Differential effects of an NMDA and a non-NMDA receptor antagonist on medullary lateral tegmental field neurons.
We microiontophoresed an N-methyl-D-aspartate (NMDA) and a non-NMDA receptor antagonist onto medullary lateral tegmental field (LTF) neurons, the naturally occurring discharges of which were correlated to the cardiac-related rhythm in sympathetic nerve discharge (SND) of dialurethane-anesthetized cats. Some of these neurons were classified as sympathoexcitatory, because their firing rate decreased during baroreceptor reflex activation. Microiontophoresis of 1,2,3,4-tetrahydro-6-nitro-2,3-dioxobenzo-[f]quinoxaline-7-sulfonamide (NBQX), a non-NMDA receptor antagonist, reduced the mean firing rates of these neurons (51 +/- 8% of control, P < 0.001, n = 20) without affecting their relationship to cardiac-related SND, as indicated by the lack of significant changes in the ratio of peak to background counts in arterial pulse (AP)-triggered histograms of LTF neuronal activity and the AP-LTF coherence value at the frequency of the heartbeat. In contrast, microiontophoresis of D(-)-2-amino-5-phosphonopentanoic acid, an NMDA receptor antagonist, onto LTF neurons reduced the ratio of peak to background counts in AP-triggered histograms to 57 +/- 9% of control (P = 0.002, n = 16) and the AP-LTF coherence value to 25 +/- 10% of control (P = 0.001, n = 10). These data support the view that non-NMDA and NMDA receptors are involved in setting the basal level of activity of LTF sympathoexcitatory neurons and in synchronizing their discharges to the AP, respectively.
Barman
Susan M
SM
Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan 48824-1317, USA. barman@msu.edu
Orer
Hakan S
HS
Gebber
Gerard L
GL
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology*; D000818:Animals; D002415:Cats; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D006339:Heart Rate / Q000502:physiology; D007478:Iontophoresis; D008526:Medulla Oblongata / Q000166:cytology / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D011311:Pressoreceptors / Q000502:physiology; D011810:Quinoxalines / Q000494:pharmacology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors* / Q000502:physiology; D013564:Sympathetic Nervous System / Q000166:cytology / Q000502:physiology; D013681:Tegmentum Mesencephali / Q000166:cytology / Q000502:physiology
D018691:Excitatory Amino Acid Antagonists; D011810:Quinoxalines; D016194:Receptors, N-Methyl-D-Aspartate; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; D015763:2-Amino-5-phosphonovalerate