The Expression Of SCN8A Gene In The Brain Tissues Of The Patients With Pharmacoresistance Epilepsy

Objective: To investigate the expression of sodium channel voltage-gated type VIII alpha(SCN8A) in the brain tissues of the pharmacoresistance epilepsy patients, and to explore the possible role in pharmacoresistance epilepsy.Materials and Methods: 40 patients were diagnosed as pharmacoresistance epilepsy. The type of seizure in the patients was determined in accordance with the International Classification of Epileptic Seizures specified by the International League Against Eepilepsy(ILAE) in 1981. There were 21 males and 19 females, whose ages ranged from 16 to 56 years, with a mean of 26.18±9.60( x±s) years. Duration of epilepsy was 3 to 27 years, with a mean of 12.88±6.49( x±s) years. 24 had partial seizure seconderly generalized tonic, clonic or tonic-clonic seizure, 12 had complex partial seizure, and 4 had diverse seizure types (tonic seizure, simple partial seizure or tonic-clonic seizure). The resected brain specimens of the pharmacoresistance epilepsy group included temporal lobe cortex (n=32) and hippocampus (n=8). This study included 20 control subjects. 15 resected brain pecimens of temporal lobes were obtained from patients with craniocerebral trauma, and 5 hippocampus specimens were obtained from subjects who died from traffic accidence, or autopsy after craniocerebral trauma. Among them, there were 11 males and 9 females, whose ages ranged from 19 to 58 years, with a mean of 27.52±11.35( x±s)years.Operative specimens from the patients and control group specimens obtained from autopsy were stored in liquid nitrogen (-196℃) immediately, which was used for gene chip scanning. Other parts were fixed in 4% paraform solution for 48 hours, then they were conventionally embedded with paraffin. In the basis of gene microarray research, the expression of Nav1.6 protein encoded by SCN8A gene in the brain specimens was evaluated by immunohistochemistry and immunofluorescence technique. The Computer Graphic Analysis System is used to test the average optical density (AOD) which is expressed as mean±SD( x±s)and tested via t-test. P value less than 0.05 as the level of significance.Results:1.Gene chip: There was significant difference between the control group and the pharmacoresistance group (Ratio=2.181). The expression of SCN8A gene was shown to be increased in the brain tissues of the pharmacoresistance epilepsy group.2.Immunohistochemical analysis: Immunostaining was located predominantly in the somata and proximal processes of neurons. No apparent immunostaining was observed in either glia or endothelial cells. No immunoreactivity in negative controls was seen. AOD value in temporal cortex tissue of the pharmacoresistance epilepsy group was determined 0.2441±0.0246( x±s), and 0.2233±0.0206( x±s) in the control group. There was significant statistic difference between the two groups (t=1.059, p=0.007). AOD value in hippocampus of pharmacoresistance epilepsy group was determined 0.2425±0.0231( x±s), and 0.2140±0.0114 ( x±s) in the control. There was significant statistic difference between the two groups (t =2.537, p=0.028).3. Immunofluorescence analysis: In the temporal lobe cortex and hippocampus, strong immunoreactivity for the staining of Nav1.6 protein was observed. There were more obvious in the pharmacoresistance epilepsy group than in control group.Conclusions:1. Immunostaining of Nav1.6 was located predominantly in the somata and proximal processes of neurons in pharmacoresistance epilepsy. The apparent confinement of Nav1.6 protein to cell soma and proximal processes is clearly of functional significance and is consistent with a role in action potential initiation and synaptic input integration. Nav1.6 involved in action potential initiation may also facilitate excitatory postsynaptic potential( EPSP ) amplification. These may promote the formation of the pharmacoresistance epilepsy.2. The overexpression of Nav1.6 possibly decrease inactivation rates of sodium channels and allowing sodium channels to reactivation rapidly, which may cause hyper-excitability of neurons, and contribute to the firing of conglomerate epileptiform discharges by neurons, finally result in pharmacoresistance epilepsy.3. The up-regulation of SCN8A expression in brian tissues with epileptiform discharges of pharmacoresistance epilepsy indicates it may play a important role in the pathogenesis.Moreover, iterative seizures in pharmacoresistance epilepsy may be alter the gene expression of SCN8A.