Effects of yohimbine and naltrexone in counteraction of the morphine straub tail and the amphetamine-potentiated morphine straub tail in mice

The alpha-adrenergic blocking agent, yohimbine, prevented the production of the morphine Straub tail reaction in mice, although on a mg dose basis it was only about $\text{1}\text{400}$ as potent as the narcotic antagonist naltrexone by subcutaneous injection. Likewise, yohimbine prevented the potentiation of the morphine Straub tail reaction by amphetamine, being about $\text{1}\text{170}$ as active as naltrexone. Preliminary studies with another alpha-adrenergic blocking agent, phentolamine, indicated that it also inhibited the production of the Straub tail reaction by morphine, although it appeared to be somewhat weaker than yohimbine in this respect. These results suggest the involvement of alpha-adrenergic mechanisms in the production of the morphine Straub tail reaction and in the potentiation of the morphine Straub tail reaction by amphetamine.