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Schifirneţ E, Bowen SE, Borszcz GS. Separating analgesia from reward within the ventral tegmental area. Neuroscience 2014; 263:72-87. [PMID: 24434773 DOI: 10.1016/j.neuroscience.2014.01.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2013] [Revised: 12/09/2013] [Accepted: 01/06/2014] [Indexed: 10/25/2022]
Abstract
Activation of the dopaminergic mesolimbic reward circuit that originates in the ventral tegmental area (VTA) is postulated to preferentially suppress emotional responses to noxious stimuli, and presumably contributes to the addictive liability of strong analgesics. VTA dopamine neurons are activated via cholinergic afferents and microinjection of carbachol (cholinergic agonist) into VTA is rewarding. Here, we evaluated regional differences within VTA in the capacity of carbachol to suppress rats' affective response to pain (vocalization afterdischarges, VADs) and to support conditioned place preference (CPP) learning. As carbachol is a non-specific agonist, muscarinic and nicotinic receptor involvement was assessed by administering atropine (muscarinic antagonist) and mecamylamine (nicotinic antagonist) into VTA prior to carbachol treatment. Unilateral injections of carbachol (4μg) into anterior VTA (aVTA) and posterior VTA (pVTA) suppressed VADs and supported CPP; whereas, injections into midVTA failed to effect either VADs or CPP. These findings corroborate the hypothesis that the neural substrates underlying affective analgesia and reward overlap. However, the extent of the overlap was only partial. Whereas both nicotinic and muscarinic receptors contributed to carbachol-induced affective analgesia in aVTA, only muscarinic receptors mediated the analgesic action of carbachol in pVTA. The rewarding effects of carbachol are mediated by the activation of both nicotinic and muscarinic receptors in both aVTA and pVTA. The results indicate that analgesia and reward are mediated by separate cholinergic mechanisms within pVTA. Nicotinic receptor antagonism within pVTA failed to attenuate carbachol-induced analgesia, but prevented carbachol-induced reward. As addictive liability of analgesics stem from their rewarding properties, the present findings suggest that these processes can be neuropharmacologically separated within pVTA.
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Affiliation(s)
- E Schifirneţ
- Behavioral and Cognitive Neuroscience Program, Department of Psychology, Wayne State University, Detroit, MI 48202, USA
| | - S E Bowen
- Behavioral and Cognitive Neuroscience Program, Department of Psychology, Wayne State University, Detroit, MI 48202, USA
| | - G S Borszcz
- Behavioral and Cognitive Neuroscience Program, Department of Psychology, Wayne State University, Detroit, MI 48202, USA.
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Phillips GD, Salussolia E, Hitchcott PK. Role of the mesoamygdaloid dopamine projection in emotional learning. Psychopharmacology (Berl) 2010; 210:303-16. [PMID: 20401751 DOI: 10.1007/s00213-010-1813-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/02/2009] [Accepted: 02/22/2010] [Indexed: 11/26/2022]
Abstract
RATIONALE Amygdala dopamine is crucially involved in the acquisition of Pavlovian associations, as measured via conditioned approach to the location of the unconditioned stimulus (US). However, learning begins before skeletomotor output, so this study assessed whether amygdala dopamine is also involved in earlier 'emotional' learning. OBJECTIVES A variant of the conditioned reinforcement (CR) procedure was validated where training was restricted to curtail the development of selective conditioned approach to the US location, and effects of amygdala dopamine manipulations before training or later CR testing assessed. METHODS Experiment 1a presented a light paired (CS+ group) or unpaired (CS- group) with a US. There were 1, 2 or 10 sessions, 4 trials per session. Then, the US was removed, and two novel levers presented. One lever (CR+) presented the light, and lever pressing was recorded. Experiment 1b also included a tone stimulus. Experiment 2 applied intra-amygdala R(+) 7-OH-DPAT (10 nmol/1.0 microl/side) before two training sessions (Experiment 2a) or a CR session (Experiment 2b). RESULTS For Experiments 1a and 1b, the CS+ group preferred the CR+ lever across all sessions. Conditioned alcove approach during 1 or 2 training sessions or associated CR tests was low and nonspecific. In Experiment 2a, R(+) 7-OH-DPAT before training greatly diminished lever pressing during a subsequent CR test, preferentially on the CR+ lever. For Experiment 2b, R(+) 7-OH-DPAT infusions before the CR test also reduced lever pressing. CONCLUSIONS Manipulations of amygdala dopamine impact the earliest stage of learning in which emotional reactions may be most prevalent.
