Differences between physiological and pathological convulsive thresholds in patients with epilepsy

BACKGROUND： Physiological convulsive thresholds degrade when the brain is in some pathologic states; thus, a level of stimulus that cannot provoke a convulsion may evoke a seizure or epileptic seizure. OBJECTIVE： To investigate the changes that occur in the brain when the physiological convulsive threshold becomes pathological, and to determine what differences occur in pathological and physiological convulsive thresholds during the development of epilepsy. DESIGN： A randomized controlled animal experiment. SETTING： Research Institute of Epilepsy of Shanxi Medical University; Department of Neurology, The Third Hospital of Shanxi Medical University; Research Institute of Function of Shanxi Medical University. MATERIALS： Thirty-six female Wistar rats were selected for this study. The rats were obtained from the experimental animal center of Shanxi Medical University. All laboratory procedures complied with animal ethical standards. The animals were randomly divided into three groups： a strong current group, a weak current group and a control group, with 12 rats in each group. An automatic determinator of seizure threshold was made at Shanxi Medical University and Taiyuan University of Technology. Two bipolar stainless steel stimulating electrodes and an electrode connector （diameter 1.2 ram） were made at Taiyuan University of Technology. METHODS： This study was performed in the laboratory of Research Institute of the Epilepsy of Shanxi Medical University between December 2005 and August 2006. The threshold of localized seizures was measured by performing direct cortical stimulation in rats under anesthesia. After 1 week of post-operative recovery, electric stimulation was started with three different kinds of stimulation. Seizure activity was induced by a ramp-shaped single train of biphasic pulses （50 Hz, total pulse duration of 2 ms, increasing from 0 to 2 000μ A in 15 seconds）. The threshold of localized seizures （TLS） has been defined as the minimum current intensity necessary to provoke convulsion of the forelimbs and/or facial muscles. Up to the TLS, if stimulation continued, the current intensity necessary to provoke the generalized seizures is called the threshold of generalized seizures （TGS）. If stimulation is continued for about 2 seconds when the TGS is reached, rats still showed generalized clonic activity after stimulation ceased. When seizures stopped, a short period of immobility can be observed. The current intensity is called the threshold of prolonged seizures （TPS）. The rats in the strong current group were stimulated up to the current level required to reach the TPS. In the course of stimulation, first, the TLS was recorded, then the TGS, and finally the TPS. The stimulation interval in one session was 10 minutes, repeated twice daily. The rats in the weak current group were only stimulated up to the current levels required to reach the TGS; first, the TLS was recorded and then the TGS was measured at the same time as the strong current group. Control animals were also equipped with a full electrode set and placed in the same conditions, but no stimulation took place, only electroencephalogram （EEG） recording at the same times as the experimental groups. MAIN OUTCOME MEASURES： ① Stimulation of the two experimental groups lasted for 11 weeks and then observation of their behavior and electroencephalogram recording continued for 4 weeks. The control group was also observed over a total of 15 weeks. ② Observing neuronal damage/loss in the hippocampus with a light microscope using a 250x visual field. RESULTS： All 36 Wistar rats were included in the final analysis. At the beginning of the experiment, the convulsive thresholds were all above 1 100 μA, although there were significant individual variations among rats of the same group. Those thresholds quickly declined during the initial 4 weeks of repetitive electrical stimulation. The convulsive thresholds approached a constant level in the 10^th week after commencement of stimulation. There were no significant changes in thresholds when stimulations lasted longer; the convulsive thresholds and the variations in rats of the same group were significantly lower than at the beginning of the trial （P 〈 0.01）. An interictal discharge was also recorded in the 3^rd week in the strong current group, and in the 8th week in the weak current group; these discharges were concomitant with neuronal damage and loss in the hippocampus. There was no abnormality observed in the control group. CONCLUSION： These findings indicated that the convulsion threshold in the brain should be divided into two stages： a physiological convulsive threshold and a pathological convulsive threshold （epileptic threshold） The epileptic threshold is created by pathologically acquired factors, which give rise to brain damage. The increase in the intensity of these pathologically acquired factors led to aggravation of damage.

