Sprouting by isolated Helisoma neurons: enhancement by glutamate.

We tested glutamate for its ability to modulate neurite outgrowth from isolated neurons of the adult snail, Helisoma trivolvis. Although glutamate did not induce neurite outgrowth from neurons maintained in defined medium, nevertheless it showed a dose-dependent ability to enhance the activity of conditioned medium. We concluded that glutamate can enhance the release and/or activity of CNS derived sprouting factor(s) present in conditioned medium. The general conclusion to be drawn from this study is that the ability of a neurotrophic factor(s) to promote neurite outgrowth can be regulated by a neurotransmitter. This mechanism may be important in the regulation of trophic factors in the adult nervous system.