Abstracts

Electrophysiological studies on hippocampal slices from temporal lobe epilepsy (TLE) patients suggest that changes in AMPA and NMDA-receptor-mediated conductances may contribute to epileptogenesis. In the present study we describe and compare features of synapses in the FD inner molecular layer (IML) between human hippocampal sclerosis (HS) and extrahippocampal mass lesions (non-HS). Morphological aspects of synapses and localization of GLUR1 and NMDAR1 subunits are described.
For EM morphology, samples of the hippocampus from TLE patients with HS (n=4) and non-HS (n=2)were used. Sections (150 [micro]m-thick) were cut with a vibratome and collected in phosphate buffered saline. Sections were a) processed for the cytochemical detection of zinc; or b) osmicated and embedded in Araldite for the EM study. For comparison, equivalent regions of 2 male Wistar rats were processed in the same manner. For immuno EM, samples immediately taken from surgery were rapidly frozen, freeze substituted, and Lowicryl embedded. Thin sections were collected on nickel grids, incubated with the primary antibodies (anti-GluR1 and NMDAR1), and protein A-gold (15nm).
Analysis of TLE cases indicated that asymetric synapses (AS) are predominant over the symetric synapses (SS). The ratio of SS/AS in the IML were not different among groups. The ratio ranged from 1:8 to 1:10, in both HS and non-HS groups, and was 1:10 in rat hipocamppi. In the HS hippocampi the number of small synaptic vesicles (SSV)/[micro]m2 was smaller (HS= 16 [plusmn] 2.28; non-HS= 43.1 [plusmn] 15.8) and the mean area of postsynaptic densities (PSD) was higher in comparison to non-HS and rat controls (HS = 0,034 [micro]m2 [plusmn] 0,01; non-HS = 0,018 [micro]m2 [plusmn] 0,009, rat = 0,019[micro]m2 [plusmn] 0,02). Gold particles labeling GluR1 were aligned along PSD and distributed mostly at the outermost portion of the PSD. NMDAR1 gold particles were located into synaptic clefts between pre- and post-synaptic membranes.
Our data suggest no alteration in the ratio of excitatory/inhibitory synapses between HS and non-HS patients. This does not support the concept that the hyperexcitability seen in HS with MFS could be due by increase of IML AS. The GluR1 receptors are localized along the post-synaptic membranes, as described for the localization in the rat hippocampus. Immuno EM indicated that the localization of GluR1 receptors is distributed mostly at the outermost portion of the PSD. This receptor distribution was described elsewhere on Punkinje cells of developing and adult rats. Immunolabeling for NMDAR1 showed gold particles on synaptic clefts and PSD as described in normal rat CA1 synapses. Our findings indicate that in the epileptic FD IML the GLUR1 and NMDAR1 subunits have a normal distribution along the surface of the postsynaptic membrane.
[Supported by: FAPESP (99/11729-2), CNPq and FAEPA.]