Specificity and response characteristics of gustatory sensilla (funnel-canal organs) on the dactyls of the shore crab, Carcinus maenas (Crustacea, Decapoda)

Abstract

1. Chemosensory cells of the funnel-canal organs, sensilla on the dactyls of the shore crab, Carcinus maenas, were investigated electrophysiologically. Activity of 51 single cells was recorded extracellularly from afferent axons. 2. Cell populations with distinct nonoverlapping response spectra were identified by testing with a variety of food-related substances. 3. Three major groups of chemosensory cells were found: (a) l-glutamate cells with a narrow tuning to l-glutamate. Some of them had an additional low sensitivity for l-glutamine. l-aspartate competitively inhibited the response of l-glutamate cells; (b) taurine cells with significantly differing tuning breadths. Some responded to taurine only, others had an additional lower sensitivity to glycine and other amino acids; (c) sucrose cells with an extremely narrow tuning to sucrose. They did not respond to various other sugars. 4. Only a few chemosensory cells had other response spectra: two glycine, two l-glutamine, one l-aspartate, and one GABA cell were characterized. 5. Dose-response curves determined for 29 chemosensory cells showed individual threshold sensitivities between 10−6M and 5×10 −4M and working ranges of at least 2 orders of magnitude. For the l-glutamate cells, mean dose-response curves gave a KM of 2×10−4M for the agonist l-glutamate and a K1 of l.2×10−6M for the antagonist l-aspartate. 6. Most cells were rapidly adapting with a response dominated by a short phasic component; only two cells responded phasic-tonic. Disadaptation occurred quickly and was complete after about 30 s. 7. From these data we conclude that the funnel-canal organs serve a gustatory function in the food search of C. maenas.