Narcolepsy type 1 (NT1) is a rare neurology disorder caused by the loss of orexin/hypocretin neurons. NT1 is characterized by excessive daytime sleepiness, sleep and wake fragmentation and cataplexy. These symptoms have been equally described in both women and men, although influences of gender and hormonal cycles have been poorly studied. Unfortunately, most studies with NT1 pre-clinical mouse models, use only male mice to limit potential variations due to the hormonal cycle. Therefore, whether gender and/or hormonal cycles impact the expression of narcoleptic symptoms remains to be determined. To address this question, we analyzed vigilance states and cataplexy in 20 female and 17 male adult orexin knock-out narcoleptic mice, with half of the females being recorded over multiple days. Mice had access to chocolate to encourage the occurrence of cataplectic episodes. A vaginal smear was performed daily in female mice to establish the state of the estrous cycle of the previous recorded night. We found that vigilance states were more fragmented in males than females, that females had less paradoxical sleep (p=0.0315) but more cataplexy (p=0.0375). Interestingly, sleep and wake features were unchanged across the female estrous cycle, but the total amount of cataplexy was doubled during estrus compared to other stages of the cycle (p=0.001), due to a large increase in the number of cataplexy episodes (p=0.0002). Altogether these data highlight sex differences in the expression of narcolepsy symptoms in orexin knock-out mice. Notably, cataplexy occurrence was greatly influenced by estrous cycle. Whether it is due to hormonal changes would need to be further explored.

The precise regulation of the cellular mechanisms underlying axonal morphogenesis is essential to the formation of functional neuronal networks. We previously identified the autism-candidate kinase NUAK1 as a central regulator of axon branching in mouse cortical neurons through the control of mitochondria trafficking. How does local mitochondrial position or function regulate axon branching during development? Here, we characterized the metabolic regulation in the developing axon and report a marked metabolic decorrelation between axon elongation and collateral branching. We next solved the cascade of event leading to presynaptic clustering and mitochondria recruitment during spontaneous branch formation. Interestingly and contrary to peripheral neurons, mitochondria are recruited after but not prior to branch formation in cortical neurons. Using flux metabolomics and fluorescent biosensors, we observed that NUAK1 deficiency significantly impairs mitochondrial metabolism and axonal ATP concentration. Upregulation of mitochondrial function is sufficient to rescue axonal branching in NUAK1 null neurons in vitro and in vivo. Altogether, our results indicate that NUAK1 exerts a dual function during axon branching through its ability to control mitochondria distribution and activity, and suggest that a mitochondrial-dependent remodeling of local metabolic homeostasis plays a critical role during axon morphogenesis. RESULTS Cortical axon elongation and collateral branching rely on distinct metabolic pathways