Dopamine release within forebrain sites perfused with tetrahydroisoquinolines or tryptoline in the rat

The localized effect of amine-aldehyde condensation products on the endogenous release of dopamine (DA) was examined in dopaminergic-rich areas of the brain. In the unanesthetized rat, dopaminergic stores were labeled by 14C-dopamine (1.0 microCi) microinjected in a volume of 1.0 microliters into the caudate nucleus, tuberculum olfactorium, nucleus accumbens or other contiguous sites within the ventral forebrain. Subsequently, each labeled site was locally perfused with an artificial CSF, by means of push-pull cannulae, at a rate of 25.0 microliters per min. Two tetrahydroisoquinolines, tetrahydropapaveroline and 4,6,7-TH-tetrahydroisoquinoline, as well as the tetrahydro-beta-carboline, tryptoline, significantly enhanced the release of 14C-DA when each alkaloid metabolite was perfused in a concentration of 250 nanograms per min. Tetrahydroisoquinoline was without effect on the local kinetics of 14C-DA, whereas salsolinol had an intermediary action on DA release. These findings suggest that an alkaloid conjugate when given in the cerebral ventricle could exert its central effects by way of a dopaminergic mechanism in the telencephalon.