Abstracts

Rationale: Traumatic brain injury (TBI) is a leading cause of acquired temporal lobe epilepsy (TLE), yet the mechanisms underlying posttraumatic epileptogenesis are not known. TBI is associated with cell loss and changes in cellular and synaptic signaling in cortical structures. Activation of the JAK/STAT3 pathway has been implicated as a participant in the reactive plasticity associated with epileptogenesis. Here, a murine model of TBI that results in spontaneous seizures was used to examine aspects of hippocampal GABA network modification shortly after brain injury. We tested the hypothesis that regional JAK/STAT3 pathway modulation and hilar GABAergic interneuron loss occurs shortly after focal brain injury. Methods: Severe controlled cortical impact (CCI; impact depth= 1.0 mm) was administered to male mice at 6-8 weeks of age. 24 hours post- injury, hippocampi from male CD-1 mice were isolated and processed for western blot analysis of STAT3 and pSTAT3 proteins, with the latter used as a marker of JAK/STAT3 activation. The effectiveness of the STAT3 inhibitor WP1066 (EMD Millipore; 30 and 90 min post-CCI; 50mg/kg; i.p.) on blocking JAK/STAT3 activation was also tested. Hilar GABA cell loss 2-3 days following CCI was examined in male mice expressing GFP in a subset of hilar interneurons (GIN mice; FVB-Tg(GadGFP)4570Swn/J). Coronal sections (30 μm) were sampled in a 1 in 5 series. GFP-positive cell counts and hilus area were analyzed using a laser scanning confocal microscope (Zeiss, LSM 5 LIVE). Results: At 24 hours following CCI an increase in hippocampal pSTAT3 protein expression ipsilateral to the injury was observed, relative to either the contralateral hemisphere or Sham-operated controls. Both Sham-operated controls and the contralateral hemisphere of injured animals exhibited low levels of hippocampal pSTAT3 protein expression. Administration of the STAT3 inhibitor WP1066 inhibited pSTAT3 protein expression in the hippocampus ipsilateral to the injury, but had little effect on the contralateral hemisphere of injured animals or Sham operated controls. Quantification of GFP positive cells from GIN mice revealed a decrease in the number of hilar interneurons within dorsal hippocampus ipsilateral to the injury relative to the contralateral hemisphere or to Sham-operated controls. Preliminary data indicate that administration of WP1066 did not inhibit hilar GABA cell loss ipsilateral to the injury. Conclusions: Early time-points following brain injury with CCI are associated with changes in hippocampal GABA networks. These changes are prominent in the hippocampus ipsilateral to the injury and include a loss of hilar GABAergic interneurons as well as activation of the JAK/STAT signaling pathway. Previous studies have associated both of these changes with alterations in GABA signaling associated with TLE. Alterations in hippocampal GABA neuron function following head injury may support the eventual expression of spontaneous seizures in posttraumatic epilepsy.