title: Dual-tracer autoradiography using 125I-iomazenil and 99Tcm-HMPAO in experimental brain ischaemia.
abstract: To investigate the utility of neuroreceptor imaging in ischaemic cerebrovascular disorders, dual-tracer autoradiography using 99Tcm-hexamethylpropyleneamine oxime (HMPAO) for the evaluation of cerebral blood flow and 125I-iomazenil for the evaluation of central-type benzodiazepine receptor density was performed in experimental brain ischaemia created by occlusion of the unilateral middle cerebral artery of the rat. In the acute phase of ischaemia, 125I-iomazenil accumulation showed less of a decrease than 99Tcm-HMPAO in the cerebral cortex of the lateral convexity and in the lateral segment of the caudate putamen in the lesioned cerebral hemisphere. In the sub-acute phase, both 125I-iomazenil and 99Tcm-HMPAO accumulation increased in the lesion compared with the acute phase. A large accumulation of 99Tcm-HMPAO and 125I-iomazenil in the lesion was considered to be due to luxury perfusion and penetration of 125I-iomazenil hydrophilic metabolites from the blood into the brain tissue through the altered blood-brain barrier. In the chronic phase, 125I-iomazenil accumulation showed a more marked decrease than 99Tcm-HMPAO in the lesion. Moreover, the ipsilateral thalamus, which is remote from the lesion, revealed decreased 125I-iomazenil accumulation despite normal 99Tcm-HMPAO accumulation. Since the central-type benzodiazepine receptors are principally located not on the glial cells but on the neurons, the receptor density may exhibit a change that parallels the neuron density. These results suggest that central-type benzodiazepine receptor imaging is useful for the evaluation of neuronal damage when used in conjunction with brain perfusion imaging in ischaemic cerebrovascular disorders, except in the sub-acute phase.
mesh_terms: D000208:Acute Disease; D000818:Animals; D001345:Autoradiography / Q000379:methods*; D001921:Brain / Q000000981:diagnostic imaging* / Q000378:metabolism; D002545:Brain Ischemia / Q000000981:diagnostic imaging* / Q000378:metabolism; D002908:Chronic Disease; D005442:Flumazenil / Q000031:analogs & derivatives* / Q000378:metabolism; D007839:Functional Laterality; D007457:Iodine Radioisotopes / Q000378:metabolism; D008297:Male; D009928:Organ Specificity; D015609:Organotechnetium Compounds; D010091:Oximes; D011877:Radionuclide Imaging; D051381:Rats; D011919:Rats, Inbred Strains; D011963:Receptors, GABA-A / Q000032:analysis; D019690:Technetium Tc 99m Exametazime
chemical_list: D007457:Iodine Radioisotopes; D015609:Organotechnetium Compounds; D010091:Oximes; D011963:Receptors, GABA-A; D019690:Technetium Tc 99m Exametazime; D005442:Flumazenil; C063038:iomazenil