Abstracts

Nitirc oxide (NO) has been proposed as an agent involved in epileptogenesis, and increased expression of neuronal nitric oxide synthase (nNOS) has been demonstrated in post-mortem cortical samples from epileptic patients. Cortical dysplasia (CD) is a frequent cause of pharmacoresistent epilepsy. Previous studies have shown increased expression of the N-Methyl-D-Aspartate (NMDA) receptor NR2B subunit in epileptic dysplastic human neocortex. In normal rodent cortex, NR2B and nNOS are physically linked to the same scaffolding protein (PSD-95). In this study we investigate whether (1) nNOS is increasingly expressed in focal-epileptic, compared to extrafocal neocortex from patients with epileptic cortical dysplasia, and whether (2) increase in nNOS expression is correlated with increase in NR2B. Ten patients with medically intractable epilepsy due to CD and 2 patients with mesial temporal sclerosis (controls) were submitted to pre and/or intra-operative invasive monitoring evaluation in order to define epileptogenic and non-epileptogenic cortical areas. During the surgical resection, cortical samples from epileptogenic and non-epileptogenic areas were collected from each patient. The matched samples were processed for CV staining, immunocytochemistry for nNOS, NeuN and NR2B and immunoflurescence analyses in order to evaluate co-localized immunoreactivity between nNOS and NR2B. Different degrees of CD were noted in all epileptogenic samples. In non-epileptogenic samples, CV staining revealed normal cortical architecture in 3 samples but mild degree of CD in 6 patients. The histological analysis of lateral temporal lobe from patients with mesial temporal sclerosis was normal. We identified nNOS expressing neurons in both epileptogenic and non-epileptogenic samples. The density and intensity of nNOS stained neurons was remarkably increased in the epileptogenic samples. Two types of nNOS stained neurons were identified: type 1, expressing strong nNOS immunoreactivity in larger neurons, and type 2, expressing weak nNOS immunoreactivity in slightly smaller neurons. Differently from type 1 neurons, type 2 nNOS stained neurons revealed immunoreactivity co-localization with NR2B antibody. The overexpression of nNOS in the epileptogenic samples and the immunoreactivity co-localization between nNOS and NR2B may suggest a possible role of nNOS and NO in the mechanisms related to in situ epileptogenicity. NO and nNOS may constitute a target for improvement of diagnostic tools and new pharmacotherapeutic approaches for epilepsy. (Supported by NINDS for Imad M Najm (K08NS02046 and 1R21 NS42354))