CHANGES IN THE KINETICS OF THE ACIDIC AMINO-ACID BRAIN AND CSF UPTAKEDURING DEVELOPMENT IN THE RAT

Using a bilateral in situ brain perfusion technique, the rate of influ x 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 ne onatal (1-week-old) and adult (7-10 weeks-old) rats were calculated; t he half saturation constant (K-m) at both barriers did not change with age, whereas the maximal transport (V-max) at both barriers was great er in the younger age group, and reduced by more than 50% with maturit y. The diffusion constant K-d at the blood-brain barrier was not diffe rent from zero at either age, although at the blood-CSF barrier there was some diffusion at both ages, which did not change with maturity. T he entry of these amino acids into the neonatal brain shown in our pre vious study can be explained by a greater maximal transport in the neo nates which, coupled with the elevated plasma amino acid concentration s of the young animal, would result in higher blood-to-brain and blood -to-CSF flux in the neonate. (C) 1997 Elsevier Science B.V.