Abstracts

Rationale: Traumatic brain injury (TBI) is a well-established cause of epilepsy. Lateral fluid percussion injury (LFPI) in rats is commonly used to model TBI and post-traumatic epilepsy. Seizures typically start 3 months after LFPI, with the 15% incidence, peaking at 50% by 12 months. Biomarker studies have been focusing on the “silent” period; however, it has not been well known whether during this time the animals have increased propensity to epilepsy. We used the kindling paradigm to examine whether LFPI increased the susceptibility to epilepsy at 1 month, when seizures are either absent or rare. Methods: The experiments involved 17 Sprague-Dawley rats, starting age 50 days. LFPI (target impact 2.0 atm) was induced in 6 males and 6 females. The severity of injury was gauged by the duration of apnea, suppression of toe-pinch and righting reflexes immediately after LFPI, and the neuromotor score 24 hrs later. Three males and 2 females underwent sham LFPI (shLFPI). One months after LFPI/shLFPI, rats were implanted with a bipolar stimulating electrode into basolateral amygdala (BLA), and tripolar skull screw recording electrode over sensorimotor cortex, contralateral to the LFPI. One week later, afterdischarge threshold (ADT) was detected by stimulating BLA (10 s, 20 Hz, 1 ms square monophasic pulse, starting with 0.1 mA, 0.1 mA increments, maximal 1.0 mA, every 15 min). Kindling was induced using stimuli at the ADT parameters, applied twice a day, 8 hrs apart. The rat was considered kindled upon developing 3 consecutive stage 4-5 Racine seizures. Stimulations were discontinued either after the animal was kindled, or after 24 trials, whichever occurred first. In the latter case, the number of trials was assigned as 25-27, depending on the severity of the last 3 seizures. Before, during and up to 1 week after kindling, the animals were under continuous video- and up to 8 hrs/day EEG- monitoring to capture spontaneous seizures. Results: LFPI was of a moderately high severity: apnea 45±3.9 s; suppression of pinch reflex 238±44 s, righting reflex - 14±2.3 min; neuromotor score decreased by 50-65%. As no effect of sex on kindling was detected (F[1.13]=0.18, p=0.68), data from males and females were pooled. shLFPI rats kindled after (here and further) minimum/median/maximum 14/15/19 trials and LFPI rats- after 4/13.5/27 trials (p>0.05, Mann-Whitney). LFPI subjects were next analyzed individually, vis-à-vis the range observed in the shLFPI rats. Six LFPI rats kindled faster (4/7.5/13 trials; p<0.01); 2 rats were in the shLFPI range (14/14.5/15 trials; p>