Protein synthesis is required for the initiation of dendritic growth in embryonic rat sympathetic neurons in vitro.

We have utilized an experimental paradigm which allows the manipulation of dendritic growth in sympathetic neurons in culture to examine the effects of inhibitors of protein synthesis and RNA synthesis on the development of dendrites. Embryonic rat sympathetic neurons extend only axons when they are grown in serum-free medium on a polylysine substrate. The addition of an extract of basement membrane proteins (BME) to this culture system elicits dendritic growth within 48 h. Both cycloheximide and actinomycin-D inhibited BME-induced dendritic growth in greater than 80% of the neuronal population and reduced the number of dendrites extended by greater than or equal to 97%. In contrast, cycloheximide was found to have minimal effects on axonal growth in short-term (less than or equal to 18 h) cultures as measured with respect to the percentage of the population with axons and the number of axons per neuron. However, this inhibitor did significantly reduce (84%) the length of the axonal plexus extended. These results indicate that dendritic and axonal growth in sympathetic neurons are differentially dependent on protein synthesis such that the formation of dendrites requires protein synthesis whereas the initiation, but not the elongation, of axons is relatively independent of protein synthesis.