Early life selective knockdown of the TrkB receptor and maternal separation modulates adult stress phenotype

Glial-restricted precursors stimulate endogenous cytogenesis and effectively recover emotional deficits in a model of cytogenesis ablation

Adult cytogenesis, the continuous generation of newly-born neurons (neurogenesis) and glial cells (gliogenesis) throughout life, is highly impaired in several neuropsychiatric disorders, such as Major Depressive Disorder (MDD), impacting negatively on cognitive and emotional domains. Despite playing a critical role in brain homeostasis, the importance of gliogenesis has been overlooked, both in healthy and diseased states. To examine the role of newly formed glia, we transplanted Glial Restricted Precursors (GRPs) into the adult hippocampal dentate gyrus (DG), or injected their secreted factors (secretome), into a previously validated transgenic GFAP-tk rat line, in which cytogenesis is transiently compromised. We explored the long-term effects of both treatments on physiological and behavioral outcomes. Grafted GRPs reversed anxiety-like deficits and demonstrated an antidepressant-like effect, while the secretome promoted recovery of only anxiety-like behavior. Furthermore, GRPs elicited a recovery of neurogenic and gliogenic levels in the ventral DG, highlighting the unique involvement of these cells in the regulation of brain cytogenesis. Both GRPs and their secretome induced significant alterations in the DG proteome, directly influencing proteins and pathways related to cytogenesis, regulation of neural plasticity and neuronal development. With this work, we demonstrate a valuable and specific contribution of glial progenitors to normalizing gliogenic levels, rescuing neurogenesis and, importantly, promoting recovery of emotional deficits characteristic of disorders such as MDD.

Genetic insights into the neurobiology of anxiety

Anxiety and fear are evolutionarily conserved emotions that increase the likelihood of an organism surviving threatening situations. Anxiety and vigilance states are regulated by neural networks involving multiple brain regions. In anxiety disorders, this intricate regulatory system is disturbed, leading to excessive or prolonged anxiety or fear. Anxiety disorders have both genetic and environmental risk factors. Genetic research has the potential to identify specific genetic variants causally associated with specific phenotypes. In recent decades, genome-wide association studies (GWASs) have revealed variants predisposing to neuropsychiatric disorders, suggesting novel neurobiological pathways in the etiology of these disorders. Here, we review recent human GWASs of anxiety disorders, and genetic studies of anxiety-like behavior in rodent models. These studies are paving the way for a better understanding of the neurobiological mechanisms underlying anxiety disorders.

Antidepressant-Like Effects of Edaravone and Minocycline: Investigation of Oxidative Stress, Neuroinflammation, Neurotrophic, and Apoptotic Pathways

Depression is a very common mental disorder and mechanism that is associated with mitochondrial dysfunction. In the present study, we examined the mechanisms of action of isolated brain mitochondria in rats with depression for the first time. This will help identify the mitochondrial protective pathways of the two drugs and shed light on new therapeutic goals for developing antidepressants. Forced swimming, tail suspension, and sucrose preference tests were used to assess depressive-like behaviors and the oxidative stress factors of brain tissue, and measure the gene expression of apoptotic and anti-apoptotic, neuroplasticity, and neuroinflammatory factors by RT-PCR and acetylcholinesterase (AChE) activity in brain tissue (hippocampus and prefrontal) and the serum levels of corticosterone and fasting blood sugar. The results showed that the separation of neonatal rats from their mothers induced depressive-like behaviors, weight loss, mitochondrial dysfunction, increased expression of genes involved in neuroinflammation, apoptosis, genes involved in the depressive process, and decreased expression of genes involved in mood in both the hippocampus and prefrontal cortex. Maternal separation increased serum corticosterone levels, caused dysfunction of the cholinergic system, and also increased AChE activity. Treatment with different concentrations of minocycline and edaravone (1, 20, and 50 mg/kg), 5MTHF, and citalopram for 14 days showed that these drugs improved depression-like behaviors and mitochondrial function. It also reduced the expression of genes involved in neuroinflammation, apoptosis, and depression and increased the expression of genes involved in mood. In conclusion, minocycline and edaravone have neuroprotective, mitochondrial protective, antioxidant, anti-inflammatory, and anti-apoptotic effects against depressive-like behaviors caused by chronic stress.

Enduring effects of early-life adversity on reward processes: A systematic review and meta-analysis of animal studies

Two-thirds of individuals experience adversity during childhood such as neglect, abuse or highly-stressful events. Early-life adversity (ELA) increases the life-long risk of developing mood and substance use disorders. Reward-related deficits has emerged as a key endophenotype of such psychiatric disorders. Animal models are invaluable for studying how ELA leads to reward deficits. However, the existing literature is heterogenous with difficult to reconcile findings. To create an overview, we conducted a systematic review containing multiple meta-analyses regarding the effects of ELA on reward processes overall and on specific aspects of reward processing in animal models. A comprehensive search identified 120 studies. Most studies omitted key details resulting in unclear risk of bias. Overall meta-analysis showed that ELA significantly reduced reward behaviors (SMD: -0.42 [-0.60; -0.24]). The magnitude of ELA effects significantly increased with longer exposure. When reward domains were analyzed separately, ELA only significantly dampened reward responsiveness (SMD: -0.525[-0.786; -0.264]) and social reward processing (SMD: -0.374 [-0.663; -0.084]), suggesting that ELA might lead to deficits in specific reward domains.

