Differential actions of adenosine A1 and A2A antagonists on the effort-related effects of dopamine D2 antagonism.
Adenosine and dopamine receptors in striatal areas interact to regulate a number of different functions, including aspects of motor control and motivation. Recent studies indicate that adenosine A(2A) receptor antagonists can reverse the effects of dopamine (DA) D(2) antagonists on instrumental tasks that provide measures of effort-related choice behavior. The present experiments compared the ability of the adenosine A(2A) antagonist KW6002, the nonselective adenosine antagonist caffeine, and the adenosine A(1) receptor selective antagonist DPCPX, to reverse the behavioral effects of the DA D(2) antagonist haloperidol. For these studies, a concurrent choice procedure was used in which rats could select between lever pressing on a fixed ratio 5 schedule for a preferred food or approaching and consuming a less preferred lab chow that was concurrently available in the chamber. Under baseline or control conditions, rats show a strong preference for lever pressing, and eat little of the chow; IP injections of 0.1 mg/kg haloperidol significantly reduced lever pressing and substantially increased chow intake. The adenosine A(2A) antagonist KW6002 (0.125-0.5 mg/kg IP) and the nonselective adenosine antagonist caffeine (5.0-20.0 mg/kg) significantly reversed the effects of haloperidol. However, the adenosine A(1) antagonist DPCPX (0.1875-0.75 mg/kg IP) failed to reverse the effects of the D(2) antagonist. The rank order of effect sizes in the reversal experiments was KW6002>caffeine>DPCPX. None of these drugs had any effect on behavior when they were injected in the absence of haloperidol. These results indicate that the ability of an adenosine antagonist to reverse the effort-related effects of a D(2) antagonist depends upon the subtype of adenosine receptor being blocked. Together with other recent results, these experiments indicate that there is a specific interaction between DA D(2) and adenosine A(2A) receptors, which could be related to the co-localization of these receptors on the same population of striatal neurons.
Division of Behavioral Neuroscience, Department of Psychology, University of Connecticut, Storrs, CT 06269-1020, USA. john.salamone@uconn.edu
John D
JD
Salamone
Andrew M
AM
Farrar
Laura
L
Font
Vatsal
V
Patel
Devra E
DE
Schlar
Eric J
EJ
Nunes
Lyndsey E
LE
Collins
Thomas N
TN
Sager
D058916:Adenosine A1 Receptor Antagonists; D058917:Adenosine A2 Receptor Antagonists; D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D002110:Caffeine / Q000494:pharmacology; D002491:Central Nervous System Agents / Q000494:pharmacology; D002755:Choice Behavior / Q000187:drug effects; D003216:Conditioning, Operant / Q000187:drug effects; D018492:Dopamine Antagonists / Q000494:pharmacology; D065127:Dopamine D2 Receptor Antagonists; D005247:Feeding Behavior / Q000187:drug effects; D006220:Haloperidol / Q000494:pharmacology; D008297:Male; D009042:Motivation; D011687:Purines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012055:Reinforcement Schedule; D014970:Xanthines / Q000494:pharmacology
D058916:Adenosine A1 Receptor Antagonists; D058917:Adenosine A2 Receptor Antagonists; D002491:Central Nervous System Agents; D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D011687:Purines; D014970:Xanthines; C111599:istradefylline; D002110:Caffeine; C051360:1,3-dipropyl-8-cyclopentylxanthine; D006220:Haloperidol