Sensory Feedback in the Operating Stomatogastric Nervous System of the Crab (Cancer pagurus)
In vivo performance of the stomatogastric networks and the influence of the anterior gastric stretch receptor (AGR) was analyzed by multiple nerve recordings in both free-ranging and feeding crabs, and after immobilization of the intact crabs to allow endoscopic inspection of the stomach, so that the rhythmic movements could be correlated with activity of identified neurons of the pyloric and gastric network.
Unfed crabs always show a pyloric rhythm which can incorporate a few gastric motoneurons in the absence of a gastric rhythm. Feeding induces gastric cycling and strong interaction of both networks. This involves even neurons which have been considered purely gastric in experiments on isolated preparations.
Existing hypotheses about the role of AGR have been confirmed by our experiments under closed loop conditions. The AGR reflex loop can indeed switch the operation of the medial tooth from positive to negative feedback; but AGR possibly can also support the initiation of gastric cycling in a chain reflex manner, if firing during activity of the antagonistic dorsal gastric motoneuron (DG). Finally, the integration of AGR into the performance of the central pattern generator networks gets even more complicated, as it also can express endogenous bursting and generate spikes at a second, central spike-initiating zone.
KeywordsTransportation Immobilization Acetylcholine Sorting Pilocarpine
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