Activation and role of the medial prefrontal cortex (mPFC) in extinction of ethanol-induced associative learning in mice
Introduction
Rehabilitation from drug- and alcohol-associated addictive behaviors represents a uniquely difficult task in the clinic. Because patients who pursue rehabilitation treatments have most often spent many years with an addiction, breaking the control that these drug-seeking behaviors exert over a patient’s everyday life is a daunting task—one that most often ends in relapse. Development of, and relapse to, addictive disorders is thought to be strongly influenced by a broad spectrum of drug-associated environmental cues and contexts that, following years of drug-related learning, are able to initiate and maintain drug-seeking behaviors (for review see Duka, Crombag, & Stephens, 2010). It is for this reason that rehabilitation treatments of drug- and alcohol-associated addictive disorders have included cue-exposure therapy (CET)—a type of extinction training during which previously drug-paired cues are presented in a nonreinforced manner in hopes of reducing their valence and subsequent behavioral control (e.g., Drummond & Glautier, 1994). However, despite the effectiveness of extinction to reduce drug-seeking behavior in animals (for review see Millan, Marchant, & McNally, 2011), cue-exposure therapy has been largely ineffective at increasing rates of abstinence (Conklin & Tiffany, 2002). Therefore, it is important to continue to further our understanding of the neurobiological substrates underlying extinction of drug- and alcohol-seeking behavior in animals in order to improve rehabilitation treatments, including CET, in humans.
In the conditioned place preference (CPP) model of drug-induced associative learning, a neutral stimulus attains significant incentive value after being repeatedly paired with a drug of abuse such as ethanol (EtOH) (Cunningham, Groblewski, & Voorhees, 2011). Following this straightforward Pavlovian-conditioning procedure, approach behavior to the EtOH-paired conditioned stimulus (CS) is assessed during a preference test. In subsequent extinction of CPP, animals are exposed to the same set of cues, but in a nonreinforced manner (i.e., in the absence of EtOH). Similar to acquisition, extinction of CPP represents associative learning that depends on reward-prediction error, and both phases of learning can be represented by negative exponential functions of associative strength, as reflected in the model described by Rescorla and Wagner (1972). The extinction phase of associative behaviors such as CPP is thought to weaken the conditioned response elicited by the CS through an inhibitory mechanism (Konorski, 1967, Pavlov, 1927). Furthermore, the behavioral inhibition observed during extinction is thought to involve de novo memory formation that leaves the original association intact (Bouton, 2004).
Recent evidence suggests that the medial prefrontal cortex (mPFC) is involved in both the expression and extinction of conditioned fear and operant drug-seeking behavior (for review see Peters, Kalivas, & Quirk, 2009). Specifically, the prelimbic (PL) subregion has been suggested to be primarily involved in expression of conditioned behaviors while the infralimbic (IL) subregion is involved in consolidation (and therefore also retrieval) of extinction (Quirk and Mueller, 2008, Vidal-Gonzalez et al., 2006). Following extinction, exposure to cues capable of reinstating drug-seeking behavior has been shown to cause significant activation of both the PL and IL subregions of the mPFC (Zavala, Biswas, Harlan, & Neisewander, 2007). With regards to expression of non-operant drug-induced associative learning, a brief cocaine-CPP expression test resulted in significant activation of the PL (Miller & Marshall, 2005) while inactivation of the mPFC (both PL & IL) impaired extinction of amphetamine-CPP (Hsu & Packard, 2008). Additionally, inactivation of the mPFC reinstated heroin-CPP, an effect the authors attributed to a disinhibition of place preference expression (Ovari & Leri, 2008). Contrary to these findings however, Zavala, Weber, Rice, Alleweireldt, and Neisewander (2003) reported that PL lesions had no effect on acquisition, expression, or extinction of cocaine-induced CPP. Thus, despite its broad support for a role in extinction of conditioned fear and drug-induced operant behavior, there remains conflicting evidence for the role of the mPFC in extinction of CPP.
The involvement of the mPFC in extinction of ethanol (EtOH)-induced associative learning has received even less attention and it remains unknown if the PL and IL subregions within the mPFC are necessary for extinction of Pavlovian-conditioned EtOH-seeking behaviors such as EtOH-CPP in mice. Previous reports that involved operant EtOH procedures have shown inconsistent evidence for the involvement of mPFC in extinction of EtOH-seeking behavior. Specifically, Dayas, Liu, Simms, and Weiss (2007) reported cue-induced activation of the mPFC following exposure to cues capable of reinstating self-administration in rats after extinction. In contrast, however, Hamlin, Newby, and McNally (2007) reported no significant effect of extinction on mPFC activation after contextual renewal of EtOH-responding. Interestingly, Topple, Hunt, and McGregor (1998) showed significant PL activation following exposure to the EtOH-paired operandum during an extinction session. Thus, although the data remain somewhat inconsistent, it appears that the mPFC may be activated in situations when EtOH is expected but not received (i.e., a large EtOH-reward prediction error exists), such as extinction and/or reinstatement. However, the aforementioned experiments were performed using operant procedures in rats and thus it remains unknown how extinction of the EtOH-cue contingency would affect mPFC activation elicited by a Pavlovian-conditioned cue in the absence of an instrumental response.
Therefore, although the literature supports the assertion that the PL and IL subregions exhibit differential roles in expression and extinction of cue-induced behaviors (e.g., Peters et al., 2009), these studies have primarily been performed in operant procedures in rats with drugs other than EtOH, and it is therefore unclear if the distinction between these subregions generalizes across species and to extinction of EtOH-induced associative learning in mice.
