Cellular mRNA expression of the transcription factor NGFI-B suggests a gene regulatory role in striatal opiate-peptide neurons

Haloperidol-induced Nur77 expression in striatopallidal neurons is under the control of protein phosphatase 1 regulation by DARPP-32

Impaired dopaminergic signaling in the striatum is involved in diseases as diverse as Parkinson's disease, addiction, and schizophrenia. An important pathophysiological aspect is the loss of balance between striatopallidal and striatonigral pathways. Nur77 is an orphan nuclear receptor and dopamine-regulated immediate-early gene. Classical antipsychotic drugs widely used in the treatment of schizophrenia, such as haloperidol, increase Nur77 mRNA expression in the striatum. However, little is known about the intracellular signaling pathways involved in Nur77 induction. Here, using pharmacological approaches and transgenic mutant mice, we investigated the mechanisms underlying the up-regulation of Nur77 protein expression in the dorsal striatum after haloperidol injection. In drd1a::EGFP transgenic mice that express GFP in D1 neurons, Nur77 up-regulation induced by haloperidol occurred predominantly in GFP-negative neurons. In Gαolf heterozygous mutant mice, in which cAMP production in response to A2A stimulation is impaired in the striatum, haloperidol effect was not altered. In contrast, in DARPP-32 knock-in mutant mice bearing a T34A point mutation of the site responsible for cAMP-dependent phosphatase 1 inhibition, Nur77 up-regulation by haloperidol was prevented. Haloperidol also induced Nur77 protein in D2 neurons of the nucleus accumbens core of wild type but not T34A knock-in mice. Thus, our results show that expression of Nur77 is induced by haloperidol in D2 receptors-expressing medium-sized spiny neurons, through cAMP-dependent regulation of protein phosphatase 1, which is likely to modulate the effects of other protein kinases. Our results clarify the mechanisms of Nur77 induction by antipsychotic and its possible contribution to extrapyramidal effects.

Repeated amphetamine administration outside the home cage enhances drug-induced Fos expression in rat nucleus accumbens

Induction of the immediate early gene protein product Fos has been used extensively to assess neural activation in the striatum after repeated amphetamine administration to rats in their home cages. However, this technique has not been used to examine striatal activation after repeated administration outside the home cage, an environment where repeated drug administration produces more robust psychomotor sensitization. We determined the dose-response relationship for amphetamine-induced psychomotor activity and Fos expression in nucleus accumbens and caudate-putamen 1 week after repeated administration of amphetamine or saline in locomotor activity chambers. Repeated administration of amphetamine enhanced amphetamine-induced locomotor activity and stereotypy and Fos expression in nucleus accumbens, but not in caudate-putamen. In comparison, levels of Fos expression induced by 1mg/kg amphetamine were not altered in nucleus accumbens or caudate-putamen by repeated amphetamine administration in the home cage. Double-labeling of Fos protein and enkephalin mRNA indicates that Fos is expressed in approximately equal numbers of enkephalin-negative and enkephalin-positive neurons in nucleus accumbens and caudate-putamen following injections outside the home cage. Furthermore, repeated amphetamine administration increased drug-induced Fos expression in enkephalin-positive, but not enkephalin-negative, neurons in nucleus accumbens. We conclude that repeated amphetamine administration outside the home cage recruits the activation of enkephalin-containing nucleus accumbens neurons during sensitized amphetamine-induced psychomotor activity.

Stimulation of adenosine receptors selectively activates gene expression in striatal enkephalinergic neurons

In the striatum, adenosine A2A and dopamine D2 receptors exert reciprocal antagonistic interactions that modulate the function of GABAergic enkephalinergic neurons. We have previously shown that stimulation of adenosine A1 receptors allows the stimulation of A2A receptors to overcome a tonic inhibitory effect of D2 receptors and induce striatal expression of c-fos. In the present work, by studying co-localization of c-Fos immunoreactivity and preproenkephalin and preprodynorphin transcripts, we show that co-administration of the A1 receptor agonist CPA and the A2A receptor agonist CGS 21680 increases the striatal expression of c-fos in GABAergic enkephalinergic but not in GABAergic dynorphinergic neurons. Co-administration of CPA and CGS 21680 also induced a significant increase in the striatal expression of preproenkephalin. The results underscore the role of adenosine in the activation of gene expression in the GABAergic enkephalinergic neuron.

