Effects Of Hippocampal Stimulation On Expressions Of GABA Receptors And Sodium Channel Current In Pharmacoresistant Epileptic Rats

Objective:To establish a multi-drug resistant model of temporal lobe epilepsy, and the extracellular levels of GABA, the expression of GABA(A) and GABA(B) receptors, the mRNA expression of GABA(A) and GABA(B) receptors, the sodium current of pyramidal neurons in CA1 areas of the hippocampus were used as indexes to observe the effect of hippocampal stimulation on pharmacoresistant epileptic rats.Methods:Two hundreds and thirty Wistar rats were selected to prepare the amygdaloid kindled model of epilepsy by chronic stimulation of amygaloid basal lateral nucleus. After the kindled model of epilepsy was prepared successfully, pharmacoresistant epileptic rats were selected according their response to phenobabital and phenytoin. The selected pharmacoresistant epileptic rats were divided into a hippocampal stimulation group and a pharmacoresistant control group, and the following experiments were performed.1) Extracellular fluid were collected by microdialysis and the samples were used to determine the levels of GABA by HPHC method after hippocampal stimulation;2) Immunohistochemical method was used to detect the expression of GABA(A) and GABA(B) receptors; 3) Real-time PCR were used to detect and quantitate the expression of GABA(A) and GABA(B) mRNA; 4) The whole-cell recording technique by patch-clamp was used to observe the changes of sodium current of hippocampal pyramidal neurons.Results:A total of 120 rats were kindled successfully in all the 230 Wistar rats, the rate of kindling was 52%. Thirty pharmacoresistant epileptic rats were selected from the kindled model by their responses to phenobabital and phenytion. The pharmacoresistant epileptic rats in hippocampal stimulation group underwent stimulation with low frequency for two weeks and compared with the pharmacoresistant control group. The results were as follows:The extracellular level of GABA was increased in different stages as compared with the control group; The up-regulation of GABA(A) and GABA(B) receptors were observed, also the expression of GABA(A) and GABA(B) receptor mRNA, a significant difference was noted as compared with the pharmacoresistant control group; The sodium current of hippocampal pyramidal neurons in CA1 areas was inhibited by hippocampal stimulation.Conclusions:Hippocampal stimulation might up-regulate the expression of GABA(A) and GABA(B) receptors, increase the extracellular levels of GABA in brain tissues, and inhibit the sodium channel current of pyramidal neurons in CA1 areas of hippocampus. The mechanism of hippocampal stimulation in the treatment of pharmacoresistant epilepsy might be achieved partly by increasing the function of GABA-ergic system and inhibiting the sodium channel current so as to decrease the excitability of hippocampal neurons.