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Affiliation(s)
- Gavin D Phillips
- Department of Psychology, University of York, Heslington, York, YO10 5DD, UK.
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Phillips GD, Hitchcott PK. Blockade of the acquisition, but not expression, of associative learning by pre-session intra-amygdala R(+) 7-OH-DPAT. Psychopharmacology (Berl) 2009; 203:161-73. [PMID: 18949458 DOI: 10.1007/s00213-008-1382-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/28/2008] [Accepted: 10/13/2008] [Indexed: 12/17/2022]
Abstract
RATIONALE Two issues were addressed regarding the effects of amygdala dopamine manipulations on associative learning: first, an apparent contradiction between the effects of post- vs. pre-session dopaminergic manipulations and second, the ability of dopaminergic infusions to affect association formation vs. its expression following extended training. OBJECTIVES The ability of pre-session infusions of a dopamine receptor agonist (R(+) 7-OH-DPAT) to inhibit acquisition of a conditioned approach response was examined and compared with the same manipulation following overtraining. Further experiments extended these findings. MATERIALS AND METHODS Experiment 1 infused pre-session intra-amygdala R(+) 7-OH-DPAT (0, 0.1, 1 nmol) during conditioned approach acquisition. Experiment 2 applied pre-session intra-amygdala R(+) 7-OH-DPAT (0, 0.01, 0.1, 1 nmol) during expression of the same response, once well learned. Experiment 3 required the inhibition of a conditioned approach response following unconditioned stimulus (US) removal. Experiment 4 examined the ability of animals with prior drug experience to acquire a conditioned response to a novel stimulus. RESULTS Experiments 1-3 showed that pre-session amygdala R(+) 7-OH-DPAT impaired acquisition of either excitatory or inhibitory conditioned responding, but was ineffective following overtraining. Drug-induced impairments in acquisition of a specific conditioned stimulus (CS)-US relationship continued well beyond the cessation of drug treatment, but were found not to transfer to an alternate CS in Experiment 4. CONCLUSIONS Pre-session dopamine receptor activation within the amygdala may impair the acquisition, but not expression, of CS-US associations. Enhanced learning reported earlier following post-session dopamine receptor activation may occur indirectly through reduced interference with the consolidation of recent learning.
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Affiliation(s)
- Gavin D Phillips
- Department of Psychology, University of York, Heslington, York, YO10 5DD, UK.
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Abstract
Emotion plays a critical role in many contemporary accounts of decision making, but exactly what underlies its influence and how this is mediated in the brain remain far from clear. Here, we review behavioral studies that suggest that Pavlovian processes can exert an important influence over choice and may account for many effects that have traditionally been attributed to emotion. We illustrate how recent experiments cast light on the underlying structure of Pavlovian control and argue that generally this influence makes good computational sense. Corresponding neuroscientific data from both animals and humans implicate a central role for the amygdala through interactions with other brain areas. This yields a neurobiological account of emotion in which it may operate, often covertly, to optimize rather than corrupt economic choice.
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Affiliation(s)
- Ben Seymour
- Wellcome Trust Centre for Imaging Neuroscience, University College London, 12 Queen Square, London WC1N3BG, UK.
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5
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Heidbreder CA, Gardner EL, Xi ZX, Thanos PK, Mugnaini M, Hagan JJ, Ashby CR. The role of central dopamine D3 receptors in drug addiction: a review of pharmacological evidence. ACTA ACUST UNITED AC 2005; 49:77-105. [PMID: 15960988 PMCID: PMC3732040 DOI: 10.1016/j.brainresrev.2004.12.033] [Citation(s) in RCA: 212] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2004] [Revised: 10/21/2004] [Accepted: 12/06/2004] [Indexed: 10/25/2022]
Abstract
The cDNA for the dopamine D3 receptor was isolated and characterized in 1990. Subsequent studies have indicated that D3 receptors, as well as D3 receptor mRNA, are primarily localized in limbic regions in mammals. This finding led to the postulate that D3 receptors may be involved in drug dependence and addiction. However, this hypothesis has been difficult to test due to the lack of compounds with high selectivity for central D3 receptors. The interpretation of results from studies using mixed D2/D3 agonists and/or antagonists is problematic because these agents have low selectivity for D3 over D2 receptors and it is likely that their actions are primarily related to D2 receptor antagonism and possibly interaction with other neurotransmitter receptors. Currently, with the synthesis and characterization of new highly selective D3 receptor antagonists such as SB-277011-A this difficulty has been surmounted. The purpose of the present article is to review, for the first time, the effects of various putative D3 receptor selective compounds in animal models of drug dependence and addiction. The results obtained with highly selective D3 receptor antagonists such as SB-277011-A, SB-414796, and NGB-2904 indicate that central D3 receptors may play an important role in drug-induced reward, drug-taking, and cue-, drug-, and stress-induced reinstatement of drug-seeking behavior. Provided these results can be extrapolated to human drug addicts, they suggest that selective DA D3 receptor antagonists may prove effective as potential pharmacotherapeutic agents to manage drug dependence and addiction.
