Functional studies with the opioid peptide dynorphin: acute effects of injections into the substantia nigra reticulata of naive rats.

When injected into the substantia nigra reticulata of naive rats, dynorphin-(1-17) caused a dose dependent contralateral rotation which was inhibited by naloxone in a dose dependent manner. Met-enkephalin injected in the same coordinates as the ones used with dynorphin also induced rotation but of lower intensity, while Leu-enkephalin did not elicit any significant response at the doses tested. D-amphetamine, injected subcutaneously 60 min after dynorphin, significantly enhanced the contralateral rotation induced by the intranigral administration of dynorphin. Experiments with dynorphin injections combined with D-amphetamine suggest that the dynorphin effects are mediated by neuronal loops involving dynorphin dopamine interactions.