The Journal of Neuroscience, November 1, 2002, 22(21):9595–9603 Dopamine D3 Receptor Antagonism Inhibits Cocaine-Seeking and Cocaine-Enhanced Brain Reward in Rats Stanislav R. Vorel,1,2 Charles R. Ashby Jr,4 Mousumi Paul,5 Xinhe Liu,3 Robert Hayes,2 Jim J. Hagan,6 Derek N. Middlemiss,6 Geoffrey Stemp,6 and Eliot L. Gardner1,2,3 1Intramural Research Program, National Institute on Drug Abuse, Baltimore, Maryland 21224, Departments of 2Neuroscience and 3Psychiatry and Behavioral Sciences, Albert Einstein College of Medicine, Bronx, New York 10461, 4Department of Pharmaceutical Sciences, College of Pharmacy and Allied Health Professions, Saint John’s University, Jamaica, New York 11439, 5Eon Laboratories, Laurelton, New York 11413, and 6Psychiatry Centre of Excellence for Drug Discovery, GlaxoSmithKline, Harlow, Essex CM19 5AW, United Kingdom The dopamine D3 receptor is preferentially localized to the (2) dose-dependently attenuate cocaine-induced conditioned mesocorticolimbic dopaminergic system and has been hypoth- place preference, and (3) dose-dependently attenuate cocaine- esized to play a role in cocaine addiction. To study the involve- triggered reinstatement of cocaine seeking behavior. Thus, D3 ment of the D3 receptor in brain mechanisms and behaviors receptor blockade attenuates both the rewarding effects of commonly assumed to be involved in the addicting properties cocaine and cocaine-induced drug-seeking behavior. These of cocaine, the potent and selective D3 receptor antagonist data suggest an important role for D3 receptors in mediating the trans-N-[4-[2-(6-cyano-1,2,3,4-tetrahydroisoquinolin-2-yl)ethyl] addictive properties of cocaine and suggest that blockade of cyclohexyl]-4-quinolininecarboxamide (SB-277011-A) was ad- dopamine D3 receptors may constitute a new and useful target ministered to laboratory rats, and the following measures were for prospective pharmacotherapies for cocaine addiction. assessed: (1) cocaine-enhanced electrical brain-stimulation re- ward, (2) cocaine-induced conditioned place preference, and Key words: cocaine; addiction; dopamine; mesolimbic; me- (3) cocaine-triggered reinstatement of cocaine seeking behav- socorticolimbic; D3 receptor; D3 antagonist; brain stimulation ior. Systemic injections of SB-277011-A were found to (1) block reward; BSR; self-stimulation; ICSS; conditioned place prefer- enhancement of electrical brain stimulation reward by cocaine, ence; CPP; self-administration; reinstatement; relapse Aberration in brain dopamine (DA) function is hypothesized to genetic- and drug history-induced vulnerability (Nestler, 1993; underlie drug addiction (Wise and Rompre, 1989; Koob, 1992). Gardner, 1999) and in acute withdrawal from addictive drugs Of the five major DA receptor subtypes (Gardner and Ashby, (Parsons et al., 1991; Weiss et al., 1992). Also, recruitment of 2000), the D3 receptor shows preferential localization in the “opponent process” neural mechanisms may occur during re- mesocorticolimbic system (Levant, 1998; Suzuki et al., 1998), has peated drug taking such that mesolimbic reinforcement function a unique pharmacological profile (Emilien et al., 1999), and is diminished, producing a decreased reward “set point” and activates unique presynaptic and postsynaptic signaling systems consequent drug-seeking and drug-taking behavior (Koob et al., (Emilien et al., 1999; Kuzhikandathil and Oxford, 1999) com- 1993). From such evidence, it has been postulated that mesolim- pared with D1 and D2 receptors. In view of its association with bic hypo-DA function may be a fundamental substrate of addic- limbic loci, the D3 receptor is suggested to play a role in emo- tion (Gardner, 1999). The present experiments addressed the tional, motivational, and reinforcement functions, including the effects of selective DA D3 receptor antagonism in animal models reinforcement produced by addictive drugs (Caine and Koob, relevant to addiction, experiments that to date have been ham- 1993; Pilla et al., 1999). Some evidence suggests that D receptor 3 pered by lack of D3-selective compounds. For the present experi- activation inhibits mesocorticolimbic DA function (Gilbert et al., ments, a novel brain-penetrant, highly selective D3 receptor antag- 1995; Lejeune and Millan, 1995) and that D3 receptor inhibition onist was used, trans-N-[4-[2-(6-cyano-1,2,3,4-tetrahydroisoquinolin- activates the mesocorticolimbic DA system (Nissbrandt et al., 2-yl)ethyl]cyclohexyl]-4-quinolininecarboxamide (SB-277011-A; 1995); however, many of these studies have been confounded by a Reavill et al., 2000; Stemp et al., 2000). SB-277011-A has high lack of selective pharmacological tools. affinity for both human and rat D3 receptors, with 80- to 100-fold Decreased basal mesolimbic DA function in laboratory