INVITRO EVIDENCE FOR MULTIPLE NEURITOGENIC FACTORS IN THE CENTRAL-NERVOUS-SYSTEM OF PULMONATE MOLLUSKS

Previous work has shown that neurons of the fresh water pond snails, L ymnaea and Helisoma, require soluble factors produced by neural tissue s for neurite outgrowth to occur in vitro. In the present study, we sh ow that mammalian nerve growth factor (NGF) stimulates neurite outgrow th of specific Lymnaea neurons. In contrast to motoneurons and interne urons, which show a robust dose response to NGF, no response was obser ved in neurosecretory cells. In an attempt to localize neuritogenic ac tivity to specific ganglia or organs, we show that the dorsal bodies, endocrine structures of the cerebral ganglia, promote neurite outgrowt h of specific neurons. In general, however, the spectrum of neurons th at respond to dorsal body cell conditioned medium differs from that wh ich respond to NGF. We conclude that Lymnaea neurons respond both to N GF and also to a separate factor derived from the dorsal body cells.