Sex differences in corticotropin-releasing factor receptor-2α expressing neurons in acutely stressed mice.

Females are 2-3 times more likely than males to be diagnosed with mood disorders, including depression and anxiety, yet the neurobiological mechanisms contributing to this sex difference are not fully understood. Corticotropin-releasing factor receptor 2 (CRFR2) plays a key role in regulating stress responses, with evidence suggesting it may dampen hypothalamic-pituitary-adrenal (HPA) axis activation and behavioral stress responses. Although CRFR2 has been implicated in stress buffering, little is known about how its expression and activation differs by sex, particularly in the mouse model. To address this gap, we used newly generated CRFR2-Cre-2α-TdTomato mice to investigate sex differences in CRFR2-expressing neurons and their activation across stress-regulating brain regions following an acute restraint. Males exhibited significantly more CRFR2-expressing neurons in the lateral septum, bed nucleus of the stria terminalis, paraventricular nucleus of the hypothalamus, and central amygdala, while females had more CRFR2-expressing neurons in the medial amygdala and ventromedial hypothalamus. Activation of CRFR2 neurons also showed region-specific sex differences, with males generally exhibiting greater CRFR2 colocalization with c-Fos, a marker for neural activation. Corticosterone levels following restraint were correlated with CRFR2 expression or activation in several brain regions, including the paraventricular hypothalamus, medial amygdala, and bed nucleus of the stria terminalis. These findings identify novel sex differences in CRFR2 expression and stress-induced activation of CRFR2 neurons across multiple stress-regulating brain areas. Together, these results suggest that sex differences in CRFR2 signaling may mediate sex differences in HPA axis responsivity as well as behavioral stress responses.