Is There a Role for NO in Epileptogenesis in Patients with Cortical Heterotopia (CH)?
Zanella1,2, CB; Neder3, L; Chimelli5, L; Anselmi1, AM; Leite2, JP; Machado4, HR; Carlotti4, CG; Cukiert6, A and Martins1, AR
Depts of Pharmacology1, Neurology2, Pathology3 and Surgery4 FMRP-USP; Dept of Pathology5, UFRJ; Brigadeiro Hospital6
Purpose. CH is a neuronal migration disorder characterized by neurons within the white matter. CH is commonly associated to drug-resistant epilepsy. CH can be connected to other regions, allowing propagation of intrinsic epileptogenic activity, as is the case for periventricular heterotopia. GABAergic and glutamatergic systems are usually involved in an excitation-inhibition imbalance, which might be related to epileptogenesis.
NO is a neurotransmitter/neuromodulator that exhibits anti- and proconvulsant activities. NO can participate in neuronal synchronization through activation of NMDA-receptors.
In this context, we report a comprehensive characterization of CH, and the expression of neuronal NO synthase (nNOS) in CH as compared to normal cortex.
Methods. Tissue sections were stained with hematoxylin-eosin, silver (Bielschowsky), and were processed for immunohistochemistry using an antigen retrieval technique. Sections were incubated with antibodies against GFAP, NeuN, nNOS, parvalbumin (PV) and NMDAR1. Detection was done using a biotinylated second antibody and the kit Elite ABC, using DAB as chromogen. Control cortex was obtained at autopsy from patients without neurological disorder.
Results. Pathological findings included neurons within the white matter (>8), irregular neuronal clustering, and abnormal cortical lamination. In CH, there was a conspicuous nNOS labeling of neurons, varicose fibers and neuronal processes. In contrast, control cortex showed a smaller number of nNOS-neurons and a decreased nNOS staining than in CH. PV-labeled neurons count was smaller in CH than in control cortex, where they were detected in layers II-IV. NMDAR1 neurons were barely detectable in normal cortex, but were detectable in CH.
Conclusion. We found a concomitant increase of nNOS-neuron and puncta counts, a decrease of GABA-positive neurons and an increased detectability of NMDAR1 neurons in CH as compared to control cortex. Taken together, the above results and the NO ability to spatially synchronize and enhance glutamate release, has led us to suggest that NO may play a role in epileptogenesis.
Supported by FAPESP, FAEPA, CAPES and CNPq
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