In Vitro Autoradiography of NMDA Receptors in the Hippocampus of Patients with Temporal Lobe Epilepsy

Purpose: Excitatory amino acids are one of the factors related to epileptogenesis. We studied the excitatory amino acid receptors, N-methyl-D-aspartate receptor (NMDAR) and a-amino-3-hydroxy-5-methyl-4-isoxazol propionate receptor (AMPAR), with in vitro auto-radiography in resected specimens from patients with temporal lobe epilepsy (TLE) and compared them with the benzodiazepine receptor (BZDR) we had previously studied. Methods: Twenty-three resected specimens from patients with intractable TLE were obtained by anterior temporal lobectomy (17 cases) or amygdalo-hippocampectomy (six cases). We divided them into a mesial temporal lobe epilepsy (MTLE) group (n = 17; age at onset, 0.5–18 years; mean, 7.2 years; and age at the operation, 14–39 years; mean, 23.4 years) and a non-MTLE group (n = 6; age at onset, 0.5–27 years; mean, 13.6 years; and age at the operation, 11–36 years; mean, 26.5 years). All specimens from the MTLE group had mesial temporal sclerosis. Three of the specimens from the non-MTLE group had a dysembryoplastic neuroepithelial tumor, and the remaining three specimens had no obvious histologic abnormalities. The specimens were frozen and used for in vitro autoradiography with [3H]CGP39653, [3H]AMPA, and [125I]iomazenil, and the receptor densities in each area of the hippocampus and neocortex were quantified. In the non-MTLE group, we measured receptor densities in the neocortex without histologic lesions. For the quantification of receptor densities in the hippocampus, we analyzed mainly the pyramidal cell layers in CAI-CA4, and the granule cell and molecular layers of the dentate gyrus (mDG). Neuronal cell densities were evaluted by using the Dam method in cresyl violet-stained sections adjacent to those used for receptor density analysis. Results: By statistical analysis with the Spearman rank-order correlation test, the correlations of the NMDAR and AMPAR to neuronal cell density were significant only in CA3 (NMDAR, p < 0.005; and AMPAR, p < 0.01). In contrast, the correlations of the BZDR to neuronal cell density were significant in CAI, CA3, and CA4 (p < 0.005), and in CA2 (p < 0.05). We analyzed the differences of receptor densities between the MTLE group and the non-MTLE group by using the Mann-Whitney U test. In the MTLE group, they were reduced in general. The NMDAR densities of the MTLE group were reduced in CAI (p < 0.001) and CA4 (p < 0.01) compared with the non-MTLE group. The AMPAR densities of the MTLE group were reduced only in CAI (p < 0.001). In contrast, BZDR densities of the MTLE group were reduced in CA1 (p < 0.001). CA3 (p < 0.01). and CA4 (P < 0.001). We compared the reduction of all three types of receptors in the MTLE group to the non-MTLE group in each area of the hippocampus. We found a tendency for the densities of the NMDAR receptors to be higher than those of the BZDR in all areas of the hippocampus, mDG, and neocortex. Conclusions: The densities of receptors related to neuronal excitation and inhibition are differentially reduced during neuronal cell loss. Moreover, the NMDAR and AMPAR were reduced differentially in the sclerotic hippocampi. This variability in the reduction of receptor densities may contribute to the genesis of the epileptic disorders.