THE CAUSAL ROLE OF NEUROENDOCRINE STRESS RESPONSES VIA THE HYPOTHALAMIC-PITUITARY-ADRENAL AXIS IN EMPATHY-LIKE BEHAVIORS IN RATS

Stress is ubiquitous in modern society and impacts emotions, cognition, and social interactions. Importantly, stress may alter the capacity for empathy toward others. This change is thought to involve the hypothalamic-pituitary-adrenal (HPA) axis, particularly glucocorticoids released from the adrenal cortex. In this study, we focused on physiological stress responses, specifically peripheral glucocorticoid levels, and examined whether they influence empathy-like behavior in rats. Male Sprague-Dawley rats were assigned to one of four conditions: injection of corticosterone (the primary glucocorticoid in rodents; 1 or 10 mg/kg), the glucocorticoid synthesis inhibitor metyrapone (50 or 100 mg/kg), or a vehicle control. We assessed social affective preference for unfamiliar conspecifics that were distressed (nauseated by lithium chloride [LiCl] injection; 150 mg/kg). The time spent sniffing toward LiCl- and saline-treated rats was measured for 10 minutes. Consistent with our previous findings, control rats tended to prefer the LiCl-treated conspecific; however, this preference was diminished by metyrapone treatment, suggesting that the inhibition of corticosterone synthesis impairs socioemotional approach behaviors. The preference was also diminished by corticosterone administration. These suggest that there may be an optimal level of peripheral corticosterone secretion for distinguishing between distressed and non-distressed conspecifics. In summary, our findings suggest that peripheral corticosterone secretion is involved in empathic concern, specifically in the recognition of individuals in distress. We are currently evaluating serum corticosterone concentrations and glucocorticoid receptor activity to further investigate their associations with behavior.