Alford, W. | bioRxiv Science

bioRxiv2025

Recurrent connectivity supports carbon dioxide sensitivity in Aedes aegypti mosquitoes

The mosquito Aedes aegyptis 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. One Sentence SummaryConnectomic analysis of carbon dioxide circuitry in the disease-vector mosquito Aedes aegypti.

neuroscience↗

bioRxiv2019

Spatiotemporal input reorganization and enhancement of input-output gain sharpen cortical direction selectivity during development

Some neural circuits are constructed through an overproduction of initial connections followed by activity-dependent refinement. Under this paradigm, functional receptive fields would be expected to be narrowed from a diffuse immature condition to a sharper mature condition. Alternatively, neural activity might lead to formation of new connections, leading to expansion of an initially compact receptive field. In the simple cells of the ferret visual cortex undergoing developmental enhancement of direction selectivity, we found evidence for a mixed mechanism: an expansion of the spatiotemporal receptive fields along the temporal dimension combined with a narrowing in space-time through a marked loss of inputs with certain space-time selectivities. Further, the resulting increase in subthreshold direction selectivity was accompanied by increases in near-spike-threshold excitability and input-output gain that resulted in dramatically increased spiking responses. Increases in subthreshold membrane responses and the increased input-output spiking gain were both necessary to explain firing rates in experienced ferrets. These results demonstrate that cortical direction selectivity develops through a combination of plasticity in synaptic and cell-intrinsic properties.

neuroscience↗