Re-Examination of Presumed Feeding Motor Activity in the Isolated Nervous System of Pleurobranchaea

Abstract

ABSTRACT In most isolated gastropod nervous systems, presumed feeding motor patterns are thought to be represented by the alternating motor activity in buccal roots, which underlies rhythmic radula movement. Since this movement accompanies several types of behaviour in the gastropod Pleurobranchaea (McClellan, 1979, 1980, 1982), the presumed feeding motor activity in the isolated nervous system of this animal was re-examined in more detail. Alternating buccal root activity was shown here to be associated with other types of behaviour besides feeding, and is, therefore, not sufficiently unique to serve as a ‘neural correlate’ for feeding in Pleurobranchaea and presumably other gastropods. Unlike the isolated nervous systems of most gastropods, which generate only one buccal rhythm, that of Pleurobranchaea generates two different buccal motor patterns which alternate: (1) a slow ‘primary’ rhythm whose behavioural identity is unclear, and (2) brief periods of a relatively fast rhythm which underlie bouts of vomiting. In general, a buccal rhythm generated by an isolated gastropod nervous system can only be assigned a function if there are features of the rhythm that are unique to only one of the several behavioural responses involving the buccal mass.