Mechanisms and function of adaptation at central synapses of the Drosophila olfactory system

• Applicant: Carlotta Martelli, Ph.D.
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells ; Cognitive, Systems and Behavioural Neurobiology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 455076181

Animals use the sense of smell to extract chemical information from the environment. This is particularly important for foraging animals to orient towards food sources and avoid noxious substrates. Odor stimuli carry information about the chemical identity of a source, but also about its location. The identity is encoded by a large population of sensory neurons, each with a specific affinity to the odorant. The location of a source, instead, can be inferred by changes in the concentration of the odor. Depending on the environmental conditions, odor concentration in space and time can vary smoothly or more transiently following very different statistics. How the olfactory system integrates changes in the stimulus on multiple timescales is largely unknown. Adaptation of peripheral and secondary neurons to a sustained odor stimulus has been described as a decrease in responsiveness, both at the physiological and behavioral level. Mechanistically, the adaptation of the peripheral Olfactory Receptor Neurons (ORNs) to a static background is poorly understood. In both insects and vertebrates, adaptation to a background suppress the response to subsequent stimuli, but whether a sensory modality that employs tens or hundreds of sensors with different affinity for the same stimulus needs to shift the sensitivity of the individual sensors, is unclear. My published and preliminary data suggest that adaptation in olfaction might not occur in the single ORNs, but rather involve a coordinated change in activity in the population of secondary neurons through feedforward and lateral modulation of synaptic release. In Drosophila melanogaster, we will combine electrophysiology and functional imaging with genetic and pharmacological approaches to investigate the cellular and circuit mechanisms underlying adaptation in the first processing center of the insect brain, the antennal lobe. A complementary computational approach will test whether the identified mechanisms can support odor coding and behavior downstream of the antennal lobe.Furthermore, sensory systems change their response as a function of the statistics of the inputs in order to optimize encoding of behaviorally relevant features. But what features are relevant to olfactory behavior? Do animals for example respond proportionally to concentration or to relative changes in concentration, and how do past stimuli affect current response? Here, I propose an experimental and computational approach to study the behavioral consequences of adaptation in olfaction. I will identify key stimulus features that elicit an behavioral odor response and study how identified mechanisms mediate these responses in different adapted conditions. This project aims at identifying key computation that allow odor recognition and navigation in foraging animals.

• DFG Programme: Research Grants