The current experiments were performed in order to first understand how extinction of an EtOH-cue association affects cue-induced activation of the mPFC and second, to examine the effects of direct manipulations of the mPFC on extinction of EtOH-induced associative learning in mice. Experiment 1 utilized immunohistochemical (IHC) analysis of the activated transcription factor, phospho-cAMP response element-binding protein (pCREB), to examine the effects of extinction on mPFC (PL and IL) activation following a brief exposure to an EtOH-paired cue capable of eliciting approach behavior in mice. Experiment 2 then used electrolytic lesions of the mPFC to confirm a functional role of this region in extinction of EtOH-CPP in mice. It was hypothesized that: (1) the mPFC would show cue-induced expression of pCREB that was sensitive to changes in the EtOH-cue contingency following extinction, and (2) mPFC lesions would impair extinction of EtOH-CPP. These experiments were intended to further clarify the roles of the PL and IL subregions of the mPFC in processing changes of EtOH-cue contingencies that underlie extinction of EtOH-induced associative learning in mice.
Section snippets
Subjects
Adult, male DBA/2 J mice (n = 111) were obtained from Jackson Laboratory (Sacramento, CA) at 6–7 weeks of age and allowed to acclimate to the animal colony for 2 weeks before experiments commenced. Mice were housed, four to a cage, in cob bedding in a Thoren rack with water and food available ad libitum throughout each experiment. All experiments were conducted during the light phase (7:00–19:00). The Oregon Health & Science University IACUC approved all experimental procedures.
Drugs
Ethanol (20% v/v in
Experiment 1
A total of two animals (approximately 9%) were removed from analysis for exhibiting less than 50% preference on Test 1.
Cue-induced activation of mPFC-CREB is sensitive to extinction of EtOH-induced associative learning in mice
The results of Experiment 1 revealed that the PL and IL subregions of the mPFC were activated following a brief exposure to an EtOH-paired cue that was capable of eliciting Pavlovian approach behavior. Interestingly, the cue-induced CREB activation observed in both of these regions was absent when the EtOH-cue contingency was extinguished. In contrast to the mPFC, analysis of the NAc (core and shell) and BLA revealed no evidence of activation induced by exposure to the EtOH-paired cue. These
Acknowledgments
This research was supported by Grants from the National Institutes of Health (AA018052, AA007702, AA007468) and awards from the American Psychological Association and the N.L. Tartar Research Fund.
References (48)
- et al.
Goal-directed instrumental action: Contingency and incentive learning and their cortical substrates
Neuropharmacology
(1998) - et al.
Distinct patterns of neural activation associated with ethanol seeking: Effects of naltrexone
Biological Psychiatry
(2007) - et al.
Blockade of opioid receptors in anterior cingulate cortex disrupts ethanol-seeking behavior in mice
Behavioural Brain Research
(2011) - et al.
Inhibition of extracellular signal-regulated kinase (ERK) activity with SL327 does not prevent acquisition, expression, and extinction of ethanol-seeking behavior in mice
Behavioural Brain Research
(2011) - et al.
The neural correlates and role of D1 dopamine receptors in renewal of extinguished alcohol-seeking
Neuroscience
(2007) - et al.
Control of recruitment and transcription-activating function of CBP determines gene regulation by NMDA receptors and L-type calcium channels
Neuron
(1999) - et al.
Inducible and constitutive transcription factors in the mammalian nervous system: Control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins
Brain Research. Brain Research Reviews
(1998) - et al.
FOS expression induced by an ethanol-paired conditioned stimulus
Pharmacology, Biochemistry, and Behavior
(2007) - et al.
Medial prefrontal cortex infusions of bupivacaine or AP-5 block extinction of amphetamine conditioned place preference
Neurobiology of Learning and Memory
(2008) - et al.
What turns CREB on?
Cellular Signalling
(2004)
Extinction of drug seeking
Behavioural Brain Research
Inactivation of the ventromedial prefrontal cortex mimics re-emergence of heroin seeking caused by heroin reconditioning
Neuroscience Letters
Time course of phosphorylated CREB and Fos-like immunoreactivity in the hypothalamic supraoptic nucleus after salt loading
Brain Research. Molecular Brain Research
Phosphorylated cAMP response element binding protein in the mouse brain after fear conditioning: Relationship to Fos production
Brain Research. Molecular Brain Research
Possible neural substrates of beer-craving in rats
Neuroscience Letters
Fos and glutamate AMPA receptor subunit coexpression associated with cue-elicited cocaine-seeking behavior in abstinent rats
Neuroscience
Role of the prelimbic subregion of the medial prefrontal cortex in acquisition, extinction, and reinstatement of cocaine-conditioned place preference
Brain Research
MAPK regulation of gene expression in the central nervous system
Acta Neurobiologiae Experimentalis (Wars)
Alcohol-induced c-Fos expression in the Edinger–Westphal nucleus: Pharmacological and signal transduction mechanisms
The Journal of Pharmacology and Experimental Therapeutics
Post-retrieval disruption of a cocaine conditioned place preference by systemic and intrabasolateral amygdala beta2- and alpha1-adrenergic antagonists
Learning & Memory
Context and behavioral processes in extinction
Learning & Memory
Applying extinction research and theory to cue-exposure addiction treatments
Addiction
Pavlovian drug conditioning
Apparatus bias and place conditioning with ethanol in mice
Psychopharmacology (Berl)
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