title: Cocaine-seeking behavior in response to drug-associated stimuli in rats: involvement of D3 and D2 dopamine receptors.
abstract: Previous studies employed a second-order schedule paradigm maintained by cocaine reinforcement to show that BP897, a dopamine D(3) partial agonist, selectively modulated drug-seeking behavior. We investigated its effect on drug-seeking behavior induced by presentation of stimuli associated with and predictive of cocaine availability after a period of extinction and in the absence of any further cocaine. Male rats were trained to associate discriminative stimuli (S(D)) with the availability of intravenous (i.v.) 0.25 mg/0.1 ml/infusion cocaine (S(D+)) or no-reward (S(D-)) saline solution. Each infusion of cocaine or saline was followed by a response-cue signaling 20-s time-out (TO). After meeting the self-administration training criterion rats were placed on extinction conditions during which i.v. solutions and S(D)s were withheld. Every other 3 days on which rats met the extinction criterion, reinstatement tests were conducted, presenting the S(D+) or S(D-) noncontingently together with a contingent presentation of cocaine- or saline-cues signaling 20-s TO. Regardless of the order of presentation or the nature of the stimuli (auditory or visual), cocaine-associated but not saline-associated stimuli reinstated responding on the previously active lever. Presentation of cocaine-associated stimuli induced lasting drug-seeking behavior for at least eight test sessions. BP897 (1.0 mg/kg i.p.) significantly attenuated this behavior. Since it has been reported that BP897 can interact with a panel of different receptors with high affinity, we evaluated the effects of 7-OH-DPAT, an agonist to D(3) receptors, raclopride, a preferential antagonist to D(2) receptors, and WAY 100,635, an antagonist at 5-HT(1A) receptors, on drug-seeking behavior. 7-OH-DPAT (0.1-3.0 mg/kg i.p.) had biphasic effects on reinstatement induced by the cocaine-associated cues, low dosages reducing and high dosages increasing the impact of cocaine-associated stimuli on rats' behavior. Raclopride (0.1, 0.3 mg/kg s.c.) completely prevented drug-seeking behavior induced by the reintroduction of cocaine-associated stimuli. WAY 100,635 (0.1-1.0 mg/kg s.c.) had no effect on this behavior. These results, while confirming that the partial agonist at the D(3) receptors, BP897, might be a useful medication, also suggest a role of D(2) receptors in cue-induced cocaine-seeking behavior.
authors.affiliation: Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy. cervo@marionegri.it
authors.forename: L
authors.initials: L
authors.lastname: Cervo
authors.forename: F
authors.initials: F
authors.lastname: Carnovali
authors.forename: J A
authors.initials: JA
authors.lastname: Stark
authors.forename: T
authors.initials: T
authors.lastname: Mennini
mesh_terms: D000818:Animals; D016739:Behavior, Addictive / Q000523:psychology*; D003042:Cocaine / Q000008:administration & dosage*; D003463:Cues; D005108:Extinction, Psychological / Q000187:drug effects / Q000502:physiology; D008297:Male; D010879:Piperazines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000819:agonists / Q000502:physiology*; D050637:Receptors, Dopamine D3; D012646:Self Administration / Q000379:methods / Q000523:psychology; D013764:Tetrahydronaphthalenes / Q000494:pharmacology
chemical_list: C493595:Drd3 protein, rat; D010879:Piperazines; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; D013764:Tetrahydronaphthalenes; C120565:BP 897; D003042:Cocaine; C031349:7-hydroxy-2-N,N-dipropylaminotetralin