Non-effective dose of exogenously applied L-dopa itself stereoselectively potentiates postsynaptic D2 receptor-mediated locomotor activities of conscious rats.
We attempted to clarify whether or not under inhibition of central dopa decarboxylase non-effective i.p. doses of L-dopa potentiate D2 receptor-mediated locomotor activities without conversion to dopamine in normal and i.v.t. 6-hydroxydopamine-treated rats. In normal rats, only the highest dose of quinpirole, a selective D2 agonist, at ranges used (0.01-1 mg/kg, s.c.) slightly increased the total counts of locomotor activities for 140 min after injection. A simultaneously injected non-effective dose of L-DOPA (30 mg/kg) potentiated locomotor activities by quinpirole (0.1 and 1 mg/kg). L-dopa potentiated quinpirole (1 mg/kg)-induced locomotor activities 90 to 140 min after the injection with marked increase in basal release of L-DOPA without increase in dopamine release simultaneously monitored during striatal microdialysis, compared to quinpirole alone. D-dopa (30 mg/kg) produced no potentiation. In 6-hydroxydopamine-treated rats, a non-effective dose of L-dopa (10 mg/kg) also potentiated quinpirole (0.3 mg/kg)-induced locomotor activities. L-dopa acting on a recognition site for itself stereoselectively potentiates postsynaptic D2 receptor-mediated locomotor activities of rats.
Nakamura
S
S
Department of Pharmacology, Yokohama City University School of Medicine, Japan.
Yue
J L
JL
Goshima
Y
Y
Miyamae
T
T
Ueda
H
H
Misu
Y
Y
D000818:Animals; D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D003891:Desipramine / Q000494:pharmacology; D015259:Dopamine Agents / Q000494:pharmacology; D004873:Ergolines / Q000494:pharmacology; D006834:Hydrazines / Q000494:pharmacology; D007276:Injections, Intraventricular; D007980:Levodopa / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D017551:Microdialysis; D009043:Motor Activity / Q000187:drug effects*; D009412:Nerve Fibers / Q000187:drug effects; D016627:Oxidopamine / Q000008:administration & dosage / Q000494:pharmacology; D019257:Quinpirole; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000187:drug effects*; D013237:Stereoisomerism
D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D015259:Dopamine Agents; D004873:Ergolines; D006834:Hydrazines; D017448:Receptors, Dopamine D2; D019257:Quinpirole; D007980:Levodopa; D016627:Oxidopamine; C004297:3-hydroxybenzylhydrazine; D003891:Desipramine