Sexual differences in locus coeruleus neurons and related behavior in C57BL/6J mice

Abstract

Background In addition to social and cultural factors, sex diferences in the central nervous system have a criti‑ cal infuence on behavior, although the neurobiology underlying these diferences remains unclear. Interestingly, the Locus Coeruleus (LC), a noradrenergic nucleus that exhibits sexual dimorphism, integrates signals that are related to diverse activities, including emotions, cognition and pain. Therefore, we set-out to evaluate sex diferences in behaviors related to LC nucleus, and subsequently, to assess the sex diferences in LC morphology and function. Methods Female and male C57BL/6J mice were studied to explore the role of the LC in anxiety, depressive-like behavior, well-being, pain, and learning and memory. We also explored the number of noradrenergic LC cells, their somatodendritic volume, as well as the electrophysiological properties of LC neurons in each sex. Results While both male and female mice displayed similar depressive-like behavior, female mice exhibited more anxiety-related behaviors. Interestingly, females outperformed males in memory tasks that involved distinguishing objects with small diferences and they also showed greater thermal pain sensitivity. Immunohistological analysis revealed that females had fewer noradrenergic cells yet they showed a larger dendritic volume than males. Patch clamp electrophysiology studies demonstrated that LC neurons in female mice had a lower capacitance and that they were more excitable than male LC neurons, albeit with similar action potential properties. Conclusions Overall, this study provides new insights into the sex diferences related to LC nucleus and associated behaviors, which may explain the heightened emotional arousal response observed in females