PROJECT SUMMARY/ABSTRACT
The goal of this project is to determine the relationships between odor-induced calcium fluorescence signals and
spike responses across morphologically distinctive types of insect olfactory receptor neurons (ORNs). Millions
of lives are threatened annually by devastating insect-borne diseases—such as malaria, dengue, and West Nile
fever—which are transmitted by vectors that heavily rely on their sense of smell for host-seeking.
Correspondingly, growing efforts are dedicated to better understanding insect olfaction to develop tools and
strategies to interfere with host-seeking behavior. With the advent of CRISPR genome editing technology in a
wide range of insects, in vivo calcium imaging has become a method of choice for identifying ORNs that respond
to host odors. However, calcium-induced fluorescence signals may be difficult to interpret, because response
amplitudes and dynamic ranges are determined not only by the degree of receptor activation, but also by the
intrinsic electrotonic property of neurons which can vary markedly across neuronal types. For example, a 10%
increase in fluorescence signal may correspond to a high-frequency, near-saturating spike response for one
ORN type, but may instead represent a low spike response at the rising phase of the dosage curve for another.
In order to accurately interpret calcium imaging data, it is imperative to understand the spike-calcium relationship
associated with individual neuronal types. To achieve this goal, this proposal leverages the powerful genetic
toolkit and tractable olfactory system of Drosophila. Similar to other insect species, Drosophila ORNs are
categorized under morphological classes based on the sensillum types that encapsulate their sensory dendrites.
Each sensillum typically contains two to four ORNs, which exhibit distinctive extracellular spike amplitudes that
reflect the size differences between compartmentalized neurons. Given that the electrotonic properties of
sensory neurons are influenced by their morphological and morphometric features, any such differences across
ORN morphological types will likely impact their spike-calcium relationship. The general hypothesis—that the
odor-induced spike and calcium response relationship vary across distinctive ORN morphological types—will be
tested via simultaneous in vivo trans-cuticle fluorescence imaging and single-sensillum electrophysiological
recording. In this proposal, Aim 1 will determine the calcium response dynamic range and spike-fluorescence
relationship in select ORNs representing all morphological classes. Aim 2 will focus on the comparison between
compartmentalized ORNs which typically exhibit distinctive morphometric features. Successful execution of the
proposal will yield a rich dataset to facilitate meaningful interpretation of calcium-induced fluorescence signals
recorded from Drosophila ORN types. Importantly, this information is expected to be generalizable to other
insects, including disease vectors and agricultural pests, as these ORN morphological classes are found across
insect species. Moreover, this systematic survey will lay the foundation for future studies to determine the
mechanistic underpinnings of sensory neurons’ calcium responses.