CEREBRAL ENERGY-METABOLISM, GLUCOSE-TRANSPORT AND BLOOD-FLOW - CHANGES WITH MATURATION AND ADAPTATION TO HYPOGLYCEMIA

Brain maturation is characterized by a peak of cerebral energy metabol ism and blood flow occurring between 3 and 8 years of age in humans an d around 14-17 days of postnatal life in rats. This high activity coin cides with the period of active brain growth. The human brain is depen dent on glucose alone during th al period, whereas rat brain uses both glucose and ketone bodies to cover its energetic and biosynthetic nee ds. The maturation of the density of glucose transporter sites-GLUT1 l ocated at the blood-brain barrier and GLUT3 at the neuronal membrane-p arallels the development of cerebral glucose utilization. During moder ate acute hypoglycaemia, there are no changes in cerebral functional a ctivity; cerebral glucose utilization decreases and blood flow increas es only when hypoglycaemia is severe (lower than 2 mu mol/ml). During chronic hypoglycaemia, the brain adapts to the low circulating levels of glucose :the number of glucose transporter sites is increased, and cerebral glucose utilization and function are maintained at normal lev els while cerebral blood flow is more moderately increased than during acute hypoglycaemia. Neuronal damage consecutive to severe and prolon ged hypoglycaemia occurs mainly in the cerebral cortex, hippocampus an d caudate-putamen as a result of active release of excitatory amino ac ids.