Propofol Inhibits Neuronal Firing Activities in the Caudal Ventrolateral Medulla

Background: Propofol is a potent intravenous anesthetic. The action of propofol on the medullary depressor area, the caudal ventrolateral medulla (CVLM), has not been well established. We therefore performed extracellular recordings to study the neuronal activity of the CVLM in cats before and after intravenous propofol administration, to investigate its influence on neuronal firings. Methods: Experiments were performed on 31 cats anaesthetized with a mixture of α-chloralose and urethane administered intraperitoneally. Mean systemic arterial pressure, heart rate, and the neuronal firing (NF) rate were continuously recorded before and after intravenous injection of a single dose of 2 mg.kg^-1 propofol or separate supplemental doses of 1, 2, and 4 mg.kg^-1 propofol until those parameters had returned to the premedication level. Results: Propofol dose-dependently and reversibly inhibited the NF rate after the supplemental doses of 1, 2, and 4 mg.kg ^-1 propofol. The control NF rate of 17.9 ± 8.6 Hz was depressed to 15.8 ± 8.5 Hz after the first dose of propofol (p < 0.05 vs. the control), and was further depressed to 12.8 ± 8.3 Hz (p < 0. 05 vs. the control) and 10.0 ± 7.9 Hz (p < 0.05 vs. the control) after the second and the third doses of propofol, respectively. Conclusion: The dose-dependent inhibition of the spontaneous neuronal firing rate is the main pharmacological action of propofol in the caudal ventrolateral medulla of cats.