Endogenously released L-dopa itself tonically functions to potentiate postsynaptic D2 receptor-mediated locomotor activities of conscious rats.
A non-effective dose of exogenously applied L-dopa itself stereoselectively potentiates postsynaptic D2 receptor-mediated locomotor activities of rats. We further attempted to clarify whether or not endogenously released L-dopa tonically functions to potentiate activities of these receptors, simultaneously monitoring locomotor activities and basal release of L-dopa and dopamine during striatal microdialysis in conscious rats. Quinpirole (1 mg/kg, s.c.) alone, a selective D2 agonist, increased locomotor activities and decreased basal L-dopa and dopamine release 20-140 min after injection. Pretreatment with alpha-methyl-p-tyrosine (3 mg/kg, i.p.), a tyrosine hydroxylase inhibitor, decreased locomotor activities and further decreased L-dopa release without modification of dopamine release, compared to quinpirole alone, whereas 3-hydroxybenzylhydrazine (100 mg/kg, i.p.), a central dopa decarboxylase inhibitor, further increased locomotor activities and markedly increased L-dopa release without modification of dopamine release. Endogenously released L-dopa itself functions tonically to potentiate activities of postsynaptic D2 receptors relevant to locomotor movement of rats.
Yue
J L
JL
Department of Pharmacology, Yokohama City University School of Medicine, Japan.
Nakamura
S
S
Ueda
H
H
Misu
Y
Y
D000818:Animals; D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D004295:Dihydroxyphenylalanine / Q000378:metabolism / Q000502:physiology*; D004298:Dopamine / Q000378:metabolism; D015259:Dopamine Agents / Q000494:pharmacology; D004873:Ergolines / Q000494:pharmacology; D006834:Hydrazines / Q000494:pharmacology; D008297:Male; D008781:Methyltyrosines / Q000494:pharmacology; D017551:Microdialysis; D009043:Motor Activity / Q000187:drug effects*; D019257:Quinpirole; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000187:drug effects / Q000502:physiology*; D013237:Stereoisomerism; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors; D019805:alpha-Methyltyrosine
D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D015259:Dopamine Agents; D004873:Ergolines; D006834:Hydrazines; D008781:Methyltyrosines; D017448:Receptors, Dopamine D2; D019257:Quinpirole; D004295:Dihydroxyphenylalanine; D019805:alpha-Methyltyrosine; C004297:3-hydroxybenzylhydrazine; D014446:Tyrosine 3-Monooxygenase; D004298:Dopamine