Comparative responsiveness of early chick neural tube neurons to muscle-conditioned medium, laminin, NGF and fibronectin.

Dissociates from the metencephalic basal plate of early chick embryo neural tubes containing the trigeminal (V) motor nucleus were cultured on substrates conditioned with appropriate target-derived muscle conditioned medium (MCM), laminin (LAM), MCM with nerve growth factor (NGF) in the medium, and fibronectin (FN). Comparisons were made of neuronal survival, the number of neurons with processes, and the length of processes elaborated. It was found that both MCM and LAM significantly enhanced survival and neuritic production from this population when compared to controls grown on a collagen-polyornithine substrate, but MCM surpassed LAM in these measures. When the neurons were grown on an MCM-conditioned substrate with an NGF-supplemented medium, no improvements were produced over the MCM or the NGF conditions alone. Therefore, the two do not appear to act in synergy, as NGF and LAM have been shown to do. FN produced no enhancement of any of the measures taken from this population. An ELISA analysis revealed no detectable LAM in the early target MCM. These results indicate that the specific responsiveness of this early neural tube population to its target MCM is not mediated by LAM, but the growth-enhancing component acts in a similar manner, although its influence is more potent.