The long-term goal of this project is to understand how learning can influence olfactory odorant representations at the first level of processing within the olfactory bulb. While the mammalian olfactory system has been shown to have a remarkable capability for undergoing experience-dependent plasticity, how such odor memories are imprinted in the adult olfactory neural circuit remains unclear. Although this process most likely involves changes at multiple stages in the olfactory pathway, one interesting site for plasticity is the olfactory glomerular layer. Within this layer, the anatomical organization of receptor neuron input allows odorant information to be transformed into an odorant-specific topographical map of glomerular activity. This activity pattern can be visualized in vivo using a newly-developed transgenic mouse with a GFP-based calcium indicator (G-CaMP2) expressed exclusively in olfactory bulb output neurons immediately postsynaptic to receptor input. Unlike previous imaging methods, this mouse allows us to observed purely postsynaptic odor maps in the glomerular layer for the first time. Using this mouse model we can directly test the hypothesis that olfactory learning significantly alters olfactory bulb postsynaptic glomerular odorant representations for the trained odorant. This will be accomplished by comparing odorant-evoked glomerular activity patterns in the same animal before and after associative conditioning. Preliminary data suggests that conditioning with a given odorant significantly alters glomerular responses to that odorant following training. Based on this, we plan to extend our findings by testing the hypothesis that these changes will serve to reduce the representational overlap between the trained odorant and similar odorants. Together, these studies will have a significant impact on our understanding of the neural basis of odor coding and role plasticity plays in shaping neural responses to sensory stimuli.

Public Health Relevance

The sense of smell plays an important role in our daily life. Olfaction dysfunction is often times an early indicator of several major neurological diseases in humans including Alzheimer's disease, Parkinson's disease, and schizophrenia. The general goal of this grant is to understand the neural basis of olfactory processing which could help in the diagnosis and treatment of these diseases.

National Institute of Health (NIH)
National Institute on Deafness and Other Communication Disorders (NIDCD)
Small Research Grants (R03)
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Special Emphasis Panel (ZDC1-SRB-L (46))
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Sullivan, Susan L
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University of Tennessee Health Science Center
Anatomy/Cell Biology
Schools of Medicine
United States
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Nagayama, Shin; Fletcher, Max L; Xiong, Wenhui et al. (2014) In vivo local dye electroporation for Ca²? imaging and neuronal-circuit tracing. Cold Spring Harb Protoc 2014:940-7
Pavesi, Eloisa; Heldt, Scott A; Fletcher, Max L (2013) Neuronal nitric-oxide synthase deficiency impairs the long-term memory of olfactory fear learning and increases odor generalization. Learn Mem 20:482-90
Kikuta, Shu; Fletcher, Max L; Homma, Ryota et al. (2013) Odorant response properties of individual neurons in an olfactory glomerular module. Neuron 77:1122-35
Pavesi, Eloisa; Gooch, Allison; Lee, Elizabeth et al. (2012) Cholinergic modulation during acquisition of olfactory fear conditioning alters learning and stimulus generalization in mice. Learn Mem 20:6-10
Fletcher, Max L (2011) Analytical processing of binary mixture information by olfactory bulb glomeruli. PLoS One 6:e29360
Fletcher, Max L; Chen, Wei R (2010) Neural correlates of olfactory learning: Critical role of centrifugal neuromodulation. Learn Mem 17:561-70
Fletcher, Max L; Masurkar, Arjun V; Xing, Junling et al. (2009) Optical imaging of postsynaptic odor representation in the glomerular layer of the mouse olfactory bulb. J Neurophysiol 102:817-30