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J Comp Physiol A (2009) 195:947954 DOI 10.1007/s00359-009-0470-3
ORIGINAL PAPER
Response of the hammerhead shark olfactory epithelium to amino acid stimuli
Timothy C. Tricas Stephen M. Kajiura Adam P. Summers
Received: 31 March 2009 / Revised: 31 July 2009 / Accepted: 7 August 2009 / Published online: 27 August 2009 Springer-Verlag 2009
Abstract Sharks and rays are highly sensitive to chemical stimuli in their natural environment but several hypotheses predict that hammerhead sharks, with their expanded head and enlarged olfactory epithelium, have particularly acute olfactory systems. We used the electro-olfactogram (EOG) technique to compare the relative response of the scalloped hammerhead shark (Sphyrna lewini) olfactory epithelium to 20 proteinogenic amino acids and determine the sensitivity for 6 amino acids. At micromolar concentrations, cysteine evoked the greatest EOG response which was approximately twice as large as that of alanine. The weakest response was obtained for proline followed by aspartic acid and isoleucine. The olfactory epithelium showed adaptation to sequential stimulation, and recovery was related to the inter-stimulus time period. Estimated EOG response thresholds were in the sub-nanomolar range for both alanine (9.2 9 10-11 M)
and cysteine (8.4 9 10-10 M) and in the micromolar range for proline and serine. These thresholds from 10-10 to
10-6 M for the scalloped hammerhead shark are comparable or lower than those reported for other teleost and elasmobranch species. Future work should focus on binary and more complex compounds to test for competition and cross-adaptation for different classes of peripheral receptors, and their responses to molecules found in biologically relevant stimuli.
Keywords Amino acid Chemoreception EOG
Hammerhead shark Olfactory epithelium
Introduction
Soluble chemical stimuli provide environmental cues or signals for the detection and location of prey, predators, and mates in aquatic environments. In jawed shes, olfaction is mediated by a sensory epithelium that responds to dissolved substances that ow through the nares and across chemosensory receptors that respond to several forms of organic compounds, especially amino acids and nucleotides that are common constituents of natural prey. Additional compounds such as steroids and prostaglandins are also involved in chemical mediation of social and reproductive behaviors (Hara 1992; Sorenson 1992).
Olfaction in sharks is an important sense used in the detection and localization of prey. The sensory epithelium consists of microvillous sensory...