A Quantitative Study of Central Benzodiazepine Receptors in Surgically Resected Specimens with Temporal Lobe Epilepsy Using [125I]iomazenil Autoradiography
Authors: Sata Yoshimi , Matsuda Kazurni , Nishimura Shigeko , Kubota Yuko , Ohtsubo Toshiaki , Tottori Takayasu , Mihara Tadahiro , Yagi Kazuichi 
Published: August 2009

Purpose: We measured the density of central‐type benzodiazepine receptors (BZRs) in the surgically resected tissues from patients with temporal lobe epilepsy (TLE) by means of [125I]iomazenil (IMZ) autoradiography, and investigated the correlations between the BZDK density and neuronal cell density in the hippocampus.

Methods: Resected tissues from 49 patients with TLE were studied after obtaining informed consent. The mean age at the onset of seizures was 9.4 years. and it was 25.7 years at surgery; the mean time between seizure onset and the operation was 16.3 years. In all patients, medically intractable complex partial seizures had occurred more than once per month before surgery. Anterior temporal lobectomy was conducted in 40 patients and selective amygdalohippocampectomy in nine patients. One group of 37 patients had mesial TLE (MTLE), and the other group or 12 patients had non‐MTLE. Of the 12 patients, three patients had a dysembryoplastic neuroepithelial tumor, three patients had an angioma, and three patients had a nonpathologic disease. Sixteen mi‐crometer‐thick cryostat sections were prepared from surgical specimens frozen immediately after resection. Those sections were incubated at 37°C for 1 h in a potassium phosphate buffer containing 150 mM NaCl and0.2 nM [125I]IMZ. Nonspecific binding was determined by coincubation with 1 μM diazepam (DZP). Autoradiographs were made by placing the radiolabeled slides on Hyperfilm‐3H. The densities of BZDR were calculated by using TVIP‐4100II and Image Command 4198 as TV image processors with [125I]microscale for the standard scale. The mean BZDR densities were calculated from several regions of interest (ROIs) in the identified lesions. The density of neurons in the hippocampal region also was quantified by using the Dam method.

Results: In the non‐MTLE group, the laminated structures of the hippocampus had high accumulations of BZDR, especially in the molecular and granule cell layers of the dentate gym (mDG) and the molecular. radial, and pyramidal layers of the comuammonis (CA). In the MTLE group, decreased accumulation of BZDR binding corresponding to the severity of neuronal loss, especially in the radial and pyramidal layers of the CA, were observed. The decreased densities of the BZDR paralleled the loss of neurons in the hippocampal regions. In the MTLE group, the mean BZDR densities (fmol/mg tissue) were CAI, 4.25 ± 3.23; CA3, 8.44 ± 4.24; CA4, 11.64 ± 8.29; CM, 15.44 ± 5.77; and mDG, 52.89 ± 28.00. In the non‐MTLE group, these densities were CA1, 80.68 ± 29.33; CA4, 40.94 ± 4.24; CA3. 35.69 ± 6.76; CA2, 28.97 ± 6.11; and DGM, 87.5 ± 32.29. Significant differences between the MTLE and non‐MTLE BZDR densities were found in all regions of CA (p < 0.001) and in mDG (p < 0.001j. In the MTLE group, we investigated the correlations of the mean BZDR densities between each area of the hippocampus and the lateral temporal cortex. A positive correlation for the BZDR density was found between the mDG and the lateral cortex (p = 0.01; r= 0.744).

Conclusions: The BZDR densities of the hippocampus in patients with ILE decreased in proportion to the severity of the neuronal loss. In the MTLE group, the BZDR density in the DGM was highly correlated with that of the temporal cortex. The positive correlation of the BZDR density between the mDG and the temporal lobe cortex suggests that hippocampal sclerosis or the epileptogenic foci affected the lateral cortex in patients with TLE. These results support the theory that functional imaging of the BZR is useful for diagnosing MTLE.