A synaptic locus for TrkB signaling underlying ketamine rapid antidepressant action.

Ketamine produces rapid antidepressant action in patients with major depression or treatment-resistant depression. Studies have identified brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin receptor kinase B (TrkB), as necessary for the antidepressant effects and underlying ketamine-induced synaptic potentiation in the hippocampus. Here, we delete BDNF or TrkB in presynaptic CA3 or postsynaptic CA1 regions of the Schaffer collateral pathway to investigate the rapid antidepressant action of ketamine. The deletion of Bdnf in CA3 or CA1 blocks the ketamine-induced synaptic potentiation. In contrast, ablation of TrkB only in postsynaptic CA1 eliminates the ketamine-induced synaptic potentiation. We confirm BDNF-TrkB signaling in CA1 is required for ketamine's rapid behavioral action. Moreover, ketamine application elicits dynamin1-dependent TrkB activation and downstream signaling to trigger rapid synaptic effects. Taken together, these data demonstrate a requirement for BDNF-TrkB signaling in CA1 neurons in ketamine-induced synaptic potentiation and identify a specific synaptic locus in eliciting ketamine's rapid antidepressant effects.

Part 7: Systems of Care: 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care.

Survival after cardiac arrest requires an integrated system of people, training, equipment, and organizations working together to achieve a common goal. Part 7 of the 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care focuses on systems of care, with an emphasis on elements that are relevant to a broad range of resuscitation situations. Previous systems of care guidelines have identified a Chain of Survival, beginning with prevention and early identification of cardiac arrest and proceeding through resuscitation to post-cardiac arrest care. This concept is reinforced by the addition of recovery as an important stage in cardiac arrest survival. Debriefing and other quality improvement strategies were previously mentioned and are now emphasized. Specific to out-of-hospital cardiac arrest, this Part contains recommendations about community initiatives to promote cardiac arrest recognition, cardiopulmonary resuscitation, public access defibrillation, mobile phone technologies to summon first responders, and an enhanced role for emergency telecommunicators. Germane to in-hospital cardiac arrest are recommendations about the recognition and stabilization of hospital patients at risk for developing cardiac arrest. This Part also includes recommendations about clinical debriefing, transport to specialized cardiac arrest centers, organ donation, and performance measurement across the continuum of resuscitation situations.

Part 2: Evidence Evaluation and Guidelines Development: 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care.

The 2020 American Heart Association (AHA) Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care is based on the extensive evidence evaluation performed in conjunction with the International Liaison Committee on Resuscitation. The Adult Basic and Advanced Life Support, Pediatric Basic and Advanced Life Support, Neonatal Life Support, Resuscitation Education Science, and Systems of Care Writing Groups drafted, reviewed, and approved recommendations, assigning to each recommendation a Class of Recommendation (ie, strength) and Level of Evidence (ie, quality). The 2020 Guidelines are organized in knowledge chunks that are grouped into discrete modules of information on specific topics or management issues. The 2020 Guidelines underwent blinded peer review by subject matter experts and were also reviewed and approved for publication by the AHA Science Advisory and Coordinating Committee and the AHA Executive Committee. The AHA has rigorous conflict-of-interest policies and procedures to minimize the risk of bias or improper influence during development of the guidelines. Anyone involved in any part of the guideline development process disclosed all commercial relationships and other potential conflicts of interest.

Chronic lithium treatment elicits its antimanic effects via BDNF-TrkB dependent synaptic downscaling.

Lithium is widely used as a treatment for Bipolar Disorder although the molecular mechanisms that underlie its therapeutic effects are under debate. In this study, we show brain-derived neurotrophic factor (BDNF) is required for the antimanic-like effects of lithium but not the antidepressant-like effects in mice. We performed whole cell patch clamp recordings of hippocampal neurons to determine the impact of lithium on synaptic transmission that may underlie the behavioral effects. Lithium produced a significant decrease in α-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated miniature excitatory postsynaptic current (mEPSC) amplitudes due to postsynaptic homeostatic plasticity that was dependent on BDNF and its receptor tropomyosin receptor kinase B (TrkB). The decrease in AMPAR function was due to reduced surface expression of GluA1 subunits through dynamin-dependent endocytosis. Collectively, these findings demonstrate a requirement for BDNF in the antimanic action of lithium and identify enhanced dynamin-dependent endocytosis of AMPARs as a potential mechanism underlying the therapeutic effects of lithium.

