Robison AJ, Vialou V, Mazei-Robison M, Feng J, Kourrich S, Collins M et al. Behavioral and Structural Responses to Chronic Cocaine Require a Feedforward Loop Involving DeltaFosB and Calcium/Calmodulin-Dependent Protein Kinase II in the Nucleus Accumbens Shell. J Neurosci 33: 4295-4307

Fishberg Department of Neuroscience and Friedman Brain Institute, Mount Sinai School of Medicine, New York, New York, 10029, Departments of Neuroscience and Psychology, Institute of Human Genetics, University of Minnesota, Minneapolis, Minnesota 55455, Committee on the Neurobiology of Addictive Disorders, The Scripps Research Institute, La Jolla, California 92037 Depressive Disorders Program, Douglas Mental Health University Institute and McGill University, Montréal, Québec, Canada, H4H 1R3, and Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 03/2013; 33(10):4295-4307. DOI: 10.1523/JNEUROSCI.5192-12.2013
Source: PubMed


The transcription factor ΔFosB and the brain-enriched calcium/calmodulin-dependent protein kinase II (CaMKIIα) are induced in the nucleus accumbens (NAc) by chronic exposure to cocaine or other psychostimulant drugs of abuse, in which the two proteins mediate sensitized drug responses. Although ΔFosB and CaMKIIα both regulate AMPA glutamate receptor expression and function in NAc, dendritic spine formation on NAc medium spiny neurons (MSNs), and locomotor sensitization to cocaine, no direct link between these molecules has to date been explored. Here, we demonstrate that ΔFosB is phosphorylated by CaMKIIα at the protein-stabilizing Ser27 and that CaMKII is required for the cocaine-mediated accumulation of ΔFosB in rat NAc. Conversely, we show that ΔFosB is both necessary and sufficient for cocaine induction of CaMKIIα gene expression in vivo, an effect selective for D1-type MSNs in the NAc shell subregion. Furthermore, induction of dendritic spines on NAc MSNs and increased behavioral responsiveness to cocaine after NAc overexpression of ΔFosB are both CaMKII dependent. Importantly, we demonstrate for the first time induction of ΔFosB and CaMKII in the NAc of human cocaine addicts, suggesting possible targets for future therapeutic intervention. These data establish that ΔFosB and CaMKII engage in a cell-type- and brain-region-specific positive feedforward loop as a key mechanism for regulating the reward circuitry of the brain in response to chronic cocaine.

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    • "One might expect from the published literature, which shows that transgenic ΔFosB overexpressing mice show increased sensitivity to cocaine reward and self-administration at low drug doses (Kelz et al., 1999; Colby et al., 2003; Vialou et al., 2010; Robison et al., 2013), that the ΔFosB-overexpressing rats in the current experiment would display increased propensity for cocaine self-administration and seeking. In the current experiments, however, overexpressing ΔFosB in the NAc shell decreased cocaine intake and cocaine seeking during extinction and reinstatement, indicating reduced motivation for cocaine. "
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    ABSTRACT: Environmental enrichment produces protective addiction and depression phenotypes in rats. ΔFosB is a transcription factor that regulates reward in the brain and is induced by psychological stress as well as drugs of abuse. However, the role played by ΔFosB in the protective phenotypes of environmental enrichment has not been well studied. Here, we demonstrate that ΔFosB is differentially regulated in rats reared in an isolated condition (IC) compared to those in an enriched condition (EC) in response to restraint stress or cocaine. Chronic stress or chronic cocaine treatment each elevates ΔFosB protein levels in the nucleus accumbens (NAc) of IC rats, but not of EC rats due to an already elevated basal accumulation of ΔFosB seen under EC conditions. Viral-mediated overexpression of ΔFosB in the NAc shell of pair-housed rats (i.e., independent of environmental enrichment/isolation) increases operant responding for sucrose when motivated by hunger, but decreases responding in satiated animals. Moreover, ΔFosB overexpression decreases cocaine self-administration, enhances extinction of cocaine seeking, and decreases cocaine-induced reinstatement of intravenous cocaine self-administration; all behavioral findings consistent with the enrichment phenotype. In contrast, however, ΔFosB overexpression did not alter responses of pair-housed rats in several tests of anxiety- and depression-related behavior. Thus, ΔFosB in the NAc the shell mimics the protective addiction phenotype, but not the protective depression phenotype of environmental enrichment.
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    ABSTRACT: Synaptic modifications in nucleus accumbens (NAc) medium spiny neurons (MSNs) play a key role in adaptive and pathological reward-dependent learning, including maladaptive responses involved in drug addiction. NAc MSNs participate in two parallel circuits, direct and indirect pathways that subserve distinct behavioral functions. Modification of NAc MSN synapses may occur in part via changes in the transcriptional potential of certain genes in a cell type-specific manner. The transcription factor FosB is one of the key proteins implicated in the gene expression changes in NAc caused by drugs of abuse, yet its effects on synaptic function in NAc MSNs are unknown. Here, we demonstrate that overexpression of FosB decreased excitatory synaptic strength and likely increased silent synapses onto D1 dopamine receptor-expressing direct pathway MSNs in both the NAc shell and core. In contrast, FosB likely decreased silent synapses onto NAc shell, but not core, D2 dopamine receptor-expressing indirect pathway MSNs. Analysis of NAc MSN dendritic spine morphology revealed that FosB increased the density of immature spines in D1 direct but not D2 indirect pathway MSNs. To determine the behavioral consequences of cell type-specific actions of FosB, we selectively overexpressed FosB in D1 direct or D2 indirect MSNs in NAc in vivo and found that direct (but not indirect) pathway MSN expression enhances behavioral responses to cocaine. These results reveal that FosB in NAc differentially modulates synaptic properties and reward-related behaviors in a cell type- and subregion-specific fashion.
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