TNRNFLRFamide and SDRNFLRFamide modulate muscles of the stomatogastric system of the crab Cancer borealis

The effects of the extended FLRFamide-like peptides, TNRNFLRFamide and SDRNFLRFamide, were studied on the stomach musculature of the crab Cancer borealis. Peptide-induced modulation of nerve-evoked contractions was used to screen muscles. All but 2 of the 17 muscles tested were modulated by the peptides. In several muscles of the pyloric region, peptides induced long-lasting myogenic activity. In other muscles, the peptides increased the amplitude of nerve-evoked contractions, excitatory junctional potentials, and excitatory junctional currents, but produced no apparent change in the input resistance of the muscle fibers. The threshold concentration was 10^–10 M for TNRNFLRFamide and between 10^–9 M to 10^–8 M for SDRNFLRFamide. The absence of direct peptidecontaining innervation to these muscles and the wide-spread sensitivity of these muscles to the peptides suggest that TNRNFLRFamide and SDRNFLRFamide may be released from neurosecretory structures to modulate stomatogastric musculature hormonally. We speculate that hormonally released peptide will be crucial for maintaining appreciable muscle contraction in response to low-frequency and low-intensity motor discharge.Abbreviations cpv muscles cardiopyloric valve muscles - CG commissural ganglion - DG neuron dorsal gastric neuron - dgn dorsal gastric nerve - dvn dorsal ventricular nerve - EJC excitatory junctional current - EJP excitatory junctional potential - FaRPs FMRF-amide related peptides - gm muscles gastric mill muscles - lvn lateral ventricular nerve - mvn medial ventricular nerve - p muscles pyloric muscles - STG stomatogastric ganglion