Animals of dominant, sub-dominant and subordinate status exhibit different neurobiological features. These differences likely are related to the differential requirements of animals of each rank in behaviors including social cognition, spatial cognition, feeding, drinking, activity, sleep, aggression, social reward etc. An important step to understanding how the brain facilitates status-specific behavior is to characterize how variation in key neurobiological markers is associated with social status.
In one study, we used autoradiography to examine whether variation in social status was associated with levels of oxytocin (OTR) and vasopressin 1a (V1aR) receptor binding in socially relevant brain regions.
We found that patterns of OTR and V1aR binding differed between mice of high and low social status. In particular, we observed that dominant males have markedly increased levels of OTR binding in the Nucleus Accumbens compared to subordinate individuals. Differences in receptor density in social brain regions may underlie behavioral differences that promote or inhibit the acquisition of social status. Alternatively, the different social experiences of dominant and subordinate animals shift receptor expression, potentially facilitating the expression of adaptive social behaviors.
We also use candidate gene approaches to study individual differences in the brain associated with social status. Using quantitative real-time PCR we identified that mRNA levels of two neural plasticity genes, DNA methyltransferase 1 and 3a (DNMT1 and DNMT3a) , in the hippocampus were negatively correlated with measures of social dominance and power. DNA methylation via DNMT is one epigenetic mechanism that cells use to inhibit gene expression. Higher levels of DNMT1 in more subordinate mice may suggest that these mice are experiencing a social suppression of gene expression in the hippocampus. Differential gene expression between more and less dominant individuals in specific brain regions may enable status-specific contextually appropriate behaviors.
In our current work, we are taking a more explorative approach to investigate brain gene expression profiles of mice varying in social status. Using Tag-based RNA-Sequencing (Tag-Seq) we have identified genes and gene networks that are differentially regulated between dominant and subordinate male mice in both the forebrain and midbrain.
Lee W, Hiura L, Yang E, Broekman KA, Ophir AG, Curley JP. 2019. Social status in mouse social hierarchies is associated with variation in oxytocin and vasopressin 1a receptor densities. Hormones and Behavior 114:104551. PDF Online Article
Williamson CM, Franks B, Curley JP. 2016 Mouse social network dynamics and community structure are associated with plasticity-related brain gene expression. Front. Behav. Neurosci. 10, 152. PDF Online Article
Williamson CM, Lee W, Decasien AR, Lanham A, Romeo RD, Curley JP. 2019 Social hierarchy position in female mice is associated with plasma corticosterone levels and hypothalamic gene expression. Scientific Reports. 9:7324. PDF Online Article