Effects of acrous gramimeus and its main component alpha-asarone on the reactivity and convulsive threshold of immature rats to electric stimulation

BACKGROUND： The traditional Chinese medicine acrous gramimeus is the dry rhizome of Acrous gramimeus Soland, a kind of Araceae familial perennial herb, which has a sedation action, anticonvulsant and antiepileptic effect. Its effective component has not been known yet, and α-asarone, the major component of the volatile oil extracted from acrous gramineus, has been supposed to play a necessary role in it. OBJECTIVE： To explore the effects of acrous gramimeu and α-asarone on the reactivity and convulsive threshold to electric stimulation in immature rats, furthermore, attempt to definitize the anticonvulsant effect of α-asarone. DESIGN： A randomized controlled study.SETTINGS： Department of Pediatrics, First Hospital of Jilin University; Department of Histology and Embryology, School of Basic Medical Sciences of Jilin University; Department of Neurology, First Clinical Hospital affiliated to Harbin Medical University; Department of Internal Medicine, Children＇s Hospital of Changchun City. MATERIALS ： Seventy 3-week immature Wistar rats （either males or females） of 34-40 g were used. Acrous gramimeu （1 g/bag, the content of α-oasarone was 0.046 26%-0.070 16%） with the batch number of 0307113 was provided by Tianjiang Medicine Company Limited, Jiangyin City. α-asarone tablet （60 mg per tablet） with the batch number of 030219 was provided by Tianwei Pharmaceutical Factory, Shenyang City. α-asarone injectable preparation （2 mL per piece） with the batch number of 030105 was provided by Shuanghe Medicine Limited Company, Beijing City. METHODS ： The experiments were carried out in the Neurological Laboratory of the First Hospital of Jilin University between August and October in 2004.① The 70 rats were randomly divided into intragastric subset and intraperitoneal subset. The intragastric subset included four groups of control, phenobarbital sodium, acrous gramimeu and α-asarone; the intraperitoneal subset included three groups of control, phenobarbital sodium and α-asarone. There were 10 rats per group. ② In the intragastric subset, different group was treated with saline （1 mL for each time, phenobarbital sodium （18 mg/kg per day）, acrous gramineu （2 350 mg/kg per day） and α-asarone （29 mg/kg per day） respectively twice every day for 5 days. In the intraperitoneal subset, different group was treated with saline （0.5 mL）, phenobarbital sodium （29 mg/kg） and α-asarone （2.9 mg/kg） respectively. ③ Before and after administration for 5 days in the intragastric subset as well as before and after administration for about 1 hour in the intraperitoneal subset respectively, the rats were given electric stimulation with the NIHOM KOMDEM multifunctional electrophysiological recorder, and the reactivity and convulsive threshold to electric stimulation of the rats were recorded. MAIN OUTCOME MEASURES： The reactivity and convulsive threshold to electric stimulation in immature rats were compared. RESULTS： All the rats were involved in the analysis of results. ① Results for intragastric administration： Before intragastric administration, there were no obvious differences in the reactivity and convulsive threshold to electric stimulation among the groups （P 〉 0.05）. After intragastric administration for 5 days, the reactivity and convulsive threshold to the electric stimulation had no obvious changes in the control group, but those were significantly higher than before administration in the drug administration groups （t=-3.317-7.401, P 〈 0.01）, which were also obviously higher than those in the control group （t=3.027-8.941, P 〈 0.01）, and those in the acrous gramimeu group and α-asarone group were not markedly different from those in the phenobarbital sodium group. ② Results for intraperitoneal injection： Before intraperitoneal injection, the reactivity and convulsive threshold to the electric stimulation had no obvious differences among the groups. After the intraperitoneal injection for 1 hour, the reactivity and convulsive threshold to the electric stimulation had no obvious change in the control group, but those were significantly higher than before administration in the drug administration groups （P 〈 0.01）, which were also obviously higher than those in the control group （t=6.211-7.237, P 〈 0.01; t=4.085-5.633, P 〈 0.05）, and there was no marked difference between α-asarone group and phenobarbital sodium group （P 〉 0.05）.CONCLUSION ： ① As effective anticonvulsants, both acrous gramineu and α-asarone can enhance the reactivity and convulsive threshold of immature rats to electric stimulation. ② As one of the major effective components against convulsion of acrous gramineu, α-asarone is equivalent to phenobarbital sodium.

