Changes in dopamine receptors in mouse striatum following morphine treatments

Abstract

Presynaptic opiate receptors previously evidenced on striatal dopaminergic nerve-endings might mediate an inhibition of dopaminergic transmission by morphine. We have now assessed on behavioral and biochemical tests the development of disuse hypersensitivity to dopamine (DA) following morphine treatments. 1. 1. A long-lasting increase in behavioral responsiveness to apomorphine regarding the climbing behavior, a stereotyped motor behavior mediated by striatal DA receptors, is shown to develop after a single dose of morphine. However after chronic treatments the behavioral data are difficult to interpret. 2. 2. After an initial rise, striatal HVA levels are significantly depressed for several days. 3. 3. Binding of 3H-domperidone to striatal DA receptors is slightly enhanced. All these changes, although less marked, are reminiscent of those observed during typical hypersensitivity developing following chronic blockade of DA receptors by neuroleptics. The primary action of morphine on DA transmission is discussed.