Abstract
ABSTRACTThe heart and pyloric rhythms of crustaceans have been studied separately and extensively over many years. Local and hormonal neuromodulation and sensory inputs into these central pattern generator circuits play a significant role in an animal's response to perturbations, but are usually lost or removed during in vitro studies. To examine simultaneously the in vivo motor output of the crustacean heart and pyloric rhythms, we used photoplethysmography. In the population measured (n=49), the heart rhythm frequency ranged from 0.3 to 2.3 Hz. The pyloric rhythm varied from 0.2 to 1.6 Hz. We observed a weak correlation between the frequencies of the heart and pyloric rhythms. During multiple hour-long recordings, many animals held at a controlled temperature showed strong inhibitory bouts in which the heart decreased in frequency or become quiescent and the pyloric rhythm decreased in frequency. We measured the simultaneous responses of the rhythms to temperature ramps by heating or cooling the saline bath while recording both the heart and pyloric muscle movements. Q10, critical temperature (temperature at which muscle function is compromised) and changes in frequency were calculated for each of the rhythms tested. The heart rhythm was more robust to high temperature than the pyloric rhythm.
Highlights
Central pattern generators (CPGs) are neuronal circuits that produce rhythmic motor patterns
Mechanisms of central pattern generation have been studied using the cardiac ganglion (CG), which produces heart movements, and the stomatogastric ganglion (STG), which generates the rhythmic movements of the stomach (Cooke, 2002; Maynard, 1972)
We systematically explored the potential relationships between stomach and heart rhythms, and asked whether they are coordinately sensitive to perturbation by temperature
Summary
Central pattern generators (CPGs) are neuronal circuits that produce rhythmic motor patterns. Mechanisms of central pattern generation have been studied using the cardiac ganglion (CG), which produces heart movements, and the stomatogastric ganglion (STG), which generates the rhythmic movements of the stomach (Cooke, 2002; Maynard, 1972). These ganglia, when isolated, can generate rhythmic motor patterns in vitro that resemble those seen in vivo. The heart is found in the animal just posterior to the stomach, and pumps hemolymph through the ophthalmic artery, directly bathing the STG.
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