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

BackgroundIn addition to social and cultural factors, sex differences in the central nervous system have a critical influence on behavior, although the neurobiology underlying these differences 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 differences in behaviors related to LC nucleus, and subsequently, to assess the sex differences in LC morphology and function.MethodsFemale 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.ResultsWhile 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 differences 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.ConclusionsOverall, this study provides new insights into the sex differences related to LC nucleus and associated behaviors, which may explain the heightened emotional arousal response observed in females. Exploring sex differences in the brain is important to understand the impact of such differences in pathological conditions characterized by gender bias, as well as their therapeutic implications. In this manuscript, we examined sex differences in the mouse locus coeruleus (LC) and how this might affect related behaviours. The LC is a sexually dimorphic nucleus that integrates signals associated with attention, anxiety, stress, arousal, pain, memory and learning. Our findings reveal that female mice exhibit more intense anxiety-related behaviors but that they perform better than males in recognizing small differences between objects. Additionally, we found pronounced sex differences in the LC, which contained fewer noradrenergic cells in females, with a larger dendritic volume and displaying enhanced cell excitability. These differences in the LC, a nucleus that fulfils a pivotal role in stress and pain, could be important for understanding the higher prevalence of stress-related disorders in women, such as anxiety and depression, but also of chronic pain. Hence, it is clearly important to consider sex differences in both preclinical and clinical research studies that attempt to understand pathologies related to these phenomena. Female mice exhibit stronger anxiety-related behaviors than males, yet both show similar depressive-like behaviors.The discrimination index to distinguish similar objects with small differences is higher in females than in males.Females exhibit greater thermal pain sensitivity than males, yet both respond similarly to mechanical stimuli.Females have fewer noradrenergic cells in the LC yet they show a larger dendritic volume than males.LC neurons from female mice have a smaller cell capacitance but stronger excitability than those in males.