FURTHER EVIDENCE FOR STIMULATION OF RAT-BRAIN DOPAMINE RECEPTORS BY A CYCLIC ANALOG OF DOPAMINE

In female rats anesthetized with urethane, extracellular recordings of action potentials were obtained from single neurons in the caudate nucleus using standard stereotaxic techniques. Iontophoretic ejection of drugs was used. All of the neurons were stimulated to fire by the continuous application of homocysteic acid. Dopamine caused complete inhibition of firing of the cells. Every neuron inhibited by dopamine was also completely inhibited by 2-amino-6,7-dihydroxy-1,2,3,4-tetra-hydronaphthalene (ADTN). ADTN was approximately equipotent with dopamine. Neurons not affected by dopamine were similarly insensitive to ADTN. Behavioral experiments were performed on adult male rats with unilateral lesions of the nigro-striatal pathway produced by the injection of 6-hydroxy-dopamine hydrobromide. Nine days after the induction of the lesion the rats were injected with 150 g ADTN into the lateral ventricle. The injections of ADTN were made unilaterally on the same side as the lesion. Each animal responded to ADTN with strong and long-lasting turning towards the innervated side.