In vitro evidence for multiple neuritogenic factors in the central nervous system of pulmonate molluscs.

Previous work has shown that neurons of the fresh water pond snails, Lymnaea and Helisoma, require soluble factors produced by neural tissues for neurite outgrowth to occur in vitro. In the present study, we show that mammalian nerve growth factor (NGF) stimulates neurite outgrowth of specific Lymnaea neurons. In contrast to motoneurons and interneurons, which show a robust dose response to NGF, no response was observed in neurosecretory cells. In an attempt to localize neuritogenic activity to specific ganglia or organs, we show that the dorsal bodies, endocrine structures of the cerebral ganglia, promote neurite outgrowth of specific neurons. In general, however, the spectrum of neurons that respond to dorsal body cell conditioned medium differs from that which respond to NGF. We conclude that Lymnaea neurons respond both to NGF and also to a separate factor derived from the dorsal body cells.