animals selectivity over D2 receptors and 66 other receptors, enzymes, appears correlated with high vulnerability to drug seeking and and ion channels (Reavill et al., 2000). Also, SB-277011-A readily drug taking (Nestler, 1993; Gardner, 1999) in animals with both enters the brain after systemic administration (Reavill et al., 2000; Stemp et al., 2000). The compound has been shown to lack effects Received April 4, 2002; revised Aug. 9, 2002; accepted Aug. 16, 2002. on spontaneous amphetamine- and phencyclidine-stimulated lo- We thank Matus Knoblich for preliminary training of animals for the cocaine self-administration protocol and Arlene Campos for assistance with the figures. comotor activity and is free from cataleptic effects even at high Correspondence should be addressed to Dr. Charles R. Ashby Jr, Department of doses (Reavill et al., 2000). Pharmaceutical Sciences, College of Pharmacy and Allied Health Professions, Saint Specifically, the present experiments in rats were undertaken to John’s University, 8000 Utopia Parkway, Jamaica, NY 11439. E-mail: crashby@ ix.netcom.com. determine the effect of acute D3 receptor antagonism on (1) the Copyright © 2002 Society for Neuroscience 0270-6474/02/229595-09$15.00/0 enhancement of electrical brain stimulation reward (BSR) by • 9596 J. Neurosci., November 1, 2002, 22(21):9595–9603 Vorel et al. D3 Blockade Inhibits Cocaine Reward and Relapse cocaine, (2) cocaine-seeking behavior as measured by cocaine- Conditioned place preference experiments induced conditioned place preference (CPP), and (3) cocaine- Apparatus. An automated CPP apparatus was used as described previ- seeking behavior as measured by cocaine-triggered reinstatement ously (Horan et al., 2000). The conditioning chambers had distinctive of operant behavior (lever pressing) previously reinforced by visual and tactile cues, white walls with commercial rodent bedding on intravenous cocaine injections. In addition, the effect of sub- the floor versus white and black checkerboard walls and a smooth Plexiglas floor. The visual and tactile cues were balanced such that no chronic D receptor antagonism on cocaine-induced CPP was 3 side preference was exhibited before conditioning. assessed. Finally, the ability of acute D3 receptor antagonism to Procedure. CPP acquisition and expression were both assessed as produce catalepsy was assessed. described previously (Horan et al., 2000). Acquisition had four phases: acclimation, handling, conditioning, and testing. During days 1–3, ani- MATERIALS AND METHODS mals were acclimated to the animal facility. During handling (days 4–6), animals were transported to the laboratory and handled for 5 min each. Animals During conditioning (days 7–14), animals were exposed to once-daily For the BSR and cocaine-triggered reinstatement experiments, male conditioning sessions. For each conditioning session, animals were in- Long–Evans rats (350–475 gm at time of surgery) were used, housed jected with either vehicle or SB-277011-A (0.3, 1.0, 3.0, or 10.0 mg/kg, individually. For the CPP and catalepsy experiments, male Sprague i.p.) in the home cage, followed 30 min later by cocaine (15.0 mg/kg, i.p.) Dawley rats (200–225 gm at start of drug–cue or food–cue pairings) were or vehicle, and then immediately confined for 30 min in an appropriate used, housed two per cage. The use of the two different strains was cue-specific chamber. During conditioning, cocaine was always paired because of the fact that the work was performed at two different insti- with one cue-specific environment, and vehicle was paired with the other; tutions, each maintaining a different strain as the standard colony stock cocaine or vehicle exposure (and appropriate environmental pairing) animal. Rats were kept on a 12 hr light/dark schedule, with food and alternated from day to day. On the test day (day 15), animals were water available ad libitum except for reinstatement animals during pre- allowed to move freely between both cue-specific chambers for 15 min, liminary food-reinforced operant training and CPP animals in the food- and the amount of time spent in each was recorded. paired studies. Animals were allowed to acclimate to the animal facility Expression studies with acute SB-277011-A or vehicle were divided for 3–5 d before handling. Experiments were performed in accord with into four phases: acclimation, handling, conditioning, and testing. The the National Institutes of Health Guide for the Care and Use of Laboratory acclimation and handling phases were identical to those of acquisition. Animals, in compliance with all applicable state and federal animal The expression conditioning phase differed from that of acquisition in welfare regulations, and were reviewed by appropriate institutional ani- that, during