| Epilepsy is a common disorder of nervous system, which affects more than 50 million individuals worldwide and 9 million individuals in China—about 1% of the population. By now about 75% patients are controlled by antiepileptic drugs and operation. But there are at least 25% patients cannot be controlled by any available therapy, especially the patients whose epileptogenic cortex is overlapped with eloquent cortex. So the clinic treatment of epilepsy with epileptic focus overlapped with eloquent cortex is difficult and it is necessary to set up new therapies. Electric stimulation is an encouraging strategy for the treatment of intractable epilepsy. The targets of electric stimulation include vagus nerve, cerebellum, caudate nucleus, thalamic nuclei and reticular formation of substantia nigra. But the stimulation of targets above is non-specific. So it is maybe a good way to stimulate the epileptic focus directly. However, the effect of electric cortical stimulation on epileptic focus localized on the neocortex is not clear.In this study, the rat models of acute and chronic focal epilepsy induced by intracortical injection of ferric chloride solution were used. In the first part, we studied the suppressive effects of the electric cortical stimulation on the seizures in the acute epileptic rat by investigated the frequency and duration of seizures induced by ferric chloride. In the second part, we studied the effects of the electric cortical stimulation on the cortical excitability in the chronic epileptic rat by investigated the threshold and duration of cortical afterdischarge and the behavior score. Results: (1) Spontaneous seizures were observed in all acute epileptic rats following intracortical injection of ferric chloride solution. (2) In 6h EEG recording, 1-Hz and 100-Hz electric cortical stimulation significantly decreased the number of seizures in the acute epileptic rat (6.67±5.65 and 8.33±5.38, respectively) compared with that of the control group (18.33±6.93, P<0.01 and P<0.05, respectively). (3) In 6h EEG recording, 1-Hz and 100-Hz electric cortical stimulation significantly decreased the duration of seizures in the acute epileptic rat (37.38±15.53s and 39.60±11.82s, respectively) compared with that of the control group (61.43±16.61s, P<0.05). (4) When we calculated the number of seizures in each hour in 6h EEG recording after electric cortical stimulation, we found that downtrend was observed in 1-Hz and 100-Hz electric cortical stimulation groups and transient upgrade followed downtrend was observed in control group. (5) After 1-Hz and 0.1mA repetitive electric cortical stimulation in 5d, the cortical afterdischarge threshold (2.10±0.38mA) significantly ascended in the chronic epileptic rat induced by intracortical injection of ferric chloride solution compared with that of the control group (1.5±0.33mA, P<0.05) and compared with the initial cortical afterdischarge threshold before electric cortical stimulation (1.55±0.35mA, P<0.01). There was no statistic difference of cortical afterdischarge thresholds after 1-Hz and 1.0mA, 100-Hz and 0.1mA, 100-Hz and 1.0mA repetitive electric cortical stimulation compared with that of the control group. But the cortical afterdischarge threshold after 1-Hz and 1.0mA repetitive electric cortical stimulation (1.85±0.35mA) significantly ascended compared with the initial cortical afterdischarge threshold before electric cortical stimulation (1.45±0.35mA, P<0.05). (6) There was no statistic difference of behavior score after repetitive electric cortical stimulation in 5d compared with that of the control group. But there was significantly difference of behavior score after 1-Hz and 0.1mA repetitive electric cortical stimulation (3.83±0.98) compared with the initial behavior score before electric cortical stimulation (4.83±1.17, P<0.05). (7) There was no statistic difference of duration of cortical afterdischarge after repetitive electric cortical stimulation in 5d compared with that of the control group. (8) The ratio of behavior score and cortical afterdischarge threshold after 1-Hz and 0.1mA (1.88±0.60) or 1-Hz and 1.0mA (2.18±0.38) repetitive electric cortical stimulation in 5d was significantly lower than that of the control group (3.22±0.67, P<0.01 and P<0.05, respectively). At the same time, the ratio of behavior score and cortical afterdischarge threshold after 1-Hz and 0.1mA or 1-Hz and 1.0mA repetitive electric cortical stimulation was significantly lower than initial ratio before electric cortical stimulation (3.22±1.05 or 3.17±0.71, respectively, P<0.01). There was no statistic difference of the ratio of behavior score and cortical afterdischarge threshold after 100-Hz and 0.1mA (2.50±0.33) or 1-Hz and 1.0mA (3.66±0.73) repetitive electric cortical stimulation in 5d compared with that of the control group. But the ratio of behavior score and cortical afterdischarge threshold after 100-Hz and 1.0mA repetitive electric cortical stimulation was significantly higher than initial ratio before electric cortical stimulation (3.10±0.37, P<0.05).Conclusions: (1) 1-Hz square pulse electric cortical stimulation can significantly decreased the number and the duration of seizures in the acute epileptic rat just following the intracortical injection of ferric chloride solution. (2) 100-Hz square pulse electric cortical stimulation can also significantly decreased the number and the duration of seizures in the acute epileptic rat just following the intracortical injection of ferric chloride solution. (3) After the repetitive low frequency and low amplitude or low frequency and high amplitude electric cortical stimulation the cortical afterdischarge threshold significantly ascended in the chronic epileptic rat induced by intracortical injection of ferric chloride solution. It means the depression of cortical excitability after electric cortical stimulation, especially the repetitive low frequency and low amplitude electric cortical stimulation. (4) After the repetitive high frequency and high amplitude electric cortical stimulation the ratio of behavior score and cortical afterdischarge threshold was significantly higher than initial ratio before electric cortical stimulation. It means the rise of cortical excitability. (5) The results of this study showed that electric cortical stimulation with suitable parameter can produce a suppressive effect on the epileptic rat induced by intracortical injection of ferric chloride solution. The results of this study provide a new proof for the treatment of epilepsy by electric cortical stimulation. |
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