Rhythmic and Bilaterally Coordinated Motor Activity in the Isolated Brain of Pleurobranchaea

Rhythmic ingestive behaviour in the predatory marine snail Pleurobranchaea is characterized by cycles of protraction and retraction of the buccal mass, during which food material is taken into the buccal cavity and swallowed (Davis & Mpitsos, 1971). Fictive feeding is demonstrable in the isolated nervous system; the rhythmic motor programme appropriate to feeding behaviour can occur spontaneously or can be elicited by stimulation of different populations of 'command' neurones (Davis et al. 1975; Gillette & Davis, 1977; Croll & Davis, 1981; Gillette & Gillette, 1983). Oscillatory motor output is most striking in the isolated buccal ganglion; however, cyclic activity has been recorded in the brain (the cerebropleural ganglion) when it was isolated from the buccal ganglion by cutting the cerebrobuccal connectives (CBCs) (Davis, Siegler & Mpitsos, 1973). Such cyclic activity was recorded in the nerves of the brain while the CBC was stimulated by repetitive electrical shocks. These and other results were interpreted as indicating that oscillators existed both in the brain and the buccal ganglion. Interneurones were identified in both the brain and buccal ganglion which appeared to coordinate the oscillators via axons in the CBCs (Davis et al. 1973; Gillette & Davis, 1977; Gillette, Kovac & Davis, 1978, 1982).