Differential effects of dopamine receptor subtype blockade on performance of rats in a reaction-time paradigm.
BACKGROUND
Pharmacological manipulation of the dopaminergic system with antipsychotic agents disrupts motor behavior. Although most antipsychotic drugs have high affinity for D2 receptors, they also interact with other dopamine receptor subtypes. Therefore, the role of each of these receptor subtypes on motor performance is unclear.


OBJECTIVE
The present study sought to investigate the relative importance of D1, D2, and D3 receptors on performance in a conditioned reaction-time task known to be extremely sensitive to dysfunction of the dopaminergic nigrostriatal pathway.


METHODS
Rats were trained to release a lever in response to a visual cue within a reaction-time limit to receive a reinforcer (45mg food pellet). After the behavior of the rats had stabilized, the effects of a D1 (A69024), D2 (eticlopride), and D3 (nafadotride) receptor antagonists were assessed.


RESULTS
A-69024 had no effect on performance at any dose tested (0.3, 0.6, and 1.3 mg/kg s.c.). Nafadotride (0.1, 0.3, and 1 mg/kg s.c.) produced only a mild deficit in performance at the highest dose. This deficit was characterized by an increase in the number of delayed responses with a non-significant decrease in the number of premature responses indicative of non-specific sedative effects. In contrast, the D2 receptor antagonist eticlopride (0.005, 0.01, and 0.02 mg/kg s.c.) produced profound deficits in performance as evidenced by a dose-dependent decrease in the number of correct responses. This decrease was accompanied by an increase in the number of delayed responses and a lengthening of the reaction time at the highest doses.


CONCLUSIONS
These results provide further evidence that the execution of the reaction-time task is dependent preferentially upon the activation of D2 receptors, but not D1 or D3 receptors.
Smith
A D
AD
Department of Neuropharmacology, The Scripps Research Institute, La Jolla, California, USA. smithad@msx.upmc.edu
Smith
D L
DL
Zigmond
M J
MJ
Amalric
M
M
Koob
G F
GF
D000818:Animals; D003216:Conditioning, Operant / Q000187:drug effects; D003463:Cues; D018492:Dopamine Antagonists / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D008297:Male; D009281:Naphthalenes / Q000494:pharmacology; D017072:Neostriatum / Q000187:drug effects / Q000502:physiology; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology; D011759:Pyrrolidines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000187:drug effects*; D017447:Receptors, Dopamine D1 / Q000187:drug effects*; D017448:Receptors, Dopamine D2 / Q000187:drug effects*; D050637:Receptors, Dopamine D3; D012457:Salicylamides / Q000494:pharmacology; D013378:Substantia Nigra / Q000187:drug effects / Q000502:physiology
D018492:Dopamine Antagonists; C493595:Drd3 protein, rat; D009281:Naphthalenes; D011759:Pyrrolidines; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; D012457:Salicylamides; C045989:eticlopride; C097285:nafadotride