Development of radiodiagnostics for image diagnosis of intracerebral dopamine receptor

Single photon emission tomography (SPECT) able to evaluate the local blood flow in the brain is a safety and effective system for clinical diagnosis and pathological evaluation of incurable neulopsychotic diseases. Development of receptor imaging agents for SPECT, which has not been approved are progressing now. Using gerbits as an animal model for cerebrovascular diseases, an investigation was made on 125I-Iomazenil (Ro16-0154), an antagonist of benzodiazepin receptor in CNS as well as dopamine receptor ligands. 125I-Iomazenil was found to markedly accumulate in the regions; cerebral cortex (especially, layer VI and V), amygdala, thalamus, hypothalamus, nigra, cerebellar cortex, etc., where benzodiazepin is specifically localized. The accumulation was inhibited by preadministered flumazenil, indicating that 125I-Iomazenil can bind to the benzodiazepin receptor in CNS. The present study demonstrated that the late images of 123I-Iomazenil-SPECT are useful for detecting a lesion in the crebral cortex and cerabellar one, but it was unable to image out a lesion in the dentate-red nuclei due to DRPLA or Joseph disease. Therefore, 123I-Iomazenil was thought to be a valuable radiomedicine for imaging out and pathological evaluation. (M.N.)