TEMPORAL EFFECTS OF PRE-EXISTING STRESS ON POST-TBI SLEEP ARCHITECTURE, GLYMPHATIC MARKERS, AND NEUROINFLAMMATORY RESPONSES IN A GYRENCEPHALIC MODEL

Traumatic Brain Injury (TBI) causes significant disability and death, and is linked to neurodegenerative diseases and sleep disorders. Sleep activates the glymphatic system, which removes brain metabolites via aquaporin-4 (AQP4) channels. Chronic stress disrupts this process, causing sleep disorders and exacerbating stress. Despite the intrinsic relationship between stress and TBI, few studies have examined how pre-existing stress influences TBI outcomes. This study investigated the temporal effects of pre-injury stress exposure in ferrets with TBI, focusing on activity/sleep patterns, glymphatic components and neuroinflammatory response. Adult male ferrets were assigned to Control (CON), Injury (IN), or Injury+Stress (I+S) groups, each undergoing distinct protocols. Activity/sleep was monitored. Brain tissue was analysed using immunofluorescent markers for astrocytes, AQP4 and microglia. At 1-month-post-injury (1MPI), CON exhibited distinct clusters of sustained high-activity with 50% active for over 50 minutes. Clustering was reduced and more random in IN and I+S. At 6-month-post-injury (6MPI), I+S had more high-activity clusters than IN but less sustained than CON. These changes suggest sleep disturbances and impaired functionality. Elevated astrocytic and AQP4 immunoreactivity persisted in IN and I+S up to 6MPI, consistent with TBI and impacting neuroinflammation, sleep regulation, post-traumatic oedema and secondary injury progression. IN exhibited microglial activation at 1MPI, transitioning to amoeboid morphology by 6MPI. I+S showed reduced microglial immunoreactivity. In conclusion, pre-existing stress can influence TBI outcomes over time, affecting activity/sleep patterns, astrocytic reactivity and microglial response. Paradoxically, pre-injury stress showed some neuroprotective effects in TBI, highlighting the complex relationship between stress and brain injury outcomes.