MODULATION OF THE FEEDING SYSTEM BY A RADULAR MECHANOSENSORY NEURON IN THE TERRESTRIAL SLUG, INCILARIA-FRUHSTORFERI

We investigated the modulatory role of a radular mechanoreceptor (RM) in the feeding system of Incilaria. RM spiking induced by current inje ction evoked several cycles of rhythmic buccal motor activity in quies cent preparations, and this effect was also observed in preparations l acking the cerebral ganglia. The evoked rhythmic activity included seq uential activation of the inframedian radular tenser, the supramedian radular tenser, and the buccal sphincter muscles in that order. In add ition to the generation of rhythmic motor activity, RM spiking enhance d tonic activities in buccal nerve 1 as well as in the cerebrobuccal c onnective, showing a wide excitatory effect on buccal neurons. The exc itatory effect was further examined in the supramedian radular tenser motoneuron. RM spiking evoked biphasic depolarization in the tenser mo toneuron consisting of fast excitatory postsynaptic potentials and pro longed depolarization lasting after termination of RM spiking. These d epolarizations also occurred in high divalent cation saline, suggestin g that they were both monosynaptic. When RM spiking was evoked in the fictive rasp phase during food-induced buccal motor rhythm, the activi ty of the supramedian radular tenser muscle showed the greatest enhanc ement of the three muscles tested, while the rate of ongoing rhythmic motor activity showed no increase.