Wiring and connectivity enabling CO2 sensitization in the Aedes aegypti mosquito

Abstract

The mosquito Aedes aegypti’s human host-seeking behavior depends upon the integration of multiple sensory cues. One of these cues, carbon dioxide (CO2), primes and activates host-seeking behavior, but the neuronal circuits underlying the transduction and processing of CO2 information remain only vaguely understood. In this thesis, I leverage data from synapse-resolution electron microscopy to investigate the central cells and synapses processing CO2 information in the Ae. aegypti brain, uncovering connectivity motifs and subcellular features that may form a neural substrate for robust behavioral and functional response to CO2. In Chapter 1, I describe the collection of, and connectivity analyses within, a transmission electron microscopy (TEM) dataset of the female Ae. aegypti palp glomeruli; this dataset includes the glomerulus selectively responsive to CO2. While olfactory sensory neurons (OSNs) innervating the CO2 glomerulus do not make more feedforward synapses onto one projection neuron compared to surrounding maxillary palp glomeruli, CO2 OSNs make a relatively high number of recurrent connections among themselves. In Chapter 2, I investigate unique ribbon-synapse-like structures that occur at a subset of these contacts between CO2 OSNs, which may reinforce the recurrent network. In Chapter 3, I describe comparative analyses between the CO2 glomerulus in Ae. aegypti and relevant glomeruli in the well-studied dietary generalist Drosophila melanogaster, finding that the connectivity of the Ae. aegypti CO2 glomerulus is more consistent with a strongly attractive glomerulus (DM1) than the state-dependent aversive CO2 glomerulus (V). Together, this work suggests that attractive glomerular circuits may share feedforward connectivity principles across species and elevated levels of recurrent connectivity and ribbon-like structures may help to support mosquito attraction and sensitization to CO2 .