The transcriptional response to six commonly-abused drugs was assessed in the mouse brain revealing common modules of drug-induced genes.

Chronic opioid use leads to the structural reorganization of neuronal networks, involving genetic reprogramming in neurons and glial cells. Our previous in vivo studies have revealed that a significant fraction of the morphine-induced alterations to the striatal transcriptome included glucocorticoid (GC) receptor (GR)-dependent genes. Additional analyses suggested glial cells to be the locus of these changes. In the current study, we aimed to differentiate the direct transcriptional effects of morphine and a GR agonist on primary striatal neurons and astrocytes. Whole-genome transcriptional profiling revealed that while morphine had no significant effect on gene expression in both cell types, dexamethasone significantly altered the transcriptional profile in astrocytes but not neurons. We obtained a complete dataset of genes undergoing the regulation, which includes genes related to glucose metabolism (Pdk4), circadian activity (Per1) and cell differentiation (Sox2). There was also an overlap between morphine-induced transcripts in striatum and GR-dependent transcripts in cultured astrocytes. We further analyzed the regulation of expression of one gene belonging to both groups, serum and GC regulated kinase 1 (Sgk1). We identified two transcriptional variants of Sgk1 that displayed selective GR-dependent upregulation in cultured astrocytes but not neurons. Moreover, these variants were the only two that were found to be upregulated in vivo by morphine in a GR-dependent fashion. Our data suggest that the morphine-induced, GR-dependent component of transcriptome alterations in the striatum is confined to astrocytes. Identification of this mechanism opens new directions for research on the role of astrocytes in the central effects of opioids. V V C 2013 Wiley Periodicals, Inc.

The present results suggest that prenatal exposure to VPA may lead to the decreased activity of the striatal enkephalinergic system and in consequence to increased anxiety and disregulated basal hedonic tone observed in VPA rats. Presented results are discussed in light of interactions between enkephalinergic, GABAergic, and dopaminergic systems in the striatum and mesolimbic areas of the brain.

Chronic exposure to opiates produces dependence and addiction, which may result from neuroadaptations in the dopaminergic reward pathway and its target brain regions. The neuronal protein ␣-synuclein has been implicated in neuronal plasticity and proposed to serve as a negative regulator of dopamine neurotransmission. Thus, ␣-synuclein could mediate some effects of opiates in the brain. The present study investigated the influence of acute and chronic morphine administration on ␣-synuclein mRNA and protein expression in the brains of mice. Downregulation of ␣-synuclein mRNA was observed in the basolateral amygdala, dorsal striatum, nucleus accumbens, and ventral tegmental area of mice withdrawn from chronic morphine treatment. The changes were the most pronounced after longer periods of withdrawal (48 h). In contrast, levels of ␣-synuclein protein, as assessed by Western blotting, were significantly increased in the amygdala and striatum/accumbens (but not in the mesencephalon) of morphine-withdrawn mice. In both brain regions, levels of ␣-synuclein were elevated for as long as 2 weeks after treatment cessation. Because ␣-synuclein is a presynaptic protein, the detected opposite changes in its mRNA and protein levels are likely to take place in different populations of projection neurons whose somata are in different brain areas. Axonal localization of ␣-synuclein was confirmed by immunofluorescent labeling. An attempt to identify postsynaptic neurons innervated by ␣-synuclein-containing axon terminals revealed their selective apposition to calbindin D28K-negative projection neurons in the basolateral amygdala. The observed changes in ␣-synuclein levels are discussed in connection with their putative role in mediating suppression of dopaminergic neurotransmission during opiate withdrawal.

This study provides a new operant model in mice for the evaluation of food-taking behavior and reveals specific changes in the dopamine and opioid system associated to the behavioral responses directed to obtain a natural reward.

Our results demonstrate that inter-strain differences in PENK and PDYN genes expression in the nucleus accumbens parallel sensitivity of the selected mouse strains to rewarding effects of morphine. They suggest that high expression of PDYN may protect against drug abuse by limiting drug-produced reward, which may be due to dynorphin-mediated modulation of dopamine release in the nucleus accumbens.

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