Abstracts

Rationale: Post traumatic epilepsy (PTE) is the cause of 20% of symptomatic epilepsy. While the precipitating brain injury is well-identified, the incidence, progression, and treatment of PTE are not well understood. Astrogliosis is a common consequence of severe brain injury. We have demonstrated that astrogliosis, associated with overexpression of adenosine kinase and resulting adenosine deficiency, is linked to hippocampal hyperexcitability. We hypothesized that by blocking the ADK upregulation, we could maintain an adenosinergic tone in the injured brain, and thus minimize seizure susceptibility following severe TBI. Methods: Male Sprague Dawley rats (n=15) received severe TBI by fluid percussion injury (FPI). 48 hours after FPI, they received either vehicle injection (lactated ringers, n=9) or an AAV8 virus expressing ADK mRNA antisense with a GFP promoter (1x1010 genomic particles/ml). Vehicle or virus injection was disbursed in the hippocampus (3 l) and the cortex (3 l) at the site of FPI. The GABA inhibitor pentylenetetrazol (PTZ, Sigma) was used to assess seizure susceptibility. Pretreatment with the adenosine A1 receptor antagonist DPCPX (8-Cyclopentyl-1,3-dipropylxanthine, Sigma) was used to assess the role of adenosine in seizure susceptibility. Results: The PTZ seizure threshold in severely injured rats with vehicle treatment was 35.0 /- 3.5 mg/kg, not significantly different from na ve rats (35.5 /- 3.2 mg/kg). However, in the severely injured rats with ADK-antisense virus, the threshold increased to 44.2 /- 5.1 mg/kg PTZ. In a subsequent study, seizure severity was assessed by the Racine scale following three PTZ administrations (25mg/kg): baseline PTZ, DPCPX PTZ, and PTZ alone. A minimum of 48 hours passed between tests. For the baseline PTZ test, there was no difference among the groups, with an average Racine score of 2.9 for na ve, 3.2 for severe FPI vehicle, and 3.0 for severe ADK-antisense treated rats. When the PTZ treatment was preceded by DPCPX, the na ve rats average Racine score was 3.1, and the Severe ADK antisense 3.0. However, the Severe vehicle treated animals Racine score increased to 4.0. A final PTZ dose showed a PTZ response similar to the baseline Racine score, indicating the absence of kindling in these studies. Conclusions: Our data demonstrate (i) that epileptiform bursts already occur within a short time span (4-6 weeks) after severe TBI, (ii) that those epileptiform bursts determine seizure susceptibility, and (iii) that an ADK antisense approach can be used to reduce seizure susceptibility following TBI. These results are of importance regarding therapeutic prospects for both civilian and military victims of TBI.