Eye-extract factors promote the expression of acetylcholine sensitivity in chick dorsal root ganglion neurons.

We have examined the development of acetylcholine (ACh) responses in chick sensory neurons and their regulation by growth factors. Between Embryonic Days E13 and E18 in vivo, the proportion of freshly dissociated dorsal root ganglion (DRG) neurons that were appreciably sensitive to 500 microM ACh increased from approximately 40 to > 90% and the size of the ACh response per unit membrane area increased nearly 10-fold. Nerve growth factor (NGF) supports the survival, growth, and differentiation of central, sympathetic, and sensory neurons. NGF also promotes ACh sensitivity in PC12 cells and nodose ganglion neurons grown in cell culture. When E13 chick DRG neurons were maintained in culture with NGF for 4-6 days, however, only approximately 50% had appreciable ACh sensitivity, and large responses comparable to those observed at E18 in vivo were rare. Chick-eye extract contains a 21.5-kDa trophic factor termed growth-promoting activity (GPA) that supports survival of sympathetic and DRG neurons for 24 hr in culture and an activity of approximately 50 kDa that promotes increases in choline acetyltransferase activity, ACh sensitivity, and ACh receptors (AChRs) in ciliary ganglion neurons (Nishi and Berg, 1981; Halvorsen et al., 1991). In the present study, whole-eye extract supported full survival of E13 DRG neurons for up to 6 days in culture and promoted ACh sensitivity in > 90% of the neurons tested. GPA-containing eye-extract fractions and NGF individually supported full DRG neuron survival for up to 6 days in culture, but neither promoted ACh sensitivity. Adding eye-extract fractions containing material of approximately 50 kDa for 4-6 days to either GPA- or NGF-supplemented media led to appreciable ACh sensitivity in approximately 90% of the DRG neurons tested. The levels of ACh sensitivity observed in DRG neurons maintained either in whole-eye extract or in fractions containing 50-kDa material were close to those observed at an equivalent developmental age in vivo. The results indicate that components in the 50-kDa eye-extract fraction promote the ACh sensitivity of DRG neurons in culture and suggest that similar factors may influence the appearance of AChRs on the neurons in vivo.