Actions of kinin peptides in the stomatogastric ganglion of the crab Cancer borealis.

To fully understand neuronal network operation, the influence of all inputs onto that network must be characterized. As in most systems, many neuronal and hormonal pathways influence the multifunctional motor circuits of the crustacean stomatogastric ganglion (STG), but the actions of only some of them are known. Therefore, we characterized the influence of the kinin peptide family on the gastric mill (chewing) and pyloric (filtering of chewed food) motor circuits in the STG of the crab Cancer borealis. The kinins are myoactive in arthropods and they occur within the arthropod central nervous system (CNS), but their CNS actions are not well characterized in any species. The pevkinins were first identified in the shrimp Penaeus vannamei, but they have yet to be studied in the STG of any species. We identified kinin-like immunolabeling (KLI) in the pericardial organs (POs) in C. borealis, but there was no KLI within the STG. The POs are a major source of hormonal influence on the STG. Pevkinin peptides activated the pyloric circuit and they caused a modest increase in the speed of ongoing pyloric rhythms. This modest influence on cycle speed resulted in part from pevkinin excitation of the lateral pyloric neuron, whose strengthened inhibitory synapse onto the pyloric pacemaker neurons limited the pevkinin-mediated increase in cycle speed. The pevkinin excitation of the pyloric rhythm was not strong enough to interfere with the previously documented, gastric mill rhythm-mediated weakening of the pyloric rhythm. Pevkinin also had little influence on the gastric mill rhythm. These results indicate that the kinin peptides have distinct and selective modulatory actions on the pyloric rhythm.