Activity-dependent role of NMDA receptors in transmission of cardiac mechanoreceptor input to the NTS.
Evidence suggests that transmission of barosensitive input from arterial baroreceptors and cardiac mechanoreceptors at nucleus tractus solitarius (NTS) neurons involves non-N-methyl-d-aspartate (NMDA) glutamate receptors, but there is a possibility that the contribution of NMDA receptors might increase during periods of increased afferent input, when enhanced neuronal depolarization could increase the activation of NMDA receptors by removal of a Mg(2+) block. Thus the effects of NMDA on cardiac mechanoreceptor-modulated NTS neuronal discharges were examined at different levels of arterial pressure used to change cardiac mechanoreceptor afferent input. To determine whether the response was specific to NMDA, (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid (AMPA) was also administered at different levels of neuronal discharge. In anesthetized dogs, neuronal activity was recorded from the NTS while NMDA or AMPA was picoejected at high versus low arterial stimulating pressures. NMDA, but not AMPA, produced a significantly greater discharge of mechanoreceptor-driven NTS neurons at higher versus lower levels of stimulating pressure. These data suggest that the role played by NMDA receptors is greater during periods of enhanced neuronal depolarization, which could be produced by increases in afferent barosensitive input.
Seagard
J L
JL
Zablocki Department of Veterans Affairs Medical Center, Medical College of Wisconsin, Milwaukee, Wisconsin 53295, USA. jseagard@mcw.edu
Dean
C
C
Hopp
F A
FA
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D004285:Dogs; D004333:Drug Administration Routes; D006321:Heart / Q000294:innervation* / Q000502:physiology; D008465:Mechanoreceptors / Q000502:physiology*; D016202:N-Methylaspartate / Q000008:administration & dosage; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D017552:Solitary Nucleus / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000008:administration & dosage
D016194:Receptors, N-Methyl-D-Aspartate; D016202:N-Methylaspartate; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid