title: Thiopental directly depresses lumbar dorsal horn neuronal responses to noxious mechanical stimulation in goats.
abstract: BACKGROUND
  Thiopental has hypnotic actions in the brain, but it also depresses nociceptive transmission. In this study we examined whether thiopental had direct (spinal) and/or indirect (supraspinal) effects on the responses of single lumbar dorsal horn neurons to noxious mechanical stimulation, using a method to deliver thiopental differentially to either the torso or cranial circulation in goats.
  
  
  METHODS
  Goats (n=10) were anesthetized with isoflurane and neck dissections performed to permit cranial bypass. A lumbar laminectomy was made to permit single-unit recording of lumbar dorsal horn neuronal activity (1-2 neurons/animal). Isoflurane was maintained at 0.8+/-0.1% to both head and torso throughout the study. During cranial bypass, thiopental was separately administered to the torso (low dose, 1.5+/-0.5 mg/kg; high dose, 3.7+/-0.5 mg/kg) or cranial (low dose, 0.12+/-0.03 mg/kg; high dose, 0.2 mg/kg) circulation.
  
  
  RESULTS
  Thiopental administered to the torso significantly depressed dorsal horn neuronal responses to noxious stimulation at the high dose: 757+/-471 to 392+/-305 impulses/min at 1 min post-injection, P<0.006 (n=14); evoked responses recovered at 5 min post-injection. At the low dose, there was a similar numerical decrease, but this did not reach significance: 876+/-780 to 407+/-499 impulses/min at 1 min post-injection, P>0.05 (n=6). No significant change was observed when thiopental was administered to the cranial circulation: low dose, 1061+/-1167 to 965+/-874 impulses/min at 1 min post-injection, P>0.05 (n=10); high dose, 864+/-331 to 917+/-525 impulses/min at 1 min post-injection, P>0.05 (n=8).
  
  
  CONCLUSIONS
  Thiopental has a direct (spinal) depressant effect on dorsal neuronal responses to noxious stimulus, but no significant supraspinal effect.
authors.affiliation: Department of Anesthesiology and Resuscitology, Ehime University School of Medicine, Ehime, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Sudo
authors.forename: S
authors.initials: S
authors.lastname: Sudo
authors.forename: X G
authors.initials: XG
authors.lastname: Chen
authors.forename: M
authors.initials: M
authors.lastname: Piercy
authors.forename: E
authors.initials: E
authors.lastname: Carstens
authors.forename: J F
authors.initials: JF
authors.lastname: Antognini
mesh_terms: D018686:Anesthetics, Intravenous / Q000493:pharmacokinetics / Q000494:pharmacology*; D000818:Animals; D001784:Blood Gas Analysis; D001786:Blood Glucose / Q000378:metabolism; D003326:Coronary Circulation / Q000187:drug effects; D003864:Depression, Chemical; D006041:Goats; D006400:Hematocrit; D010146:Pain / Q000517:prevention & control*; D010147:Pain Measurement / Q000187:drug effects; D010812:Physical Stimulation; D020671:Posterior Horn Cells / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects; D013874:Thiopental / Q000493:pharmacokinetics / Q000494:pharmacology*
chemical_list: D018686:Anesthetics, Intravenous; D001786:Blood Glucose; D013874:Thiopental