Abstracts

Rationale: One of the detrimental consequences associated with traumatic brain injuries (TBIs) is the development of epilepsy. It is estimated that > 6% of all epilepsies are due to TBIs. TBI-induced seizures are accompanied by increased excitability, reactive astrogliosis, cytotoxic and vasogenic edema, and breakdown of the blood-brain-barrier. While there are currently no FDA-approved treatments for TBIs, it has been shown that anti-convulsant treatments introduced after TBI protect against acute post-traumatic seizures, but do not reduce the development of post-traumatic epilepsy (PTE). Therapeutic targeting of astrocytes may be of additional benefit, as they play important roles in moderating excitability by lowering the extracellular concentrations of K+ ions and glutamate, and are critical for self-repair mechanisms after brain injury. Our hypothesis is that a multi-targeted approach to reduce neuronal excitability and recruit astrocytes will ameliorate cellular damage following TBI and act as prophylaxis against PTE. We propose a therapeutic approach that both targets neurons, by activating M-type potassium (K+) ion channels using the anticonvulsant retigabine (RTG), and targets astrocytes using the P2Y1-receptor agonist, MRS2365. This abstract will present early results regarding drug effects on post-traumatic seizure frequency in mice, with longer-term assays of epilepsy development to follow. Methods: Mice were subjected to controlled closed-cortical impacts (CCCI) using a pneumatic impact device. TBI or sham mice were administered the M-channel opener (RTG, i.p. 1mg/kg), the P2Y1-receptor agonist, MRS2365 (i.p. 0.85mg/kg), or both drugs (RTG and MRS2365) or only vehicle (saline) within 30 minutes of induced trauma. 24 hrs after the TBI, mice were implanted with EEG electrodes and electrical activity recorded the following day to assess spontaneous seizures. To assay for changes in seizure susceptibility by chemoconvulsants, mice were challenged with i.p. injections of pilocarpine hydrochloride (75 mg/kg) at 30-min intervals at 6 days post-TBI. Methylscopolamine (1 mg/kg) was administered i.p. 30 min before application of pilocarpine to minimize peripheral cholinergic effects and mortality. Seizure susceptibility was assayed 24 hrs after the 3 injections of pilocarpine. Seizures in the mouse groups were simultaneously monitored by behavioral video monitoring, EEG recording. Clinical or sub-clinical events were scored for frequency and duration comparing different treatment cohorts. Results: Our preliminary data show TBI to cause acute seizures in 54% of mice (n=13) within two days following trauma. The strongest protective effect against acute seizures was obtained with RTG treatment with fewest animals having seizures (18%, n=11). MRS2365-treated mice also showed lower seizure occurrence (36%, n=11), but there was no further effect with combined RTG/MRS2365 treatment (31.3%, n=16). However, we found that combined RTG/MRS2365 treatment was much more protective after TBI to a pilocarpine-induced seizure susceptibility challenge (21% seizures, n=14) as compared to no treatment (69%, n=13) or single treatments with RTG (46%, n=11), or MRS2365 (55%, n=11). Conclusions: Our data thus far indicate CCCI can be used as a model to significantly increase the occurrence of acute post-traumatic seizures in mice. Both MRS2365 and RTG appear to reduce the incidence of acute post-traumatic seizures, and seizure susceptibility after TBI and thus may serve as a novel and effective treatment to control and/or prevent epilepsy. Our continuing work will determine if a combinatorial treatment approach will prevent the development of post-TBI epilepsy. Funding: DoD CDMRP grants W81XWH-15-1-0284 (M.S. and R.B. and J.L.).