RESUMO
The molecular processes that underlie long-term memory formation involve signaling pathway activation by neurotransmitter release, which induces the expression of immediate early genes, such as Zif268, having a key role in memory formation. In this work, we show that the cannabinoid CB1 receptor signaling is necessary for the effects of dexamethasone on the behavioral response in an inhibitory avoidance task, on dexamethasone-induced ERK phosphorylation, and on dexamethasone-dependent Zif268 expression. Furthermore, we provide primary evidence for the mechanism responsible for this crosstalk between cannabinoid and glucocorticoid-mediated signaling pathways, showing that dexamethasone regulates endocannabinoid metabolism by inhibiting the activity of the Fatty acid amide hydrolase (FAAH), an integral membrane enzyme that hydrolyzes endocannabinoids and related amidated signaling lipids. Our results provide novel evidence regarding the role of the endocannabinoid system, and in particular of the CB1 receptor, as a mediator of the effects of glucocorticoids on the consolidation of aversive memories.
Assuntos
Canabinoides , Consolidação da Memória , Endocanabinoides/metabolismo , Receptor CB1 de Canabinoide/genética , Canabinoides/farmacologia , Transdução de Sinais , Glucocorticoides/farmacologia , Dexametasona/farmacologia , Amidoidrolases , Moduladores de Receptores de Canabinoides/farmacologiaRESUMO
Benzodiazepines are among the most prescribed drug class worldwide to treat disorders such as anxiety, insomnia, muscle spasticity, and convulsive disorders, and to induce presurgical sedation. Although benzodiazepines exhibit a high therapeutic index and low toxicity in short-term treatments, prolonged administration induces tolerance to most of their therapeutic actions. The mechanism of this tolerance remains unclear. The central actions of benzodiazepines are mediated by binding to GABAA receptors, which mediate most fast inhibitory transmission in the brain. The majority of GABAA receptors are composed of two α-(1-6), two ß-(1-3) and one γ-subunits (1-3). In a previous report, we demonstrated that the prolonged exposure of cerebrocortical neurons to diazepam produces a transcriptional repression of the GABAA receptor α1 subunit gene via a mechanism dependent on the activation of L-type voltage-gated calcium channels (L-VGCCs). The results reported here confirm that the diazepam-induced downregulation of the α1 subunit is contingent upon calcium influx from extracellular space. In addition, this regulatory mechanism involves the activation of protein kinase A (PKA) and is accompanied by the activation of two transcription factors, the cAMP-response element-binding protein (CREB) and the inducible cAMP early repressor (ICER). Together, our results suggest that diazepam s activation of an L-VGCC/Ca2+/PKA/CREB-ICER signaling pathway is responsible for the regulation of GABAA receptors. This elucidation of the intracellular signaling cascade activated by a prolonged benzodiazepine exposure, itself potentially involved in the development of tolerance, may contribute to locating molecular targets for future therapeutic interventions.
Assuntos
Diazepam , Receptores de GABA-A , Diazepam/farmacologia , Receptores de GABA-A/metabolismo , Regulação para Baixo , Benzodiazepinas/farmacologia , Transdução de Sinais , Canais de Cálcio/genética , Ácido gama-Aminobutírico/metabolismo , Proteínas Quinases Dependentes de AMP Cíclico/metabolismoRESUMO
Dopamine replacement therapy with L-DOPA is the treatment of choice for Parkinson's disease; however, its long-term use is frequently associated with L-DOPA-induced dyskinesia (LID). Many molecules have been implicated in the development of LID, and several of these have been proposed as potential therapeutic targets. However, to date, none of these molecules have demonstrated full clinical efficacy, either because they lie downstream of dopaminergic signaling, or due to adverse side effects. Therefore, discovering new strategies to reduce LID in Parkinson's disease remains a major challenge. Here, we have explored the tyrosine kinase Fyn, as a novel intermediate molecule in the development of LID. Fyn, a member of the Src kinase family, is located in the postsynaptic density, where it regulates phosphorylation of the NR2B subunit of the N-methyl-D-aspartate (NMDA) receptor in response to dopamine D1 receptor stimulation. We have used Fyn knockout and wild-type mice, lesioned with 6-hydroxydopamine and chronically treated with L-DOPA, to investigate the role of Fyn in the induction of LID. We found that mice lacking Fyn displayed reduced LID, ΔFosB accumulation and NR2B phosphorylation compared to wild-type control mice. Pre-administration of saracatinib (AZD0530), an inhibitor of Fyn activity, also significantly reduced LID in dyskinetic wild-type mice. These results support that Fyn has a critical role in the molecular pathways affected during the development of LID and identify Fyn as a novel potential therapeutic target for the management of dyskinesia in Parkinson's disease.