TrkB Signaling in Dorsal Raphe Nucleus is Essential for Antidepressant Efficacy and Normal Aggression Behavior.

Brain-derived neurotrophic factor (BDNF) and its high affinity receptor, tropomyosin receptor kinase B (TrkB), have important roles in neural plasticity and are required for antidepressant efficacy. Studies examining the role of BDNF-TrkB signaling in depression and antidepressant efficacy have largely focused on the limbic system, leaving it unclear whether this signaling is important in other brain regions. BDNF and TrkB are both highly expressed in the dorsal raphe nucleus (DRN), a brain region that has been suggested to have a role in depression and antidepressant action, although it is unknown whether BDNF and TrkB in the dorsal raphe nucleus are involved in these processes. We combined the adeno-associated virus (AAV) with the Cre-loxP site-specific recombination system to selectively knock down either Bdnf or TrkB in the DRN. These mice were then characterized in several behavioral paradigms including measures of depression-related behavior and antidepressant efficacy. We show that knockdown of TrkB, but not Bdnf, in the DRN results in loss of antidepressant efficacy and increased aggression-related behavior. We also show that knockdown of TrkB or Bdnf in this brain region does not have an impact on weight, activity levels, anxiety, or depression-related behaviors. These data reveal a critical role for TrkB signaling in the DRN in mediating antidepressant responses and normal aggression behavior. The results also suggest a non-cell autonomous role for BDNF in the DRN in mediating antidepressant efficacy.

MeCP2 and histone deacetylases 1 and 2 in dorsal striatum collectively suppress repetitive behaviors.

Class I histone deacetylases (HDACs) Hdac1 and Hdac2 can associate together in protein complexes with transcriptional factors such as methyl-CpG-binding protein 2 (MeCP2). Given their high degree of sequence identity, we examined whether Hdac1 and Hdac2 were functionally redundant in mature mouse brain. We demonstrate that postnatal forebrain-specific deletion of both Hdac1 and Hdac2 in mice impacts neuronal survival and results in an excessive grooming phenotype caused by dysregulation of Sap90/Psd95-associated protein 3 (Sapap3; also known as Dlgap3) in striatum. Moreover, Hdac1- and Hdac2-dependent regulation of Sapap3 expression requires MECP2, the gene involved in the pathophysiology of Rett syndrome. We show that postnatal forebrain-specific deletion of Mecp2 causes excessive grooming, which is rescued by restoring striatal Sapap3 expression. Our results provide new insight into the upstream regulation of Sapap3 and establish the essential role of striatal Hdac1, Hdac2 and MeCP2 for suppression of repetitive behaviors.

A role for histone deacetylases in the cellular and behavioral mechanisms underlying learning and memory.

Histone deacetylases (HDACs) are a family of chromatin remodeling enzymes that restrict access of transcription factors to the DNA, thereby repressing gene expression. In contrast, histone acetyltransferases (HATs) relax the chromatin structure allowing for an active chromatin state and promoting gene transcription. Accumulating data have demonstrated a crucial function for histone acetylation and histone deacetylation in regulating the cellular and behavioral mechanisms underlying synaptic plasticity and learning and memory. In trying to delineate the roles of individual HDACs, genetic tools have been used to manipulate HDAC expression in rodents, uncovering distinct contributions of individual HDACs in regulating the processes of memory formation. Moreover, recent findings have suggested an important role for HDAC inhibitors in enhancing learning and memory processes as well as ameliorating symptoms related to neurodegenerative diseases. In this review, we focus on the role of HDACs in learning and memory, as well as significant data emerging from the field in support of HDAC inhibitors as potential therapeutic targets for the treatment of cognitive disorders.

