AI Insight
Researchers used electron microscopy to map the neural circuitry in Aedes aegypti mosquitoes that detects carbon dioxide, a key signal for finding human hosts. They discovered that CO2-sensitive olfactory neurons form unusually high levels of recurrent synaptic connections with each other, along with ribbon-like structures that may amplify signals. Computational modeling demonstrated these recurrent connections are necessary for robust CO2 detection, enabling mosquitoes to reliably detect this host cue even in complex odorant environments.
Why it matters
Understanding how mosquitoes detect CO2 could inform the development of more effective mosquito traps or repellents, potentially reducing transmission of diseases like dengue, Zika, and yellow fever that Aedes aegypti mosquitoes spread to hundreds of millions of people annually.
Understand the Science
by Jialu Bao, Wesley Alford, Avinash Khandelwal, Laurel Walsh, George Lantz, Santiago Poncio, Laia Serratosa Capdevila, Yervand Azatian, Brian DePasquale, David G. C. Hildebrand, Meg A. Younger, Wei-Chung Allen Lee
The mosquito Aedes aegypti’s human host-seeking behavior depends on the integration of multiple sensory cues. One of these cues, carbon dioxide (CO2), gates odorant and heat pathways and activates host-seeking behavior. The neuronal circuits underlying processing of CO2 information remain unclear. We used automated serial-section transmission electron microscopy (EM) to image and reconstruct the circuitry of the glomeruli that are innervated by the Ae. aegypti maxillary palp, including the glomerulus that responds to CO2. Notably, CO2-sensitive olfactory sensory neurons (OSNs) make high levels of recurrent synaptic connections with one another, while making a low density of feedforward synapses. At some of these contacts between CO2 OSNs, we observe ribbon-like presynaptic structures, which may further enhance recurrent signaling. We compared both feedforward and recurrent connectivity with all olfactory glomeruli in Drosophila melanogaster, and we found more recurrent connections between the Ae. aegypti CO2-responsive OSNs than in any D. melanogaster glomeruli. We developed a computational circuit model that demonstrates recurrent synapses are necessary for robust CO2 detection under normal physiological conditions. Together, elevated levels of recurrent connectivity and ribbon-like structures may amplify sensory information detected by CO2-sensitive OSNs to support mosquito activation and sensitization by CO2, even in the presence of high levels of other odorants in the environment. We propose that this circuit organization supports the salience of CO2 as a mosquito host cue.