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 injection evoked several cycles of rhythmic buccal motor activity in quiescent preparations, and this effect was also observed in preparations lacking the cerebral ganglia. The evoked rhythmic activity included sequential activation of the inframedian radular tensor, the supramedian radular tensor, and the buccal sphincter muscles in that order.In addition to the generation of rhythmic motor activity, RM spiking enhanced tonic activities in buccal nerve 1 as well as in the cerebrobuccal connective, showing a wide excitatory effect on buccal neurons. The excitatory effect was further examined in the supramedian radular tensor motoneuron. RM spiking evoked biphasic depolarization in the tensor motoneuron consisting of fast excitatory postsynaptic potentials and prolonged depolarization lasting after termination of RM spiking. These depolarizations also occurred in high divalent cation saline, suggesting that they were both monosynaptic.When RM spiking was evoked in the fictive rasp phase during food-induced buccal motor rhythm, the activity of the supramedian radular tensor muscle showed the greatest enhancement of the three muscles tested, while the rate of ongoing rhythmic motor activity showed no increase.Abbreviations CPG central pattern generator - EPSP excitatory postsynaptic potential - RBMA rhythmic buccal motor activity - RM radular mechanosensory neuron - SMT supramedian radular tensor neuron