Oxytocin Regulation of Social Buffering Following Stress

In this dissertation, the neurobiological mechanisms that govern the effects of social buffering on stress were evaluated in female prairie voles (Microtus ochrogaster). As reviewed in Chapter 1, social living is beneficial for many species, resulting in increased individual survival and fitness. One factor that seems to lead to such benefits is the anxiolytic effects of social contact with a bonded partner, referred to as social buffering. While stressful life events can enhance the risk of mental disorders, positive social interactions, particularly with a significant other, can propagate good mental health and normal behavioral routines. Still, the functional neural systems that promote these benefits via regulation of the hypothalamic-pituitary-adrenal (HPA) axis recovery are undetermined. Prairie voles engage in and depend on a social environment, including male-female pair-bonds, biparental care, and living in extended families. Like other monogamous mammals, male-female interactions can reduce basal HPA axis activity while promoting stress-reducing neuropeptidergic pathways in prairie voles. In Chapter 2, I evaluated the variability of the behavioral and physiological response as a function of the nature of the stressor in female prairie voles. This is important, as little research has been conducted to study the stress response in voles and determining the responsivity of prairie voles to various stressors will lead to better models of stress in this socially and physiologically unique species. I found stress-specific effects on physiological and behavioral response that varied as a function of the source, intensity, and predictability of the stressor. Furthermore, these data highlight the utility of immobilization within an acute paradigm to characterize the stress response in female prairie voles. Chapter 3 revealed that social buffering from a bonded partner can reverse the aversive effects of immobilization stress on behavior, physiology, and neurochemistry through local activation of the oxytocin (OT) system in the paraventricular nucleus of the hypothalamus (PVN). Recovering from immobilization stress with their bonded partner lead to a reduction in the stress response in female prairie voles. This social buffering by the male partner was accompanied by increased OT release in the PVN. In addition, an intra-PVN OT injection reduced behavioral and physiological responses to immobilization stress whereas an injection of an oxytocin receptor antagonist blocked the effects of the social buffering. This provides evidence for a neural mechanism underlying the social buffering effect from a pair bonded partner in female prairie voles. Finally, in Chapter 4, I discuss these findings and their implications in a general context and suggest future directions for related research.