ReviewSex differences in the locus coeruleus-norepinephrine system and its regulation by stress

•Psychiatric disorders linked to stress and hyperarousal are more prevalent in women.•There are structural sex differences in the locus coeruleus (LC) arousal center.•Estrogens increase norepinephrine levels in LC target regions.•Female LC neurons are more sensitive to the stress neuropeptide CRF.•Collectively, these effects may contribute to sex biases in psychiatric disorders.

Women are more likely than men to suffer from post-traumatic stress disorder (PTSD) and major depression. In addition to their sex bias, these disorders share stress as an etiological factor and hyperarousal as a symptom. Thus, sex differences in brain arousal systems and their regulation by stress could help explain increased vulnerability to these disorders in women. Here we review preclinical studies that have identified sex differences in the locus coeruleus (LC)-norepinephrine (NE) arousal system. First, we detail how structural sex differences in the LC can bias females towards increased arousal in response to emotional events. Second, we highlight studies demonstrating that estrogen can increase NE in LC target regions by enhancing the capacity for NE synthesis, while reducing NE degradation, potentially increasing arousal in females. Third, we review data revealing how sex differences in the stress receptor, corticotropin releasing factor 1 (CRF1), can increase LC neuronal sensitivity to CRF in females compared to males. This effect could translate into hyperarousal in women under conditions of CRF hypersecretion that occur in PTSD and depression. The implications of these sex differences for the treatment of stress-related psychiatric disorders are discussed. Moreover, the value of using information regarding biological sex differences to aid in the development of novel pharmacotherapies to better treat men and women with PTSD and depression is also highlighted.This article is part of a Special Issue entitled SI: Noradrenergic System.