Abstracts

The recent discovery that fluid percussion injury (FPI) induces posttraumatic epilepsy (PTE) in the rat has revealed chronic recurrent spontaneous partial seizures (CRSPSs) that evolve over time in frequency and duration^1,2. Epileptiform electrocorticographic (ECoG) events were found to range in duration from 0.5 seconds in the earlier weeks, to 1.5 minutes 7 months post-injury. To better understand the properties of these partial seizures we evaluated 1) their behavioral correlate, and 2) their power spectra. Severe rostral parasaggital FPI was induced in 5 week old Sprague-Dawley male rats (3.25-3.5 atm). Chronic video-ECoG with 5 epidural electrodes placed above frontal-parietal and parietal-occipital cortex was performed from 2 to 28 weeks post-injury. Data are shown as mean [plusmn] S.E.M. The dominant frequency of each electrical seizure was determined by Fast Fourier Transformation. [italic]Behavioral analysis:[/italic]A software randomizer was used to select 100 random ECoG events at weeks 2-17 post-FPI (6 animals). The behavior of the animal at each random or epileptiform ECoG event was scored, assigning 0 to no change and 1 to a change in behavior. Only 8.7% of random ECoG events were associated with a behavioral score=1, while 98.6% of epileptiform ECoG events were associated with a behavioral score=1 (p[lt]0.0001; statistics with Mann-Whitney U test).
[italic]Electrophysiological analysis:[/italic] Grade 1 seizures were characterized by a dominant frequency of 6.4[plusmn]0.12 Hz at 2-3 weeks, that increased to 7.7[plusmn]0.29 Hz at 27-28 weeks post-injury (p[lt]0.001). Grade 2 seizures presented a dominant frequency of 6.6[plusmn]0.07 Hz at 2-3 weeks, that increased to 7.9 [plusmn] 0.16 Hz at 27-28 weeks post-injury (p[lt]0.001). Similarly, grade 3 seizures were characterized by 6.1 [plusmn] 0.34 Hz at 2-3 weeks, that increased to 8.1 [plusmn] 0.14 Hz at 27-28 weeks post-injury (p[lt]0.001; Statistics with t-test.). These results demonstrate that:1) FPI-induced epileptiform ECoG events are statistically associated with alterations in behavior of the animal, demonstrating that, regardless of their duration, epileptiform ECoG events are ictal; 2) FPI-induced CRSPSs are characterized by a dominant frequency that increases over time post-injury, demonstrating that the epileptic condition worsens over time. Overall, these observations further outline the ictal nature of FPI-induced partial seizures in the first weeks post-injury, and the progressive nature of FPI-induced PTE. (Supported by NS040823 to RD.)