Neurons from the snail Helisoma require a brain-derived factor(s) for neurite outgrowth in both organ and isolated cell culture. This factor is released from the CNS of Helisoma when brains are incubated in defined medium, producing a conditioned medium (CM). In addition to its growth-promoting activity, CM also enhances total uptake of 3H-choline and the incorporation of 3H-choline into specific metabolites: acetylcholine, phosphorycholine and lipid.
This choline metabolism-enhancing factor(s) is distinct and separable from neurite growth-promoting factor: 1. Over 95% of neurite growth-promoting activity can be removed from CM by adsorption to a polylysine surface while there is no loss of choline metabolism-enhancing activity. 2. When central ganglia were treated with anisomycin, a potent inhibitor of molluscan protein synthesis, the choline metabolism-enhancing activity was completely absent from the resulting CM, while the growth promoting activity was reduced by only 35%. These results suggest that the Helisoma CNS produces a variety of trophic factors that are involved in regulating the interaction between neuronal growth and metabolism.