TNRNFLRFAMIDE AND SDRNFLRFAMIDE MODULATE MUSCLES OF THE STOMATOGASTRIC SYSTEM OF THE CRAB CANCER-BOREALIS

The effects of the extended FLRF amide-like peptides, TNRNFLRFamide an d SDRNFLRFamide, were studied on the stomach musculature of the crab C ancel borealis. Peptide-induced modulation of nerve-evoked contraction s 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, p eptides induced long-lasting myogenic activity. In other muscles, the peptides increased the amplitude of nerve-evoked contractions, excitat ory junctional potentials, and excitatory junctional currents, but pro duced no apparent change in the input resistance of the muscle fibers. The threshold concentration was 10(-10) M for TNRNFLRFamide and betwe en 10(-9) M to 10(-8) M for SDRNFLRFamide. The absence of direct pepti de-containing innervation to these muscles and the wide-spread sensiti vity of these muscles to the peptides suggest that TNRNFLRFamide and S DRNFLRFamide may be released from neurosecretory structures to modulat e stomatogastric musculature hormonally. We speculate that hormonally released peptide will be crucial for maintaining appreciable muscle co ntraction in response to low-frequency and low-intensity motor dischar ge.