Journal of Neuroscience, Vol 8, 2361-2370, Copyright © 1988 by Society for Neuroscience
Chronic treatment with dopamine receptor antagonists: behavioral and pharmacologic effects on D1 and D2 dopamine receptors
EJ Hess, AB Norman and I Creese
Center for Molecular and Behavioral Neuroscience, Rutgers State University of New Jersey, Newark 07102.
Rats were treated for 21 d with the selective D1 dopamine receptor
antagonist SCH23390, the selective D2 dopamine receptor antagonist
spiperone, the nonselective dopamine receptor antagonist cis- flupentixol,
or a combination of SCH23390 and spiperone. In addition, a group of rats
received L-prolyl-L-leucyl-glycinamide (PLG) for 5 d after the 21 d chronic
spiperone treatment. Chronic treatment with SCH23390 resulted in a
significant increase in D1 dopamine receptor density with no change in the
D2 dopamine receptor density. Conversely, spiperone treatment resulted in a
significant increase in D2 dopamine receptors and no change in D1 dopamine
receptor density. PLG treatment had no effect. SCH23390 plus spiperone
treatment resulted in a significant increase in both D1 and D2 dopamine
receptor densities. However, although in vitro cis-flupentixol has an equal
affinity for D1 and D2 dopamine receptors, only the D2 dopamine receptor
density increased after chronic treatment with cis-flupentixol. In vivo
treatment with the protein-modifying reagent N-ethoxycarbonyl-2-ethoxy-
1,2-dihydroquinoline (EEDQ), which irreversibly inactivates D1 and D2
dopamine receptors, was used to investigate the paradoxical, selective D2
dopamine receptor up-regulation induced by cis-flupentixol treatment. In
vivo treatment with cis-flupentixol before EEDQ administration prevented
the D1 and D2 dopamine receptor reductions induced by EEDQ. However,
cis-flupentixol protected, in a dose- dependent manner, a greater
percentage of D2 dopamine receptors than of D1 dopamine receptors from
EEDQ-induced modification. These data indicate that, in vivo,
cis-flupentixol preferentially interacts with D2 dopamine receptors and
could explain why only D2 dopamine receptors were up-regulated following
chronic treatment with cis-flupentixol. Rats were tested for their
cataleptic response to the administered drug over the course of the chronic
drug treatment. Catalepsy scores of rats receiving spiperone decreased over
the course of treatment, with a significant reduction in catalepsy
occurring by treatment day 5. The profound catalepsy observed in rats
receiving SCH23390 did not change over the 21 d of treatment. Rats
receiving cis-flupentixol demonstrated tolerance to its cataleptogenic
effects, with a significant reduction in catalepsy observed by treatment
day 7. During the 3 week treatment, the time between drug injection and a
full cataleptic response to cis- flupentixol increased from 20 to 60 min,
suggesting a tolerance to the D2, but not D1, dopamine receptor antagonism
by cis- flupentixol.(ABSTRACT TRUNCATED AT 400 WORDS)