Abstracts

Rationale: Brain-derived neurotrophic factor (BDNF) is a neurotrophin that regulates a wide variety of cell signaling pathways including pro- survival and cell death machinery in a receptor-specific manner. Previous studies in rats have demonstrated an increase in BDNF expression after status epilepticus (SE), which activates inducible cAMP early repressor (ICER) transcription via Signal Transducer and Activator of Transcription 3 (STAT3) activation. ICER activation mediates a downstream decrease in the expression of the alpha 1 subunit of the GABAA receptor in the hippocampal dentate gyrus of rats. BDNF actions are mediated by TrkB and p75 neurotrophin receptor (NTR), but the specific receptor meditating BDNF-induced JAK/STAT activation is not known. Recent studies have shown that modulation of p75NTR prevents BDNF-induced activation of the JAK/STAT pathway in rat cultured hippocampal neurons, suggesting that proBDNF, the high affinity ligand for p75NTR, may play a critical role. The goal of this project is to investigate the relative contribution of proBDNF signaling to the JAK/STAT pathway after seizures through the use of BDNF-tagged transgenic C57BL/6J mice. Methods: Mice that possess a transgene for hemagglutinin-tagged BDNF were subjected to a repetitive low-dose pilocarpine regimen to induce seizures and were then sacrificed acutely after seizure and levels of proBDNF and mBDNF were probed via western blot and localized using immunohistochemistry. Results: In contrast to previous publications reporting that proBDNF does not increase until 72 hours after seizures, our studies indicate proBDNF levels in hippocampus were markedly increased within three hours after the induction of seizures continuing on to 24 hours. Immunohistochemistry studies indicate that seizure-induced BDNF increases occur primarily in hippocampal principal neurons after seizures in all hippocampal subfields but most exquisitely in the mossy fibers of the CA3. Conclusions: These studies suggest that proBDNF increases very rapidly following the onset of SE, suggesting that the increase in proBDNF levels may be due to altered proBDNF cleavage. Further studies will look at the role of the proteolytic machinery in regards to elevated levels of proBDNF after SE.