Study Of Refractory Epilepsy

Background Epilepsy is one of common neurological diseases, its pathophysiological dysfunctions are abnormal discharges originating simultaneously in partial or both hemispheres of the brain, characterized by the periodic and unpredictable occurrence of seizures. Antiepileptic drugs and surgical resection are the commonly therapy to epilepsy. About 30% people are refractory epilepsy patients who have uncontrolled seizures despite antiepileptic drugs therapy. Though some of them benefit from surgical resection, many patients are not candidates for surgical resection, and still need new therapeutic approaches. Therefore, it is necessary to study profoundly the mechanism of epileptogensis and more effective antiepileptic drugs or methods.Recent successes of deep brain stimulation for movement disorders have encouraged consideration of brain stimulation therapy for epilepsy. Deep brain stimulation has the potential to become a new treatment for those patients with epilepsy who are currently unresponsive to pharmacologic therapy or who are not candidates for surgical resection. However, the mechanisms of DBS are not clear, and the fundamental questions of where to stimulate and what type of stimulation will be most effective must be resolved.γ -aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian central nervous system. Inhibitory functions of GABA are mediated by two distinct classes of receptors, the GABAa and GABAb receptors. G-protein coupled GABAb receptors are responsible for the late inhibitory postsynaptic potentials (IPSP) elicited by GABA through opening inwardly rectifying K⁺ channels. GABA receptors also exist on nerve terminals, regulating the release of neurotransmitters,such as glutamic acid , via the inhibition of Ca²⁺ channels. GABA_B1 receptor is the major of the two of the GABA_b receptors: GABA_B1 and GABA_B1 receptors. Abnormalities of GABA_B1 receptors' function may play an important role in the pathophysiology of epilepsy.So, in this study we explored the role of GABA_B1 recepter in the mechanism of epileptogensis. And we also investigated the anticonvulsanteffects of two patterns of DBS on amygdala kindling rat and the possible mechanisms of the anticonvulsant effects.Materials and Methods This study is divided into two main parts. In the first part, the model of refractory epilepsy was established by kindling of amygdale. Brain tissue surgically resected from 20 patients with refractory epilepsy and 20 controls were collected. The expression of GABA_B1 receptor was investigated in brain of human and amygdala kindled rats using the means of RT-PCR, Western-blot , immunohistochemistry; Then the functional activity of GABA_B1 receptor was research by specific antagonist and agonist in amygdala kindled rats. In the second part, two targets of DBS (amygdala and subthalamic nucleus) were applied, the process of kindling and seizures activity was observed; The expression of GABA_B1 receptor was investigated in brain of amygdala kindled rats accepted DBS using the means of in situ hybridization, Western-blot and immunohistochemistry.Results The results of first part: Compared with control groups, GABA_B1 receptor expression in brain of patients with refractory epilepsy showed an obviously statistical decreasing at both the mRNA and the protein levels (P<0.05); Compared with control groups, GABA_B1 receptor expression was decreasing during the course of kindling . After kindling, the expression of GABA_B1 receptor was partly recovered but was still lower than the control. Specific agonist of GABA_B1 receptor could shorten the ADD (after charge duration) and reduce the Racine's degree (P<0.05); specific antagonist of GABA_B1 receptor could prolong the ADD(P<0.05). The results of second part: amygdale-LFS(≥100μ A) and STN-HFS could shorten the ADD and reduce the Racine's degree (P<0.05).The expression of GABA_B1 receptor was upregulated in hippocampus of kindled rats applied these two kinds DBS. Conclusions 1. The expression of GABA_B1 receptor was downregulated in brain of rats and patients with refractory epilepsy; Specific agonist of GABA_B1 receptor could inhibit the kinding seizures. 2. amygdale-LFS(=100μA) and STN-HFS could inhibit effectively kindling seizures; increasing the downregulated expression of GABA_B1 receptor would participate with the treatment mechanisms of the two DBS.