title: Effect of differential delivery of isoflurane to head and torso on lumbar dorsal horn activity.
abstract: BACKGROUND
  The spinal cord appears to be the site where anesthetic agents prevent movement in response to noxious stimuli. When isoflurane is differentially delivered to the head and torso (with low torso concentrations), cranial anesthetic requirements increase compared with systemic administration. The aim of the current study was to test the hypothesis that isoflurane action in the brain has descending influences on spinal cord dorsal horn neurons. A secondary aim was to determine the association, if any, of high cranial concentrations of isoflurane (>6%) with dorsal horn activity.
  
  
  METHODS
  Ten goats were anesthetized with isoflurane and the carotid arteries and jugular veins isolated and cannulated for cerebral bypass. A laminectomy was performed for recording from single lumbar dorsal horn neurons with hind limb mechanical receptive fields (one cell per goat). A standard noxious mechanical stimulus was applied to the dew claw or hoof bulb during a control period with end-tidal isoflurane at 1.3% and during bypass with the following head/torso isoflurane concentrations: 1.3%/1.3%, 3.2%/1.3%, 9.4%/1.3%, 1.3%/0.2%, 3.0%/0.2% and 8.8%/0.3%.
  
  
  RESULTS
  When torso isoflurane concentration was 1.3%, increasing cranial isoflurane concentration to 3% or 9% had no significant effect on the activity of dorsal horn units. When torso isoflurane was 0.2-0.3%, spontaneous activity increased; however, at these torso concentrations, evoked responses were significantly decreased (-60%) only when cranial isoflurane concentration was increased to 9%.
  
  
  CONCLUSIONS
  Isoflurane action in the brain had an inhibitory effect on dorsal horn activity with the combination of supraclinical cranial and low torso concentrations.
authors.affiliation: Department of Anesthesiology, University of California, Davis, 95616, USA. jfantognini@ucdavis.edu
authors.forename: J F
authors.initials: JF
authors.lastname: Antognini
authors.forename: E
authors.initials: E
authors.lastname: Carstens
authors.forename: E
authors.initials: E
authors.lastname: Tabo
authors.forename: V
authors.initials: V
authors.lastname: Buzin
mesh_terms: D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006041:Goats; D007530:Isoflurane / Q000008:administration & dosage / Q000494:pharmacology*; D008161:Lumbosacral Region; D013116:Spinal Cord / Q000187:drug effects*; D013126:Spinal Nerve Roots / Q000187:drug effects
chemical_list: D018685:Anesthetics, Inhalation; D007530:Isoflurane