The survival of early chick sympathetic neurons in vitro is dependent on a suitable substrate but independent of NGF.

The neuronal cell population of lumbosacral sympathetic ganglia from 7-day-old chick embryos is characterized by a high proportion of cells with the ability to proliferate in culture (Rohrer and Thoenen, 1987). It is now demonstrated that neither proliferation nor survival of these neurons depend on the presence of nerve growth factor (NGF). However, neuronal survival did depend on the culture substrate used: on laminin, E7 neurons survived and their number increased due to proliferation, whereas on fibronectin (FN) or a substrate of molecules from heart cell-conditioned medium (HCM) a significant number of the cells died during early culture periods. Less than 70 and 50% of the number of neurons surviving on a laminin substrate were found on FN and HCM, respectively, after 3 days in culture. Although NGF did not affect neuronal survival, a small increase in neurite extension on these substrates was observed in the presence of NGF. Furthermore, although NGF did not prevent neuronal death after extended culture periods, this could be prevented by elevated extracellular potassium concentrations. Sympathetic neurons of E8 chick embryos however showed a strikingly different response to NGF compared with those of E7: whereas neuronal survival on laminin was not influenced by NGF, a significant effect of NGF on survival and on neurite extension was observed for E8 neurons on a HCM substrate. In contrast to cells from E7 and E8 embryos, the majority of neurons from E11 chick embryos required NGF for survival even on a laminin substrate as described previously (D. Edgar, R. Timpl, and H. Thoenen, 1984, EMBO J. 3, 1463-1468). These results demonstrate that while sympathetic neurons from E7 chick embryos do not depend on the soluble neurotrophic factor NGF for survival in vitro, they are dependent on molecules of the extracellular matrix. With increasing age, the survival requirements demonstrated in vitro change toward the classical pattern of NGF dependency. Low amounts of laminin-like immunoreactivity were shown to be present in sympathetic ganglia of E7 chick embryos which were then shown to increase as development proceeded. These data indicate that laminin may play a role in the survival and development of chick sympathetic neurons not only in vitro, but also in vivo.