Evidence for plasticity in neurotransmitter expression in neuronal cultures derived from 3-day-old chick embryo

We have previously reported the developmental profiles of glutamate decarboxylase (GAD) and choline acetyltransferase (ChAT) bio- and immunocytochemically, assessing GABAergic and cholinergic neuronal phenotypes respectively, in neuroblast-enriched cultures from 3-day-old chick embryo, plated on poly-L-lysine. We have also reported that collagen as culture substrate inhibits neuronal aggregation and neuritic fasciculation in this culture system. In this study we assessed the same parameters for cultures on collagen. In addition, we evaluated the effects of nerve growth factors (NGF) on cholinergic and GABAergic expression on neurons plated either on polylysine or collagen. We found that non-neuronal cells and NGF prolonged the survival of cholinergic and GABAergic neuronal populations and that both markedly stimulated GABAergic expression. In contrast, cholinergic expression was only enhanced by NGF. Immunostaining for GABA and ChAT reflected the biochemical findings. Glutamine synthetase and cyclic nucleotide phosphohydrolase, used as markers for astrocytes and oligodendrocytes respectively, showed very low activity in both substrata and were not related to GAD or ChAT peak activities. Our findings suggest that humoral factors and cell-cell contacts markedly influence neuronal phenotypic expression in culture. Moreover, it appears that during early neuronal differentiation GABAergic neurons are more responsive to microenvironmental regulation compared to cholinergic neurons.