Postnatal changes of GABAergic and glutamatergic parameters.

In the rat cortex and striatum, glutamate decarboxylase, a marker for GABAergic nerve terminals, increased almost linearly for the first postnatal month, in agreement with previous reports. High affinity GABA and glutamate transport appeared to develop earlier, reaching, respectively, 170-190% and 72-80% in adult rates by the fifteenth postnatal day. Glial and neuronal uptakes of GABA in infant and adult tissues were investigated using beta-alanine and cis-3-aminocyclohexane-carboxylic acid. The relatively high striatal uptake of GABA observed in 2-day-old rats was found to be mainly due to early development of neuronal rather than glial transport in this region. Both neuronal and glial uptake, however, contributed equally to the enhanced uptake of GABA obtained in both regions at day 15. Neuron/glia ratios were estimated to increase by more than 12-fold in the cortex, and about 4-fold in the striatum from newborns to adults. The present results also indicate that there may exist in the immature striatum some glioblasts which might accumulate beta-alanine but not GABA. The 2-fold developmental increase in ornithine aminotransferase activity is consistent with the hypothesis that this enzyme may be enriched in glutamatergic neurons.