2 NOVEL TACHYKININ-RELATED PEPTIDES FROM THE NERVOUS-SYSTEM OF THE CRAB CANCER-BOREALIS

Immunocytochemical and biochemical studies have indicated the presence of many neuroactive substances in the stomatogastric nervous system ( STNS) of the crab Cancer borealis, In electrophysiological studies, ma ny of these substances modulate the motor output of neural networks co ntained within this system, Previous work in the STNS suggested the pr esence of neuropeptides related to the invertebrate tachykinin-related peptide (TRP) family, Here we isolate and characterize two novel pept ides from the C. borealis nervous system that show strong amino acid s equence identity to the invertebrate TRPs, The central nervous systems of 160 crabs were extracted in an acidified solvent, after which four reversed-phase HPLC column systems were used to obtain pure peptides, A cockroach hindgut muscle contraction bioassay and a radioimmunoassa y (RIA) employing an antiserum to locustatachykinin I (LomTK I) were u sed to monitor all collected fractions, The amino acid sequences of th e isolated peptides were determined by Edman degradation, Mass spectro metry and chemical synthesis confirmed the sequences to be APSGFLGMR-N H2 and SGFLGMR-NH2. APSGFLGMR-NH2 is approximately 20-fold more abunda nt in the crab central nervous system than is SGFLGMR-NH2. We have nam ed these peptides Cancer borealis tachykinin-related peptide Ia and Ib (CabTRP Ia and Ib), respectively. Both peptides are myoactive in the cockroach hindgut muscle contraction bioassay, with CabTRP Ia being ap proximately 500 times more potent than CabTRP Ib. RIA performed on HPL C-separated C. borealis stomatogastric ganglion (STG) extract revealed that CabTRP Ia is the only detectable TRP-like moiety in this ganglio n, Incubation of synthetic CabTRP Ia with the isolated STG excited the pyloric motor pattern, These effects were suppressed by the broad-spe ctrum tachykinin receptor antagonist Spantide I, Spantide I had no eff ect on the actions of the unrelated endogenous peptide proctolin in th e STG, There was no consistent influence of CabTRP Ib on the pyloric r hythm, Given its amino acid sequence and minimal biological activity i n the crab, CabTRP Ib may be a breakdown product of CabTRP Ia.