A comparison of two factors affecting the proliferation of non-neuronal (glial) cells in vitro.

Earlier studies have shown that the proliferation of sympathetic non-neuronal cells in vitro can be stimulated either by direct contact with growing neurons or by addition of sonicated neurons of the same type to the culture medium. Several lines of evidence presented herein suggest that intact neurons and neuronal sonicate probably stimulate [3H]thymidine incorporation by distinctly different mechanisms. First, mitogenic factors are present in sonicates of cell types (fibroblasts and non-neuronal cells) which do not stimulate non-neuronal cell proliferation when added as intact cells. Second, neuronal sonicate and intact neurons differ in the types of cells which are responsive to their mitogenic influence. Third, intact neurons do not appear to stimulate non-neuronal cell proliferation by the same mechanism as that of neuronal sonicate. Further similarities between stimulation of non-neuronal cell proliferation in vitro and reactive gliosis in vivo are discussed.