Dishabituation of the Tritonia escape swim

Abstract

When repeatedly elicited, the oscillatory escape swim of the marine mollusc Tritonia diomedea undergoes habituation of the number of cycles per swim. Although similar in most respects to habituation observed in vertebrates and other invertebrates, one key feature, dishabituation, has been surprisingly difficult to demonstrate. Here we evaluate the hypothesis that this is due to interference from short-term sensitization, which is manifested as a reduction in swim onset latency, that occurs simultaneously during habituation training. Robust dishabituation was obtained using a multisession habituation protocol designed to allow this sensitization to dissipate before the dishabituatory stimulus was applied. These results extend the similarity of habituation in Tritonia to that described in other species, strengthening the usefulness of this preparation as a model system for studies of the cellular basis of habituation.

Figure 1

Repeated stimulation produces both habituation and sensitization of the escape swim. (A) Ten consecutive salt stimuli applied to the tail produced a progressive habituation of the number of cycles per swim [(*)P < 0.001]. (B) The same training produced an immediate sensitization of swim onset latency. Latency was shorter on the second trial and was still significantly shorter on the tenth trial [(*) P < 0.001].

Figure 2

Duration of sensitization. Seventy animals were divided into 10 groups. One group received a single stimulus to the tail. Each of the other groups received a tail stimulus at the indicated interval following a sensitizing head stimulus. Sensitization was still present at 1 hr, but not at 2 hr [(***) P < 0.001, (**) P < 0.01, (*) P < 0.05].

Figure 3

Dishabituation of swim cycle number. Eight animals were given seven sessions of habituation training, spaced at 4-hr intervals. Each session consisted of 10 salt stimuli applied to the tail with a 2-min intertrial interval. Five minutes before the start of the seventh session, all animals received a single dishabituatory salt stimulus to the head. Each point represents the mean cycle number for that trial [(*) P < 0.001].