ALLATOSTATIN DECREASES STOMATOGASTRIC NEUROMUSCULAR-TRANSMISSION IN THE CRAB CANCER-BOREALIS

The effects of insect allatostatins (ASTs) 1-4 were studied on the sto mach musculature of the crab Cancer borealis. Of these, Diploptera-all atostatin 3 (D-AST-3) was the most effective. D-AST-3 (10(-6) mol l(-1 )) reduced the amplitude of nerve-evoked contractions, excitatory junc tional potentials and excitatory junctional currents at both cholinerg ic and glutamatergic neuromuscular junctions. Muscle fiber responses t o ionophoretic applications of both acetylcholine and glutamate were r educed by the peptide, but D-AST-3 produced no apparent change in the input resistance of the muscle fiber. D-AST-3 reduced the amplitude of muscle contractures evoked by both acetylcholine and glutamate, but h ad no effect on contractures induced by a high [K+]. These data sugges t that D-AST-3 decreases the postsynaptic actions of both neurally rel eased acetylcholine and glutamate, Because an AST-like peptide is foun d in peripheral sensory neurons that innervate stomatogastric muscles and in the pericardial organs, we suggest that an AST-like peptide may play a role in controlling the gain of the excitatory neuromuscular j unctions in the stomach.