Changes in free amino acid levels in developing human foetal brain regions.

The levels of free amino acids were determined in human foetal brain regions during prenatal development. Variation in the distribution of amino acids and their rate of change in five segments of the CNS at different stages of ontogeny was observed. Striking developmental changes were found in the levels of aspartic acid in medulla-pons and spinal cord, glycine in the spinal cord, gamma-aminobutyric acid in the cerebral cortex, glutamic acid in the cerebral cortex, midbrain, and spinal cord, and taurine in the medulla-pons and spinal cord. At a late gestational period, glutamic acid was found most abundantly over all the brain regions, whereas the level of taurine was highest at an early gestational stage but not in spinal cord.