Signal discrimination in the semicircular canals: a role for group I metabotropic glutamate receptors.
Fluorescence immunocytochemistry indicates that enzymatically isolated semi-circular canal (SCC) hair cells express metabotropic glutamate receptors (mGluRs) 1a and 5. Antibody-antigen preadsorption controls proved entirely negative. Applied while mechanically stimulating the posterior SCC with a piezo-electric bimorph, the non-competitive, mGluR5-selective antagonist MPEP-HCl (1 microM-3 mM) dose-dependently reduces mechanically evoked facilitation of afferent discharge rate (IC50 136 microM; n = 4), while having no effect on tonic, unstimulated afferent discharge. It thus appears that group I mGluRs on SCC hair cells are activated during mechanical stimulation, but are not activated under tonic transmitter release conditions. We conclude that group I mGluRs expressed by SCC hair cells may serve as a mechanism for the selective amplification of mechanically evoked transmitter release, thereby enhancing signal discrimination at the VHC-vestibular afferent synapse.(50)
Hendricson
Adam W
AW
Department of Pharmacology SL83, Tulane University School of Medicine, New Orleans, LA 70112, USA.
Guth
Paul S
PS
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018069:Hair Cells, Vestibular / Q000187:drug effects / Q000378:metabolism*; D007150:Immunohistochemistry; D040542:Mechanotransduction, Cellular / Q000187:drug effects / Q000502:physiology*; D010812:Physical Stimulation; D011725:Pyridines / Q000494:pharmacology; D011894:Rana pipiens; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000187:drug effects / Q000378:metabolism*; D012665:Semicircular Canals / Q000378:metabolism*; D009435:Synaptic Transmission / Q000502:physiology*
D018691:Excitatory Amino Acid Antagonists; D011725:Pyridines; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; C104077:metabotropic glutamate receptor type 1; C121465:6-methyl-2-(phenylethynyl)pyridine