Seizure Susceptibility and Sleep Disturbance as Biomarkers of Epileptogenesis after Experimental TBI

Abstract

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.

Epilepsy and its neurobehavioral comorbidities: Insights gained from animal models

“…Furthermore, sleep disturbance in rats with epileptiform activity or seizures after TBI manifested as a reduced duration of rapid eye movement sleep periods and increased numbers of transitions, particularly from the N3 to awake stages, indicating sleep instability in this seizure‐prone sleep period. Combining sleep parameters with PTZ parameters did not improve the biomarker performance 128 …”

“…In line with this view, in patients, cognitive problems often exist from the onset of epilepsy, if not before. 199 As described in Section 5, Andrade et al 128 recently reported that susceptibility to PTZ and sleep disturbances predict epileptogenesis in the rat FPI model of PTE. ROC AUC values were .743 (p = .05) for PTZ test parameters and .857 (p < .01) for sleep parameters.…”

“…In a subsequent study in the same model, Andrade et al 128 examined whether rats develop chronic sleep disturbance after TBI and whether sleep disturbance parameters—alone or in combination with PTZ test parameters—could serve as biomarkers for the development of PTE. Compared to sham controls, the susceptibility to PTZ (30 mg/kg ip) increased over the 6 months after FPI.…”

Large-volume and deep brain imaging in rabbits and monkeys using COMPACT two-photon microscopy

“…For EEG recording in rabbits, two holes (1.5 mm in diameter) were drilled with an electric mill above the visual cortex and cerebellum 33 – 36 . Two silver-plated screws (2 mm in diameter) connected to two epoxy-coated silver wire (0.008 inch (0.203 mm) in diameter, A-M Systems) were inserted into the two holes separately and were used as electrodes to record cortical EEG.…”

Understanding Acquired Brain Injury: A Review

“…These particulate lesions can cause a mass effect, as well as an upsurge in ICP and brain herniation [ 17 , 65 , 67 , 68 ]. As a primary injury, brain laceration may predispose the sufferer to convulsions and epilepsy [ 69 , 70 ].…”