METABOLIC MATURATION OF THE BRAIN - A STUDY OF LOCAL CEREBRAL GLUCOSE-UTILIZATION IN THE DEVELOPING CAT

Previously, using positron emission tomography (PET), we showed that local cerebral metabolic rates for glucose (1CMR(glc)) in children undergo dynamic maturational trends before reaching adult values. In order to develop an animal model that can be used to explore the biological significance of the different segments of the 1CMR(glc) maturational curve, we measured lCMR(glc) in kittens at various stages of postnatal development and in adult cats using quantitative [C-14]2-deoxyglucose autoradiography. In the kitten, very low 1CMR(glc) levels (0.14 to 0.53 mu-mol min-1 g-1) were seen during the first 15 days of life, with phylogenetically older brain regions being generally more metabolically mature than newer structures. After 15 days of age, many brain regions (particularly telencephalic structures) underwent sharp increases of 1CMR(glc) to reach, or exceed, adult rates by 60 days. This developmental period (15 to 60 days) corresponds to the time of rapid synaptic proliferation known to occur in the cat. At 90 and 120 days, a slight decline in 1CMR(glc) was observed, but this was followed by a second, larger peak occurring at about 180 days, when sexual maturation occurs in the cat. Only after 180 days did 1CMR(glc) decrease to reach final adult values (0.21 to 2.04-mu-mol min-1 g-1). In general, there was good correlation between the metabolic maturation of various neuroanatomical regions and the emergence of behaviors mediated by the specific region. At least in the kitten visual cortex, which has been extensively studied with respect to developmental plasticity, the "critical period" corresponded to the portion of that 1CMR(glc) maturational curve surrounding the 60-day metabolic peak. These normal maturational 1CMR(glc) data will serve as baseline values with which to compare anatomical and metabolic plasticity changes induced by age-related lesions in the cat.