Perception of breath components by the tropical bont tick, Amblyomma variegatum Fabricius (Ixodidae): II. Sulfide-receptors
Guerin, Patrick M.
Date de parution
Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology, Springer, 1992/170/6/677-685
Wall-pore sensilla in the capsule of Haller's organ on foreleg tarsi of the tick, <i>Amblyomma variegatum</i>, show multicellular responses upon stimulation with human and bovine breath. Filtering breath through charcoal removes the stimulant for some of these receptors. Analysis by gas chromatography coupled with olfactory sensillum electrophysiological recordings indicates that an ethanol extract of the breath components trapped on charcoal contains a major stimulant eluting at the same retention time as H<sub>2</sub>S. Two types of H<sub>2</sub>S-sensitive receptors have been identified. They are housed in separate sensilla, and are called sulfide-receptor 1 and 2. <br> Although, both receptor types are characterized by a high sensitivity to H<sub>2</sub>S with an estimated threshold of ca. 0.1 ppb and a response range covering 5–6 log orders of magnitude, their overall response to sulfides and mercaptans is nevertheless dissimilar. The type 1 receptor fires slightly more upon stimulations with H<sub>2</sub>S than type 2, whereas ethylmercaptan induces a stronger response from type 2, and dimethyl sulfide activates only receptor 2. <br> In a bioassay, H<sub>2</sub>S tested at concentrations of ca. 0.02 ppm and 1 ppm equally arouses 60% of resting ticks. Two-thirds of these ticks quest the air with their first pair of legs, and the remainder start active search. By contrast, H<sub>2</sub>S at ca. l ppm in a mixture with CO<sub>2</sub> severely diminishes the locomotor stimulating effect of CO<sub>2</sub>.
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Resource Types::text::journal::journal article
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