Electroconvulsive threshold and nerve damage in different parts of rat cerebral cortex

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Objective To measure the electroconvulsive threshold in different parts of rat cerebral cortex and observe the pathophysiological changes after the convulsive threshold is stable. Methods Healthy female SD rats weighing 180-220 g were randomly divided into a study group and a control group. Electrodes were placed in the frontal lobe, temporal lobe, and cerebellar cortex of all rats. Direct current stimulation was applied twice daily in the study group, but not in the control group. After stable convulsive threshold was achieved in the study group, the SNK-q test was used to compare the convulsive threshold in different subgroups. The rats were then sacrificed to observe the changes of hippocampal neuron damage by Nissl's staining. The number of neurons in the hippocampus of rats in each group was counted and then compared using the SNK-q test. Results At the first and second days, the convulsive threshold in the three stimulation subgroups was high, which was ~1100 μA in the frontal lobe, ~1200 μA in the temporal lobe, and ~2100 μA in the cerebellar cortex. With the increase in the duration of stimulation, the threshold of the three groups continued to decrease, eventually reaching a stable level. The mean stable threshold was (511.00±10.97) μA in the frontal lobe, (440±12.46) μA in the temporal lobe, and (1300±53.63) μA in the cerebellar cortex. Although the mean stable threshold did not differ significantly between the frontal lobe and temporal lobe (P>0.05), there was a significant difference between the cerebellum and frontal lobe and between the cerebellum and temporal lobe (P<0.05). With the extension of stimulation time, compared with the control group, hippocampal CA3 area in rats of the study group exhibited varying degrees of changes, such as disordered neuron arrangement and neuron loss. The average number of neurons was 36 in the control group, 22 in the frontal lobe subgroup, 17 in the temporal lobe subgroup, and 26 in the cerebellum subgroup. Compared with the control group, the number of neurons in the study group decreased significantly (P<0.05). There was also a significant difference in the neuron number among the three subgroups (P<0.05). The symptoms of rats after electrical stimulation in the cerebellar cortex subgroup were different from those in the frontal and temporal lobe subgroups. The frontal and temporal lobe groups showed typical epileptiform convulsion, such as nodding, limb convulsion, and tonic-clonic seizures; however, the cerebellum group was characterized by systemic tetanic convulsion of limbs and trunk, running, and jumping. Conclusions At the same intensity of electrical stimulation, the temporal lobe and frontal lobe are more sensitive than cerebellar cortex and are easier to develop pathological changes, and the susceptibility to electrical stimulation is comparable between the temporal lobe and frontal lobe. Electrical stimulation can cause pathological changes in the hippocampus, and the hippocampal damage in the temporal lobe subgroup is the most serious. Cerebellar cortex stimulation has the minimum effect on the hippocampus. Key words: Epilepsy; Cortex convulsive threshold; Neuron damage; Electrical kindling model; Rats