Abstracts

RATIONALE: Recently, we have demonstrated that principal neurons of the entorhinal cortex (EC) of pilocarpine epileptic rats display an increase in TTX-sensitive voltage-dependent persistent sodium current (INaP) relative to age-matched controls. Activating at subthreshold potentials and having very slow inactivation, INaP has been proposed to contribute to subthreshold oscillations, excitability and epileptogenesis. In this study, we investigated whether the physiological increase in INaP was due to plasticity in levels of sodium channel message and/or levels of protein expression after the silent period, post-status epilepticus.
METHODS: Male Long-Evans rats were made epileptic following a lithium-pilocarpine protocol consisting of LiCl (3 mEq/kg, 24-hours pre-treatment), scopolamine methlybromide (1 mg/kg), and pilocarpine hydrocholoride (30 mg/kg), with a final post-application of diazepam (1 mg/kg) two hours after status epilepticus (SE). Only animals that displayed SE were selected for the epileptic population. Control animals were treated identically except with the administration of saline instead of pilocarpine. Horizontal brain slices (400 [mu]) were prepared, the EC Layers were dissected out for 1) total RNA isolation and extraction and 2) protein extraction. Semi-quantitative RT-PCR was performed for brain sodium channel alpha-subunit subtypes Nav1.1, 1.2, 1.3, and 1.6; Western blot analysis was performed for the same subtypes as well as for sodium [beta]-1 and [beta]-2 subunits. Only rats at ~10 weeks post-pilocarpine and their age-matched controls were studied.
RESULTS: Our preliminary results indicate changes in the expression of sodium channel alpha subunit type III, with no detectable significant changes in the other subunits (n=4). Semi-quantitative real-time RT-PCR is being carried out to confirm these results.
CONCLUSIONS: These data may indicate that changes in the expression of sodium channels in the entorhinal cortex of the pilocarpine epileptic rats may be correlated with an upregulation of INaP. The increase in plasticity of the persistent sodium current may contribute to neuronal hyperexcitability in the temporal lobe. Identification of localized sodium channel protein targets may help in understanding or developing improved drug therapies for the treatment of temporal lobe epilepsy.
[Supported by: the Canadian Institutes for Health Research, the Medical Research Council, and the Savoy Foundation. Newton Agrawal was supported by a fellowship from the Savoy Foundation.]