Abstracts

Rationale: Traumatic brain injury (TBI) is a leading cause of acquired temporal lobe epilepsy (TLE), however the signals that initiate pro-epileptic mechanisms after injury are not understood. Multiple lines of evidence suggest brain inflammation contributes to the development of epilepsy by affecting cell loss and cell excitability, but few studies have employed experimental models to assess the role of inflammation in the process of posttraumatic epileptogenesis. Here, the role of Interleukin-6 (IL-6) in epilepsy development was tested in a controlled cortical impact (CCI) model of TBI in mice. It was hypothesized that reducing IL-6 acutely following brain injury suppresses posttraumatic seizure development, whereas acutely increasing IL-6 has the opposite effect. Methods: CCI (depth 1.0 mm; velocity 3.5 m/s; duration 500 ms) was given to 6-8 week old male CD-1 mice. Sham-injured mice received identical treatment except no impact. IL-6 was manipulated (10 minutes before and 30 minutes after CCI) by intranasal administration of either recombinant IL-6 (400 ng/animal) or IL-6 neutralizing antibody (IL-6NA; 100 g/animal). A subset of mice (Sham or CCI) received isotype control antibody (100 g/animal) at matching time-points. Mice were monitored for spontaneous seizures during random 1-2 hour intervals (6 hr/animal/wk) during wks 7-10 post-injury. Seizures were classified by a modified Racine scale, omitting category 1 behavior. An animal was considered to have acquired epilepsy if a minimum of three spontaneous seizures (category 2-5) were observed. Cresyl violet- and Timm-stained sections (6-13 wks post-CCI) were used to test for the presence of mossy fiber sprouting (MFS) and to examine lesion size. Mean MFS scores were determined in an 800 m region under the injury epicenter. Results: Preliminary results indicate the following rates of spontaneous seizure expression within each group: Sham 0%, CCI 31%, CCI+IL-6 33% and CCI+IL-6NA 22%. In the CCI+IL-6 group, 4/12 mice exhibited dramatic tissue damage proximal to the impact site, including extensive loss of cortical and hippocampal tissue near the injury. This exacerbated tissue loss was not observed in other experimental groups. Mean Timm scores were similar in all CCI groups: CCI 1.9, CCI+IL-6 1.7 and CCI+IL-6NA 1.7, whereas no MFS was detected in Sham animals. Conclusions: Exacerbated tissue damage associated with CCI+IL-6 treatment provides evidence that this inflammatory cytokine promotes cell loss in the injured brain. Characterization of the spatial extent of cell loss and the identity of cell types affected is underway. Effects of dose and timing of IL-6 on posttraumatic epileptogenesis in CCI animals is also being assessed, as is the effectiveness of intranasal delivery for IL-6NA. Alternative routes of administration are currently being investigated. Based on this cytokine s ability to affect cell loss, but not mossy fiber sprouting, in the injured brain, IL-6 may contribute to posttraumatic epileptogenesis.