Effect of exogenous L-dopa on behavior in the rat: an in vivo voltammetric study.
L-DOPA was administered intraperitoneally (i.p.) or intraventricularly (i.v.t.) to freely moving rats to investigate the effects of exogenous L-DOPA itself on behavior. Striatal dopamine (DA) in the extracellular fluid was examined with microcomputer-controlled in vivo voltammetry, and behavioral change was observed. When L-DOPA was administered (i.p.) after pretreatment with benserazide, a peripheral DOPA decarboxylase inhibitor, behavioral change was elicited before the elevation in DA and suppressed before its reduction. After pretreatment with NSD-1015, a central DOPA decarboxylase inhibitor, behavioral change was also elicited, although DA was still not increased. When L-DOPA was injected (i.v.t.), the behavioral effect was manifested at once; DA was still unchanged at this time, but it increased after behavioral activity reached the maximum level. L-DOPA was also injected (i.v.t.) into rats with striatal lesions induced by 6-hydroxydopamine (i.v.t.). Behavioral change was manifested promptly after the injection. When the dose-response curves to different dosages of L-DOPA were examined in normal rats without striatal lesions, it was found to exhibit a steeper rise than that of DA. Finally, when rats were injected (i.p. or i.v.t.) with 3-O-methyl-DOPA (3-methoxytyrosine), a major metabolite of L-DOPA, no behavioral change was elicited, and no increase in DA was recognized. These experimental results indicated that L-DOPA is related directly to the manifestation of behavioral change.
Department of Neurology, Juntendo University School of Medicine, Tokyo, Japan.
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Nakazato
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Akiyama
D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D004298:Dopamine / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004563:Electrochemistry; D007274:Injections, Intraperitoneal; D007276:Injections, Intraventricular; D007980:Levodopa / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains
D015102:3,4-Dihydroxyphenylacetic Acid; D007980:Levodopa; D004298:Dopamine