Quantitative evaluation of central-type benzodiazepine receptors with [(125)I] Iomazenil in experimental epileptogenesis. I. The rat kainate model of temporal lobe epilepsy.

This study aimed at quantitatively evaluating hippocampal central-type benzodiazepine receptors (BZRs) in the kainate model of temporal lobe epilepsy (TLE) by in vitro autoradiography (ARG) using [(125)I] Iomazenil (IMZ) specific ligand for central-type BZRs. Kainate (1 microg/0.5 microl) was injected into the left amygdala to induce limbic status epilepticus. One, three, or six months after injection, in vitro ARG with [(125)I] IMZ and cell counts were performed in the hippocampal CA1-4 regions and dentate gyrus ipsilateral to the kainate injection site, and were compared with the vehicle-injected control group. In all kainate-treated rats, clear pyramidal neuron loss was observed in left hippocampal areas CA1-4. Compared with the control group, progressive reduction of [(125)I] IMZ binding was also observed. This resulted in a marked binding decrease paralleling pyramidal neuron loss in hippocampal areas CA1 (down to 83% of control), CA2 (76%), CA3 (75%), and CA4 (90%) at 6 months after kainate administration. Conversely, [(125)I] IMZ binding significantly increased in the dentate gyrus (up to 106% of control) at 1 month, but returned to nearly normal at 3-6 months. These results suggest that central-type BZR neuroimaging is useful in detecting hippocampal sclerosis in the mesial TLE, though central BZR alterations differ depending on hippocampal subfields and post-seizure time-courses.