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The Journal of Neuroscience, December 3, 2008, 28(49):13088-13093; doi:10.1523/JNEUROSCI.4187-08.2008

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Cellular/Molecular
Norepinephrine Is Coreleased with Serotonin in Mouse Taste Buds

Yijen A. Huang,¹ Yutaka Maruyama,¹ and Stephen D. Roper^1,2

¹Department of Physiology and Biophysics, and ²Program in Neuroscience, University of Miami School of Medicine, Miami, Florida 33136

Correspondence should be addressed to Dr. Stephen D. Roper, Department of Physiology and Biophysics, University of Miami School of Medicine, 1600 North West 10th Avenue, Miami, FL 33136. Email: roper{at}miami.edu

ATP and serotonin (5-HT) are neurotransmitters secreted from taste bud receptor (type II) and presynaptic (type III) cells, respectively. Norepinephrine (NE) has also been proposed to be a neurotransmitter or paracrine hormone in taste buds. Yet, to date, the specific stimulus for NE release in taste buds is not well understood, and the identity of the taste cells that secrete NE is not known. Chinese hamster ovary cells were transfected with _1A adrenoceptors and loaded with fura-2 ("biosensors") to detect NE secreted from isolated mouse taste buds and taste cells. Biosensors responded to low concentrations of NE (10 nM) with a reliable fura-2 signal. NE biosensors did not respond to stimulation with KCl or taste compounds. However, we recorded robust responses from NE biosensors when they were positioned against mouse circumvallate taste buds and the taste buds were stimulated with KCl (50 mM) or a mixture of taste compounds (cycloheximide, 10 µM; saccharin, 2 mM; denatonium, 1 mM; SC45647, 100 µM). NE biosensor responses evoked by stimulating taste buds were reversibly blocked by prazosin, an _1A receptor antagonist. Together, these findings indicate that taste bud cells secrete NE when they are stimulated. We isolated individual taste bud cells to identify the origin of NE release. NE was secreted only from presynaptic (type III) taste cells and not receptor (type II) cells. Stimulus-evoked NE release depended on Ca²⁺ in the bathing medium. Using dual biosensors (sensitive to 5-HT and NE), we found all presynaptic cells secrete 5-HT and 33% corelease NE with 5-HT.

Key words: biosensors; taste; serotonin; transmitters; calcium imaging; phospholipase C β2

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Received Aug. 29, 2008; revised Oct. 3, 2008; accepted Oct. 15, 2008.

Correspondence should be addressed to Dr. Stephen D. Roper, Department of Physiology and Biophysics, University of Miami School of Medicine, 1600 North West 10th Avenue, Miami, FL 33136. Email: roper{at}miami.edu

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				Y. A. Huang, R. Dando, and S. D. Roper Autocrine and Paracrine Roles for ATP and Serotonin in Mouse Taste Buds J. Neurosci., November 4, 2009; 29(44): 13909 - 13918. [Abstract] [Full Text] [PDF]

				C. D. Roberts, G. Dvoryanchikov, S. D. Roper, and N. Chaudhari Interaction between the second messengers cAMP and Ca2+ in mouse presynaptic taste cells J. Physiol., April 15, 2009; 587(8): 1657 - 1668. [Abstract] [Full Text] [PDF]

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