Stress amplifies memory for social hierarchy: Neurobiological mechanisms
Carmen Sandi1*, Marjan Timmer1 and Isabel M Cordero1
1 Brain Mind Institute, EPFL, Lausanne, Switzerland
Individuals differ in their social status and societies in the extent of social status differences among their members. I will show how stress affects the development of social hierarchies in rats by influencing the rank achieved and by facilitating a long-term memory for the specific hierarchy, and will address key molecular mechanisms mediating such effects. We have shown that given equal opportunities to become either dominant or submissive, stress experienced by one of the individuals during their first encounter determines the long-term establishment of a social hierarchy by acting as a two-stage rocket: (1) by influencing the rank achieved after the social encounter; and (ii) by having a long-term impact on the subsequent status of the individual in future encounters with either the same (by promoting a long-term memory for the specific hierarchy) or with other (winner-loser effects) individual/s. For the investigation of the neurobiological mechanisms implicated in the long-term influences of social hierarchy by stress, we are exploring the regulation of selected genes (OTR, V1aR, GR, AR, MAO-A, NCAM) in brain areas implicated in the regulation of stress, social behaviors and/or memory formation. In the stressed subordinate rats, we found time-specific down-regulations in oxytocin receptor (OTR) mRNA and vasopressin receptor (V1aR) in the medial amygdala (MeA) and the lateral septum, respectively. Pharmacological experiments applying a specific V1aR antagonist in the medial amygdala immediately after, but not before, a first social encounter were able to mimic the long-term memory potentiation induced by stress suggesting that the observed V1aR down-regulation might underlie the enhancement of the memory for the hierarchy induced by stress. These results will be discussed within a broader context implying stress as a strong modulator of social interactions and, particularly, on the induction of social imbalance.