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ANESTHETIC PHARMACOLOGY

Neurons in the Ventral Spinal Cord Are More Depressed by Isoflurane, Halothane, and Propofol Than Are Neurons in the Dorsal Spinal Cord

JongBun Kim, MD, PhD^*, Aubrey Yao, MD^*, Richard Atherley, BS^*, Earl Carstens, PhD, Steven L. Jinks, PhD^*, and Joseph F. Antognini, MD^*

From the *Department of Anesthesiology and Pain Medicine, University of California, Davis, California; Department of Anesthesia and Pain Medicine, Catholic University of Korea, Seoul, Korea; and Section of Neurobiology, Physiology and Behavior, University of California, Davis, California.

Address correspondence and reprint requests to Joseph F. Antognini, MD, Department of Anesthesiology, TB-170, University of California, Davis, Davis, CA 95616. Address e-mail to jfantognini{at}ucdavis.edu.

BACKGROUND: Volatile anesthetics act primarily in the spinal cord to produce immobility but their exact site of action is unclear. Between 0.8 and 1.2 minimum alveolar anesthetic concentration (MAC), isoflurane does not depress neurons in the dorsal horn, suggesting that it acts at a more ventral site within the spinal cord such as in premotor interneurons and motoneurons. We hypothesized that isoflurane, halothane, and propofol would exert a greater depressant effect on nociceptive responses of ventral horn neurons when compared with dorsal horn neurons.

METHODS: Rats were anesthetized with isoflurane or halothane and responses of dorsal (<1200 µm deep) and ventral (>1200 µm) lumbar neurons to noxious mechanical stimulation of the hindpaw were determined at 0.8 and 1.2 MAC. In a third group anesthetized with isoflurane at 0.8 MAC, we administered 5 mg/kg propofol while recording responses from dorsal horn or ventral horn neurons.

RESULTS: Dorsal horn neuronal responses were not significantly affected when either isoflurane or halothane was increased from 0.8 to 1.2 MAC; propofol also had no significant effect. On the other hand, with increased isoflurane or halothane concentration, responses of ventral horn neurons were depressed by 60% and 45%, respectively. Propofol profoundly depressed (>90%) ventral horn neurons.

CONCLUSIONS: These data suggest that, in the peri-MAC range, isoflurane, halothane, and propofol have little or no effect on neuronal responses to noxious mechanical stimulation in the spinal dorsal horn but depress such responses in the ventral horn. Immobility produced in the 0.8–1.2 MAC range by these anesthetics appears to result from a depressant action in the ventral horn.

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				R. D. Sanders, J. Xu, Y. Shu, A. Fidalgo, D. Ma, and M. Maze General Anesthetics Induce Apoptotic Neurodegeneration in the Neonatal Rat Spinal Cord Anesth. Analg., June 1, 2008; 106(6): 1708 - 1711. [Abstract] [Full Text] [PDF]

				A. Yao, J. Kim, R. Atherley, S. L. Jinks, E. Carstens, S. Shargh, A. Sulger, and J. F. Antognini The Effects of Aromatic Anesthetics on Dorsal Horn Neuronal Responses to Noxious Stimulation Anesth. Analg., June 1, 2008; 106(6): 1759 - 1764. [Abstract] [Full Text] [PDF]

Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999