Chemosensory stimuli for the walking legs of the crayfish Procambarus clarkii

Studies of chemoreception in crustaceans have shown that flesh-eating species can detect amino acids, nucleotides and derivatives, and amines, while most herbivorous and omnivorous species are additionally sensitive to carbohydrates. We used extracellular recording techniques to evaluate the effectiveness of a range of nitrogen-containing compounds (mostly amino acids), bile acids, and carbohydrates in stimulating chemoreceptor cells present in the second and third pereopods of the omnivorous crayfish Procambarus clarkii. When applied at a final concentration of similar to 100 muM, effective stimuli were trehalose, leucine, cellobiose, glycine, sucrose, maltose, and ammonium (from most to least effective). The other 17 compounds tested, many chosen because they are potent stimuli for other crustaceans, were ineffective stimuli for P. clarkii. Concentration-response functions were determined for three single cells that were sensitive to ammonium, for five multiunit fibers sensitive to glycine, and for six multiunit fibers sensitive to leucine. Thresholds ranged from 10 nM to 10 muM, functions were generally linear when plotted against the log of the stimulus concentration, and there was little evidence of saturation. While P. clarkii is sensitive to only seven of 24 compounds tested, the compounds that proved stimulatory should serve as cues for location and identification of food items preferred by this omnivorous crustacean.