Modulation of rhythmic motor activity by pyrokinin peptides

Area of Science:

• Neuroscience
• Peptide Signaling
• Crustacean Neurobiology

Background:

• Pyrokinin (PK) peptides are found in arthropod nervous systems, but their central nervous system (CNS) functions remain largely unstudied.
• The stomatogastric ganglion (STG) controls vital digestive motor patterns in crustaceans, making it a model for studying neural circuits.

Purpose of the Study:

• To identify pyrokinin peptide family members in the crab Cancer borealis.
• To characterize the actions of identified pyrokinins on the gastric mill (chewing) and pyloric (filtering) motor circuits within the STG.

Main Methods:

• Immunolabeling was used to localize PK-like immunoreactivity in the STG and associated neuroendocrine organs.
• MALDI mass spectrometry and ESI tandem MS identified the amino acid sequences of two novel crab pyrokinins (CabPKs).
• Superfusion of isolated STG preparations with CabPKs assessed their effects on motor circuit activity.

Main Results:

• PK-like immunoreactivity was detected in the STG neuropil and projection neuron inputs.
• Two CabPKs, sharing the conserved FXPRLamide C-terminus, were identified.
• CabPKs primarily excited gastric mill neurons and activated the gastric mill rhythm, with minimal effect on the pyloric rhythm. The PK-elicited rhythm was independent of the projection neuron MCN1, suggesting a different underlying central pattern generator (CPG) or altered CPG composition.

Conclusions:

• Pyrokinin peptides are present in the crab STG and act as potent neuromodulators of the gastric mill circuit.
• The identified CabPKs function similarly to pyrokinins in other arthropods.
• Neuromodulation by pyrokinins can alter the composition of the core central pattern generator, demonstrating a flexible mechanism for motor control.