Response-specific inhibition during general facilitation of defensive responses in Aplysia.

Siphon responses of Aplysia have been used to examine the neural basis of nociceptive behavioral inhibition. The authors tested the response specificity and functional significance of this inhibition. Video analysis showed that strong tail-nerve shock decreased the duration of siphon constriction evoked by weak siphon shock. Tail-nerve shock also caused the appearance of a novel flaring response to the test stimulus, which resembled the siphon response to tail-nerve shock. Novel flaring responses were expressed to both mechanical and electrical siphon stimuli. Tailshock facilitated another defensive response, inking, during the period of inhibited siphon constriction. Tailshock also facilitated tail contractions evoked by weak contralateral tail stimulation during this period. These results indicate that inhibition is not generalized across defensive responses and is specific to siphon responses that interfere with directed ink ejection toward an injured site.