Abstract
Exhaled CO2 is an important host-seeking cue for Anopheles mosquitoes, which is detected by a highly conserved heteromeric receptor consisting of three 7-transmembrane proteins Gr22, Gr23, and Gr24. The CO2 receptor neuron has been shown to also respond sensitively to a variety of odorants in Aedes aegypti. The detection of CO2 is important for upwind navigation and for enhancing the attraction to body heat as well as to skin odorants. The orthologs of the CO2 receptor proteins are present in malaria-transmitting mosquitoes like Anopheles coluzzii and Anopheles sinensis. Activators and inhibitors of the CO2-neuron were tested on the maxillary palps in these two species by single-sensillum electrophysiology. The electrophysiological testing of three prolonged-activator odorants identified originally in Aedes aegypti also showed varying ability to reduce the CO2-ellicited increase in spikes. These findings provide a foundation for comparing the functional conservation with the evolutionary conservation of an important class of odorant receptor. The identification of a suite of natural odorants that can be used to modify the CO2-detection pathway may also contribute to odor-blends that can alter the behavior of these disease transmitting mosquitoes.
Highlights
Vector-borne diseases cause significant morbidity and mortality throughout the globe
The odorants that evoked the strongest activation from the An. coluzzii capitate peg sensillum A neuron (cpA) neuron were further evaluated in www.nature.com/scientificreports
In order to test whether inhibitory odorants of the An. coluzzii cpA neuron could be of utility in An. sinensis, four of the strong inhibitors were tested at two concentrations using electrophysiology
Summary
In order to test these longer-term responses, recordings were performed as before with three known odorants (Fig. 2A) This analysis revealed that two of three odorants are conserved in their ability to evoke ultraprolonged activation in An. coluzzii. Among the odorants that induced responses lower than the solvent, six odors inhibited the baseline activity of the An. coluzzii cpA neuron when tested with the headspace from 10−2 concentration odor cartridges (Fig. 1A). In order to test whether inhibitory odorants of the An. coluzzii cpA neuron could be of utility in An. sinensis, four of the strong inhibitors (propanal, ethyl pyruvate, thiophene-2-thiol, and 4-methyl piperidine) were tested at two concentrations using electrophysiology. Taken together these results indicate that the An. sinensis CO2 receptors respond to Ae. aegypti and An. coluzzi when it comes to CO2 response inhibition
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