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 tomography (SPET) system, a sequential whole-volume imaging protocol has been devised to evaluate the regional distribution of iodine-123 iomazenil binding to GABA, receptors in the entire brain. The protocol was piloted in eight normal volunteers (seven males and one female; mean age, 24.8+/-3.9 years). The patterns obtained were largely compatible with the known distribution of GABA, receptors in the brain as reported in autoradiographic studies, with cerebral cortical regions, particularly the occip ital and frontal cortices, displaying the highest I-123-iomazenil uptake. Measures of time to peak uptake and tracer washout rates presented with the same pattern of regional variation, with later times to peak and slower washout rates in cortical regions compared to other brain areas. Semiquantitative analysis of the data using white matter/ventricle regions as reference demonstrated a plateau of specific I-123-iomazenil binding in neocortical and cerebellar regions from 60-75 min onwards. These data demonstrate the feasibility of sequential, dynamic whole-volume I-123-iomazenil SPET imaging. The protocol may be particularly useful in the investigation of neuropsychiatric conditions which are likely to involve more than one focus of GABA abnormalities, such as anxiety disorders and schizophrenia.