title: Effect of quinpirole on timing behaviour in the free-operant psychophysical procedure: evidence for the involvement of D2 dopamine receptors.
abstract: BACKGROUND
  Operant timing behaviour is sensitive to dopaminergic manipulations. It has been proposed that this effect is mediated principally by D(2)-like dopamine receptors. However, we recently found that the effect of d-amphetamine on timing in the free-operant psychophysical procedure was mediated by D(1)-like dopamine receptors. It has not been established whether stimulation of D(2)-like receptors affects timing in this schedule.
  
  
  OBJECTIVE
  To examine the effects of a D(2)-like receptor agonist quinpirole on second-range timing and the ability of dopamine receptor antagonists to reverse quinpirole's effects.
  
  
  METHODS
  Rats responded on two levers (A and B) under a free-operant psychophysical schedule in which reinforcement was provided intermittently for responding on A during the first half, and B during the second half, of 50-s trials. Logistic functions were fitted to the relative response rates [percent responding on B (%B) vs time (t)] under each treatment; quantitative timing indices [T (50) (value of t when %B = 50) and Weber fraction] were compared among treatments.
  
  
  RESULTS
  Quinpirole (0.04, 0.08 mg kg(-1)) reduced T (50). This effect was attenuated by D(2)-like receptor antagonists haloperidol (0.05, 0.1 mg kg(-1)), eticlopride (0.04, 0.08 mg kg(-1)) and sulpiride (30, 60 mg kg(-1)), but not by the D(3) receptor-preferring antagonist nafadotride (0.5, 1 mg kg(-1)), the D(4) receptor antagonist L-745870 (1, 3 mg kg(-1)) or the D(1)-like receptor antagonist SKF-83566 (0.015 mg kg(-1)).
  
  
  CONCLUSIONS
  Results suggest that quinpirole reduced T (50) via an action at D(2) receptors. D(1)-like and D(2)-like receptors may mediate behaviourally similar but pharmacologically distinct effects on timing behaviour.
authors.affiliation: Psychopharmacology Section, Division of Psychiatry, University of Nottingham, Medical School, Queen's Medical Centre, Nottingham, UK.
authors.forename: T H C
authors.initials: TH
authors.lastname: Cheung
authors.forename: G
authors.initials: G
authors.lastname: Bezzina
authors.forename: C L
authors.initials: CL
authors.lastname: Hampson
authors.forename: S
authors.initials: S
authors.lastname: Body
authors.forename: K C F
authors.initials: KC
authors.lastname: Fone
authors.forename: C M
authors.initials: CM
authors.lastname: Bradshaw
authors.forename: E
authors.initials: E
authors.lastname: Szabadi
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D003216:Conditioning, Operant; D018492:Dopamine Antagonists / Q000494:pharmacology*; D065127:Dopamine D2 Receptor Antagonists; D004347:Drug Interactions; D005260:Female; D006220:Haloperidol / Q000494:pharmacology; D019257:Quinpirole / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000187:drug effects*; D012457:Salicylamides / Q000494:pharmacology; D013469:Sulpiride / Q000494:pharmacology
chemical_list: D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D012457:Salicylamides; D019257:Quinpirole; D013469:Sulpiride; D006220:Haloperidol; C045989:eticlopride