By using high-density oligonucleotide arrays, we profiled gene expression in reward-related brain regions of rats that developed escalated cocaine intake after extended access to cocaine (6 h per day). Rats allowed restricted daily access to cocaine (only 1 h) that displayed a stable level of cocaine intake and cocaine naive rats were used for controls. Four analysis methods were compared: Affymetrix MICROARRAY SUITE 4 and MICROARRAY SUITE 5, which use perfect-match-minus-mismatch models, and DCHIP and RMA, which use perfect-match-only models to generate expression values. Results were validated by RT-PCR in individual animals from an independent replication of the experiment. A small number of genes was associated with escalated cocaine intake (ESC genes). Unexpectedly, of the brain regions examined [prefrontal cortex, nucleus accumbens, septum, lateral hypothalamus (LH), amygdala, and ventral tegmental area], the LH was the most transcriptionally responsive in escalation of cocaine intake. Most of the ESC genes identified are also expressed during synaptogenesis and synaptic plasticity and include genes that code for several presynaptic and postsynaptic proteins involved in neurotransmission. These results suggest that LH intrinsic circuitry undergoes a structural reorganization during escalation of cocaine use. This remodeling of LH circuitry could contribute to the chronic deficit in reward function that has been hypothesized to drive the transition to drug addiction. Results also support the value of using multiple analysis strategies to identify the most robust changes in gene expression and to compensate for the biases that affect each strategy.release machinery ͉ ␦-catenin ͉ Glu receptor-interacting protein 2 ͉ PKC␥ ͉ fractalkine A current challenge for the neuroscience of drug addiction is to understand the molecular mechanisms responsible for the development of compulsive drug use (1). Such a transition is generally associated with a pattern of escalating drug use whereby consumption increases over time and becomes increasingly difficult to control. In the present study, we investigated gene expression changes associated with drug addiction by using an animal model that demonstrates escalation of cocaine intake. In this model, drug intake gradually escalates when daily access to the drug is increased to Ն6 h [long access (LgA)] (2, 3), whereas with only 1 h of access per day [short access (ShA)], drug intake remains low and stable over time. The difference in cocaine consumption between ShA and LgA animals has been hypothesized to model the difference drawn by clinicians between controlled and compulsive drug use (2, 3). This view is supported by recent results showing that escalation in cocaine intake in LgA animals is associated with an increased motivation to seek and to take cocaine and with a persistent downregulation of brain reward function when compared with ShA animals (3-5). Therefore, escalation of cocaine intake in LgA rats appears to replicate the behavioral and neuroadaptive changes assoc...

Intermittent models of alcohol exposure that mimic human patterns of alcohol consumption produce profound physiological and biochemical changes and induce rapid increases in alcohol self-administration. We used high-density oligonucleotide microarrays to investigate gene expression changes during chronic intermittent alcohol exposure in three brain regions that receive mesocorticolimbic dopaminergic projections and that are believed to be involved in alcohol's reinforcing actions: the medial prefrontal cortex, the nucleus accumbens and the amygdala. An independent replication of the experiment was used for RT-PCR validation of the microarray results. The protein kinase A inhibitor alpha (PKI-alpha, Pkia), a member of the endogenous PKI family implicated in reducing nuclear PKA activity, was found to be increased in all three regions tested. Conversely, we observed a downregulation of the expression of several PKA-regulated transcripts in one or more of the brain regions studied, including the activity and neurotransmitter-regulated early gene (Ania) - 1, -3, -7, -8, the transcription factors Egr1 and NGFI-B (Nr4a1) and the neuropeptide NPY. Reduced expression of PKA-regulated genes in mesocorticolimbic projection areas may have motivational significance in the rapid increase in alcohol self-administration induced by intermittent alcohol exposure.

Adaptations in the anterior cingulate cortex (ACC) have been implicated in alcohol and drug addiction. To identify genes that may contribute to excessive drinking, here we performed microarray analyses in laser microdissected rat ACC after a single or repeated administration of an intoxicating dose of alcohol (3g/kg). Expression of the small G protein K-ras was reduced following both single and repeated alcohol administration. We also observed that voluntary alcohol intake in K-ras heterozygous null mice (K-ras +/− ) did not increased after withdrawal from repeated cycles of intermittent ethanol vapor exposure, unlike in their wild-type littermates. To identify K-ras regulated pathways, we then profiled gene expression in the ACC of K-ras +/− , heterozygous null mice for the K-ras negative regulator Nf1 (Nf1 +/− ) and wild-type mice following repeated administration of an intoxicating dose of alcohol. Pathway analysis showed that alcohol differentially affected various pathways in a K-ras dependent manner -some of which previously shown to be regulated by alcohol -including the insulin/PI3K pathway, the NF-kB, the phosphodiesterases (PDEs) pathway, the Jak/Stat and the adipokine signaling pathways. Altogether, the data implicate K-ras-regulated pathways in the regulation of excessive alcohol drinking after a history of dependence.

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