Differential effect of systemic administration of bromocriptine and L-dopa on the release of acetylcholine from striatum of intact and 6-OHDA-treated rats.
A presumed balance between striatal dopaminergic and cholinergic systems forms a major theoretical framework for the development of new agents for the treatment of Parkinson's disease. We therefore studied the effect of two drugs currently used as anti-parkinsonian agents, bromocriptine (BROMO) and L-beta-3,4-dihydroxyphenylalanine (L-DOPA), on the release of striatal acetylcholine (ACh) in intact and 6-hydroxy-dopamine-treated rats using in vivo microdialysis. Lesioned rats with a > 90% tissue depletion of striatal dopamine (DA) had a significantly higher output of striatal ACh than unlesioned rats (88 fmol/min vs. 52 fmol/min; 0.3 mumol/l neostigmine in perfusate). BROMO (4 mg/kg) inhibited the output of striatal ACh in both groups. Whereas the lowest dose of L-DOPA (50 mg/kg) potently stimulated ACh output in lesioned rats, unlesioned rats were significantly less responsive. A higher dose of L-DOPA (100 mg/kg) stimulated ACh output to the same extent in both groups. At the highest dose tested, L-DOPA (200 mg/kg) given to intact rats did not further increase striatal ACh output. Thus, BROMO decreases whereas L-DOPA increases striatal ACh release after systemic application. Therapeutic as well as side effects of L-DOPA may therefore be mediated by neurochemical alterations that are more complex than previously thought.
DeBoer
P
P
Center for Molecular and Behavioral Neuroscience, Aidekman Research Center, Rutgers University, Newark, NJ 07102.
Abercrombie
E D
ED
Heeringa
M
M
Westerink
B H
BH
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology*; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism*; D003956:Dialysis; D007980:Levodopa / Q000494:pharmacology*; D008297:Male; D016627:Oxidopamine / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
D001971:Bromocriptine; D007980:Levodopa; D016627:Oxidopamine; D000109:Acetylcholine