NEURITE OUTGROWTH AND SYNAPSE FORMATION BY LYMNAEA NEURONS - TOWARDS A CHARACTERIZATION OF MOLLUSCAN NEUROTROPHIC FACTORS

For the last several years we have endeavoured to characterize the end ogenous neurotrophic factors of the pulmonate snail, Lymnaea stagnalis . When plated in brain conditioned medium, motoneurons, interneurons a nd neurosecretory cells of Lymnaea all exhibited neurite outgrowth. We showed earlier that the motoneurons and interneurons respond to a Ner ve Growth Factor-like (NGF-like) component of conditioned medium. Neur osecretory cells, however, appear to be under the control of a factor derived from the endocrine dorsal body cells. Most recently, we were s urprised to learn that motoneurons and interneurons also respond to an other vertebrate neurotrophic factor, i.e., Ciliary Neurotrophic Facto r (CNTF). The outgrowth in CNTF differs both in appearance and in func tional outcome. Specifically, neurites in CNTF are thin, have small gr owth cones and elongate more quickly than their counterparts in NGF. R egarding functional consequences, both dopaminergic and peptidergic in terneurons fail to form synapses on target neurons when cultured in CN TF, but do so in NGF, as expected from our previous studies in conditi oned medium. These data shed new light on the functions of neurotrophi c factors and provide the first evidence that outgrowth and synaptogen esis can be differentially regulated.