Roles Of Endothelin On Pilocarpine Induced Epileptic Seizures And Hippocampal Sclerosis In Rats

ObjectiveTo better understand the role of endogenous endothelin (ET) and endothelin receptor (ETR) subtypes in the initiation and development of acute epileptic seizures, we observed the effects of intracerebroventricular (ICV) administration of endothelin receptor (ETR) antagonists on piloca-rpine induced acute epileptic seizures and hippocampus sclerosis in rats.MethodsRepeated low-dose treatment with lithium chloride combined with pilocarpine to produce acute epileptic seizures in rats. Normal saline (control group,9 rats; pilocarpine group, n= 30), a specific endothelin ETAR antagonist (BQ123,15 nmol, n= 30), a specific endothelin ETBR antagonist (BQ788,15 nmol, n= 30) or a non specific endothelin ETA&BR antagonist (PD145065, 15 nmol, n= 30) was ICV administration into the left lateral ventricle of Sprague-Dawley male rats in a total volume of 1.5μL respectively before intraperitoneal (i.p.) injection of pilocarpine. Rats in control group were treated with NS instead of pilocarpine. All pilocarpine induced behavioral alterations, the ET concentration in tissue homogenate of hippocampus and pathological changes were evaluated.Results1. No seizures were seen in control group. Pilocarpine produced convulsive seizures (CS) in 56.7% animals of pilocarpine group.88.2% of rats that experienced convulsive seizures developed into SE. BQ123 and significantly decreased the incidence of animals that produced convulsive seizures compared to pilocarpine group. The incidence of rats that showed convulsive seizures subsequently developed SE in BQ788 group and PD145065 group were significant lower than that in pilocarpine group. However, the average latency to onset of convulsive seizure remained no significant differences among all the 4 group of animals treated with pilocarpine.2. The ET concentration in hippocampal tissue homogenate of rats with convulsive seizu-res in pilocarpine group was significantly higher than control group and the ETR antagonists pretreated animals at 7 d.3. There is no significant neuron loss, gliosis and mossy fiber sprouting (MFS) in rats of control group and animals with non convulsive seizures (NCS) at each time point. In the CA1,CA3 and hilar subfield, varying degrees of neuron loss and gliosis were observed among 4 groups of animals treated with pilocarpine and developed CS at 7 d and 28 d. The most significant neuron loss and gliosis occur at 7 d time point. It is more severe that the extent of neuron loss and gliosis in CA3 subfield compared to CA1, and gliosis was related to the severity of pyramidal cell loss. The CA3 subfield of all animals developed CS presented significantly MFS at 28 d. The ET immunohistochemistry positive cells mostly located in the pyramidal cell layer, especially the pyramidal cell of CA3 which contained high level of ET. No significant expression of ET was observed in the widespread glial cells.Conclusions1. Endogenous ET may produce convulsive seizures by acting on central ETAR, and stimulation of central ETBR may be involved in the generalizing process of epileptic seizures. Endogenous ET, at least, is partly involved in the initiation and development of acute epileptic seizures. CS is an important factory of hippocampal sclerosis, Pretreatment with ETR antagonists can not directly stop the process of hippocampal sclerosis in the rats with lithum-pilocarpine induced CS.2. Endogenous ET in hippocampal tissue homogenate of rats with lithum-pilocarpine induced CS significantly increases at 7d time point. The ET immunohistochemistry positive cells mostly locate in the pyramidal cell layer of CA subfield, the pyramidal cell of CA3 contains high level of ET. No significant expression of ET is observed in the widespread glial cells.