Background: The prevalence of post-traumatic stress disorder (PTSD) and anxiety disorders is higher in women than men. The severity of hallmark symptoms including hypervigilance and fear reactivity to unpredictable threats varies with sex and reproductive cycle, but the underlying mechanisms remain unclear. Here, we investigated corticotropin-releasing factor (CRF) neurons in the dorsolateral bed nucleus of the stria terminalis (BNSTDL) as a potential nexus for the influence of biological sex and reproductive cycle on fear- and anxiety-related behaviors. Methods: 103 male and 132 cycle-monitored female CRF-Cre rats were used. BNSTDL-CRF neuron excitability and synaptic activity was recorded with slice electrophysiology. Chemogenetic inhibition of BNSTDL-CRF neurons was performed before elevated-plus maze, predator odor exposure, shock-induced startle sensitization, and anxiety-potentiated startle (APS) following unpredictable fear conditioning. Results: BNSTDL-CRF neurons in females exhibit higher excitability (cycle-independent) and lower sensitivity to excitatory synaptic inputs (proestrus and diestrus) compared to males. BNSTDL-CRF neuron inhibition reduces open-arm time in estrous females but not males, suggesting that BNSTDL-CRF neurons reduce anxiety during sexual receptivity. In the APS, BNSTDL-CRF neuron inhibition attenuates short-term startle potentiation in males, whereas it causes persistent APS in diestrous females. Conclusions: Unpredictable fear conditioning elicits sex- and estrous phase-specific APS, differentially regulated by BNSTDL-CRF neurons. Persistent APS in females align with hormonal phases marked by low reproductive hormones, mirroring human PTSD findings. Our findings underscore the sex- and hormone-specific role of BNSTDL-CRF neurons in APS. Widely used in human studies, APS may bridge animal and human research, supporting biomarker development and more effective pharmacotherapies.
