Chemosensory stimulation of the oral cavity of the snail Helisoma

Food extracts, perfused through the oral cavity of the snailHelisoma trivolvis, lead to synaptic activation of identifiedbuccal ganglia motor neurons. Both retractor and protractormotor neurons displayed cyclic bursts of firing characteristicof that observed during expression of the central feeding motorprogram(CFM). The possibility that leakage of food extracts from theoral cavity had a pharmacological effect on buccal neurons wasconsidered. Direct application of the extracts to the exposedganglionic surface did not evoke similar neuronal activity.Oral perfusion with a behaviorally aversive compound inhibitedboth the activity evoked by acceptable taste solutions and "spontaneously"generated activity in some preparations. It is concluded thatoral chemosensory receptors in the snail exert both an excitatoryand inhibitory influence on buccal motor neurons. The significanceof these results for cellular neurophysiological investigationof the synaptic events underlying the central processing ofafferent chemosensory information is discussed.