Repeated association of drugs of abuse with context leads to long-lasting behavioral responses that reflect reward-controlled learning and participate in the establishment of addiction. Reactivation of consolidated memories is known to produce a reconsolidation process during which memories undergo a labile state. We investigated whether reexposure to drugs had similar effects. Cocaine administration activates extracellular signal-regulated kinase (ERK) in the striatum, and ERK activation is required for the acquisition of cocaine-induced conditioned place preference (CPP). When mice previously conditioned for cocaine-place preference were reexposed to cocaine in the drug-paired compartment after systemic administration of SL327, an inhibitor of ERK activation, CPP response was abolished 24 h later. This procedure also abolished the phosphorylation of ERK and glutamate receptor-1 observed in the ventral and dorsal striatum, 24 h later, during CPP test. Erasure of CPP by SL327 required the combination of cocaine administration and drug-paired context and did not result from enhanced extinction. Similarly, reexposure to morphine in the presence of SL327 long-lastingly abolished response of previously learned morphine-CPP. The effects of SL327 on cocaine-or morphine-CPP were reproduced by protein synthesis inhibition. In contrast, protein synthesis inhibition did not alter previously acquired locomotor sensitization to cocaine. Our findings show that an established CPP can be disrupted when reactivation associates both the conditioned context and drug administration. This process involves ERK, and systemic treatment preventing ERK activation during reexposure erases the previously learned behavioral response. These results suggest potential therapeutic strategies to explore in the context of addiction.cocaine ͉ locomotor sensitization ͉ morphine ͉ protein kinase inhibitor ͉ reconsolidation A ddiction to licit or illicit drugs is a major public health issue worldwide. This behavioral disease results from a combination of environmental and genetic factors that are the focus of intense research. One important property of drugs of abuse is their common ability to increase extracellular dopamine (DA) in the nucleus accumbens (NAcc) (1). They are thought to mimic and divert thereby a physiological learning mechanism that results from the ability of DA neurons to code for errors in reward prediction (2). In support of this model, electrophysiological studies indicate that DA controls the flow of information through the striatum as well as the plasticity of corticostriatal synapses and plays a critical role in the acquisition and expression of drug-related behaviors (3, 4).Some molecular mechanisms underlying long-lasting behavioral alterations produced by drugs of abuse have been identified (see refs. 5 and 6 for reviews). Recently, the role of extracellular signal-regulated kinase (ERK) 1 and 2, and more specifically ERK2, an intracellular pathway activated by most drugs of abuse, has attracted much attention (7-10). In ...

SummaryDopamine orchestrates motor behavior and reward-driven learning. Perturbations of dopamine signaling have been implicated in several neurological and psychiatric disorders, and in drug addiction. The actions of dopamine are mediated in part by the regulation of gene expression in the striatum, through mechanisms that are not fully understood. Here, we show that drugs of abuse, as well as natural reinforcement learning, promote the nuclear accumulation of dopamine-and cAMPregulated phosphoprotein Mr=32,000 . This accumulation is mediated through a signaling cascade involving dopamine D1 receptors, cAMP-dependent activation of protein phosphatase-2A, dephosphorylation of DARPP-32 at Ser-97 and inhibition of its nuclear export. The nuclear accumulation of DARPP-32, a potent inhibitor of protein phosphatase-1, increases phosphorylation of histone H3, an important component of nucleosomal response. Mutation of Ser-97 profoundly alters behavioral effects of drugs of abuse, and decreases motivation for food, underlining the functional importance of this signaling cascade.Midbrain dopamine (DA) neurons, activated following unexpected rewarding stimuli, are essential in reinforcement learning 1 . Drugs of abuse mimic the physiological action of DA neurons by increasing their firing rate or preventing DA uptake. Thus, they enhance extracellular DA levels in the forebrain, especially in the nucleus accumbens (NAc), a key structure required for the reinforcing effects of addictive drugs [2][3][4] . To understand how DA mediates reward-controlled learning, it is necessary to identify the intracellular events that trigger gene transcription alterations supporting long-lasting synaptic changes [5][6][7] . DARPP-32 (dopamine-and cAMP-regulated phosphoprotein, Mr=32,000) 8 is a prominent mediator of DA NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript signaling in the striatum 9 . DARPP-32 is highly enriched in striatal GABAergic mediumsize spiny neurons (MSN) 10 . Following activation of DA D1 receptors (D1R), DARPP-32 is phosphorylated by cAMP-dependent protein kinase (PKA) at Thr-34 and converted into a potent inhibitor of the multifunctional serine/threonine protein phosphatase-1 (PP1) 11 . DARPP-32-mediated inhibition of PP1 increases the phosphorylation of neurotransmitter receptors and ion channels crucial for synaptic function and plasticity 9 . DARPP-32 also regulates nuclear events, as demonstrated by alterations of drug-induced gene expression in mice lacking DARPP-32 or bearing a point mutation of 13 . Part of the control exerted by DARPP-32 on transcription is mediated by activation of the ERK pathway, dependent on the concomitant stimulation of D1R and glutamate NMDA receptors 13,14 . However, the precise mechanisms of information transfer from the cytoplasm to the nucleus of striatal neurons are still poorly characterized. Drugs of abuse and reinforcement learning trigger nuclear accumulation of DARPP-32 in striatal neuronsDARPP-32 has been extensively characterized as a cytoplasmic...