• Patterns of Endocrine, Behavioural, and Neural Function Underlying Social Deficits after Social Instability Stress in Adolescent Rats

      Hodges, Travis; Department of Psychology
      Adolescence is a time of social learning as well as a period of heightened vulnerability to stressors and enhanced plasticity, compared with adulthood. Previous research found that repeated social instability stress (SS; daily isolation and return to an unfamiliar peer from postnatal day (PND) 30 - 45) administered in adolescent rats alters social function when tested in adulthood. The main goal of my thesis research was to characterize how SS in adolescent rats affects the development of social brain regions and social behaviour when tested soon after the procedure. In chapter 2, I found that SS potentiated corticosterone release in rats repeatedly paired with an unfamiliar cage-mate after isolation compared with rats that were paired with an unfamiliar cage-mate for the first time after isolation on PND 45. In chapter 3, I found that in social interaction tests (i.e., not in home cage), SS rats had lower social interactions despite having higher social approach with unfamiliar peers relative to control (CTL) rats. Social stimuli carried the same reward value for SS and CTL rats based on tests of conditioned place preference, and SS in adolescence impaired social recognition. Further, SS increased oxytocin receptor density in the nucleus accumbens and dorsal lateral septum in rats compared with CTL rats. In chapter 4, I found that the correlations between time spent in social interaction with an unfamiliar peer and Fos immunoreactivity (a marker of neural activity) in the arcuate nucleus, dorsal lateral septum, and posterior medial amygdala were in the opposite direction in SS rats to those in CTL rats. In chapter 5, I found differences in the expression of proteins relevant for synaptic plasticity and in dendritic arborisation in the lateral septum and medial amygdala. My findings of behavioural and neural differences between SS and CTL rats highlight the heightened vulnerability of the brain to the quality of social experiences during the adolescent period that may lead to long-lasting deficits in social function in adulthood.