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The Journal of Neurophysiology Vol. 82 No. 1 July 1999, pp. 60-68
Copyright ©1999 by the American Physiological Society
1Zablocki Veterans Affairs Medical Center,
Krolo, M.,
E. A. Stuth,
M. Tonkovic-Capin,
Z. Dogas,
F. A. Hopp,
D. R. McCrimmon, and
E. J. Zuperku.
Differential Roles of Ionotropic Glutamate Receptors in Canine
Medullary Inspiratory Neurons of the Ventral Respiratory Group. J. Neurophysiol. 82: 60-68, 1999.
The relative roles of ionotropic
N-methyl-D-aspartate (NMDA) and non-NMDA
glutamate receptors in supplying excitatory drive to inspiratory (I)
augmenting pattern neurons of the ventral respiratory group were
studied in anesthetized, ventilated, paralyzed, and vagotomized dogs.
Multibarrel micropipettes were used to record simultaneously
single-unit neuronal activity and pressure microeject the NMDA
antagonist, 2-amino-5-phosphonovalerate (AP5; 2 mM), the non-NMDA
antagonist
2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX; 0.25 mM), and an artificial cerebrospinal fluid vehicle. Ejected
volume-rates were measured directly via meniscus level changes. The
moving time average of phrenic nerve activity was used to determine
respiratory phase durations and to synchronize cycle-triggered
histograms of the discharge patterns. Both AP5 and NBQX produced
dose-dependent reductions in peak spontaneous I neuronal discharge
frequency (Fn). The average (± SE) maximum reduction in peak Fn produced by AP5 was
69.1 ± 4.2% and by NBQX was 47.1 ± 3.3%. Blockade of both
glutamate receptor subtypes nearly silenced these neurons, suggesting
that their activity is highly dependent on excitatory synaptic drive
mediated by ionotropic glutamate receptors. Differential effects were
found for the two glutamatergic antagonists. AP5 produced downward,
parallel shifts in the augmenting pattern of discharge, whereas NBQX
reduced the slope of the augmenting discharge pattern. These results
suggest that time-varying excitatory input patterns to the canine I
bulbospinal neurons are mediated by non-NMDA glutamate receptors and
that constant or tonic input patterns to these neurons are mediated by
NMDA receptors.
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