title: Behavioral activity and stereotypy in rats induced by L-DOPA metabolites: a possible role in the adverse effects of chronic L-DOPA treatment of Parkinson's disease.
abstract: L-3,4-Dihydroxyphenylalanine (L-DOPA) is a common and effective treatment for Parkinson's disease, but dyskinesia continues to be a serious adverse effect with chronic use. Evidence suggests that L-DOPA induces increases in dopamine, which then binds to supersensitive dopamine receptors, resulting in dyskinesia. We have shown previously that L-DOPA directly causes stereotypy in rats, suggesting that chronic L-DOPA-induced dyskinesia is also caused by L-DOPA itself. This raises the possibility that other L-DOPA metabolites have a role in dyskinesia. We examined the behavioral effects of five L-DOPA metabolites (3-methoxytyramine, 3-MT; 3,4-dihydroxyphenylalanine, DOPAC; dopamine; homovanillic acid, and 3-o-methyl-DOPA) in rats. A unilateral, intracerebroventricular injection of 3-MT (10-200 microg, 40 microl) over 30 min, dose-dependently increased behavioral activity and stereotypy. This effect was suppressed by the dopamine D1/5-receptor antagonist SCH 23390, but not by the dopamine D2/3/4-receptor antagonist sulpiride. Dopamine denervation resulted in behavioral supersensitivity to 3-MT. Neither dopamine nor DOPAC levels increased in the striatum after 3-MT administration, as measured using in vivo voltammetry. The behavioral changes paralleled a rise in 3-MT in the contralateral striatum. DOPAC also caused behavioral changes and stereotypy, but to a smaller degree than 3-MT. Dopamine-denervated rats did not exhibit a supersensitive response to DOPAC, however. Other L-DOPA metabolites did not cause behavioral effects. These data suggest that 3-MT directly induced dopamine-D1/5-receptor-mediated behavioral changes in rats, and that 3-MT may have a role in dyskinesia due to chronic L-DOPA treatment in Parkinson's disease patients.
authors.affiliation: Department of Physiology, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. nakazato@med.juntendo.ac.jp
authors.forename: Taizo
authors.initials: T
authors.lastname: Nakazato
authors.forename: Akitane
authors.initials: A
authors.lastname: Akiyama
mesh_terms: D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D000978:Antiparkinson Agents / Q000009:adverse effects* / Q000378:metabolism / Q000494:pharmacology*; D001522:Behavior, Animal / Q000187:drug effects*; D001552:Benzazepines / Q000494:pharmacology; D004298:Dopamine / Q000031:analogs & derivatives* / Q000378:metabolism; D007276:Injections, Intraventricular; D007700:Kinetics; D007980:Levodopa / Q000009:adverse effects* / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D010300:Parkinson Disease / Q000150:complications* / Q000188:drug therapy*; D051381:Rats; D017208:Rats, Wistar; D013239:Stereotyped Behavior / Q000187:drug effects*
chemical_list: D000978:Antiparkinson Agents; D001552:Benzazepines; D015102:3,4-Dihydroxyphenylacetic Acid; D007980:Levodopa; C001746:3-methoxytyramine; D004298:Dopamine