Physiological characterization of lip and tentacle nerves in Lymnaea stagnalis

The lip and tentacle nerves of the pond snail, Lymnaea stagnalis, were char acterized using electrophysiological techniques. When the activity of those nerves was induced in lip-tentacle preparations, aversive taste signals we re transmitted through all the lip and tentacle nerves, but appetitive sign als could be recorded only through the superior lip nerve. In the CNS immer sed in high Mg2+-high Ca2+ saline, electrical stimuli applied to any of the nerves failed to induce action potentials in one of the regulatory neurons (cerebral giant cell: CCC) involved in feeding responses, implying that th e signals are polysynaptically transmitted to the CGC. Intracellular record ings revealed that the CGCs in semi-intact half-body preparations received both appetitive and aversive taste signals not only through the superior li p nerve but also through the median lip nerve. In addition, an osphradium w as ruled out as a candidate for appetitive reception. The present results, together with our preceding data arrived at by the histochemical analyses, indicate that the appetitive taste transduction responsible for generating feeding responses is performed through the superior lip nerve with some con tribution of the median lip nerve. The data showing that the CGC can receiv e various taste signals suggests that it may play a crucial role in feeding behavior as demonstrated in the study of conditioned taste-aversion. (C) 1 999 Elsevier Science Ireland Ltd. All rights reserved.