Glucocorticoids are the most effective antiinflammatory agents for the treatment of chronic inflammatory diseases even though some diseases, such as chronic obstructive pulmonary disease (COPD), are relatively glucocorticoid insensitive. However, the molecular mechanism of this glucocorticoid insensitivity remains uncertain. We show that a defect of glucocorticoid receptor (GR) deacetylation caused by impaired histone deacetylase (HDAC) 2 induces glucocorticoid insensitivity toward nuclear factor (NF)-κB–mediated gene expression. Specific knockdown of HDAC2 by RNA interference resulted in reduced sensitivity to dexamethasone suppression of interleukin 1β–induced granulocyte/macrophage colony-stimulating factor production. Loss of HDAC2 did not reduce GR nuclear translocation, GR binding to glucocorticoid response element (GRE) on DNA, or GR-induced DNA or gene induction but inhibited the association between GR and NF-κB. GR becomes acetylated after ligand binding, and HDAC2-mediated GR deacetylation enables GR binding to the NF-κB complex. Site-directed mutagenesis of K494 and K495 reduced GR acetylation, and the ability to repress NF-κB–dependent gene expression becomes insensitive to histone deacetylase inhibition. In conclusion, we show that overexpression of HDAC2 in glucocorticoid-insensitive alveolar macrophages from patients with COPD is able to restore glucocorticoid sensitivity. Thus, reduction of HDAC2 plays a critical role in glucocorticoid insensitivity in repressing NF-κB–mediated, but not GRE-mediated, gene expression.

BACKGROUND AND PURPOSEDeficient transmission at the glutamate NMDA receptor is considered a key component of the pathophysiology of schizophrenia. However, the effects of antipsychotic drugs on the release of the endogenous NMDA receptor partial agonist, D-serine, remain to be clarified. EXPERIMENTAL APPROACHWe determined the interaction between antipsychotic drugs (clozapine and haloperidol) and transmission-modulating toxins (tetanus toxin, fluorocitrate, tetrodotoxin) on the release of L-glutamate and D-serine in the medial prefrontal cortex (mPFC) of freely moving rats, using microdialysis, and primary cultures of astrocytes using extreme high-pressure liquid chromatography. KEY RESULTSRelease of L-glutamate and D-serine in the mPFC and in cultured astrocytes was inhibited by tetanus toxin (a synaptobrevin inhibitor) and fluorocitrate (a glial toxin), whereas tetrodotoxin (a voltage-sensitive Na + blocker) inhibited depolarization-induced L-glutamate release in the mPFC without affecting that of D-serine. Clozapine (1 and 5 mg·kg -1 ), but not haloperidol (0.5 and 1 mg·kg -1 ), dose-dependently increased L-glutamate and D-serine release from both astrocytes and mPFC. Clozapine-induced release of L-glutamate and D-serine was also reduced by tetanus toxin and fluorocitrate. Tetrodotoxin reduced clozapine-induced mPFC L-glutamate release but not that of D-serine. Clozapine-induced L-glutamate release preceded clozapine-induced D-serine release. MK-801 (a NMDA receptor antagonist) inhibited the delayed clozapine-induced L-glutamate release without affecting that of D-serine. CONCLUSIONS AND IMPLICATIONSClozapine predominantly activated glial exocytosis of D-serine, and this clozapine-induced D-serine release subsequently enhances neuronal L-glutamate release via NMDA receptor activation. The enhanced D-serine associated glial transmission seems a novel mechanism of action of clozapine but not haloperidol.

The dopaminergic terminal projecting from the VTA received inhibitory GABA-mediated NMDA/glutamatergic regulation, but not stimulatory AMPA/glutamatergic regulation. However, both dopaminergic and noradrenergic terminals from the LC received stimulatory AMPA/glutamatergic regulation from the MTN, but not inhibitory GABA-mediated NMDA/glutamatergic regulation. These findings correlating neuronal activities in nuclei with neurotransmitter release suggested that the effects of QTP on neurotransmission in the mPFC depend on activated neuronal projections located outside the mPFC. Furthermore, positive interaction between LC and MTN afferents are potentially important in the pharmacological mechanisms of neurotransmitter regulation by QTP and hint at mechanisms underlying the atypical profile of this drug for treatment of schizophrenia and as a mood stabilizer and proconvulsive agent.

