INVESTIGATING SEX DIFFERENCES IN THE HYPOTHALAMIC BRAIN CIRCUITRY OF STRESS USING GENOMIC TECHNOLOGIES

Stress is a major risk factor for mental health conditions, including depression, which alone affects over 300 million people worldwide. These conditions exhibit profound sex differences in prevalence, symptomatology and treatment responses, yet the underlying mechanisms remain poorly understood. Stress responses are coordinated by the hypothalamic-pituitary-adrenal (HPA) axis, initiated by activation of neurons in the paraventricular nucleus of the hypothalamus (PVN). Moreover, sex differences in HPA axis activity have been previously reported, providing a potential link between stress and sex-differential vulnerability to mental health conditions. However, the molecular basis of sex-specific HPA axis regulation is currently unclear. Here, we aimed to characterise sex-dimorphic neuroendocrine, molecular and transcriptomic differences along the HPA axis using a mouse model of acute restraint stress. Our data indicate that adult males exhibit a greater and more sustained HPA axis response following acute stress compared to adult females, with increased neuronal activation in the PVN. Consistent with this, males showed elevated circulating levels of the stress hormones, adrenocorticotropic hormone (ACTH) and corticosterone, alongside slower recovery to baseline. Bulk RNA sequencing of the hypothalamus revealed that males expressed stress-responsive genes at higher levels compared to females following acute restraint. These included genes involved in glucocorticoid metabolism and signalling (Hsd11b1, Sgk1), and serotonergic pathways (Slc6a4, Tph2), both of which are known modulators of HPA axis activity and have been implicated in depression. Together, these findings identify candidate molecular pathways that may drive sex differences in stress responsivity and contribute to differential vulnerability to stress-related mental health conditions.