AJP - Regulatory, Integrative and Comparative Physiology, Vol 263, Issue 2 437-R446, Copyright © 1992 by American Physiological Society
Splanchnic nerve response to A5 area stimulation in rats
D. Huangfu, L. J. Hwang, T. A. Riley and P. G. Guyenet
Department of Pharmacology, University of Virginia Health Sciences Center, Charlottesville 22908.
Microinjection of the excitatory amino acid N-methyl-D-aspartate (NMDA, 0.5
nmol) into ventrolateral pons (the A5 area) of halothane-anesthetized,
paralyzed rats increased splanchnic (sSND) and renal sympathetic nerve
discharges (approximately 45%) and usually decreased lumbar SND. These
effects were accompanied by 1) regionally specific changes in vascular
resistances, 2) an increase in the gain of the sympathetic baroreflex, and
3) modest reductions in blood pressure and heart rate. sSND activation was
greatest when NMDA injections were made in the vicinity of A5 noradrenergic
(NE) cells. Injection of 6-hydroxydopamine (6-OH-DA) into A5 area (after 15
days) destroyed 83% of NE neurons and reduced NMDA activation of sSND by
76%. Stimulation of sSND by NMDA in A5 area was reduced 1) 1-2 h after
bilateral intraspinal injection of 6-OHDA, but not vehicle or
5,7-dihydroxytryptamine, and 2) by administration of prazosin [alpha 1-NE
receptor antagonist, 1 mg/kg iv or 10-20 micrograms intrathecal (it)], but
not by idazoxan (alpha 2-NE receptor antagonist, 10-20 micrograms it) or
propranolol (0.2 mg/kg iv). We conclude that A5 NE cells have a visceral
vasomotor sympathoexcitatory function mediated in large part by their
spinal projection.