Prenatal and neonatal exposure to bisphenol-A affects the morphine-induced rewarding effect and hyperlocomotion in mice

Bisphenol-A (BPA), one of the most common environmental endocrine disrupters, has been extensively evaluated for toxicity and carcinogenicity. However, little is still known about its action on the CNS. Here we found that prenatal and neonatal exposure to BPA resulted in the enhancement of the rewarding effect and hyperlocomotion induced by morphine in mice. Under these conditions, no change in the G-protein activation by morphine and mu-opioid receptor expression in the lower midbrain was observed by prenatal and neonatal exposure to BPA. These results suggest that chronic exposure to BPA produces the supersensitivity of the morphine-induced rewarding effect and hyperlocomotion without direct changes in mu-opioid receptor function in the lower midbrain. The present data provide further evidence that prenatal and neonatal exposure to BPA can directly influence the development of the central dopaminergic system.

Repeated cocaine administration alters the expression of genes in corticolimbic circuitry after a 3-week withdrawal: a DNA macroarray study

Addiction to psychostimulants elicits behavioral and biochemical changes that are assumed to be mediated by alterations of gene expression in the brain. The changes in gene expression after 3 weeks of withdrawal from chronic cocaine treatment were evaluated in the nucleus accumbens core and shell, dorsal prefrontal cortex and caudate using a complementary DNA (cDNA) array. The level of mRNA encoded by several genes was identified as being up- or down-regulated in repeated cocaine versus saline subjects. The results from the cDNA array were subsequently confirmed at the protein level with immunoblotting. Of particular interest, parallel up-regulation in protein and mRNA was found for the adenosine A1 receptor in the accumbens core, neuroglycan C in the accumbens shell, and the GluR5 glutamate receptor subtype in dorsal prefrontal cortex. However, there was an increase in TrkB protein in the nucleus accumbens core of cocaine-treated rats without a corresponding alteration in mRNA. These changes of gene expression in corticolimbic circuitry may contribute to the psychostimulant-induced behavioral changes associated with addiction.

Acute methamphetamine administration upregulates NGFI-B mRNA expression in the striatum: co-localization with c-Fos immunoreactivity

In this study, the effects of acute methamphetamine administration on expression of the nuclear transcription factor NGFI-B mRNA and its co-localization with c-Fos immunoreactivity in the striatum were evaluated in animals receiving a single dose of methamphetamine (4 mg/kg) given at 2 or 6 h prior to perfusion. All animals received a daily saline injection for 6 days prior to methamphetamine treatment. We have found that, similar to c-fos activation, NGFI-B mRNA levels were significantly increased 2 h after methamphetamine treatment and returned to basal levels 6 h later. Induction of NGFI-B mRNA levels by methamphetamine was highest in central striatum as compared to the dorsomedial distribution pattern observed in control animals. After acute methamphetamine treatment, the distribution pattern of NGFI-B mRNA upregulation was very similar to that of methamphetamine induced c-Fos immunoreactivity. However, co-localization studies with c-Fos immunoreactivity showed that not all NGFI-B-positive cells contained c-Fos after methamphetamine treatment. Forty-five percent of all NGFI-B mRNA expressing neurons contained c-Fos immunoreactivity in the dorsomedial striatum as compared to 60% in central and 35% in ventrolateral striatum. This study provides a detailed description of the differential spatial and temporal modulation of NGFI-B and c-Fos expression in the striatum by acute methamphetamine treatment over time.