The effect of microinjections of morphine and haloperidol into the neostriatum and the nucleus accumbens on self-stimulation behaviour.

The effect of stereotaxic injections of morphine and haloperidol via permanently implanted cannulas into the neostriatum, the nucleus accumbens or the ventricular system was studied on self-stimulation behaviour of rats with electrodes implanted into the ventral tegmentum. The self-stimulation rate was depressed by injections of haloperidol into the neostriatum or into the nucleus accumbens. Unilateral injections of haloperidol into the neostriatum depressed the self-stimulation rate either with applications ipsilateral to the electrode or contralateral to the electrode. Bilateral applications of haloperidol into the neostriatum (2 X 2.5 mug) were more effective as unilateral applications (5 mug) and were more effective as applications into the ventricular system (5 mug). Morphine had a strong depressant action on self-stimulation when applied into the ventricular system and was ineffective when applied into the neostriatum. It is concluded that these results do not favour the hypothesis that morphine interferes with dopaminergic transmission with the neostriatum.