Development of spontaneous motility in chick embryos. Inhibitory effect of glycine and gamma-aminobutyric acid.

The effect of glycine (100 mg/kg egg weight) and gamma-aminobutyric acid (GABA, 103 mg/kg egg weight) on spontaneous motility was studied in chick embryos from the 11th to 21st day of incubation. Neither substance affected 11- and 13-day embryos (except for transient augmentation of spontaneous motility in some of the 13-day embryos after glycine). From the 15th day of incubation, both substances inhibited spontaneous motility, the effect being most pronounced in 17-day embryos. Their effect on 21-day embryos was weaker than their effect on younger embryos. The results are evaluated as evidence of later maturation of inhibitory mechanisms during development of the chick embryo CNS.