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Patterned activity of the buccal ganglion of the nudibranch mollusc Archidoris pseudoargus.

In recent years there have been a number of analyses of patterned activity in invertebrate ganglia. Examples include the studies of crayfish swimmeret beat (Hughes & Wiersma, i960), the flight system of insects (Weis-Fogh, 1964; Wilson, 1966; Wyman, 1966) and crustacean heart-beat control (Maynard, 1966). In the Mollusca, Horridge (i960) described the production of patterned discharges from the cerebral ganglia of the clam Mya by electrical stimulation of the cerebral nerves, and Turner (1966) described a similar type of response from the pedal ganglion of AgrioUmax. More recently, Dorsett, Willows & Hoyle (1969) have described the production of a patterned sequence of bursts of impulses by a small group of symmetrically placed cells in the pedal ganglion of Tritoniagilberti during swimming. These swimming movements were elicited by contact with certain echinoderms, by liquid soap applied to the body surface, or by direct electrical stimulation of certain cells, although the sequence production could also be produced in the isolated brain by electrical stimulation of the cerebral nerves which supply the oral veil. Kandel, Frazier & Wachtel (1969) have also discussed the importance of inhibition in burst production by the abdominal ganglion of Aplysia calif ornica. Until recently the only electrophysiological study of the buccal ganglion was that of Strumwasser (1967), who showed that synchronous bursts were produced in the buccal ganglion of Aplysia calif ornica as a result of common synaptic input to symmetrically placed cells. This work has been extended by Gardner (1969), who described both common input and the presence of a single interneurone with input to six cells in the ipselateral ganglion. Levitan, Segundo & Tauc (1970), in another study on the ophistobranch Navanax inermis, have described electrical connexions between ten identifiable cells and have given a quantitative description of the coupling coefficients between these cells. The buccal mass of molluscs has been the subject of many investigations from the point of view of functional morphology (Fretter & Graham, 1962; Nisbet, 1954), but there have been no electrophysiological interpretations of radula movements. In the present study a natural stimulus has been used to induce feeding movements in the isolated buccal mass, and extracellular recording methods have been used to show that the buccal ganglion produces a sequence of bursts during radula movement. An account of the structure and nerve supply of the buccal mass of A. pseudoargus has been given elsewhere (Rose, 1970).