A new electromyographic (EMG) method described by Bieger et al. (1972) was developed for the quantitative evaluation of narcotic analgesics in rats anesthetized with urethane. d-Amphetamine increased the amplitude and the frequency of myoclonic twitch activities (MTA) of suprahyoideal muscle. Morphine and several other narcotic analgesics antagonized the amphetamine-induced MTA and their relative inhibitory potency closely paralleled their analgesic potencies. Etorphine was 2000-3500 times more potent than morphine, while meperidine showed only 2% of the activity of morphine. Levorphanol was 3-4 times more potent than morphine, while dextrorphan was inactive. l-Methadone was 10 times as potent as d-methadone. The inhibition of MTA by morphine was completely reversed by naloxone. On the other hand, the inhibition of MTA by haloperidol or by pentobarbitone was not influenced by naloxone. The measurement of the EMG of suprahyoideal muscle in rats appears to provide a convenient test and reliable means to assess the central effect of narcotic analgesics.
Bibliographical noteFunding Information:
Acknowledgements-These studiesw erep artly supprtedb y the Medical Research Service, Veterans Administration and partly by NIMH Grant DA-00564 and U.S. Army ResearchC ontract DADA-17-73-C-3~6 (Both to H. H. Loh). Dr Loh is a recipiento f a NIMH ResearchS cientist DevelopmenAt ward, K2-DA-70554.
- myoclonic twitches
- narcotic analgesics
- potency ratios