The effect of social status on patterns of oxidative stress in the brain

Aging and environmental stressors can increase reactive oxygen species and derail antioxidant defense, leading to oxidative stress in the brain and the rest of body. The brain is particularly susceptible to oxidative stress due to its high oxygen consumption. Cumulative oxidative damage in the brain has been implicated in several mental and neurodegenerative disorders. Competition for social dominance in social species can lead to increased oxidative stress. Previous studies have shown that chronic social defeat in low ranking individuals increased oxidative stress in specific brain regions relevant to mood disorders. However, fewer studies have examined the effect of high rank on oxidative stress in the brain. Here we tested how high and low social rank influences patterns of oxidative stress in the brain. Since highly ranked individuals have an upregulated reproductive system (hypothalamic-pituitary-gonadal (HPG) axis), we also tested how the degree of HPG axis activity is correlated with oxidative stress in the brain in a highly social cichlid fish, Astatotilapia burtoni. Male A. burtoni exist as two reversible phenotypes: dominant males are brightly color, defend a territory, and have large testes; subordinate lack bright coloration, school with females, and are reproductively suppressed. Using macrodissected brain divisions (forebrain, hypothalamus, midbrain, and hindbrain), we found distinct social status differences in oxidative stress, however these effects varied by marker of oxidative stress and across brain division. For example, we saw increased DNA damage in the midbrain of subordinate males while DNA damage tended to be lower in the hypothalamus of dominant males. Conversely, total antioxidant capacity was higher in both the midbrain and hypothalamus for subordinate males. Hierarchical cluster analysis revealed correlations in gonadosomatic index and dominance index, both of which are indicators of HPG axis activity, with markers of oxidative stress in forebrain. These findings support the idea that both social status and HPG axis regulation influence patterns of oxidative stress in the brain. Current projects are investigating oxidative damage in more specific brain regions relevant to adaptive responses to social stress as well as the role gene regulation in maintaining oxidative balance in the brain.