THE ENTRY OF ACIDIC AMINO-ACIDS INTO BRAIN AND CSF DURING DEVELOPMENT, USING IN-SITU PERFUSION IN THE RAT

Previous studies using the rapid single pass blood to tissue uptake of substances by the capillaries of the blood-brain barrier, have failed to show significant uptake of acidic amino acids. However, by the use of a bilateral in situ brain perfusion in neonatal and adult rats, ex tending the perfusion time to 30 min, the carrier-mediated uptake of a spartate and glutamate into brain and CSF has been demonstrated. The r atios of C-14-acidic amino acids in the brain and CSF to that in perfu sate were measured and represented as R(brain) and R(CSF) respectively , after 30 min, neonatal (1-week-old) R(brain) values for both amino a cids were approximately twice that of adults, while neonatal R(CSF) fo r aspartate and glutamate were 3 to 5 times that of the adult. In cont rast, there was no significant entry of NMDA into either compartment f or both adults and neonates. The transfer coefficient, K-in, into brai n and CSF was also measured in relation to stages of development. In g eneral the K-in values for brain and CSF for aspartate and glutamate w ere higher in the younger age groups than the adult group (1 week > 2 week > 3 week 2 adult). In 1- and 2-week-old rats entry into CSF appea rs to be higher than that of brain, whereas for adults entry into the brain tissue was dominant.