Change in social rank and brain dopamine levels: findings from a novel pig model

Dopamine (DA) signaling is central in hypothesized causal paths linking the influence of social and environmental variables with cognition, behavior and affective states, including vulnerability to drug dependence. Here, we study whether change in one's social rank induces DA and norepinephrine (NE) changes using a novel pig model with a social-ranking-and-re-ranking protocol to investigate social context influences on catecholamine concentrations in cerebrospinal fluid (CSF) and blood. For two weeks, 16 recently weaned male piglets were socially housed in four groups, with video-recordings for social rank assessments (, {beta}, {gamma}, and {delta}); CSF and blood were obtained from these stable social groups. Next, all four were housed together, as were all four {beta}, etc., again with video recording for blinded social ranking. CSF and blood samples were collected at three time points: prior to initial social housing, following social housing and following re-organization. Regression analyses disclosed a positive relationship between changes in social rank and post-rank change in CSF levels of DA; one unit increase of social rank predicted a 17.4 pg/ml increase in CSF dopamine concentrations (95% CI= 1.2, 33.7). Compared to piglets with downward shifts in ranks (i.e., high-to-low), piglets with upward shifts (i.e., low-to-high) had a statistically significant greater increase in CSF DA levels. No relationship was observed for CSF NE or blood concentrations of DA or NE at any phase of this experiment. This work, using a novel pig model, adds new evidence on alteration of the brain dopaminergic system induced by social rank change.