title: Presynaptic effects of 2-aminotetralins on striatal dopaminergic neurons.
abstract: The present study evaluated whether 2-amino-5,6-dihydroxy-1,2,3,4,-tetrahydronaphthalene (A-5,6 DTN) and its 6,7-dihydroxy isomer (A-6,7 DTN) had effects on striatal dopaminergic terminals in addition to their well known action as agonists on postsynaptic dopamine (DA)-receptors. The presynaptic effects of 2-aminotetralins were evaluated on rat striatal tissue slices prelabeled with [3H]DA. Both, A-5,6 and A-6,7 DTN enhanced the basal efflux of radioactive products in a concentration-dependent fashion. Benztropine (1 microM) antagonized the releasing effects of low concentrations of both drugs (0.1-3.0 microM). Apomorphine and A-5,6 DTN (alpha rotamers, trans conformation) were 3 to 5 times more potent than A-6,7 DTN (beta rotamer, trans conformation) in inhibiting rat striatal monamine oxidase. This effect could account for the 50-fold greater potency of A-6,7 than A-5,6 DTN in enhancing the efflux of [3H]dihydroxyphenylacetic acid. A-5,6 DTN, A-6,7 DTN and apomorphine (0.3 microM each), reduced by 30% the depolarization elicited overflow of radioactive products. In summary, A-5,6 and A-6,7 DTN seem to enter DA-terminals and storage vesicles to accelerate the efflux of [3H]DA and 3H-dihydroxyphenylacetic acid and act upon presynapatic receptors to inhibit transmitter release. A greater selectivity for monamine oxidase inhibition was found with the alpha rotameric agents. The present study indicates that A-5,6 and A-6,7 DTN have marked presynaptic effects on rat striatal DA-containing neurons in addition to their well known effects as agonists on postsynaptic DA receptors.
mesh_terms: D015081:2-Naphthylamine / Q000031:analogs & derivatives / Q000494:pharmacology*; D000818:Animals; D001590:Benztropine / Q000494:pharmacology; D003342:Corpus Striatum / Q000187:drug effects* / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism; D008297:Male; D008995:Monoamine Oxidase / Q000032:analysis; D009281:Naphthalenes / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011954:Receptors, Dopamine / Q000187:drug effects*; D013764:Tetrahydronaphthalenes / Q000494:pharmacology*
chemical_list: D009281:Naphthalenes; D011954:Receptors, Dopamine; D013764:Tetrahydronaphthalenes; D001590:Benztropine; C006561:2-aminotetralin; D015081:2-Naphthylamine; D008995:Monoamine Oxidase; D011188:Potassium; D004298:Dopamine