Effect of yohimbine on amitraz-induced CNS depression and bradycardia in dogs.

Yohimbine was studied to examine its effectiveness in preventing central nervous system(CNS) depression and bradycardia induced by amitraz (N'-(2,4-dimethylphenyl)-N-[(2,4-dimethylphenyl-imino)-methyl]-N-methyl- methanimide). In control open-field activity experiments, the dogs showed high numbers of grid-line crossings in the first 5 min (exploratory phase), and subsequently low numbers of grid-line crossings (nonexploratory phase). An iv injection of amitraz (1 mg/kg) abolished both the exploratory and nonexploratory phases and caused bradycardia. Yohimbine alone caused a trend to increase the open-field activity in the nonexploratory phase. In addition, yohimbine prevented the bradycardia and suppression of open-field activity induced by amitraz. The results suggest that yohimbine has a potential to be used as an antidote for amitraz overdose.