Abstracts

Posttraumatic epilepsy frequently presents after a latent period. In the rat partial cortical isolation ([quot]undercut[quot]) model of posttraumatic neocortical epileptogenesis, subdural application of tetrodotoxin (TTX), over the lesion during a critical period of the first 3 post-injury days, prevents later development of hyperexcitability. To better understand mechanisms of the TTX effect and identify potential anti-epileptogenic targets, we previously studied changes in gene expression using Affymetrix GeneChip arrays. The target sequence for neuritin (CPG15) was differentially expressed in undercut cortex with and without TTX treatment. Neuritin is a glycosylphosphatidyl inositol (GPI)-linked activity-induced protein implicated in neuritogenesis, neurite branching and maturation of synapses. Because of these known actions, and the observation that axonal sprouting of layer V pyramidal neurons is coincident with post-injury hyperexcitability in this model, we wished to further characterize changes in neuritin protein during the critical period for anti-epileptogenesis. Partial isolations of sensorimotor cortices were made in 1 month old male, Sprague-Dawley rats, and control or TTX-containing sustained release polymer, Elvax 40W, was placed subdurally over the lesioned cortex. Three days post injury, animals treated with TTX-containing Elvax, control Elvax and naive controls were processed for immunocytochemistry or protein isolation and western blot of the undercut lesions, and homotypic cortices, using an antibody against neuritin. Neuritin-like immunoreactivity was increased in the undercut cortex compared to naive control, but was reduced with TTX-treatment, consistent with results in the previous gene arrays. Western blot analysis revealed a dark band from undercut cortex that migrated near the 20 kDa marker, the appropriate molecular weight for neuritin. This band was faint in TTX-treated undercut or naive control. Prevention of a post-injury increase of neuritin occurs with TTX-treatment, coincident with prevention of hyperexcitability in this model. Hypothetically, suppression of a posttraumatic rise in neuritin expression might translate into reduced axonal injury-induced sprouting. Therefore, further studies assessing the role of neuritin in posttraumatic epileptogenesis are warranted. (Supported by NIH Grants NS 02167, NS12151 , and the Phil N. Allen Trust.)