title: Presynaptic and postsynaptic effects of the anesthetics sevoflurane and nitrous oxide in the human spinal cord.
abstract: BACKGROUND
  Reduced spinal excitability contributes to the suppression of movement responses to noxious stimuli during the anesthetic state. This study examines and compares presynaptic and postsynaptic effects of two anesthetics in the human spinal cord.
  
  
  METHODS
  The authors tested two parameters during the administration of 0.8 vol% sevoflurane or 40 vol% nitrous oxide compared with control states before and after drug administration: (1) the size of the soleus H reflex (integrating presynaptic and postsynaptic effects) at increasing stimulus intensities (recruitment curve) and (2) the amount of presynaptic inhibition on Ia afferents of the quadriceps femoris, evaluated by the heteronymous facilitation of the soleus H reflex caused by a conditioning stimulation of the femoral nerve. The study was performed in 10 subjects for each drug.
  
  
  RESULTS
  At the chosen concentrations, the maximum H reflex was reduced by 26.3 +/- 8.4% (mean +/- SD) during sevoflurane and by 33.5 +/- 15.6% during nitrous oxide administration. The averaged recruitment curves were similarly depressed under the influence of the two drugs. The reduction of H-reflex facilitation was significantly stronger for sevoflurane (28.8 +/- 20.0%) than for nitrous oxide administration (6.2 +/- 26.4%).
  
  
  CONCLUSIONS
  These results demonstrate in humans presynaptic effects of the volatile anesthetic sevoflurane but not of nitrous oxide. A possible explanation for this difference may be the different potency of the respective drugs in enhancing gamma-aminobutyric acid type A receptor-mediated inhibition, because presynaptic inhibition in the spinal cord involves this receptor subtype.
authors: Department of Anesthesiology, Charité- Universitätsmedizin Berlin, Berlin, Germany. jan.baars@charite.de
authors: Jan H
authors: JH
authors: Baars
authors: Michael
authors: M
authors: Benzke
authors: Falk
authors: F
authors: von Dincklage
authors: Josephine
authors: J
authors: Reiche
authors: Peter
authors: P
authors: Schlattmann
authors: Benno
authors: B
authors: Rehberg
mesh_terms: D000328:Adult; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D002245:Carbon Dioxide / Q000097:blood; D003627:Data Interpretation, Statistical; D005260:Female; D006181:H-Reflex / Q000187:drug effects; D006801:Humans; D016014:Linear Models; D008297:Male; D008738:Methyl Ethers / Q000494:pharmacology*; D018482:Muscle, Skeletal / Q000294:innervation; D009475:Neurons, Afferent / Q000187:drug effects; D009609:Nitrous Oxide / Q000494:pharmacology*; D017661:Receptors, Presynaptic / Q000187:drug effects*; D011999:Recruitment, Neurophysiological / Q000187:drug effects; D000077149:Sevoflurane; D013116:Spinal Cord / Q000187:drug effects*; D013569:Synapses / Q000187:drug effects*; D005680:gamma-Aminobutyric Acid / Q000502:physiology
chemical_list: D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D017661:Receptors, Presynaptic; D002245:Carbon Dioxide; D000077149:Sevoflurane; D005680:gamma-Aminobutyric Acid; D009609:Nitrous Oxide