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- Identification, release and olfactory detection of bile salts in the intestinal fluid of the Senegalese sole (Solea senegalensis)Publication . Velez, Zélia; Hubbard, Peter; Welham, K.; Hardege, Jörg D.; Barata, E. N.; Canario, Adelino V. M.Olfactory sensitivity to bile salts is wide-spread in teleosts; however, which bile salts are released in suYcient quantities to be detected is unclear. The current study identiWed bile salts in the intestinal and bile Xuids of Solea senegalensis by mass spectrometry–liquid chromatography and assessed their olfactory potency by the electro-olfactogram.
- Adaptation to reduced salinity affects the olfactory sensitivity of Senegalese sole (Solea senegalensis Kaup 1858) to Ca2+ and Na+ but not amino acidsPublication . Velez, Zélia; Hubbard, Peter; Barata, E. N.; Canario, Adelino V. M.The Senegalese sole is a marine flatfish, which often penetrates into estuarine waters to feed. It cannot, however, survive in full freshwater. The current study investigated the effect of adaptation to low salinity (10‰) on olfactory responses to changes in environmental [Ca2+] and [Na+] and amino acids by the electro-encephalogram (EEG) recorded from the olfactory bulb. The sole showed olfactory responses to increases in environmental [Na+] and decreases in environmental [Ca2+]; sensitivity to Na+ was greater at 10‰ whereas sensitivity to Ca2+ was greater at 35‰. Decreased environmental [Na+] increased sensitivity to changes in [Ca2+] whereas increased environmental [Ca2+] decreased bulbar responses to changes in [Na+]. Sensitivity to amino acids was unaffected by external salinity. However, the absence of external Na+ strongly decreased bulbar responses to amino acids in fish adapted to 35‰ seawater but not in those at 10‰. The absence of external Ca2+ had no such effect at either salinity. This suggests that odorant-receptor binding and/or olfactory transduction is reliant on external Na+ (but not Ca2+) at higher salinities but the olfactory system is able to adapt to lower environmental [Na+]. Taken together, these results suggest that reductions of external salinity modulate olfactory sensitivity to environmental Ca2+ and Na+ but not amino acids. However, at low salinities, olfactory sensitivity to amino acids is maintained by decreasing reliance on external Na+.
- Evidence that 1-methyl-l-tryptophan is a food-related odorant for the Senegalese sole (Solea senegalensis)Publication . Velez, Zélia; Hubbard, Peter; Hardege, Jörg D.; Welham, K.; Barata, E. N.; Canario, Adelino V. M.Nocturnal animals often rely heavily on olfactory cues to locate their food. This is especially true for fish whose prey live buried in the substrate. The aim of the current study was to identify non-polar odorants released by the ragworm (Hediste diversicolor) that are detected by the olfactory system of the Senegalese sole (Solea senegalensis) and therefore may be food-related cues. Ragworm-conditioned water was passed through a C18 solid-phase extraction cartridge (to remove polar compounds) and the eluate fractionated by reverse phase high-performance liquid chromatography (HPLC). The fractions were then tested for olfactory activity in the sole by the electro-olfactogram (EOG). Most olfactory activity was found in the first two fractions to elute from the HPLC column (0–4 min). Liquid chromatography-mass spectrometry (LC/MS) of both fractions revealed a base peak with a molecular mass of 219.4 Da and a fragment of 205.3 Da. These data are consistent with a methylated form of tryptophan; synthetic 1-methyl-l-tryptophan had a similar HPLC retention time (2.8 min) and similar LC/MS spectra. Furthermore, sole showed olfactory sensitivity to 1-methyl-l-tryptophan with the lower (left) epithelium being more sensitive than the upper (right). Cross-adaptation (using EOG recording) suggested that the olfactory receptors responding to 1-methyl-l-tryptophan are different in the lower epithelium from the upper. These results suggest that ragworms release 1-methyl-l-tryptophan, or similar tryptophan derivative, and that sole may use this chemical cue to locate and/or identify one of their main prey species. This may help the formation of artificial feeds that are more attractive to sole.
- Differential detection of conspecific-derived odorants by the two olfactory epithelia of the Senegalese sole (Solea senegalensis)Publication . Velez, Zélia; Hubbard, Peter; Barata, E. N.; Canario, Adelino V. M.The two olfactory epithelia of members of the family Soleidae sample two distinct water sources; the upper (right) side is in contact with the open water column whilst the lower (left) side is in contact with interstitial water. To evaluate whether there are differences in the sensitivities, and therefore functional roles, of the two epithelia the olfactory activity of conspecific-derived odorants was assessed in both using the electro-olfactogram (EOG). The upper nostril was significantly more sensitive to conspecific bile fluid, intestinal fluid and mucus than the lower nostril. Crude fractionation of these samples (solid-phase extraction with C18 and C2/ENV+ cartridges) revealed that olfactory activity in each body fluid was likely due to a mixture of compounds. In each case, the upper olfactory epithelium was significantly more sensitive than the lower. Similarly, olfactory sensitivity to a range of C24 and C27 bile acids was greater in the upper epithelium. These results suggest that intra-specific chemical communication is mediated mainly, if not entirely, by the upper olfactory epithelium. The odorants involved, and their functional roles, remain to be established.