Epigenetics and psychiatry.

Psychiatric disorders including major depressive disorder, drug addiction, and schizophrenia are debilitating illnesses with a multitude of complex symptoms underlying each of these disorders. In recent years, it has become appreciated that the onset and development of these disorders goes beyond the one gene-one disease approach. Rather, the involvement of many genes is likely linked to these illnesses, and regulating the activation or silencing of gene function may play a crucial role in contributing to their pathophysiology. Epigenetic modifications such as histone acetylation and deacetylation, as well as DNA methylation can induce lasting and stable changes in gene expression, and have therefore been implicated in promoting the adaptive behavioral and neuronal changes that accompany each of these illnesses. In this review we will discuss some of the latest work implicating a potential role for epigenetics in psychiatric disorders, namely, depression, addiction, and schizophrenia as well as a possible role in treatment.

Loss of histone deacetylase 2 improves working memory and accelerates extinction learning.

Histone acetylation and deacetylation can be dynamically regulated in response to environmental stimuli and play important roles in learning and memory. Pharmacological inhibition of histone deacetylases (HDACs) improves performance in learning tasks; however, many of these classical agents are "pan-HDAC" inhibitors, and their use makes it difficult to determine the roles of specific HDACs in cognitive function. We took a genetic approach using mice lacking the class I HDACs, HDAC1 or HDAC2, in postmitotic forebrain neurons to investigate the specificity or functional redundancy of these HDACs in learning and synaptic plasticity. We show that selective knock-out of Hdac2 led to a robust acceleration of the extinction rate of conditioned fear responses and a conditioned taste aversion as well as enhanced performance in an attentional set-shifting task. Hdac2 knock-out had no impact on episodic memory or motor learning, suggesting that the effects are task-dependent, with the predominant impact of HDAC2 inhibition being an enhancement in an animal's ability to rapidly adapt its behavioral strategy as a result of changes in associative contingencies. Our results demonstrate that the loss of HDAC2 improves associative learning, with no effect in nonassociative learning tasks, suggesting a specific role for HDAC2 in particular types of learning. HDAC2 may be an intriguing target for cognitive and psychiatric disorders that are characterized by an inability to inhibit behavioral responsiveness to maladaptive or no longer relevant associations.

An essential role for histone deacetylase 4 in synaptic plasticity and memory formation.

Histone deacetylases (HDACs), a family of enzymes involved in epigenetic regulation, have been implicated in the control of synaptic plasticity, as well as learning and memory. Previous work has demonstrated administration of pharmacological HDAC inhibitors, primarily those targeted to class I HDACs, enhance learning and memory as well as long-term potentiation. However, a detailed understanding of the role of class II HDACs in these processes remains elusive. Here, we show that selective loss of Hdac4 in brain results in impairments in hippocampal-dependent learning and memory and long-term synaptic plasticity. In contrast, loss of Hdac5 does not impact learning and memory demonstrating unique roles in brain for individual class II HDACs. These findings suggest that HDAC4 is a crucial positive regulator of learning and memory, both behaviorally and at the cellular level, and that inhibition of Hdac4 activity may have unexpected detrimental effects to these processes.

A mouse model for MeCP2 duplication syndrome: MeCP2 overexpression impairs learning and memory and synaptic transmission.

Rett syndrome and MECP2 duplication syndrome are neurodevelopmental disorders that arise from loss-of-function and gain-of-function alterations in methyl-CpG binding protein 2 (MeCP2) expression, respectively. Although there have been studies examining MeCP2 loss of function in animal models, there is limited information on MeCP2 overexpression in animal models. Here, we characterize a mouse line with MeCP2 overexpression restricted to neurons (Tau-Mecp2). This MeCP2 overexpression line shows motor coordination deficits, heightened anxiety, and impairments in learning and memory that are accompanied by deficits in long-term potentiation and short-term synaptic plasticity. Whole-cell voltage-clamp recordings of cultured hippocampal neurons from Tau-Mecp2 mice reveal augmented frequency of miniature EPSCs with no change in miniature IPSCs, indicating that overexpression of MeCP2 selectively impacts excitatory synapse function. Moreover, we show that alterations in transcriptional repression mechanisms underlie the synaptic phenotypes in hippocampal neurons from the Tau-Mecp2 mice. These results demonstrate that the Tau-Mecp2 mouse line recapitulates many key phenotypes of MECP2 duplication syndrome and support the use of these mice to further study this devastating disorder.

