Objectives: We investigated whether seizure susceptibility increases over weeks−months after experimental
traumatic brain injury (TBI), and whether seizure susceptibility in rats predicts the development of
post-traumatic epilepsy (PTE) or epileptiform activity. We further investigated whether rats develop chronic sleep disturbance after TBI, and whether sleep disturbance parameters—alone or in combination with
pentylenetetrazol (PTZ) test parameters—could serve as novel
biomarkers for the development of post-traumatic epileptogenesis. Methods: TBI was induced in adult male Sprague-Dawley rats with lateral fluid-percussion injury.
Sham-operated experimental controls underwent
craniectomy without exposure to an impact force. Seizure susceptibility was tested with a PTZ test (30 mg/kg, intraperitoneally) on day (D) 30, D60, D90, and D180 after TBI (n = 28) or
sham operation (n = 16) under video electroencephalogram (vEEG). In the 7th post-injury month, rats underwent continuous vEEG monitoring to detect spontaneous
seizures and assess sleep disturbances. At the end of the experiments, rats were perfused for brain histology. Results: In the TBI group, the percentage of rats with PTZ-induced
seizures increased over time (adjusted p < 0.05 compared with D30). Combinations of three PTZ test parameters (latency to the first epileptiform discharge (ED), number of EDs, and number of PTZ-induced
seizures) survived the leave-one-out validation for differentiating rats with or without epileptiform activity, indicating an area under the receiver operating curve (AUC) of 0.743 (95% CI 0.472−0.992, p = 0.05) with a misclassification rate of 36% on D90, and an AUC of 0.752 (95% CI 0.483−0.929, p < 0.05) with a misclassification rate of 32% on D180. Sleep analysis revealed that the number of transitions to N3 or rapid eye movement (REM) sleep, along with the total number of transitions, was increased in the TBI group during the lights-on period (all p < 0.05). The
sleep fragmentation index during the lights-on period was greater in the TBI rats than in
sham-operated rats (p < 0.05). A combination of sleep parameters showed promise as diagnostic
biomarkers of prior TBI, with an AUC of 0.792 (95% CI 0.549−0.934, p < 0.01) and a misclassification rate of 28%. Rats with
epilepsy or any epileptiform activity had more transitions from N3 to the awake stage (p < 0.05), and the number of N3−awake transitions differentiated rats with or without epileptiform activity, with an AUC of 0.857 (95% CI 0.651−1.063, p < 0.01). Combining sleep parameters with PTZ parameters did not improve the
biomarker performance. Significance: This is the first attempt to monitor the evolution of seizure susceptibility over months in a well-described rat model of PTE. Our data suggest that assessment of seizure susceptibility and sleep disturbance can provide diagnostic
biomarkers of prior TBI and prognostic
biomarkers of post-traumatic epileptogenesis.