UBC Theses and Dissertations
Combinatorial coding of salt taste in the fly labellum Jaeger, Alexandria
Salt is an important component of most of the food we ingest daily, yet its detection in food and the control of its consumption remain poorly understood. The gustatory system of an animal underlies the processing of salt taste. With the ability to taste on multiple parts of the body, Drosophila melanogaster makes critical decisions about beneficial tastants to consume, and potentially harmful tastants to avoid. Most chemicals sensed by the gustatory system drive either attraction or repulsion, but salt is unique in that it is appetitive at low concentrations and repulsive at high concentrations. How salt is encoded, processed, modulated, and drives behavior is still not well defined. Through immunolabeling, calcium imaging, and a variety of behavioral assays, we are working on understanding these questions. I have constructed a taste sensory neuron map by co-labeling different gustatory receptors and protein markers for the neurotransmitters glutamate and acetylcholine. Interestingly, while most sensory neurons are cholinergic, I have found that the ENaC family member ppk23 labels a population of glutamateric taste neurons in the fly labellum (the analog of the mammalian tongue). Using calcium imaging, I have characterized the responses of this and other major populations of taste sensory neurons, and found that most, if not all, taste sensory neurons respond to salt in some way. We look at the effect of salt deprivation on sugar and salt sensing labellar GRNs’ physiology to further understand the neural circuitry devoted to this salt sensing pathway. This work challenges the current paradigm of labelled lines coding in the gustatory system of flies, and instead presents evidence of combinatorial coding in salt. Understanding the basic neural circuitry in the fly gustatory system and how that drives behavior in the face of different internal states across modalities, will give insight into how taste information is translated into appropriate feeding responses.
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