Chemical Senses Vol. 29 No. 6 © Oxford University Press 2004; all rights reserved
Rat Gustatory Neurons in the Geniculate Ganglion Express Glutamate Receptor Subunits
1 Department of Ophthalmology, University of Miami School of Medicine, Miami, FL 33136, USA, 2 Centro Internacional de Física, Bogotá, Colombia and 3 Department of Physiology and Biophysics, University of Miami School of Medicine, Miami, FL 33136, USA
Correspondence to be sent to: Alejandro Caicedo, Department of Ophthalmology, University of Miami School of Medicine, 1638 NW 10th Avenue, William L. McKnight Vision Research Center, Miami, FL 33136, USA. e-mail: acaicedo{at}chroma.med.miami.edu
Taste receptor cells are innervated by primary gustatory neurons that relay sensory information to the central nervous system. The transmitter(s) at synapses between taste receptor cells and primary afferent fibers is (are) not yet known. By analogy with other sensory organs, glutamate might a transmitter in taste buds. We examined the presence of AMPA and NMDA receptor subunits in rat gustatory primary neurons in the ganglion that innervates the anterior tongue (geniculate ganglion). AMPA and NMDA type subunits were immunohistochemically detected with antibodies against GluR1, GluR2, GluR2/3, GluR4 and NR1 subunits. Gustatory neurons were specifically identified by retrograde tracing with fluorogold from injections made into the anterior portion of the tongue. Most gustatory neurons in the geniculate ganglion were strongly immunoreactive for GluR2/3 (68%), GluR4 (78%) or NR1 (71%). GluR1 was seen in few cells (16%). We further examined if glutamate receptors were present in the peripheral terminals of primary gustatory neurons in taste buds. Many axonal varicosities in fungiform and vallate taste buds were immunoreactive for GluR2/3 but not for NR1. We conclude that gustatory neurons express glutamate receptors and that glutamate receptors of the AMPA type are likely targeted to synapses within taste buds.
Key words: AMPA receptor, fluorogold tracing, NMDA receptor, sensory neurons, taste bud
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