The Swimmeret Rhythm and its Relationships with Postural and Locomotor Activity in the Isolated Nervous System of the Crayfish Procambarus Clarkii

Abstract

An in vitro preparation was developed consisting of the five thoracic and abdominal ganglia of the crayfish nerve cord, isolated from anterior nervous structures and from peripheral sensory inputs. The central activities of the thoracic leg, swimmeret and abdominal positioning motor systems and their relationships were studied. When motor outputs were tonic in the thoracic leg nerves (90% of the preparations), continuous rhythmic activity occurred and persisted for several hours in the swimmeret nerves. Interruptions of the swimmeret rhythm were associated with rhythmic motor outputs in the leg nerves (10% of the preparations). Motor activity in the abdominal positioning system was mainly tonic. Swimmeret rhythm reversibly disappeared during application of a sucrose block between the thoracic and abdominal parts of the nerve cord. Electrical stimulation of the connectives posterior to the block induced bouts of rhythmic swimmeret activity. Comparisons of the swimmeret rhythm (period) and the metachronal wave (duration, phase) showed that sectioning of the connectives between the thoracic and abdominal ganglia modified the period but did not affect the properties of the metachronal wave. We conclude that the presence of descending inputs from thoracic ganglia is necessary for persistent swimmeret activity.