EFFECTS OF METHAMPHETAMINE, DOPAMINE AND NORADRENALINE ADMINISTERED INTO THE NUCLEUS-ACCUMBENS OF RATS DISCRIMINATING SUBCUTANEOUS METHAMPHETAMINE

Since the nucleus accumbens has been hypothesized to centrally mediate the discriminative effects of psychomotor stimulants, the discriminat ive effects of methamphetamine (MA) as well as dopamine (DA) and norad renaline (NA) were observed by intracerebral administration of these d rugs into the nucleus accumbens in rats discriminating subcutaneous MA from saline. These rats were trained and maintained to discriminate b etween MA at 0.5 mg/kg, s.c. and saline under a fixed ratio 10 schedul e for food reinforcement in a 2-lever operant chamber situation. Guide cannulae were implanted bilaterally into the nucleus accumbens. In th e substitution tests, the drug was administered into the nucleus accum bens. MA at 10 mu g per rat substituted for subcutaneous MA in 4 out o f 5 rats but neither DA at 10-40 mu g per rat (n=7) nor NA at 10-40 mu g per rat (n=4) substituted for subcutaneous MA. On the other hand, t he same drugs administered into the nucleus accumbens induced increase d spontaneous motor activity as also observed in six other untrained r ats. MA, DA or NA alone each at 10 mu g per rat increased spontaneous motor activity. The discriminative effects of MA are considered to be mediated in the nucleus accumbens of rats. Although DA or NA alone adm inistered into the nucleus accumbens showed similar increasing motor a ctivity effects as those of MA, the discriminative effects of exogenou s DA or NA alone administered into the same brain area were different from those of MA in the present experimental condition.