title: Modulatory effects mediated by metabotropic glutamate receptor 5 on lateral geniculate nucleus relay cells.
abstract: Glutamate is thought to be the excitatory neurotransmitter in the lateral geniculate nucleus (LGN) of the cat, mediating visual transmission from the retina via ionotropic receptors of both D,L-alpha-amino-3-hydroxy-5-alpha-methyl-4-isoxazolepropionate and N-methyl-D-aspartate subtypes. Moreover, glutamate also exerts an important modulatory influence on LGN cells, where metabotropic glutamate receptors (mGluRs) seem to play a crucial role. Here we show in anesthetized adult cats that iontophoretic application of the specific mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) produced two, distinctly different, effects on LGN neurons. Visual responses to flashing spots and drifting gratings were attenuated (decreased by an average of 59%) in 13 of 23 of the cells but augmented (increased by an average of 60%) in 10 of 23 of the cells. Further, in each case when the specific mGluR5 agonist (R,S)-2-chloro-5-hydroxyphenylglycine was applied, the effects obtained were the opposite to those of MPEP. Data obtained in a second group of experiments to determine a possible interaction between mGluR5 blockade by MPEP and glutamate ionotropic receptors show that, in the majority of neurons (11 of 15, 73%), the MPEP-mediated effects seem to be independent of N-methyl-D-aspartate and D,L-alpha-amino-3-hydroxy-5-alpha-methyl-4-isoxazolepropionate receptor activity. Our results demonstrate a physiological role for mGluR5 in controlling retinal input and show, in vivo, a more intricate scenario than previously suggested, highlighting the complexity of metabotropic receptor interactions with excitatory and inhibitory elements in the thalamus.
authors.affiliation: NEUROcom (Neuroscience and Motor Control Group), Department of Medicine and INEF-Galicia, Campus de Oza, University of A Coruña, 15006, A Coruña, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: de Labra
authors.forename: Casto
authors.initials: C
authors.lastname: Rivadulla
authors.forename: Javier
authors.initials: J
authors.lastname: Cudeiro
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000704:Analysis of Variance; D000818:Animals; D002415:Cats; D004347:Drug Interactions; D005260:Female; D005829:Geniculate Bodies / Q000166:cytology*; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D007478:Iontophoresis / Q000379:methods; D008297:Male; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010648:Phenylacetates / Q000494:pharmacology; D010775:Photic Stimulation / Q000379:methods; D011725:Pyridines / Q000494:pharmacology; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
chemical_list: C107349:2-chloro-5-hydroxyphenylglycine; D010648:Phenylacetates; D011725:Pyridines; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; D016202:N-Methylaspartate; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; C121465:6-methyl-2-(phenylethynyl)pyridine; D005998:Glycine