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Affiliation(s)
- Christian A. Heidbreder
- Centre of Excellence for Drug Discovery in Psychiatry, GlaxoSmithKline Pharmaceuticals, 37135 Verona, Italy
| | - Eliot L. Gardner
- Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland 21224-6823, USA
| | - Zheng-Xiong Xi
- Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland 21224-6823, USA
| | - Panayotis K. Thanos
- Medical Department, Brookhaven National Laboratory, Upton, NY 11973-5000, USA
| | - Manolo Mugnaini
- Centre of Excellence for Drug Discovery in Psychiatry, GlaxoSmithKline Pharmaceuticals, 37135 Verona, Italy
| | - Jim J. Hagan
- Centre of Excellence for Drug Discovery in Psychiatry, GlaxoSmithKline Pharmaceuticals, 37135 Verona, Italy
| | - Charles R. Ashby
- Pharmaceutical Sciences Department, Saint John’s University, 8000 Utopia Parkway, Jamaica, NY 11439-0001, USA
- Corresponding author. Fax: +1 718 990 1877. (C.R. Ashby)
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6
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Andrzejewski ME, Spencer RC, Kelley AE. Instrumental learning, but not performance, requires dopamine D1-receptor activation in the amygdala. Neuroscience 2005; 135:335-45. [PMID: 16111818 PMCID: PMC2367315 DOI: 10.1016/j.neuroscience.2005.06.038] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2005] [Revised: 06/02/2005] [Accepted: 06/15/2005] [Indexed: 10/25/2022]
Abstract
Substantial experimental evidence exists suggesting a critical role for dopamine in reinforcer-related processes, such as learning and drug addiction. Dopamine receptors, and in particular D1 receptors, are widely considered as modulators of synaptic plasticity. The amygdala contains both dopamine terminals and dopamine D1 receptors and is intimately involved in motivation and learning. However, little is known about the involvement of D1 receptor activation in two subnuclei of the mammalian amygdala, the central nucleus and basolateral complex in instrumental learning. Following recovery from surgery and preliminary training, rats with bilateral indwelling cannulae aimed at the central nucleus or basolateral complex were trained to lever-press for sucrose pellets over 12 sessions. Infusion of the selective D1 antagonist R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (0.3 nmol and 3.0 nmol) prior to the first five training sessions dose-dependently impaired instrumental learning when compared with vehicle-infused controls. All rats were then exposed to five sessions drug-free; lever-pressing quickly reached equal levels across groups. A drug infusion prior to an 11th session revealed no effect on performance. Control experiments indicated that basic motivational processes and general motor responses were intact, such as spontaneous feeding and locomotor activity. These results show an essential role for D1-receptor activation in both the central nucleus and basolateral complex on the acquisition of lever pressing for sucrose pellets in rats, but not the performance of the behavior once conditioned. We propose that instrumental learning is dependent on plasticity in the central nucleus and basolateral complex amygdala, and that D1 receptor activation participates in transcriptional processes that underlie this plasticity.
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Affiliation(s)
- M E Andrzejewski
- Department of Psychiatry, University of Wisconsin-Madison, Madison, WI 53719, USA.
