MULTIPLE MECHANISMS FOR PERIPHERAL ACTIVATION OF THE PEPTIDE-CONTAINING RADULA MECHANOAFFERENT NEURONS B21 AND B22 OF APLYSIA

1. Recently a cluster of sensory neurons (peptidergic radula mechanoaf ferents) has been identified in the buccal ganglion of Aplysia that is likely to play an important role in influencing the activity of feedi ng motor programs. All of the neurons of this cluster, which includes the identified cells B21 and B22, send axons via the radula nerve to a layer of tissue that lies under the chitinous radula (the subradula t issue). 2. We show that the subradula tissue has contractile propertie s. In the absence of the CNS, contractions of the subradula tissue are elicited if the subradula tissue is stretched. Alternatively, contrac tions are elicited when extracellular suction electrodes are used to s timulate buccal nerve 3 or the radula nerve. 3. Previous studies have shown that neurons of the B21/B22 cluster respond to peripherally appl ied mechanical stimuli. We show that these neurons are also activated when the subradula tissue contracts. Axon spikes (A spikes) can be int racellularly recorded from radula mechanoafferent neurons when contrac tions of the subradula tissue are elicited either by stretch or by ext racellular stimulation of buccal nerve 3. 4. Mechanical stimuli that a re subthreshold when applied alone elicit A spikes if they are applied while the subradula tissue is contracting. We postulate that this typ e of interaction may play an important role in gating sensory input to the feeding central pattern generator.