The effects of exogenous nutrients on growth of chick embryo brain.

: The effect of an early addition of exogenous nutrients on brain growth has been investigated in chick embryo. The nutrients were introduced onto chorioallantoic membrane at day 6 or 7 of embryonal life, and the cerebral hemispheres examined at the end of neuronal proliferation for the following parameters: weight, DNA content (index of cell number) and protein content. L-Tryptophan produced significant inhibition, probably by creating amino acid imbalance and interference with the transport of other amino acids. D-Tryptophan (slower transport) was inactive. 5-Methyltryptophan produced significant inhibition, probably by causing deficiency of tryptophan utilization and of production of serotonin, which is a growth factor for early brain. Glycine stimulated brain growth, probably by conversion to glucose which is the main energy source for the embryo in this period. Brain weight and DNA were found to be significantly correlated with blood glucose level. It is concluded that, within genetic limits, early brain growth might be manipulated in both directions (inhibition or stimulation) by addition of proper nutrients during sensitive period of neuronal proliferation.