[The effect of extradurally administered analgesics on somatosensory evoked eyelid microvibration in rabbits]

We examined the effect of various analgesics administered lumboextradurally or intravenously on acceleration of the eyelid microvibration (EMV) due to reflex contraction which was evoked by electrical stimulation of the sciatic and ulnar nerve in rabbits. No significant difference in the inhibition of EMV was observed initially between the sciatic nerve and the ulnar nerve stimulated group after 2 mg of morphine, administered either extradurally or intravenously. However, greater inhibition of EMV by the extradural morphine than by intravenous administration of this drug was observed after 10 min in sciatic nerve stimulated and after 20 min in the ulnar nerve stimulated group. With the extradural administration of 0.05 mg fentanyl, EMV was inhibited more significantly in the sciatic stimulated group than in the ulnar nerve stimulated group. Intravenous administration of this drug failed to reveal any change in either sciatic nerve stimulated or ulnar nerve stimulated group. When butorphanol 0.5 mg or buprenorphine 0.05 mg was administered, no significant difference in the inhibition of EMV was observed between the drugs, regardless of the routes of administration or sites of stimulation. Extradural administration of ketamine 0.5 mg showed none of the inhibition of EMV in both the sciatic nerve stimulated, and the ulnar nerve stimulated groups. These results indicate that various analgesics administered into the extradural space produced characteristic actions depending on the pharmacokinetic properties of each drug, locally and/or generally. In conclusion, monitoring of EMV can be a useful procedure for evaluation of the effect of analgesics.