Actions of propofol on pontine neurons controlling arterial pressure in rats

Tonic firing of pontine neurons provides excitatory input to the vasomotor centre in the ventrolateral medulla. To increase our understanding of the actions of propofol on CNS neurons controlling the cardiovascular system, we evaluated the effects of propofol on this tonic firing of pontine neurons. The actions of propofol (doses 1-4, respectively: 24 +/- 2, 40 +/- 4, 65 +/- 3 and 104 +/- 3 mg.kg-1.hr-1) on the pontine neurons were studied using eight atropinized Wistar rats. Electrical activity of renal sympathetic nerves, systemic arterial blood pressure and heart rate were recorded. Propofol decreased renal nerve activity by 3 +/- 2%, 23 +/- 3%, 33 +/- 3% and 52 +/- 4% at the four doses. Arterial pressure and heart rate decreased similarly in a dose-dependent manner. Sympathetic and cardiovascular responses to blocking neurons in the pontine reticular formation by microinjection of glycine were depressed by propofol. Renal nerve activity was decreased by 44 +/- 5% 41 +/- 4%, 28 +/- 3% and 13 +/- 2% after pontine blockade during infusion of doses 1 to 4, respectively. Similarly, arterial pressure was decreased by 25 +/- 3, 15 +/- 2, 12 +/- 1 and 5 +/- 2 mmHg. Finally, heart rate decreased by 27 +/- 6, 20 +/- 4, 18 +/- 4 and 13 +/- 5 heats per min as the propofol dose increased. The tonic firing of pontine neurons was minimally depressed by the lower two doses of propofol but higher doses did appear to depress their firing, demonstrating dose-dependence of actions of this anaesthetic.(ABSTRACT TRUNCATED AT 250 WORDS)