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.

A Morphological Study of Synaptic Reorganization in Mossy Fibers of the Dentate Gyrus according to Hippocampal Sclerosis in Temporal Lobe Epilepsy: A Comparison of Intraoperative ECoG Findings for Tailored Resection

This study was carried out to identify synaptic reorganization by mossy fibers of epileptic dentate gyrus by Timm sulphide silver histochemistry and to investigate degree of synaptic reorganization according to both hippocampal sclerosis and epileptiform discharge in human temporal lobe epilepsy(TLE). The control group was composed of two hippocampal tissues obtained from autopsied brain without neurological abnormalities. TLE group was composed of thirteen hippocampal tissues obtained from surgically resected temporal lobe. Among thirteen hippocampal tissues, five specimens were obtained both of two areas of each hippocampus with or without prominent epileptiform discharges on electrocorticogram(ECoG) for tailored hippocampal resection. Hippocampal cell density was quantitatively analyzed in TLE group and compared with that of control group. A portion of hippocampal tissue was observed under light microscopic and transmission electron microscopes after development with Danscher method. The results were as follows : Hippocampal cell loss was noted in all TLE group. Hippocampal cell loss greater than 30% of control values was found in 12 cases and average hippocampal cell loss was 70%(range 39-88%). The remaining 1 case had 13% hippocampal cell loss. The supragranular Timm granules were noted in inner molecular layer of dentate gyrus and tended to significantly increase in proportion as severity of hippocampal sclerosis. Average of hippocampal cell loss in two areas of five hippocampal tissues with or without prominent epileptiform discharge on ECoG was 73.6%(range 53-90%) and 66.4%(range 50-86%), which showed statistically significant (p<0.05) difference between these two areas and the supragranular Timm granules also tended to increase in the hippocampal tissue with epileptiform discharge. On transmission electron microscope, there showed distinct supragranular Timm granules correspond to mossy fiber synaptic terminals. The results of this study demonstrated that mossy fiber synaptic reorganization seems to play a major role in pathogenesis of human TLE and the development of mossy fiber synaptic reorganization is closely related to severity of hippocampal sclerosis. The result also support the rationale for tailoring the extent of hippocampal resection by intraoperative acute recording(ECoG) according to individual pathophysiology.