Akira Osada1,2, Yoshihisa Fujino1,2, Jun Chen1,2, Natsu Koyama1,2. 1. Department of Anesthesiology, Shiga University of Medical Science, Seta Tsukinowa-cho, 520-21, Otsu, Japan. 2. Department of Physiology, Shiga University of Medical Science, Seta Tsukinowa-cho, 520-21, Otsu, Japan.
Abstract
PURPOSE: To clarify whether ketamine suppresses both A-fiber-and C-fiber-mediated pain and to compare the effects of ketamine with those of MK-801. METHODS: Experiments were performed on urethane/chloralose-anesthetized cats. Glass capillary microelectrodes were used to record extracellular single unit activities from wide dynamic range (WDR) neurons in the spinal dorsal horn. Responses evoked by electrical stimulation of the superficial peroneal (SP), posterior tibial (PT), or both nerves were analyzed. The responses to successive electrical stimuli were displayed on a personal computer using a raster-dot processing program. RESULTS: A subanesthetic dose of intravenous ketamine suppressed both A- and C-fiber responses of WDR neurons in a dose-dependent manner without affecting A-fiber response of low-threshold mechanoreceptive (LTM) neurons. The C-fiber response was more markedly suppressed than the A-fiber response. Intravenous administration of MK-801, a specificN-methyl-D-aspartate (NMDA) antagonist, selectively suppressed the C-fiber response of WDR neurons. CONCLUSION: Intravenous ketamine may suppress both A-and C-fiber-mediated pain at a subanesthetic dose. This finding could be a scientific basis for the usefulness of ketamine during clinical procedures such as dressing changes or débridement of the burned patient.
PURPOSE: To clarify whether ketamine suppresses both A-fiber-and C-fiber-mediated pain and to compare the effects of ketamine with those of MK-801. METHODS: Experiments were performed on urethane/chloralose-anesthetized cats. Glass capillary microelectrodes were used to record extracellular single unit activities from wide dynamic range (WDR) neurons in the spinal dorsal horn. Responses evoked by electrical stimulation of the superficial peroneal (SP), posterior tibial (PT), or both nerves were analyzed. The responses to successive electrical stimuli were displayed on a personal computer using a raster-dot processing program. RESULTS: A subanesthetic dose of intravenous ketamine suppressed both A- and C-fiber responses of WDR neurons in a dose-dependent manner without affecting A-fiber response of low-threshold mechanoreceptive (LTM) neurons. The C-fiber response was more markedly suppressed than the A-fiber response. Intravenous administration of MK-801, a specificN-methyl-D-aspartate (NMDA) antagonist, selectively suppressed the C-fiber response of WDR neurons. CONCLUSION: Intravenous ketamine may suppress both A-and C-fiber-mediated pain at a subanesthetic dose. This finding could be a scientific basis for the usefulness of ketamine during clinical procedures such as dressing changes or débridement of the burned patient.
Entities:
Keywords:
Analgesia; Ketamine; MK-801; NMDA antagonist; Wide dynamic range neuron