BACKGROUND AND PURPOSEAnticonvulsants have been developed according to the traditional neurotransmission imbalance hypothesis. However, the anticonvulsive pharmacotherapy currently available remains unsatisfactory. To develop new antiepileptic drugs with novel antiepileptic mechanisms, we have tested the antiepileptic actions of ONO-2506, a glial modulating agent, and its effects on tripartite synaptic transmission. EXPERIMENTAL APPROACHDose-dependent effects of ONO-2506 on maximal-electroshock seizure (MES), pentylenetetrazol-induced seizure (PTZ) and epileptic discharge were determined in a genetic model of absence epilepsy in mice (Cacna1a tm2Nobs/tm2Nobs strain). Antiepileptic mechanisms of ONO-2506 were analysed by examining the interaction between ONO-2506 and transmission-modulating toxins (tetanus toxin, fluorocitrate, tetrodotoxin) on release of L-glutamate, D-serine, GABA and kynurenic acid in the medial-prefrontal cortex (mPFC) of freely moving rats using microdialysis and primary cultured rat astrocytes. KEY RESULTS ONO-2506 inhibited spontaneous epileptic discharges in Cacna1atm2Nobs/tm2Nobs mice without affecting MES or PTZ. Given systemically, ONO-2506 increased basal release of GABA and kynurenic acid in the mPFC through activation of both neuronal and glial exocytosis, but inhibited depolarization-induced releases of all transmitters. ONO-2506 increased basal glial release of kynurenic acid without affecting those of L-glutamate, D-serine or GABA. However, ONO-2506 inhibited AMPA-induced releases of L-glutamate, D-serine, GABA and kynurenic acid. CONCLUSIONS AND IMPLICATIONSONO-2506 did not affect traditional convulsive tests but markedly inhibited epileptic phenomena in the genetic epilepsy mouse model. ONO-2506 enhanced release of inhibitory neuro-and gliotransmitters during the resting stage and inhibited tripartite transmission during the hyperactive stage. The results suggest that ONO-2506 is a novel potential glial-targeting antiepileptic drug. LINKED ARTICLEThis article is commented on by Onat, pp. 1086-1087 of this issue. To view this commentary visit http://dx

Background and purpose:The atypical antipsychotic drug, zotepine, is effective in treatment of schizophrenia and acute mania, but the incidence of seizures during treatment is higher than with other antipsychotics. In addition, the mechanisms underlying the clinical actions of zotepine remain uncharacterized. Experimental approach: The effects of intraperitoneal administration of zotepine and haloperidol on the extracellular levels of noradrenaline, dopamine, 5-HT, GABA, and glutamate in the medial prefrontal cortex (mPFC) were compared. Neuronal activities induced by each drug in the ventral tegmental area (VTA), locus coeruleus (LC), dorsal raphe nucleus (DRN) and mediodorsal thalamic nucleus (MTN) were also analysed. Key results: Haloperidol did not affect extracellular neurotransmitter levels in the mPFC. In contrast, zotepine activated neuronal activities in all nuclei and increased the extracellular levels of noradrenaline, dopamine, GABA, and glutamate in the mPFC, but not 5-HT levels. The zotepine-stimulated neuronal activity in the VTA, LC, DRN and MTN enhanced the release of dopamine, noradrenaline, 5-HT, glutamate and GABA in the mPFC, although the enhanced GABAergic transmission possibly inhibited noradrenaline, dopamine and 5-HT release. The other afferent to mPFC, which releases dopamine and noradrenaline, was partially insensitive to GABAergic inhibition, but possibly received stimulatory AMPA/glutamatergic regulation from the MTN. Conclusions and implications:Our results indicated that the positive interaction between prefrontal catecholaminergic transmission and AMPA/glutamatergic transmission from MTN might explain the regulatory effects of zotepine on neurotransmitter release. A mechanism is suggested to account for the pharmacological profile of this atypical antipsychotic and for its pro-convulsive action.