Central GABA mechanisms during postnatal development in the rat: neurochemical characteristics.

Various biochemical characteristics of the developing GABA system was studied in rats from 1 to 60 days of age. Endogenous GABA concentrations were high in the limbic system, midbrain, brain stem and spinal cord at birth. Until 7 days of postnatal age, GABA concentrations generally decreased, thereafter an increase was seen and at 60 days of age the GABA concentrations exceeded those found in the neonate except for the spinal cord regions. After GABA-T inhibition with AOAA, GABA concentrations increased in all brain regions, however considerably more marked in the 28 days old rats compared to the 4 days old animals. Turnover rate of GABA was estimated by investigating the rate of disappearance of GABA after GAD inhibition with 3-MPA. Calculated turnover time of whole brain GABA was 34.1 min in the 4 days old rats and 19.9 min in the 28 days old animals. The results from this investigation clearly indicate a caudal to rostral maturational gradient in the development of endogenous GABA concentrations as well as synthesis capacity. Furthermore, turnover rate of total whole brain GABA but probably not of GABA in the neuronal pool is retarded in the 4 days old rats compared to the adolescent animals.