Chemosensory afference in the tentacle nerve of Lymnaea stagnalis

Abstract

Although the neural control of behavior has been extensively studied in gastropods, basic gaps remain in our understanding of how sensory stimuli are processed. In particular, there is only patchy evidence regarding the functional roles of sense organs and the extensive peripheral nervous system they contain. Our goal was to use extracellular electrophysiological recordings to confirm the chemosensory role of the tentacles in the great pond snail, Lymnaea stagnalis. Employing a special twin-channel suction electrode to improve signal-to-noise ratio, we applied three food odors (derived from earthworm-based food pellets, algae-based pellets, and fresh lettuce) to a reduced preparation of the tentacle while recording neuronal activity in the tentacle nerve. Responses were assessed by comparing average spike frequencies produced in response to saline flow with and without odors. We report stronger neuronal responses to earthworm-based food odors and weaker responses to algae-based food odors. There were no clear neuronal responses produced when lettuce food odor or control saline was applied to the tentacle. Overall, our results provide strong evidence for the chemosensory role of the tentacles in navigation behavior by L. stagnalis. Although it is unclear whether the differences in neuronal responses to different odors are a technical consequence of our recording system or a genuine feature of the snail sensory system, these results are a useful foundation for further study of peripheral nervous system function in gastropods.