title: Glutamate may be an efferent transmitter that elicits inhibition in mouse taste buds.
abstract: Recent studies suggest that l-glutamate may be an efferent transmitter released from axons innervating taste buds. In this report, we determined the types of ionotropic synaptic glutamate receptors present on taste cells and that underlie this postulated efferent transmission. We also studied what effect glutamate exerts on taste bud function. We isolated mouse taste buds and taste cells, conducted functional imaging using Fura 2, and used cellular biosensors to monitor taste-evoked transmitter release. The findings show that a large fraction of Presynaptic (Type III) taste bud cells (∼50%) respond to 100 µM glutamate, NMDA, or kainic acid (KA) with an increase in intracellular Ca(2+). In contrast, Receptor (Type II) taste cells rarely (4%) responded to 100 µM glutamate. At this concentration and with these compounds, these agonists activate glutamatergic synaptic receptors, not glutamate taste (umami) receptors. Moreover, applying glutamate, NMDA, or KA caused taste buds to secrete 5-HT, a Presynaptic taste cell transmitter, but not ATP, a Receptor cell transmitter. Indeed, glutamate-evoked 5-HT release inhibited taste-evoked ATP secretion. The findings are consistent with a role for glutamate in taste buds as an inhibitory efferent transmitter that acts via ionotropic synaptic glutamate receptors.
authors.affiliation: Department of Physiology and Biophysics, University of Miami School of Medicine, Miami, Florida, United States of America. sroper@med.miami.edu
authors.forename: Yijen A
authors.initials: YA
authors.lastname: Huang
authors.forename: Jeff
authors.initials: J
authors.lastname: Grant
authors.forename: Stephen
authors.initials: S
authors.lastname: Roper
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D018698:Glutamic Acid / Q000378:metabolism / Q000494:pharmacology*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009433:Neural Inhibition / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D009476:Neurons, Efferent / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D018377:Neurotransmitter Agents / Q000378:metabolism / Q000494:pharmacology; D054799:Phospholipase C beta / Q000235:genetics; D044405:Receptor, Serotonin, 5-HT2C / Q000235:genetics / Q000378:metabolism; D058476:Receptors, Purinergic P2X2 / Q000235:genetics / Q000378:metabolism; D058477:Receptors, Purinergic P2X3 / Q000235:genetics / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects* / Q000235:genetics; D013650:Taste Buds / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology
chemical_list: D018377:Neurotransmitter Agents; D044405:Receptor, Serotonin, 5-HT2C; D058476:Receptors, Purinergic P2X2; D058477:Receptors, Purinergic P2X3; D049452:Green Fluorescent Proteins; D018698:Glutamic Acid; D054799:Phospholipase C beta