012. G/G mice show social dominance, resilience to SD, and increased social interaction.…”

Dominance status alters restraint-induced neural activity in brain regions controlling stress vulnerability

“…After a dominance relationship is formed, we use 5-min encounters to maintain the relationship and prevent wounding of the subordinate. Using this model, we have found that dominance relationships remain stable for at least two weeks [24, 28]. Dyads that failed to establish a clear and stable dominance relationship by the fifth encounter were excluded from analysis (n = 4 dyads).…”