Abstract
Olfactory receptor neurons (ORNs) in the antenna of insects serve to encode odors in action potential activity conducted to the olfactory lobe of the deuterocerebrum. We performed an analysis of the electrophysiological responses of olfactory neurons in the antennae of the female malaria mosquito Anopheles gambiae s.s. and investigated the effect of blood feeding on responsiveness. Forty-four chemicals that are known to be present in human volatile emanations were used as odor stimuli. We identified 6 functional types of trichoid sensilla and 5 functional types of grooved-peg sensilla (GP) based on a hierarchical cluster analysis. Generalist ORNs, tuned to a broad range of odors, moderate specialist ORNs and 2 ORNs tuned to only one odor were identified in different sensilla types. Neurons in GP were tuned to more polar compounds including the important behavioral attractant ammonia and its synergist L-lactic acid, responses to which were found only in GP. Combinatorial coding is the most plausible principle operating in the olfactory system of this mosquito species. We document for the first time both up- and downregulation of ORN responsiveness after blood feeding. Modulation of host-seeking and oviposition behavior is associated with both qualitative and quantitative changes in the peripheral sensory system.
Highlights
Insects rely to a large extent on olfactory information to locate food, mating partners, and breeding sites (Hildebrand and Shepherd 1997)
We recorded the electrophysiological responses of 45 trichoid and 20 grooved-peg sensilla (GP) on segments 6–13 of the antennae of female A. gambiae to a panel of 44 odor stimuli (Tables 1 and 2)
We present here the first systematic study on the function of olfactory neurons in 3 types of antennal sensilla of A. gambiae
Summary
Insects rely to a large extent on olfactory information to locate food, mating partners, and breeding sites (Hildebrand and Shepherd 1997). Olfactory receptor neurons (ORNs) in insects are contained in sensilla and cuticular extensions of various shapes predominantly present on their antennae and mouthparts. ORNs have been shown to encode odor quality, quantity, and temporal changes in odor concentration (Heinbockel and Kaissling 1996; De Bruyne et al 1999, 2001; Mustaparta 2002). A female A. gambiae mosquito is guided to its human hosts predominantly by olfactory cues (Takken 1991). The recent sequencing of the complete genome of A. gambiae (Holt et al 2002), containing at least 79 putative olfactory receptor (OR) genes (Hill et al 2002), has led to its adoption as a new model organism for the study of the olfactory system
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