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Dissecting Olfactory Circuits in Drosophila

Drosophila is a simple and genetically tractable model system for studying neural circuits. This dissertation consists of two studies, with the broad goal of understanding sensory processing in neural circuits using Drosophila as a model system. A key tool in the study of neural circuits is the ability to transiently inactivate specific neurons. In Drosophila, the current techniques for doing this are limited. The first study describes a novel technique for transient and specific inactivation of Drosophila neurons in vivo using a native histamine-gated chloride channel (Ort). Since many regions of the Drosophila brain are devoid of histaminergic neurons, Ort could be used to artificially inactivate specific neurons in these regions. We found that histamine effectively silenced neurons misexpressing Ort. Ort also performed favorably in comparison to the available alternative effector transgenes. Thus, Ort misexpression is a useful tool for probing functional connectivity among Drosophila neurons. Understanding the physiological effects of neurotransmitters is critical to deciphering neural circuit function. Although glutamatergic neurons are abundant in the Drosophila brain, the effects of glutamate are largely unknown. The second study investigated the role of glutamate in the olfactory system. We found that glutamate acts as an inhibitory neurotransmitter, broadly similar to the role of GABA in this circuit. The existence of two parallel inhibitory transmitter systems may increase the range and flexibility of synaptic inhibition.