Maturational Changes of Gamma-Aminobutyric Acid A Receptors Measured With Benzodiazepine Binding of Iodine 123 Iomazenil Single-Photon Emission Computed Tomography

Abstract

BackgroundIodine 123 (I-123) iomazenil is a specific ligand of the central benzodiazepine receptor, which is a part of the postsynaptic gamma-aminobutyric acid A receptor complex. We performed statistical image processing of I-123 iomazenil single-photon emission computed tomography to elucidate maturational changes in the GABAergic system. MethodsThirty patients (18 boys and 12 girls, aged 17 days to 14 years) with cryptogenic focal epilepsy were enrolled and underwent I-123 iomazenil single-photon emission computed tomography. We used a semiquantitative analytical method consisting of brain surface extraction, anatomic normalization, and a three-parameter exponential model. We then assessed developmental changes in benzodiazepine receptor binding activity in 18 regions of interest in both hemispheres. ResultsThe highest benzodiazepine receptor binding activity was observed during early infancy in all regions of interest. Benzodiazepine receptor binding activity then decreased exponentially across development. Benzodiazepine receptor binding in the primary sensorimotor cortex, primary visual cortex, cerebellar vermis, and striatum declined more rapidly than that in the cerebellar hemispheres and the frontal cortex. The pons and the thalamus had the lowest benzodiazepine receptor binding activities during the neonatal period, and benzodiazepine receptor binding in these areas declined gradually after infancy toward adolescence. There were no differences in adjusted benzodiazepine receptor binding activity according to laterality or sex. ConclusionsBenzodiazepine receptor binding activity decreased exponentially during infancy in all regions of interest. Binding activity in the primary somatosensory and motor cortices (M1 and S1), the primary and association visual areas, the cerebellar vermis, and the striatum (caudate nucleus and putamen) tended to decline more rapidly than that in the cerebellar hemisphere and the frontal association cortex.