Effects of social dominance on perineuronal nets in medial prefrontal cortex and basolateral amygdala

The development of dominance relationships generates experience-dependent plasticity in cortical circuits controlling social behavior and responses to stress. Perineuronal nets (PNN) are specialized extracellular structures that surround cortical neurons and contribute to experience-dependent neural plasticity. Using a Syrian hamster model, we investigated whether the development of dominance relationships altered the expression of PNNs in the infralimbic (IL) and prelimbic (PL) regions of the ventral medial prefrontal cortex, as well as the basolateral amygdala (BLA). We also tested whether PNN expression predicted agonistic behavior during the early or late phases of dominance interactions. Male and female hamsters were paired with same-sex partners and exposed to daily dominance interactions for two weeks. In Study 1, brains from male hamsters were collected for PNN staining 60 mins or 1-3 days following the final dominance interaction. We found that dominant males had more IL neurons surrounded by PNNs compared to subordinate males, and all hamsters showed greater PNN expression in caudal, compared to rostral, regions of the IL and PL. In Study 2, we included both males and females and collected brains 60 mins after the final dominance interaction. In Study 2, we found that subordinate females had more PL neurons surrounded by PNNs compared to dominants and social exposure controls. The rate of attacks during the late phase of dominance interactions predicted the number of PNN+ cells in the PL in dominant males, which is consistent with neural plasticity in PL neurons leading to elevated aggression in dominant males. Overall, the neural plasticity in the PL and IL induced by the formation of dominance relationships may contribute to sex differences in responses to social challenges.