Changes in the kinetics of the acidic amino acid brain and CSF uptake during development in the rat

Abstract

Using a bilateral in situ brain perfusion technique, the rate of influx of the acidic amino acids, aspartate and glutamate, into both brain and CSF, were measured in the rat. The kinetic constants for uptake of these amino acids across the blood-brain and blood-CSF barriers in neonatal (1-week-old) and adult (7-10 weeks-old) rats were calculated; the half saturation constant (K(m)) at both barriers did not change with age, whereas the maximal transport (Vmax) at both barriers was greater in the younger age group, and reduced by more than 50% with maturity. The diffusion constant Kd at the blood-brain barrier was not different from zero at either age, although at the blood-CSF barrier there was some diffusion at both ages, which did not change with maturity. The entry of these amino acids into the neonatal brain shown in our previous study can be explained by a greater maximal transport in the neonates which, coupled with the elevated plasma amino acid concentrations of the young animal, would result in higher blood-to-brain and blood-to-CSF flux in the neonate.