Abstracts

The risk of posttraumatic epilepsy positively correlates with the severity of brain injury. Up to 50% of patients with penetrating head injury can develop epilepsy later in life, whereas for moderate injury the incidence of epilepsy is only 4.2%. Our previous study with lateral fluid percussion brain injury model (FPBI) demonstrated that severe impact strength resulting in 31-33% mortality, causes development of spontaneous recurrent seizures in 43-50% of experimental animals (Kharatishvili et al., Neuroscience 2006;140:685-97). In this study, we aimed to examine if in FPBI model, similarly to humans, probability of developing epilepsy is associated with injury severity., Head trauma was induced by lateral FPBI in adult Sprague-Dawley rats (N=15, 5 shams). The pressure of the applied impact, as recorded by a transducer, varied from 2.3 to 3.3 atm. The low mortality rate (23%) indicated moderate severity of the injury. Quantitative MRI was used to monitor the progression of the lesion starting at 3 hrs post-injury and repeated at 3 d, 9 d, 2 month-, 3 month- and 6 month post-injury time-points. Morris water maze test (MWM) was used to assess the long-term behavioral outcome (spatial learning and memory) 7 months after FPBI. After that, 24h/day continuous video-EEG monitoring was performed to assess the development of seizure activity; animals were implanted with depth electrode in the ventral hippocampus ipsilateral to the injury site and contralateral cortical electrode, and followed by continuous video-EEG for 2+2 weeks with 3 week interval for up to 12 months., The mean volume of the cortical damage at 6 months post-injury was 40.8[plusmn]38.1mm³ (range 2.7-130.0 mm³). MWM test demonstrated no difference in spatial learning in injured rats compared to shams (p[gt]0.05). EEG monitoring revealed 2-20 sec runs of 6-8 Hz monomorphic rhythmic activity with a spike-like negative phase in 70% rats both in the FPBI and control groups. This rhythm was registered in drowsiness over the injury side and was responsive to movement. No epileptiform discharges/seizures were recorded during the entire monitoring period., Rats with moderate FPBI had substantial cortical lesion. However, the hippocampus-dependent spatial learning and memory deficit was not as pronounced as previously found in animals which developed epilepsy after severe FPBI (p[lt]0.05). Also, none of the rats had electrographic seizures. In lateral FPBI, the moderate force of the impact results in progressive brain damage but does not increase the likelihood of posttraumatic epileptogenesis., (Supported by Academy of Finland, Sigrid Juselius Foundation, CIMO, EUCARE, Finnish Neurological Foundation.)