Evidence that NMDA receptors mediate the responses of putative RVLM presympathetic neurons to vagal afferent stimulation in rats.
Experiments were performed in 25 urethane-anaesthetized male Sprague-Dawley rats. Forty-six RVLM neurons were identified as putative presympathetic neurons according to their arterial baroreceptor reflex related properties, i.e. they were inhibited by stimulation of the aortic nerve; silenced by elevation of blood pressure and had a cardiac cycle related rhythm of spontaneous discharge. Responses of these neurons to tripled square wave stimulation of vagal afferents was tested by means of peristimulus time histograms. In addition to a long-lasting inhibition (I2), some neurons had one (P0) or two excitatory peaks (P1 and P2), and there was a short-lasting inhibition (I1) between P1 and P2. After microinjection of CPP (0.1 microl, 50 mM) into the NTS, the inhibitory responses were blocked, but the excitatory peaks were not affected; in the CVLM, CPP microinjection of the same dose had a similar effect on the responses elicited by vagal afferent stimulation in 15 of the 24 neurons tested. No detectable effects were observed in 9 neurons. However, intravenously administered ketamine attenuated or abolished these responses, either inhibitory or excitatory, in a dose dependent way. These results suggest: (1) an NMDA mechanism is involved in both the inhibitory and the excitatory responses. For the inhibitory responses, the involvement is both in the NTS and in the CVLM; for the excitatory responses, it is probably in the RVLM. (2) There may be a direct excitatory amino acid (EAA) pathway from the NTS to the RVLM.
Wang
J
J
Department of Physiology, Faculty of Basic Medical Science, Second Military Medical University, Shanghai, China.
Rong
W
W
Hou
G
G
Wang
W
W
Yuan
W
W
D000818:Animals; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D007649:Ketamine / Q000494:pharmacology; D008297:Male; D008845:Microinjections; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology*; D010879:Piperazines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology*; D017552:Solitary Nucleus / Q000166:cytology / Q000502:physiology; D013268:Stimulation, Chemical; D013564:Sympathetic Nervous System / Q000166:cytology / Q000502:physiology*; D014630:Vagus Nerve / Q000166:cytology / Q000502:physiology*
D018691:Excitatory Amino Acid Antagonists; D010879:Piperazines; D016194:Receptors, N-Methyl-D-Aspartate; D007649:Ketamine; C050592:3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid