Propofol directly depresses lumbar dorsal horn neuronal responses to noxious stimulation in goats

Purpose: We tested the hypothesis that propofol, acting in the brain, would either enhance, or have no effect, on lumbar dorsal horn neuronal responses to a noxious mechanical stimulus applied to the hindlimb. We recorded the response of lumbar dorsal horn neurons during differential delivery of propofol to the brain and torso of goats. Methods: Goats were anesthetized with isoflurane and neck dissections performed which permitted cranial bypass. A laminectomy was made to allow microelectrode recording of lumbar dorsal horn neuronal activity. Isoflurane was maintained at 0.8 +/- 0.1% to both head and torso throughout the study. During cranial bypass propofol was separately administered to the torso (1 mg.kg(-1), n=7; 3.75 mg.kg(-1), n=8) or cranial (0.04 mg.kg(-1), n=7; 0.14 mg.kg(-1), n=8) circulations. Results: Propofol administered to the torso depressed dorsal horn neuronal responses to noxious stimulation: low dose: 500 +/- 243 to 174 +/- 240 impulses.min(-1) at one minute post-injection, P < 0.001; high dose: 478 +/- 204 to 91 +/- 138 impulses.min(-1) at one minute post-injection, P < 0.05). Propofol administered to the cranial circulation had no effect: low dose: 315 +/- 150 to 410 +/- 272 impulses.min(-1), P > 0.05; high dose: 462 +/- 261 to 371 +/- 196 impulses.min(-1), P > 0.05. Conclusions: These data indicate that propofol has a direct depressant effect on dorsal horn neuronal responses to noxious stimulation, with little or no indirect supraspinal effect.