Influence of the culture substratum on the expression of choline acetyltransferase activity in purified motoneurons from rat embryos.

Motoneurons from E14 rat embryos have been retrogradely labelled with a carbocyanine derivative and purified approximately 20-fold by density gradient centrifugation. For certain experiments, motoneurons have been purified to near homogeneity by cell sorting. These neurons were then cultured at low density on various substrata. Laminin stimulated neurite outgrowth of the identified motoneurons and stimulated choline acetyltransferase (ChAT) development by 2-fold; these cultures could not be maintained for more than 4 days. Motoneurons could be cultured for at least 7 days on monolayers of both living and lysed astrocytes from newborn cortex. The cells survived equally well on both substrata but neurite outgrowth was less elaborated on lysed astrocytes on which motoneurons displayed a mono- or bipolar, rather than a multipolar, morphology. Furthermore, ChAT developed at a 2-fold higher level on lysed, rather than living, newborn astrocytes. Such a difference was not observed using astrocytes from E14 rat embryos. In the latter case, both living and lysed astrocytes supported ChAT development at the same rate as lysed newborn astrocytes. Consequently, living astrocytes from newborn rat cortex are relatively less permissive for ChAT expression. On the other hand, both living and lysed astrocytes from newborn cortex induced ChAT expression by sympathetic neurons to the same extent. We propose that, in addition to retrograde factors from muscle origin, cell surface molecules expressed by embryonic astrocytes stimulate ChAT expression by motoneurons. Such molecules would be present in newborn astrocytes in an intracellular form and could be unmasked by cell lysis. Different cell surface molecules may induce ChAT activity in sympathetic neurons.