Proprioceptive function is more sensitive than motor function to desflurane anesthesia.
BACKGROUND
Evaluating the effects of sub-immobilizing anesthetic doses on movement will identify target neural circuits for investigation as sites of action for anesthetic-induced immobility.


METHODS
Eleven pithed Northern Leopard frogs received 0, 0.4, 0.8, and 1.2 times the 50% effective dose for production of immobility (ED(50)) of desflurane and a further 7 received 0 and 0.4 ED(50) desflurane in random order. An electric stimulus applied to the forelimb elicited a hindlimb wiping reflex that was captured on video for later analysis. Isometric tension developed in the hindlimb during the 30 s stimulus application was measured.


RESULTS
Compared to 0 ED(50), 0.4 ED(50) desflurane significantly increased latency to wipe 0.8 (0.1, 4.0) to 17.3 (0.4, 30.0) s (median [min max]), distance traveled by the hindfoot 0.42 (0.09, 1.82) to 0.89 (0.16, 4.82) m, and proximity of the hindfoot to stimulus 1 (0, 5) to 7 (1, 40) mm. It did not alter hindlimb maximum velocity or isometric tension but significantly reduced total hindlimb force 7.3 (1.7, 23.6) to 3.2 (1.4, 13.8) N. s proportionate to a reduced number of movements from 12 (3, 28) to 8 (2, 14). From 0.4 to 0.8 ED(50,) motor depressant effects of desflurane became apparent with significant reductions in maximum tension from 2.0 (0.6, 5.5) to 0.8 (0.1, 1.6) N and total force from 3.2 (1.4, 13.8) to 0.9 (0.0, 2.5) N.s.


CONCLUSIONS
Proprioceptive function is more sensitive to anesthetic-induced depression than motor function in frogs. This suggests that the most anesthetic-sensitive component of the spinal neural circuitry underlying movement generation in response to noxious stimulus is prior to the level of the motoneuron.
Barter
Linda S
LS
Department of Anesthesiology and Pain Medicine, University of California, Davis, CA, USA. lsbarter@ucdavis.edu
Mark
Laurie O
LO
Antognini
Joseph F
JF
D000758:Anesthesia; D000769:Anesthesia, Inhalation; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D000077335:Desflurane; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D006614:Hindlimb / Q000294:innervation / Q000502:physiology; D007530:Isoflurane / Q000031:analogs & derivatives* / Q000494:pharmacology; D007537:Isometric Contraction; D009046:Motor Neurons / Q000187:drug effects; D009068:Movement / Q000187:drug effects*; D011434:Proprioception / Q000187:drug effects*; D011894:Rana pipiens; D012018:Reflex / Q000187:drug effects
D018685:Anesthetics, Inhalation; D000077335:Desflurane; D007530:Isoflurane