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 α-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 α-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 α-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.
|Original language||English (US)|
|Journal||American Journal of Physiology - Heart and Circulatory Physiology|
|State||Published - Nov 1998|
- Synaptic transmission
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