Genetically Encoded Calcium Indicators for Functional Imaging of Mosquito Olfactory Neurons

Mosquitoes transmit a multitude of diseases to humans and animals through biting and blood feeding. To locate their hosts, mosquitoes primarily use their sense of smell. Therefore, an understanding of mosquito olfaction will help develop strategies to control the diseases they transmit. A mosquito's sense of smell is determined by the response of olfactory neurons on its peripheral olfactory organs. Traditionally, mosquito olfactory neuron activity has been examined using electrophysiological techniques such as electroantennography and single sensillum recordings. Electroantennography examines if an odorant is detectable by the ensemble of all antennal neurons. In contrast, single sensillum electrophysiology allows detailed recordings of the activity of two to three neurons at a time. However, single sensillum recording of olfactory neurons is difficult, laborious, and typically allows examination of only a few neurons on the antenna. A promising new approach is to use optical imaging techniques to provide a way to visualize the global response of olfactory organs to an odor, as well as the specific responses of several olfactory neurons to that odor. In particular, calcium imaging has progressed significantly, from the use of chemical calcium indicators to the development of genetically encoded calcium sensors. These advances have opened the way to study the mode of action of known mosquito attractants and repellents as well as a way to screen potential new attractants and repellents. Here, we provide an introduction to the different types of calcium indicators and their uses for investigating the function of mosquito sensory neurons.