The relationship between opioid actions and L-type calcium channel blockers has been well documented.However,there is no report relevant to L-type calcium channel blockers and morphinesensitization,which is suggested to be an analog of behaviors that are the characteristics of drug addiction.Here the effects of three L-type calcium channel blockers,nimodipine,nifedipine and verapamil,on morphine-induced locomotor activity,the development and the expression of sensitization to morphine were studied systematically.The results showed that both nimodipine and verapamil attenuated,while nifedipine had only a tendency to decrease morphine-induced locomotor activity.All the three drugs inhibited the development of sensitization to morphine.However,none of them showed any effects on the expression of morphine sensitization.These results indicate that blocking L-tpye calcium channel attenuates the locomotor stimulating effects of morphine and inhibits the development but not the expression of morphine-sensitization.
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