Evidence for dopamine D(1) receptor involvement in the stimulus selection task: overshadowing in the rat.
BACKGROUND
A number of lines of evidence suggest that dopamine might play a role in stimulus selection, the process whereby specific cues are selected to guide action.


OBJECTIVE
In order further to define the potential role for dopamine in stimulus selection, the present series of studies examined whether dopaminergic drugs modulate overshadowing, a paradigm that involves stimulus selection in rats. Overshadowing is where preferential learning occurs to one (usually the more salient) element of a stimulus compound.


METHODS
Overshadowing was measured in rats using a thirst motivated conditioned emotional response paradigm (CER). Two simultaneously presented stimuli (light and tone) were paired with an aversive unconditioned stimulus (mild footshock); overshadowing is observed when learning to the less salient stimulus is weaker than learning to the same stimulus when it is conditioned alone.


RESULTS
d-Amphetamine sulphate (1 mg/kg, IP) was found selectively to disrupt overshadowing, without affecting the CER in control animals. The dopamine (DA) D(2) receptor antagonists, haloperidol (0.2 mg/kg, IP) or raclopride (0.5 mg/kg, IP), failed to reverse amphetamine-induced disruption of overshadowing. In contrast, the selective DA D(1) antagonist SCH 23390 (0.05 mg/kg, IP) reversed amphetamine-induced disruption of overshadowing. The partial DA D(1) agonist SKF 38393 (5 mg/kg, IP) was found to abolish overshadowing when given alone.


CONCLUSIONS
These data indicate a modulatory role for the DA D(1) receptor in the expression of stimulus selection and suggest that the DA D(1) receptor might play a role in salience allocation aspects of learning.
O'Tuathaigh
C M P
CM
Department of Psychology, University of Leicester, University Road, Leicester LE1 7RH, UK.
Moran
P M
PM
D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine / Q000494:pharmacology; D000661:Amphetamine / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D001552:Benzazepines / Q000494:pharmacology; D003213:Conditioning, Psychological / Q000187:drug effects; D004193:Discrimination Learning / Q000187:drug effects*; D015259:Dopamine Agents / Q000494:pharmacology; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D065127:Dopamine D2 Receptor Antagonists; D004347:Drug Interactions; D006220:Haloperidol / Q000494:pharmacology; D008297:Male; D020891:Raclopride / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time; D017447:Receptors, Dopamine D1 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D017448:Receptors, Dopamine D2 / Q000819:agonists / Q000502:physiology
D001552:Benzazepines; D015259:Dopamine Agents; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D020891:Raclopride; D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; D000661:Amphetamine; D006220:Haloperidol