Neurochemical and behavioral evidence for a selective presynaptic dopamine receptor agonist

A new dopamine analog, 6,7-dihydroxy-2-dimethylaminotetralin (TL-99), was compared to apomorphine in three tests of dopaminergic function in the central nervous system. The tests, performed on rats, included production of changes in locomotor activity (involving both presynaptic and postsynaptic receptors), inhibition of dopa accumulation (quantifying presynaptic receptor activity), and the rotation model (quantifying postsynaptic receptor activation). Apomorphine was efficacious at both presynaptic and postsynaptic receptors, whereas TL-99 was much more efficacious at the presynaptic receptor. This result indicates not only that differences exist between presynaptic and postsynaptic dopamine receptors, but also that these differences may be exploited in the design of selective dopamine agonists.