The Research Of The Physiological And Pathological Convulsive Thresholds In Brain

Objectives:Stimulation-response is a kind of physiological attribute and instinct in the biological evolution process.The convulsion would be provoked if the centre nervous system is stimulated and the extent of the stimulation can be consider as "physiological convulsive threshold".Some clinic events showed that after a long time of injure of the CNS,the convulsion can be provoked only by some weak stimulations.Once the epilepsy produced,the CNS is in a new pathological state in which the convulsive threshold is not a physiological convulsive threshold but a pathological one.In this study,we will investigate 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.Methods:In this study determination of the threshold for convulsions is made by direct cortical stimulation in rats.We measured the convulsive threshold,while recording electroencephalograms and subsequently examined histopathological changes in the hippocampus.Results:(1)At the beginning of the experiment,convulsive thresholds were all above 1100μA although there were significant individual variations in rats of the same group(The heavy stimulation group:TLS 1145±403.37μA,TGS 1277±443.15μA,TPS 1449±472.45μA).But those thresholds quickly declined during the initial 4 weeks of repetitive electrical stimulation. The convulsive thresholds approached a constant level(The heavy stimulation group:TLS 430±34μA,TGS 480±46μA,TPS 605±70μA)at the 10^thweek.There were no significant changes in thresholds when stimulation lasted for longer,the convulsive thresholds and the variations in rats of the same group were significantly lower than that at the beginning of the trial (p＜0.01).During 11 weeks of stimulation,TGS's of the heavy current group were significantly lower than those of the weak current group(F=6.109,P＜0.05).TLS's of the two groups did not show statistical significance difference during the whole experiment.,which illustrating that heavy stimulation may decrease the TGS and cause brain lesions more easily than weak stimulation.(2)The most common pattern of the electrical activity of rats was waves(100-180uv)which ranged from 6 to 10 Hz,accompanied with a sprinkle of fast waves. Ictal single-spike(sharp)firing was observed after rats were stimulated to the TLS's and TGS's. From week 2-4,in parallel with repetition of the stimulation sessions,the firing index of spike(sharp)waves after reaching TLS's and TGS's significantly increased,thereafter there was no longer a significant change in the firing index of spike(sharp)waves when stimulation continued after week 4.ID's occurred spontaneously at week 3 in the heavy stimulation group and at week 8 respectively.When electric stimulations had continued for 11 weeks,ID's were found in all rats of the 2 experimental groups but there were no ID's observed in the control group.(3)In the 2^ndweek of the stimulation,Chromatin in parts of the nuclei is rarified and arranged unevenly.The longer of the stimulation the more serious the neuron damaged which were showed as a significant decrease in the number of normal pyramidal cells.Majority of pyramidal ceils showed as the deformation,karyopycnosis,disaggregating or vanishing of the Nissl's body and acidophilic staining of the endochylema.The damage of pyramidal cells in heavy stimulation group were more serious than that of the weak stimulation group in the week 2 and 8,but there were no significance difference in the week 11.4 week after ceasing the stimulation,although the "red neurons" and proliferative glia cells still can be seen,a few neurons displayed as clear nucleolus and caryotheca,chromatin in nucleus arranged rarity slightly,there were no damage observed in the control group.Conclusions:These findings indicated that the convulsion threshold in the brain should be divided into two stages:physiological convulsive threshold and pathological convulsive threshold(epileptic threshold).Epileptic threshold is created by pathological acquired factors which give rise to brain damage.The intensity of these pathological acquired factors are correlated with the formation of the pathological convulsive threshold.