Mossy fiber Synaptic Reorganization and the Pattern of Sprouting in the Pilocarpine Epilepsy Model

BACKGROUND: The purpose of this study is to evaluate the synaptic reorganization and pattern of mossy fiber sprouting as a pathologic mechanism of chronic seizure in pilocarpine epilepsy model through histological alterations of hippocampus. METHOD: Sprague-Dawley, a sensitively damaged by pilocarpine stimulation, served as a experimental group(n=20). And the same dose of saline injected rats were served as a control group(n=10). They were implanted depth electrode in the hippocampus by a stereotaxic surgery, and injected pilocarpine 300mg/Kg intraperitoneally. They produced status epilepticus and the survival rats were monitored by a video-EEG monitoring system whether the spontaneous recurrent seizures occurring for more than 4 weeks. If more than 3 times spontaneous recurrent seizures were identified, then the rat hippocampus was examined by light microscope. RESULT: The pilocarpine injected group produced acute limbic seizure and developed to status epilepticus. The survival rats(n=10) became to chronic epilepsy state after silent period of everage 16.5 days. H&E staining demonstrated that loss of hilar polymorphic cell with ischemic changes and destruction of CA1 with damages of pyramidal cells in hippocampal subfields. Timm stains showed mossy fiber synatic reorganization in the supragranular and intragranular layer of dentate gyrus and infrapyramidal layer of CA3 hippocampal subfieid in pilocarpine induce seizure rats. CONCLUSION: These results suggest that chronic seizures in the pilocarpine epilepsy model is largely due to mossy fiber synatic reorganization, a consequence of supragranular mossy fiber sprouting. But intragranular and infrapyramidal axonal sprouting might have parts of role in synaptic reorganization. Additional research is required to determine the various patterns of axonal sprouting.

Synaptic Reorganization of Dentate Mossy Fibers and Expression of Calcium Binding Proteins in Hippocampal Sclerosis of Temporal Lobe Epilepsy

This study was designed to identify expression of calcium-binding proteins and synaptic reorganizations of dentate mossy fibers in hippocampal sclerosis of human temporal lobe epilepsy. Hippocampal neuronal density was quantitively analyzed in temporal lobe epilepsy group (n=50) to investigate the degree of hippocampal sclerosis and it was compared with that of autopsy control (n=3). To verify the distribution of calcium-binding proteins in neurons of epileptic hippocampi, the parvalbumin (PV)-immunoreactive and calbindin-D28K (CB)-immunoreactive neurons were quantitively analyzed in each area of Ammon's horn by immunohistochemical stain. Also, to clarify synaptic reorganizations of the dentate mossy fibers, a part of each hippocampus was examined under light microscopy and transmission electron microscopy using Timm sulphide silver method. In epileptic hippocampi, severity of hippocampal sclerosis (HS) was graded four, which consisted of 3 cases with no HS, 6 mild HS, 12 moderate HS, and 29 severe HS. The hippocampal neuronal loss was most prominent in CA1, followed by CA4 and CA2. Expression of calcium-binding proteins was more prevalent in CA2 of all groups. The proportion of PV-immunoreactive neurons in CA1 and CA4 significantly increased in the moderate and severe HS group, whereas the proportion of CB-immunoreactive neurons did not correlated with the severity of HS. Timm granules were noted in inner molecular supragranular layer of dentate gyrus of epileptic hippocampi and they tended to increase in proportion along with the severity of hippocampal sclerosis. Transmission electron microscopy showed that supragranular Timm granules corresponded to synaptic terminals of mossy fibers. These results suggest that parvalbumin appears to have more protective effect against neuronal loss and that mossy fiber synaptic reorganization seems to play a major role in pathogenesis of hippocampal sclerosis of human temporal lobe epilepsy.