Brainstem regions affecting minimum alveolar concentration and movement pattern during isoflurane anesthesia.
BACKGROUND
Spinal transection or selective delivery of volatile anesthetics to the spinal cord reduces minimum alveolar concentration (MAC), whereas precollicular decerebration does not. The authors sought to determine which brainstem regions influence anesthetic requirements and movement responses with isoflurane.


METHODS
Movement (biceps femoris electromyogram) and MAC were measured in adult rats before and after decerebration at the precollicular, mid-collicular, pontine or medullary level, or decerebellation. Additional experiments assessed the effects of lidocaine inactivation of the mesencephalic locomotor region on MAC and the effects of isoflurane on nociceptive neuronal responses in this region.


RESULTS
Transections placed at the level of the mid-colliculus, rostral pons, and pontomedullary junction significantly reduced MAC by approximately 10, 40, and 45%, respectively. MAC was decreased 9% after mid-medullary transections that were placed caudal to the nucleus raphe magnus but rostral to the dorsal reticular nucleus; however, only weak, single movements occurred. Caudal medullary transections at the obex decreased MAC by 60%. Bilateral inactivation of the mesencephalic locomotor region with lidocaine caused a reversible, 32% decrease in MAC and reduced the number and amplitude of movements at sub-MAC isoflurane concentrations. Neuronal responses of mesencephalic locomotor region neurons to supramaximal noxious tail clamp were reduced by 87% by 1.2 MAC isoflurane.


CONCLUSIONS
The authors conclude that the mesencephalic locomotor region influences anesthetic requirements and promotes repetitive movement with sub-MAC isoflurane by facilitating ventral spinal locomotor circuits, where anesthetics seem to exert their key immobilizing effects. However, net brainstem influences on MAC seem to result from interaction among descending nociceptive and locomotor modulatory pathways.
Jinks
Steven L
SL
Department of Anesthesiology and Pain Medicine, University of California-Davis School of Medicine, Davis, CA 95616, USA. sljinks@ucdavis.edu
Bravo
Milo
M
Satter
Omar
O
Chan
Yuet-Ming
YM
D000758:Anesthesia; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D001933:Brain Stem / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D004576:Electromyography; D007530:Isoflurane / Q000494:pharmacology*; D008012:Lidocaine / Q000008:administration & dosage / Q000494:pharmacology; D008124:Locomotion / Q000502:physiology; D008297:Male; D008845:Microinjections; D009068:Movement / Q000187:drug effects*; D009434:Neural Pathways / Q000187:drug effects; D009474:Neurons / Q000187:drug effects; D010812:Physical Stimulation; D011650:Pulmonary Alveoli / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D018685:Anesthetics, Inhalation; D000779:Anesthetics, Local; D008012:Lidocaine; D007530:Isoflurane