Mapping orexin/hypocretin receptor expression in the central nervous system after incomplete spinal cord injury in mice

Spinal cord injury immediately impairs movement control and other essential physiological functions. Evidence has shown that a large-scale network including spinal and supraspinal structures is recruited after SCI to promote functional recovery. Orexins (hypocretins), known for promoting wakefulness, arousal, and reward-seeking behaviours, also influence muscular tone, locomotion initiation, and skilled performance, exerting a multi-systemic effect on motor control predisposing for movement execution. Despite the potential relevance of orexin transmission in motor recovery after CNS damage, the status of the orexinergic system after SCI remains unexplored. Therefore, we aimed to investigate the impact of incomplete cervical SCI on orexin receptor (OXR) expression within the CNS and its potential correlation with motor performance. C57Bl6/J mice were trained to use their forelimb to perform skilled motor tasks, including single-pellet reaching and grasping and string pulling. Motor performance in these tasks, as well as gait and skilled locomotion, were tested and video-recorded. Then, animals received either a dorsally extended unilateral hemisection (which also severed both dorsal columns) at the C4 level or a sham laminectomy. Subsets of injured and sham animals were evaluated and transcardially perfused at 4, 10, or 30 days post-injury. OXR expression was assessed by RNAscope in regions including the spinal cord, dorsal raphe, locus coeruleus, ventral tegmental area, and reticular formation. We observed an OXR expression pattern that varied across the time course after the injury in a region-specific manner. This dynamic expression map will provide valuable insights into the role of orexinergic transmission in motor function recovery following SCI.