A role for ΔFosB in calorie restriction-induced metabolic changes.

BACKGROUND: Calorie restriction (CR) induces long-term changes in motivation to eat highly palatable food and, in body weight regulation, through an unknown mechanism. METHODS: After a period of CR and refeeding, mice were assessed by behavioral and metabolic studies and for levels of the transcription factor ΔFosB. The ΔFosB levels were then increased specifically in nucleus accumbens (NAc) with viral-mediated gene transfer, and behavioral and metabolic studies were conducted. RESULTS: We show that accumulation of ΔFosB in the NAc shell after CR in mice corresponds to a period of increased motivation for high fat reward and reduced energy expenditure. Furthermore, ΔFosB overexpression in this region increases instrumental responding for a high fat reward via an orexin-dependent mechanism while also decreasing energy expenditure and promoting adiposity. CONCLUSIONS: These results suggest that ΔFosB signaling in NAc mediates adaptive responses to CR.

Chronic social defeat stress disrupts regulation of lipid synthesis.

Several psychiatric disorders increase the risk of cardiovascular disease, including posttraumatic stress disorder and major depression. While the precise mechanism for this association has not yet been established, it has been shown that certain disorders promote an unfavorable lipid profile. To study the interaction of stress and lipid dysregulation, we utilized chronic social defeat stress (CSDS), a mouse model of chronic stress with features of posttraumatic stress disorder and major depression. Following exposure to CSDS, mice were given access to either regular chow or a Western-style diet high in fat and cholesterol (HFD). The combination of social stress and HFD resulted in significant perturbations in lipid regulation, including two key features of the metabolic syndrome: increased plasma levels of non-HDL cholesterol and intrahepatic accumulation of triglycerides. These effects were accompanied by a number of changes in the expression of hepatic genes involved in lipid regulation. Transcriptional activity of LXR, SREBP1c, and ChREBP were significantly affected by exposure to HFD and CSDS. We present CSDS as a model of social stress induced lipid dysregulation and propose that social stress alters lipid metabolism by increasing transcriptional activity of genes involved in lipid synthesis.

Reciprocal interaction of serotonin and neuronal activity in regulation of cAMP-responsive element-dependent gene expression.

Neuronal activity triggers multiple signal transduction pathways and potently regulates gene expression in the brain. In the central nervous system, in addition to the synaptic input, neurons are subject to neuromodulatory influences that can activate the same signaling elements. However, the principles that govern the interaction of neuromodulators and neuronal activity in the regulation of gene expression are unclear. Here, we examine how serotonergic neuromodulation interacts with neuronal activity in the regulation of gene expression in hippocampal neurons. We show that cAMP-response element binding protein (CREB) phosphorylation and gene expression were stimulated by serotonin (5-HT) in the absence of neuronal activity. In contrast, in the presence of neuronal activity, 5-HT inhibited gene expression down to the baseline, although neuronal activity alone was sufficient to maximally activate gene expression. The ability of 5-HT to stimulate CREB phosphorylation in the absence of neuronal activity or inhibit CREB phosphorylation during activity was due to a tight balance between protein kinases and phosphatases that could be physiologically tilted by different serotonergic receptors or exogenously influenced by phosphatase and kinase inhibitors. Taken together, these results suggest a reciprocal inhibitory interaction between neuronal activity and 5-HT in the regulation of cAMP response element-dependent gene expression in hippocampal neurons.