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Aujla H, Beninger RJ. Intra-BLA or Intra-NAc Infusions of the Dopamine D₃ Receptor Partial Agonist, BP 897, Block Intra-NAc Amphetamine Conditioned Activity. Behav Neurosci 2004; 118:1324-30. [PMID: 15598141 DOI: 10.1037/0735-7044.118.6.1324] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Recent studies have shown that both systemic and intra-nucleus accumbens (NAc) or intra-amygdala administration of dopamine D3 receptor ligands modulate reward-related learning. A previous study (H. Aujla, H. Sokoloff, & R. J. Beninger. 2002) showed that systemic administration of the partial dopamine D3 receptor agonist BP 897 selectively blocked the expression, but not the acquisition, of amphetamine-conditioned activity. This suggested the hypothesis that intra-NAc or intra-basolateral amygdala (BLA) BP 897 would attenuate the expression, but not the acquisition, of amphetamine-conditioned activity. Rats were habituated to activity-monitoring chambers for 5 days, for 1 hr each day. Conditioning occurred on the next 3 days, followed by a single 1-hr test session. Intra-NAc or intra-BLA infusions of BP 897 during test, but not during conditioning, attenuated intra-NAc amphetamine conditioned activity. Results indicate that the ability of BP 897 to attenuate the expression of conditioned activity is mediated in part by the NAc and BLA.
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Affiliation(s)
- Harinder Aujla
- Department of Psychology, Queen's University, Kingston, Ontario, Canada.
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Phillips GD, Setzu E, Hitchcott PK. Facilitation of appetitive pavlovian conditioning by d-amphetamine in the shell, but not the core, of the nucleus accumbens. Behav Neurosci 2003; 117:675-84. [PMID: 12931953 DOI: 10.1037/0735-7044.117.4.675] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The effects of postsession d-amphetamine within subregions of the ventral and dorsal striatum on appetitive Pavlovian learning were assessed. Rats acquired a conditioned approach response on presentation of a stimulus predictive of 10% sucrose solution (unconditioned stimulus [US]), but not during equally frequent presentations of a stimulus uncorrelated with the US. In Experiment 1, postsession d-amphetamine infusions enhanced acquisition of conditioned responding, with no effect on control measures. In Experiment 2, rats received postsession d-amphetamine in the accumbens shell or core. Shell infusions facilitated conditioning; core infusions did not. In Experiment 3, dorsomedial striatal infusions of d-amphetamine also were ineffective. In sum, dopaminergic activation within the shell, but not the core, of the nucleus accumbens facilitates the acquisition of a Pavlovian association.
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Affiliation(s)
- Gavin D Phillips
- Department of Psychology, University of York, Heslington, United Kingdom.
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9
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Olausson P, Jentsch JD, Taylor JR. Repeated nicotine exposure enhances reward-related learning in the rat. Neuropsychopharmacology 2003; 28:1264-71. [PMID: 12700688 DOI: 10.1038/sj.npp.1300173] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Repeated exposure to addictive drugs causes neuroadaptive changes in cortico-limbic-striatal circuits that may underlie alterations in incentive-motivational processes and reward-related learning. Such drug-induced alterations may be relevant to drug addiction because enhanced incentive motivation and increased control over behavior by drug-associated stimuli may contribute to aspects of compulsive drug-seeking and drug-taking behaviors. This study investigated the consequences of repeated nicotine treatment on the acquisition and performance of Pavlovian discriminative approach behavior, a measure of reward-related learning, in male rats. Water-restricted rats were trained to associate a compound conditioned stimulus (tone+light) with the availability of water (the unconditioned stimulus) in 15 consecutive daily sessions. In separate experiments, rats were repeatedly treated with nicotine (0.35 mg/kg, s.c.) either (1) prior to the onset of training, (2) after each daily training session was completed (ie postsession injections), or (3) received nicotine both before the onset of training as well as after each daily training session. In this study, all nicotine treatment schedules increased Pavlovian discriminative approach behavior and, thus, prior repeated exposure to nicotine, repeated postsession nicotine injections, or both, facilitated reward-related learning.
