Abstract
ABSTRACTCrayfish swimmerets are paired appendages located on the ventral side of each abdominal segment that show rhythmic beating during forward swimming produced by central pattern generators in most abdominal segments. For animals with multiple body segments and limbs, intersegmental coordination of central pattern generators in each segment is crucial for the production of effective movements. Here we develop a novel pharmacological approach to analyse intersegmental modulation of swimmeret rhythm by selectively elevating nitric oxide levels and reducing them with pharmacological agents, in specific ganglia. Bath application of L-arginine, the substrate NO synthesis, increased the cyclical spike responses of the power-stroke motor neurons. By contrast the NOS inhibitor, L-NAME decreased them. To determine the role of the different local centres in producing and controlling the swimmeret rhythm, these two drugs were applied locally to two separate ganglia following bath application of carbachol. Results revealed that there was both ascending and descending intersegmental modulation of cycle frequency of the swimmeret rhythm in the abdominal ganglia and that synchrony of cyclical activity between segments of segments was maintained. We also found that there were gradients in the strength effectiveness in modulation, that ascending modulation of the swimmeret rhythm was stronger than descending modulation.
Highlights
Central pattern generators (CPGs) are essential neural elements for the organization and patterning of locomotory motor output formation
When carbachol was applied to the remaining ganglia, by exchanging the external bathing solution in the experimental chamber from normal saline to carbachol-containing saline, the cycle frequency of the burst of motor neuron spikes significantly increased to 0.38±0.03 s for each preparation (Student’s t-tests, P>0.05)
Despite many studies on the control of swimmeret beating over recent decades the results of this study reveal that the cholinergic agonist, carbachol, does not evoke rhythmic activity of the swimmerets when applied to the second abdominal ganglion
Summary
Central pattern generators (CPGs) are essential neural elements for the organization and patterning of locomotory motor output formation. For animals with multiple body segments and limbs, intersegmental coordination of CPGs in local. Three pairs of swimmerets on the third to fifth abdominal segments in males, and four pairs from the second to fifth abdominal segments in females, beat rhythmically to generate forward thrust through cycles of powerstroke and return-stroke movements. They show rhythmic beating activity during egg ventilation, righting behaviour, forward swimming and walking
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