Antidepressants and Intracellular Signaling Linked to BDNF

摘要

ABSTRACT Brain-derived neurotrophic factor (BDNF) is the most prevalent neurotrophin in brain; via actions on its high affinity trkB receptor it enhances the survival of many types of central neurons and is implicated in several forms of neural plasticity in the brain. Recent work suggests that endogenous BDNF in the hippocampus may be involved in mediating antidepressant responses, in depression models in mice. A rather surprising finding in the field of depression has been the demonstration that ketamine, an ionotropic glutamatergic n-methyl-daspartate (NMDA) receptor antagonist, has rapid and long-lasting antidepressant effects in depressed individuals. We have started to investigate the mechanisms of the antidepressant activity of ketamine, specifically the potential involvement of endogenous BDNF in the hippocampus. In preliminary experiments, we find that the NMDA receptor antagonists, ketamine, MK801 or CPP, produce fast-acting antidepressant behavioral effects in depression models in mice. The fast acting antidepressant effects of ketamine occurs via a BDNF dependent manner because these effects are lost in forebrain specific BDNF knockout mice. Our findings also suggest that the antidepressant effects of ketamine require protein translation, but not transcription, resulting in increases in BDNF protein levels that are important for the behavioral effect. Recent work has suggested a strong causal link between blockade of resting NMDA receptor activation and rapid increases in local dendritic protein translation. In agreement with recent in vitro work, we find that ketamine causes a decrease in phosphorylation of eukaryotic elongation factor 2 (eEF2), which normally impedes translation in its phosphorylated state, suggesting translational de-repression of BDNF mRNA. Importantly, we provide preliminary evidence that inhibitors of the eEF2 kinase (also called CaMKIII) that normally phosphorylates eEF2 trigger a fast-acting antidepressant-like effect in depression models in mice. These findings suggest a behavioral and clinically relevant correlate of dendritic translational de-repression by NMDA receptors. The objective of this grant is to link the regulation of translational repression to the effects of antidepressants. Collectively, these studies promise to provide fundamentally novel information concerning how endogenous BDNF in the hippocampus is involved in the fast acting antidepressant response of ketamine and offer new leads toward the development of faster acting antidepressants.