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Affiliation(s)
- Peter Olausson
- Department of Psychiatry, Laboratory of Molecular Psychiatry, Yale University, New Haven, CT, USA
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10
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Phillips GD, Setzu E, Vugler A, Hitchcott PK. Immunohistochemical assessment of mesotelencephalic dopamine activity during the acquisition and expression of Pavlovian versus instrumental behaviours. Neuroscience 2003; 117:755-67. [PMID: 12617979 DOI: 10.1016/s0306-4522(02)00799-6] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Dopaminergic activity during Pavlovian or instrumental learning in key target regions of the mesotelencephalic dopamine system was investigated immunohistochemically using antibodies raised against glutaraldehyde-conjugated dopamine. Experiment 1 examined dopamine immunoreactivity during acquisition of a Pavlovian conditioned-approach response. Observations were taken at three stages of learning: initial, intermediate and asymptotic; each with a conditioned stimulus+ (CS+) group for whom visual or auditory stimuli immediately preceded an unconditioned stimulus (sucrose), and a conditioned stimulus- (CS-) group for whom stimuli and the unconditioned stimulus were unpaired. Animals learned to approach the alcove during CS+ presentations, whilst approach behaviour of the CS- group remained low. In general, target regions exhibiting a dopaminergic reaction responded maximally during the intermediate stage of acquisition, and were less responsive initially, and not responsive at all at asymptote. Specifically, the pattern of dopaminergic response was: shell more than core of the nucleus accumbens; prefrontal cortex, central and basolateral nuclei of the amygdala also significantly responsive. Mediodorsal and laterodorsal striatal regions were reactive only very early in training. Experiment 2 examined dopaminergic reaction following acquisition of a novel conditioned instrumental response. The conditioned response+ (CR+) group responded at a much higher rate on the lever for which unconditioned stimulus-associated stimuli were presented, than on the control lever. The conditioned response- (CR-) group responded at a low rate on both levers. In contrast with experiment 1, the most responsive regions were the core of the nucleus accumbens, medial prefrontal cortex and basolateral area of the amygdala. Thus, the acquisition, but not expression of Pavlovian associations activated dopamine within several key target regions of the mesotelencephalic dopamine system, and preferentially within the shell rather than core of the nucleus accumbens. By contrast, acquisition of a novel instrumental response preferentially activated the core of the nucleus accumbens, and basolateral area of the amygdala. These data carry significant implications for the potential role of these regions in learning and memory.
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Affiliation(s)
- G D Phillips
- Department of Psychology, University of York, Heslington, York YO10 5DD, UK.
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Abstract
dopamine D3 receptor is preferentially localized to the mesocorticolimbic dopaminergic system and has been hypothesized to play a role in cocaine addiction. To study the involvement of the D3 receptor in brain mechanisms and behaviors commonly assumed to be involved in the addicting properties of cocaine, the potent and selective D3 receptor antagonist trans-N-[4-[2-(6-cyano-1,2,3,4-tetrahydroisoquinolin-2-yl)ethyl] cyclohexyl]-4-quinolininecarboxamide (SB-277011-A) was administered to laboratory rats, and the following measures were assessed: (1) cocaine-enhanced electrical brain-stimulation reward, (2) cocaine-induced conditioned place preference, and (3) cocaine-triggered reinstatement of cocaine seeking behavior. Systemic injections of SB-277011-A were found to (1) block enhancement of electrical brain stimulation reward by cocaine, (2) dose-dependently attenuate cocaine-induced conditioned place preference, and (3) dose-dependently attenuate cocaine-triggered reinstatement of cocaine seeking behavior. Thus, D3 receptor blockade attenuates both the rewarding effects of cocaine and cocaine-induced drug-seeking behavior. These data suggest an important role for D3 receptors in mediating the addictive properties of cocaine and suggest that blockade of dopamine D3 receptors may constitute a new and useful target for prospective pharmacotherapies for cocaine addiction.
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Phillips GD, Harmer CJ, Hitchcott PK. Blockade of sensitisation-induced facilitation of appetitive conditioning by post-session intra-amygdala nafadotride. Behav Brain Res 2002; 134:249-57. [PMID: 12191811 DOI: 10.1016/s0166-4328(02)00034-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Prior D-amphetamine experience has been reported to enhance appetitive Pavlovian conditioning. The present study assessed the involvement of the mesoamygdaloid dopamine projection in this effect. Bilateral post-session intra-amygdala infusions of the D3 dopamine receptor antagonist, L-nafadotride, or vehicle were given during acquisition of a Pavlovian association in sensitised and unsensitised rats. During these sessions, subjects received presentations of a stimulus (CS(+)) paired with 10% sucrose availability. A second stimulus (CS(-)) was also presented but never paired with sucrose. Sensitised animals infused post-session with vehicle acquired a Pavlovian conditioned approach response during CS(+) presentations more rapidly than controls, as we have shown previously. However, post-session intra-amygdala L-nafadotride selectively retarded conditioned responding to the CS(+) in both groups of animals, abolishing the difference between sensitised and unsensitised rats. These results, therefore, extend the evidence for the involvement of the mesoamygdaloid dopamine projection in Pavlovian conditioning, and the facilitation of associative learning following sensitisation.
