Effects of basic fibroblast growth factor on the development of GABAergic neurons in culture.

Six-day-old neuronal cultures derived from 14-day-old embryonic rat cerebral hemispheres were highly enriched in GABAergic neurons, as was demonstrated by immunocytochemistry using an anti-glutamate decarboxylase antiserum. They contained about 64% glutamate decarboxylase-positive neurons. About 8% of these neurons proliferated, as shown by a combination of glutamate decarboxylase immunocytochemistry and [3H]thymidine incorporation into cell nuclei. The proliferative activity of GABAergic precursor cells and changes in the cellular concentrations of the non-essential amino acids, including GABA under the effect of basic fibroblast growth factor were studied. When basic fibroblast growth factor was added to the cultures 4 h after seeding, the proliferation of the GABAergic neurons was stimulated about threefold. Under this culture condition, the concentration per cell of all amino acids increased, except those of GABA and beta-alanine. When basic fibroblast growth factor was added to cultures only on day four, the proliferation of the neuronal cells was no more enhanced. Under this condition of treatment, the concentrations of all non-essential amino acids, including those of GABA and beta-alanine were enhanced. Under both basic fibroblast growth factor treatments the concentration of GABA per GABAergic cell was increased. In contrast, the specific activity of glutamate decarboxylase was not stimulated under these conditions. We hypothesize that under the effect of basic fibroblast growth factor the capabilities of the cells to store GABA are improved.