Metabotropic glutamate receptors depress vagal and aortic baroreceptor signal transmission in the NTS.
We sought to determine whether metabotropic glutamate receptors contribute to frequency-dependent depression of vagal and aortic baroreceptor signal transmission in the nucleus of the solitary tract (NTS) in vivo. In alpha-chloralose-anesthetized rabbits, we determined the number of extracellular action potentials synaptically evoked by low (1 Hz)- or high-frequency vagal (3-20 Hz) or aortic depressor nerve (ADN) (6-80 Hz) stimulation and postsynaptically evoked by the ionotropic glutamate receptor agonist alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). The metabotropic glutamate receptor agonist (2S,1'S, 2'S)-2-(carboxycyclopropyl)glycine (L-CCG-I) attenuated NTS responses monosynaptically evoked by 1-Hz vagus stimulation by 34% (n = 25; P = 0.011), while augmenting AMPA-evoked responses by 64% (n = 17; P = 0.026). The metabotropic glutamate receptor antagonist alpha-methyl-4-phosphonophenylglycine (MPPG) did not affect NTS responses to low-frequency vagal stimulation (n = 11) or AMPA (n = 10) but augmented responses to high-frequency stimulation by 50% (n = 25; P = 0.0001). MPPG also augmented NTS responses to high-frequency ADN stimulation by 35% (n = 9; P = 0.048) but did not affect responses to low-frequency stimulation (n = 9) or AMPA (n = 7). The results suggest that metabotropic glutamate receptors, presumably at presynaptic sites, contribute to frequency-dependent depression of vagal and aortic baroreceptor signal transmission in NTS.
Liu
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Division of Cardiovascular Medicine and Department of Pharmacology, University of California, Davis, California 95616, USA.
Chen
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Bonham
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D000200:Action Potentials; D000409:Alanine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D011311:Pressoreceptors / Q000502:physiology*; D011817:Rabbits; D018094:Receptors, Metabotropic Glutamate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D017552:Solitary Nucleus / Q000502:physiology*; D009435:Synaptic Transmission; D014630:Vagus Nerve / Q000502:physiology; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
D018690:Excitatory Amino Acid Agonists; D018094:Receptors, Metabotropic Glutamate; C101185:alpha-methyl-4-phosphonophenylglycine; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D000409:Alanine