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Affiliation(s)
- Gavin D Phillips
- Behavioural Neuroscience Laboratory, Department of Psychology, University of York, Heslington, York YO10 5DD, UK.
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Phillips GD, Harmer CJ, Hitchcott PK. Isolation rearing-induced facilitation of Pavlovian learning: abolition by postsession intra-amygdala nafadotride. Physiol Behav 2002; 76:677-84. [PMID: 12127008 DOI: 10.1016/s0031-9384(02)00802-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
It has been shown previously in this laboratory that rats reared in social isolation acquire a Pavlovian-conditioned approach task much more rapidly than their respective controls. This study assessed the involvement specifically of the mesoamygdaloid dopamine pathway in this facilitated learning of isolates. Thus, animals were required to associate arbitrary stimuli with a pulsed light stimulus (unconditioned stimulus, US). The US, while without biological significance, was nevertheless capable of eliciting an intrinsic and sustained alerting response. Procedures ensured that the arbitrary stimuli (tone or clicker) did not elicit a response in the first instance, and were presented either paired (CS+) or unpaired (CS-) with the US. Isolates and socially reared controls received intra-amygdala infusions of the D3 dopamine receptor antagonist, L-nafadotride, or vehicle immediately following the end of each training session. The conditioned response increased over sessions in both groups of vehicle-infused rats during presentations of the CS+ stimulus, but not CS-, and isolates acquired this association more rapidly than controls. However, acquisition of this association was abolished by postsession intra-amygdala L-nafadotride. Responding to the US was largely unaffected by drug or rearing conditions. Hence, these data provide strong evidence for the specific involvement of the mesoamygdaloid dopamine projection in the facilitation of associative learning by isolation rearing.
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Affiliation(s)
- Gavin D Phillips
- Department of Psychology, University of York, Heslington, York YO10 5DD, UK.
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14
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Alvarez EO, Ruarte MB. Role of glutamate receptors in the nucleus accumbens on behavioural responses to novel conflictive and non-conflictive environments in the rat. Behav Brain Res 2001; 123:143-53. [PMID: 11399327 DOI: 10.1016/s0166-4328(01)00190-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The possible role of glutamic acid locally applied into the nucleus accumbens on exploratory behaviours measured in 'conflictive' and 'non-conflictive' environments was studied in adult male rats. As a model of conflictive environment, the elevated asymmetric-plus maze (APM) was used. As a model of a non-conflictive environment, a modified holeboard enriched with an object (OVM) was used. In order to characterize the possible glutamic acid receptors involved, the following antagonists were also used: AP3 (antagonist of the metabotropic glutamic acid receptor), AP7 (antagonist of NMDA glutamic acid receptor, and CNQX (antagonists of kainate/AMPA glutamic acid receptor). Results showed that injection of glutamic acid into the nucleus accumbens induced in the APM a decrease of exploration and an increase of the permanency score (non-exploratory behaviours) of the 'High and Low wall' arm. However, in the 'Two High Walls' arm, glutamic acid decreased permanency. In the OVM, no major changes in the motor activity were observed with glutamic acid. Nevertheless, the vertical activity (an index of rearing) and head-dipping were inhibited by the amino-acid treatment. In the APM, the decrease of exploration induced by glutamic acid was blocked by all three receptor antagonists. In the non-exploratory behaviours, the facilitatory effect observed in the 'High and Low walls' arm was blocked only by AP7 and CNQX. The inhibitory action of glutamic acid on the permanency score in the 'Two High Walls' arm was not blocked by the receptors antagonists. In the OVM, AP7 and CNQX were effective in blocking the inhibition of glutamic acid on the vertical activity, but in head-dipping, only AP3 and CNQX were able to block the effect of the amino acid on this behaviour. In conclusion, the present results are compatible with the concept that glutamatergic input fibres to the nucleus accumbens modulate the expression of exploratory behaviour induced by novelty in conflictive and non-conflictive conditions.
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Affiliation(s)
- E O Alvarez
- Unidad de Neuroquímica y Farmacología del Comportamiento, Farmacología, Facultad de Ciencias Médicas,Universidad Nacional de Cuyo, Casilla de Correo 33, Mendoza 5500, Argentina
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15
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Childress AR, O'Brien CP. Dopamine receptor partial agonists could address the duality of cocaine craving. Trends Pharmacol Sci 2000; 21:6-9. [PMID: 10637646 DOI: 10.1016/s0165-6147(99)01422-4] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- A R Childress
- Department of Psychiatry, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6178, USA.
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