Spectral Tuning of Chemoreceptor Cells of the Third Maxilliped of the Lobster, Homarus americanus

This is the first investigation of the spectral tuning properties of single chemoreceptor cells of the third maxillipeds (mouthparts) of the lobster Homarus americanus. These organs are used, among other functions, for chemical recognition of food. Based upon extracellular recordings of action potentials, we report on 53 cells identified with a 15-compound equimolar mixture of mostly amino acids in an artificial seawater background (applied mixture concentration 150 {mu}M). Subsequently, all cells were tested with each compound separately. Cells were generally narrowly tuned to a single compound. Twenty-five percent of the cells sampled responded best to L-glutamate, 17% to betaine, 11% to taurine, and 9% to ammonium chloride. There was no consistent second best stimulus for these four cell populations. Two other populations were more broadly tuned: one responded best to hydroxy-L-proline and the other to L-arginine. Some cells responded to both compounds. Arginine-sensitive cells (not necessarily "arginine-best" cells) tended to respond also to a lesser degree to leucine. Hydroxy-L-proline-sensitive cells tended to respond to a lesser degree to glycine. Among the lobster's chemoreceptive organs, the tuning of the maxillipeds is the broadest of all and resembles the tuning of the walking legs more than that of the antennules or antennae.