Comparisons of drug efficacy and time-effect among magnesium valproate,sustained-release magnesium valproate tablet and depakine chrono for epilepsy An experiment of determining cortical convulsive threshold in rats undergoing electrical stimulation

BACKGROUND： Scholars have investigated the differences in drug metabolism and pharmacodynamics between valproate and its sustained-release tablets only from the angle of pharmaceutical sciences or clinical practice. Whether the fact that differences in drug efficacy and time-effect of different doses of valproate and different types of sustained-release valproate tablets at the same concentration can be quantitatively reflected by determining the changes in convulsive threshold pre- and post-administration in rat models of determining the convulsive threshold developed by direct cortical electrical stimulation remains unclear. OBJECTIVE： This study aimed to compare the drug efficacy and time-effect among magnesium valproate, sustained-release magnesium valproate tablet and depakine chrono in the treatment of epilepsy by determining the convulsive threshold of rat models created by direct cortical electrical stimulation, and human serum drug concentration before and after administration. DESIGN： A controlled observational experiment. SETTING： Research Institute of Epilepsy, Shanxi Medical University. MATERIALS： Adult health male SD rats of clean grade, weighing 200 - 220 g, provided by the Laboratory Animal Center of Shanxi Medical University. The protocol was carried out in accordance with requests from Animal Ethics Committees for guidance. Magnesium valproate （Lot No. 041004） and sustained-release magnesium valproate tablet （Lot No. 050501） were produced in Hunan Xiangzhong Pharmaceutical Co., Ltd. METHODS： This study was carried out in the Laboratory for Epilepsy, Shanxi Medical University between June and August 2005. （1）All the SD rats were created into models for determining cortical convulsive threshold. They were randomly divided into 4 groups with 20 rats in each： magnesium valproate tablet group, sustained-release magnesium valproate tablet group, depakine chrono group and control group. After being modeled, the rats in the first 3 groups were intragastrically administrated with magnesium valproate, sustained-release magnesium valproate tablet and depakine chrono, respectively, while the control group were intragastrically administrated with the same volume of normal saline. （2）Convulsive threshold of each fasting rat was determined 0.5 hour before, and 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14 and 24 hours after single administration, separately. （3） Convulsive threshold was determined repeatedly 2 weeks after single administration. Each rat was administrated two times daily successively. Convulsive threshold was determined 0.5 hour before, and 0.5, 2.5, 7 and 12 hours after administration, separately. （4）Hepatic and renal tissues were harvested for pathological examination after 1 month of administration. （5）Nine healthy voluntary medical stuffs were recruited in this study. Written informed consents of experiment were obtained each involved subject. The study was given an approval by the Ethics Committee of Shanxi Medical University. According to the scheme, the 9 volunteers were randomly assigned into 3 groups, in which, volunteers were asked to take magnesium valproate 500 g, sustained-release magnesium valproate tablet 500 g and depakine chrono 500 g, respectively, in the morning under the condition of fasting. Serum drug concentration of each drug was determined by fluorescence polarization immunoassay at different time points. MAIN OUTCOME MEASURES： （2） Rat convulsive threshold after single and repeated administrations. （2）Hepatic and renal pathological examination results. （3） Serum drug concentration in vivo. RESULTS：（4）Rat convulsive threshold after single and repeated administrations： Drug efficacy in the magnesium valproate tablet group reached to a peak level 1 to 2 hours after single administration, and was obviously higher than that in the other groups 1 hour after administration （P 〈 0.05）. Drug efficacy in the sustained-release magnesium valproate tablet group and depakine chrono group both reached to a peak level 7 hours after administration, and was significantly higher than that in the control group （P 〈 0.05）. After repeated administrations, the average peak valley deviation of the convulsive threshold in the magnesium valproate tablet group was 120- 150 μ A, which was 2 and 2.5 times as that in the sustained-release magnesium valproate tablet group and depakine chrono group, respectively. After repeated administrations for 10 times, convulsive threshold was increased by 440 μ A in the sustained-release magnesium valproate tablet group, and by 230 μ A in the depakine chrono group in comparison with before administration. （2） Hepatic and renal pathological examination results： No obvious differences in hepatic and renal impairment were found among the 4 groups after I month of administration successively. （3） Serum drug concentration in vivo： Serum-drug concentration of magnesium valproate was increased fast and reached to a peak level 0.5 - 2 hours after administration, remained at a relatively stable level 2 - 4 hours after administration, and then was slowly decreased. The drug efficacy of sustained-release magnesium valproate tablet and depakine chrono was slowly released 1 - 6 hours after administration, reached to a peak level at about 7 hours, and could last for about 16 hours. CONCLUSION： Magnesium valproate has a rapid onset and offset of action. Sustained-release magnesium valproate tablet has a slow onset but long duration of drug efficacy. Depakine chrono can be easier to be absorbed than sustained-release magnesium valproate tablet, but its long-term effect on improving the convulsive threshold is inferior to sustained-release magnesium valproate tablet.