title: Differential effects of the adenosine A₂A agonist CGS-21680 and haloperidol on food-reinforced fixed ratio responding in the rat.
abstract: BACKGROUND
  Previous studies have shown that adenosine A(2A) receptors are colocalized with dopamine D(2) receptors on striatal neurons. Activation of these two receptors has antagonistic effects under a number of conditions suggesting that stimulation of adenosine A(2A) receptors may have behavioral effects resembling those produced by blockade of dopamine D(2) receptors, but this possibility has been investigated in a limited number of situations.
  
  
  OBJECTIVE
  We compared the effects of the adenosine A(2A) agonist CGS-21680 and the preferential D(2) dopamine antagonist haloperidol in a situation in which dopamine blockade produces a distinctive pattern of behavioral effects.
  
  
  METHODS
  Six rats were trained to lever press for food reward on a fixed ratio 15 schedule of reinforcement and then tested after being injected with various doses of CGS-21680 (0.064, 0.128, and 0.25 mg/kg) and haloperidol (0.25 and 0.1 mg/kg).
  
  
  RESULTS
  Haloperidol produced a dose-dependent suppression of lever pressing with mean response rates declining across the duration of the test session. CGS-21680 also produced a dose-dependent suppression of responding, but this effect was not temporally graded, and responding was equivalently suppressed across the duration of the session. Additionally, CGS-21680 increased post-reinforcement pause duration to a much greater extent than did haloperidol.
  
  
  CONCLUSIONS
  On this task, the behavioral effects of CGS-21680 do not resemble those produced by haloperidol. Several explanations of this discrepancy are possible, the most likely being that the observed behavioral effects of CGS-21680 result from an action at a site other than D(2) receptor-expressing striatal neurons.
authors: College of the Desert, 43-500 Monterey Avenue, Palm Desert, CA 92260, USA.
authors: Chris
authors: C
authors: Jones-Cage
authors: Thomas R
authors: TR
authors: Stratford
authors: David
authors: D
authors: Wirtshafter
mesh_terms: D000241:Adenosine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D058908:Adenosine A2 Receptor Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003216:Conditioning, Operant / Q000187:drug effects; D018492:Dopamine Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D065127:Dopamine D2 Receptor Antagonists; D004305:Dose-Response Relationship, Drug; D006220:Haloperidol / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D010627:Phenethylamines / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012055:Reinforcement Schedule; D012201:Reward
chemical_list: D058908:Adenosine A2 Receptor Agonists; D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D010627:Phenethylamines; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D006220:Haloperidol; D000241:Adenosine