Abstracts

Severe penetrating head injury often results in posttraumatic epilepsy, frequently with seizures beginning after a latent period. In the rodent undercut model of neocortical posttraumatic epileptogenesis, hyperexcitability occurs in brain slices in vitro after a latent period, but not acutely following injury. Prior investigations have suggested the presence of increased synaptogenesis in pyramidal neurons of this model. Localized treatment of the injured area with tetrodotoxin (TTX) during a critical period of three days post injury prevents the development of posttraumatic hyperexcitability. We have previously used Affymetrix GeneChips to help identify potential genes that may play a role in the antiepileptogenic effect of TTX-treatment. One candidate target sequence identified represents Narp (neuronal activity-regulated pentraxin, also known as neuronal pentraxin 2), an immediate early gene product that plays a role in excitatory synaptogenesis. We performed follow-up studies of Narp protein to confirm these findings. Partially isolated islands of sensorimotor neocortex were made in P28-30 male Sprague-Dawley rats, and thin sheets of sustained release polymer either containing TTX or control polymer placed subdurally over the lesioned areas. During the critical period of three days post injury, TTX-treated and control animals were euthanized and undercut and control cortices dissected for protein studies using polyclonal antibody against Narp. Other animals were perfused for immunohistochemical analysis. Western blotting and immunocytochemical staining for Narp was increased in undercut versus na[iuml]ve control cortex 3 days post injury. However, TTX-treatment reduced Narp immunoreactivity assessed with these techniques, as it had in gene expression studies. An increase of Narp protein in neocortical lesions is correlated with epileptogenesis, and a treatment-induced reduction correlated with antiepileptogenesis, although a causal relationship has not yet been clearly established in this model. Results suggest that 1) further studies of the role of Narp in epileptogenesis are warranted, and 2) that targeted molecular approaches might lead to effective prophylaxis for posttraumatic epileptogenesis. (Supported by NIH Grants NS02167, NS12151, and the Phil N. Allen Trust)