Biphasic effect of locally applied apomorphine and 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine on the release of striatal dopamine investigated by means of brain dialysis.

The effects of 3 kinds of dopamine (DA) agonists, apomorphine (APO), 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine (SKF-38393) and quinpirole (QPL), on DA release were examined in the caudate-putamen of the freely moving rat by means of microdialysis during local administration of various concentrations of these DA agonists. Infusion of 10(-4) M and 10(-5) M concentrations of APO and 10(-5) M and 10(-6) M of SKF-38393 induced a brief increase in DA release followed by a marked decrease. This phenomenon was sensitive to tetrodotoxin (10(-6) M) infusion. On the other hand, all the tested doses of QPL, 10(-4) M, 10(-5) M, 10(-6) M and 10(-7) M, reduced DA release without showing transient increase.