Koffarnus MN, Greedy B, Husbands SM, Grundt P, Newman AH, Woods JH. The discriminative stimulus effects of dopamine D2- and D3-preferring agonists in rats.
Psychopharmacology (Berl) 2009;
203:317-27. [PMID:
18807248 PMCID:
PMC3065021 DOI:
10.1007/s00213-008-1323-4]
[Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/02/2008] [Accepted: 08/30/2008] [Indexed: 10/21/2022]
Abstract
RATIONALE
Previous research has found the stimulus effects of dopamine D2- and D3-preferring agonists difficult to distinguish in drug discrimination studies. Antagonism studies suggest that the stimulus effects of both types of agonists may be mediated primarily through D2 receptors.
OBJECTIVES
The current study was designed to further assess the receptors mediating the stimulus effects of these agonists and to attempt to train rats to discriminate directly between D2- and D3-preferring dopamine agonists.
MATERIALS AND METHODS
Four groups of eight rats were trained to discriminate either 0.1 mg/kg of the D3-preferring agonist pramipexole from saline, 1.0 mg/kg of the D2-preferring agonist sumanirole from saline, 0.1 mg/kg pramipexole from either saline or 1.0 mg/kg sumanirole, or 1.0 mg/kg sumanirole from either saline or 0.1 mg/kg pramipexole.
RESULTS
Three of eight rats in the 0.1 mg/kg pramipexole vs. 1.0 mg/kg sumanirole or saline failed to meet the training criteria, and the discrimination in this group was tenuous. The D2-preferring antagonist L-741,626 at 1.0 mg/kg was more effective at shifting to the right the pramipexole dose-response curve in pramipexole-trained rats, while 32 mg/kg of the selective D3 antagonist PG01037 had little effect. Quinpirole and 7-OH-DPAT fully or partially substituted for both pramipexole and sumanirole in each group tested, while cocaine did not substitute in any group.
CONCLUSIONS
Antagonist data along with the pattern of training and substitution data suggested that D2 receptor activation is primarily responsible for the stimulus effects of both sumanirole and pramipexole with D3 receptor activation playing little or no role.
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