Type III ?presynaptic? taste cells respond to sour and some salty stimuli with action potentials and release neurotransmitter at conventional synapses with afferent nerve fibers. The identity of the transmitters involved, however, is still unclear. We have shown previously that all taste stimuli (including sour and salty) require ATP signaling to neural P2X receptors for transmission to afferent fibers. Nonetheless, ATP release from Type III cells has not been detected. Conversely, Type III cells do release serotonin (5-HT) which activates 5-HT3 receptors on afferent nerve fibers but neither knockout nor pharmacological inhibition of 5-HT3 completely eliminates responses to acids or salts, suggesting other neurotransmitters are involved. One problem in studying transmission from Type III cells is that the conventional stimuli used to activate these cells -- acids, salts, and KCl -- all have non-specific effects on other cell types in the taste bud. To circumvent this problem, we employ an optogenetic strategy permitting direct stimulation of Type III cells with light rather than chemicals. We developed a mouse that expresses Cre recombinase selectively in type III taste cells relying on Pkd2l1 as a Cre driver. When these Pkd2l1-Cre mice are crossed with ?floxed? channelrhodopsin (ChR2) mice ChR2 is faithfully expressed in taste cells immunoreactive for PKD2L1 with no off-target expression in other taste cell types. Flashing 470 nm light onto the tongue elicits responses in the chorda tympani and glossopharyngeal nerves that are robust and repeatable, resembling responses to sour and salty stimuli. In this proposal we will utilize these Pkd2l1-ChR2 mice plus other gene-targeted mice to investigate the neurotransmitters that are used by these cells to communicate with the nervous system, and the perceptual qualities evoked by selective stimulation of PKD2l1 Type III cells.
Aim 1 will investigate the role of ATP and other neurotransmitters (i.e., 5-HT, GABA, and NE) in activating geniculate ganglion neurons that selectively innervate Type III cells. Calcium imaging of isolated geniculate ganglion cells will identify transmitters that activate these neurons, and chorda tympani and glossopharyngeal nerve responses to light in the Pkd2l1- ChR2 mice will allow us to test the role of their cognate receptors in vivo.
Aim 2 will address the perceptual quality elicited by stimulation of Pkd2l1-ChR2 cells, using behavioral paradigms, and cFos activation will be used to address the central representation of PKD2L1-expressing Type III cells.
In Aim 3 we will test the hypothesis that PKD2L1-Type III cells participate in an intragemmal (intra taste bud) circuit, resulting in modulation of other taste qualities, particularly those transduced by Type II cells. Results from these studies will provide important new information about transduction, afferent neurotransmission, and intragemmal signaling in Type III taste cells.

Public Health Relevance

The function of the gustatory system is to discriminate nutritious substances from substances that are toxic or harmful to the body. Understanding the molecular events underlying detection and transmission of taste information may lead to the development of pharmaceutical agents that can modulate food intake, a major factor in controlling obesity. The proposed studies will utilize a newly developed mouse model to investigate how sour and some salty tastes are transmitted to the nervous system.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC012555-07
Application #
9502265
Study Section
Somatosensory and Chemosensory Systems Study Section (SCS)
Program Officer
Sullivan, Susan L
Project Start
2012-07-01
Project End
2022-06-30
Budget Start
2018-07-01
Budget End
2019-06-30
Support Year
7
Fiscal Year
2018
Total Cost
Indirect Cost
Name
University of Colorado Denver
Department
Otolaryngology
Type
Schools of Medicine
DUNS #
041096314
City
Aurora
State
CO
Country
United States
Zip Code
80045
Stratford, J M; Larson, E D; Yang, R et al. (2017) 5-HT3A -driven green fluorescent protein delineates gustatory fibers innervating sour-responsive taste cells: A labeled line for sour taste? J Comp Neurol 525:2358-2375
Wilson, Courtney E; Finger, Thomas E; Kinnamon, Sue C (2017) Type III Cells in Anterior Taste Fields Are More Immunohistochemically Diverse Than Those of Posterior Taste Fields in Mice. Chem Senses 42:759-767
Vandenbeuch, Aurelie; Kinnamon, Sue C (2016) Glutamate: Tastant and Neuromodulator in Taste Buds. Adv Nutr 7:823S-7S
Ye, Wenlei; Chang, Rui B; Bushman, Jeremy D et al. (2016) The K+ channel KIR2.1 functions in tandem with proton influx to mediate sour taste transduction. Proc Natl Acad Sci U S A 113:E229-38
Vandenbeuch, Aurelie; Anderson, Catherine B; Kinnamon, Sue C (2015) Mice Lacking Pannexin 1 Release ATP and Respond Normally to All Taste Qualities. Chem Senses 40:461-7
Larson, Eric D; Vandenbeuch, Aurelie; Voigt, Anja et al. (2015) The Role of 5-HT3 Receptors in Signaling from Taste Buds to Nerves. J Neurosci 35:15984-95
Vandenbeuch, Aurelie; Larson, Eric D; Anderson, Catherine B et al. (2015) Postsynaptic P2X3-containing receptors in gustatory nerve fibres mediate responses to all taste qualities in mice. J Physiol 593:1113-25
Kinnamon, Sue C; Finger, Thomas E (2013) A taste for ATP: neurotransmission in taste buds. Front Cell Neurosci 7:264
Kinnamon, Sue C (2013) Neurosensory transmission without a synapse: new perspectives on taste signaling. BMC Biol 11:42
Vandenbeuch, Aurelie; Anderson, Catherine B; Parnes, Jason et al. (2013) Role of the ectonucleotidase NTPDase2 in taste bud function. Proc Natl Acad Sci U S A 110:14789-94

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