Sympathetic response to stimulation of the pontine A5 region in conscious rabbits

Studies in anaesthetized animals have shown that the pontine A5 noradrenerg ic region plays an important role in the sympathetic control of arterial pr essure (AP). The aim of this study was to develop, in conscious rabbits, a technique for microinjections into the A5 region and examine the effects of stimulation of this region on renal sympathetic nerve activity (RSNA). In preliminary mapping experiments on four anaesthetized rabbits, electrical s timulation of the A5 region induced a presser response ranging between 25 a nd 75 mmHg while unilateral injection of,of glutamate (100 nmol) did not ch ange AP. The mapping experiments were used to enable guide cannulae implant ation for subsequent microinjections into the A5 region. In six conscious r abbits, unilateral injection of glutamate (100 nmol) caused a consistent in crease in RSNA (+ 45%) but did not change AP. In another eight rabbits, bil ateral injection of glutamate (0.3, 3, 30 nmol) into the A5 region dose-dep endently increased RSNA by 13%, 30% and 40%, respectively. In four rabbits, angiotensin II (0.3, 3, 30 pmol) injected bilaterally into the A5 region i ncreased RSNA by 5%, 22% and 28%, respectively. In all animals the increase in RSNA was mainly mediated by increasing amplitude of sympathetic synchro nized bursts while their frequency remained unchanged. However, both glutam ate and angiotensin II did not change AP indicating that the sympathoexcita tory response to the A5 stimulation might be relatively confined to the ren al bed. Using a novel microinjection technique developed for conscious rabb its, we found that the A5 region may provide an important excitatory and po ssibly selective input to the renal sympathetic preganglionic neurons. (C) 1999 Published by Elsevier Science B.V. All rights reserved.