A specific benzodiazepine antagonist CGS 8216 reverses the muscle relaxant effect of diazepam but not that of phenobarbitone.

The muscle relaxant effects of diazepam and phenobarbitone were studied in mutant Han-Wistar rats which exhibit spontaneous tonic activity in the electromyogram of the gastrocnemius-soleus muscle. Diazepam and phenobarbitone significantly and dose- relatedly reduced the spontaneous activity measured in the electromyogram. The benzodiazepine receptor antagonist CGS 8216 reversed the depressant effect of diazepam but not that produced by phenobarbitone. The results add further support to the suggestion that CGS 8216 may be useful to investigate the effects modified by benzodiazepine receptors in vivo.