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Neuronal Circuits Required for Drosophila Olfaction

A pivotal area of neuroscience is to understand how sensory information from the external environment is received, processed, and interpreted by the brain. For example, why does an apple smell like an apple, and an orange like an orange?  Our ability to ‘smell’ different odors is tightly linked to our sense of odor perception. Yet little is known about how odor perception is processed in the brain.

The primary goal of the lab is to characterize the anatomy, development, and function of neurons required for olfactory behaviors in Drosophila. Our initial focus is on the projection neurons (mitral/tufted cells in mammals) that connect the antennal lobe to the higher order regions of the fly brain such as the mushroom bodies and lateral horn (See Figure). We first carried out an exhaustive study of PN anatomy with the logic that their stereotyped axonal projections might underlie biological functions. Indeed, we found that ‘fruity odors’, which represent food, and pheromones, which represent sex, signal to distinct regions of the lateral horn. This organization was further respected by lateral horn output neurons. They too showed specificity to either the ‘fruity’ or ‘sex’ regions of the lateral horn. Therefore, the lateral horn region, which to the naked eye looks quite homogeneous, might actually be organized into subdomains according to the biological meanings of the stimuli.

By using neurogenetics, we can label and manipulate small populations of neurons and assay their effects on olfactory behaviors. Such detailed genetic perturbations are possible using the ‘Q-system’ we have developed: a repressible binary expression system, that when used in combination with the GAL4 system, allows for genetic silencing or activation of small neuronal populations. We have also developed a high throughput computer controlled olfactory attraction and repulsion assay. In this assay, hundreds of flies can be tracked simultaneously as they respond to different odorants at many carefully controlled odorant concentrations. From such analyses, we can effectively and efficiently link precisely defined neuronal populations to their respective odorant behaviors.

Current projects in the lab involve: 1) characterizing the function of the projection neurons in relaying odorant information to higher brain centers; 2) characterizing the adult fly’s olfactory system in eliciting stereotyped attractive or repulsive behaviors to discrete odorants; 3) identifying and characterizing additional neuronal circuitry required for olfactory behaviors; 4) developing additional genetic tools for linking neurons to their function.