IN-VIVO IMAGING OF GABA(A) RECEPTORS USING SEQUENTIAL WHOLE-VOLUME I-123 IOMAZENIL SINGLE-PHOTON EMISSION TOMOGRAPHY

Using a brain-dedicated triple-headed single-photon emission tomograph y (SPET) system, a sequential whole-volume imaging protocol has been d evised to evaluate the regional distribution of iodine-123 iomazenil b inding to GABA, receptors in the entire brain. The protocol was pilote d in eight normal volunteers (seven males and one female; mean age, 24 .8+/-3.9 years). The patterns obtained were largely compatible with th e known distribution of GABA, receptors in the brain as reported in au toradiographic studies, with cerebral cortical regions, particularly t he occip ital and frontal cortices, displaying the highest I-123-iomaz enil uptake. Measures of time to peak uptake and tracer washout rates presented with the same pattern of regional variation, with later time s to peak and slower washout rates in cortical regions compared to oth er brain areas. Semiquantitative analysis of the data using white matt er/ventricle regions as reference demonstrated a plateau of specific I -123-iomazenil binding in neocortical and cerebellar regions from 60-7 5 min onwards. These data demonstrate the feasibility of sequential, d ynamic whole-volume I-123-iomazenil SPET imaging. The protocol may be particularly useful in the investigation of neuropsychiatric condition s which are likely to involve more than one focus of GABA abnormalitie s, such as anxiety disorders and schizophrenia.