Abstracts

Rationale: Factors that contribute to the development of post-traumatic (PTE) after traumatic brain injury (TBI) are not well understood, but genetic factors may play a role. We examined the effects of controlled cortical impact (CCI) on the development of PTE and on pentylenetetrazole (PTZ) seizure threshold in Kv1.1 knockout heterozygote mice and wild type controls to test a two-hit hypothesis of susceptibility to PTE after TBI.Methods: A 4mm craniotomy over the right parietal area was performed in Kv1.1 mice. A pneumatically controlled impactor with a 3mm tip traveling at 3.5m/s compressed the exposed cortex to 1.2 mm in depth to deliver a moderate injury. The skull cap was replaced and secured with dental acrylic. Bilateral parasagittal epidural recording electrodes were implanted after a 7-day recovery period from the CCI injury. The animals were observed for 4 months after injury, during which time they were assessed with continuous EEG recording (one week at a time) for spontaneous recurrent seizures. Then they were tested in a PTZ seizure susceptibility procedure. PTZ was infused into the tail vein in awake, freely moving, animals. Times to first twitch and onset of clonus were recorded, as was the amount of PTZ required for these effects. PTZ infusion was stopped at the onset of clonus, which allowed survival. Subsequently animals were sacrificed and brains were removed for histological study.Results: Post-traumatic epilepsy: 93% of 16 heterozygote mice subjected to CCI developed seizures compared to 20% of 15 wild type mice. 10 sham-operated heterozygote mice showed a 30% incidence of seizures, as determined by EEG. PTZ threshold test: CCI lowered the threshold for PTZ-induction of seizures. Mean time to first twitch was 38.4 sec in the CCI mice vs. 49.7 sec in the control, non-CCI mice (p < 0.001) and to the onset of clonus (53.6 sec vs. 67.4 sec, p < 0.001). The amount of PTZ necessary to induce these effects was also different: 18.9 mg/kg vs. 23.3 mg/kg (p < 0.001) for the first twitch and 26.4 mg/kg vs. 32.7 mg/kg (p < 0.001) for onset of clonus.Conclusions: Kv1.1knockout heterozygote mice are more likely to develop PTE after CCI than wild type control mice and CCI lowers the threshold for PTZ-induced seizures. These data support the two hit hypothesis and provide evidence that genotype may contribute to susceptibility to the development of PTE after TBI.