Boosting amygdaloid GABAergic and neurotrophic machinery via dapagliflozin-enhanced LKB1/AMPK signaling in anxious demented rats

Anxiety is a neuropsychiatric disturbance that is commonly manifested in various dementia forms involving Alzheimer's disease (AD). The mechanisms underlying AD-associated anxiety haven't clearly recognized the role of energy metabolism in anxiety represented by the amygdala's autophagic sensors; liver kinase B1 (LKB1)/adenosine monophosphate kinase (AMPK). Dapagliflozin (DAPA), a SGLT2 inhibitor, acts as an autophagic activator through LKB1 activation in several diseases including AD. Herein, the propitious yet undetected anxiolytic potential of DAPA as an autophagic enhancer was investigated in AD animal model with emphasis on amygdala's GABAergic neurotransmission and brain-derived neurotrophic factor (BDNF). Alzheimer's disease was induced by ovariectomy (OVX) along with seventy-days-D-galactose (D-Gal) administration (150 mg/kg/day, i.p). On the 43rd day of D-Gal injection, OVX/D-Gal-subjected rats received DAPA (1 mg/kg/day, p.o) alone or with dorsomorphin the AMPK inhibitor (DORSO, 25 μg/rat, i.v.). In the amygdala, LKB1/AMPK were activated by DAPA inducing GABA_B2 receptor stimulation; an effect that was abrogated by DORSO. Dapagliflozin also replenished the amygdala GABA, NE, and 5-HT levels along with glutamate suppression. Moreover, DAPA triggered BDNF production with consequent activation of its receptor, TrkB through activating GABA_B2-related downstream phospholipase C/diacylglycerol/protein kinase C (PLC/DAG/PKC) signaling. This may promote GABA_A expression, verifying the crosstalk between GABA_A and GABA_B2. The DAPA's anxiolytic effect was visualized by improved behavioral traits in elevated plus maze together with amendment of amygdala' histopathological abnormalities. Thus, the present study highlighted DAPA's anxiolytic effect which was attributed to GABA_B2 activation and its function to induce BDNF/TrkB and GABA_A expression through PLC/DAG/PKC pathway in AMPK-dependent manner.

Deep brain stimulation improved depressive-like behaviors and hippocampal synapse deficits by activating the BDNF/mTOR signaling pathway

Our previous study demonstrated that acute deep brain stimulation (DBS) in the ventromedial prefrontal cortex (vmPFC) remarkably improved the depressive-like behaviors in a rat model of chronic unpredictable mild stress (CUS rats). However, the mechanisms by which chronic DBS altered depressive-like behaviors and reversed cognitive impairment have not been clarified. Recent work has shown that deficits in brain-derived neurotrophic factor (BDNF) and its downstream proteins, including mammalian target of rapamycin (mTOR), might be involved in the pathogenesis of depression. Therefore, we hypothesized that the antidepressant-like and cognitive improvement effects of DBS were achieved by activating the BDNF/mTOR pathway. CUS rats received vmPFC DBS at 20 Hz for 1 h once a day for 28 days. After four weeks of stimulation, the rats were assessed for the presence of depressive-like behaviors and euthanized to detect BDNF/mTOR signaling using immunoblots. DBS at the vmPFC significantly ameliorated depressive-like behaviors and spatial learning and memory deficits in the CUS rats. Furthermore, DBS restored the reduced synaptic density in the hippocampus induced by CUS and increased the expression or activity of BDNF, Akt, and mTOR in the hippocampus. Thus, the antidepressant-like effects and cognitive improvement produced by vmPFC DBS might be mediated through increased activity of the BDNF/mTOR signaling pathway.

Functional characterization and potential therapeutic avenues for variants in the NTRK2 gene causing developmental and epileptic encephalopathies

Variants within the Neurotrophic Tyrosine Kinase Receptor Type 2 (NTRK2) gene have been discovered to play a role in developmental and epileptic encephalopathies, a group of debilitating conditions for which little is known about cause or treatment. Here, we determine the functional consequences of two variants: p.Tyr434Cys (Y434C) (located in the transmembrane domain) and p.Thr720Ile (T720I) (located in the catalytic domain). Wild-type and variant cDNAs were constructed and transfected into HEK293 cells. In cell culture, variant Y434C exhibited ligand-independent activation of tropomyosin-related kinase B (TRKB) signaling with an associated abnormal response to brain-derived neurotrophic factor (BDNF) stimulation and increased levels of phosphorylated extracellular signal-regulated kinase (ERK) and ETS like-1 protein (ELK1) activity. Expression of variant T720I resulted in decreased TRKB signaling with reduced mTor activity as determined by decreased levels of phosphorylated S6. With the deleterious mechanisms characterized, we utilized mediKanren (a novel artificial intelligence tool) to identify therapeutics to compensate for the pathological effects. Downregulation of TRKB through inhibition with mediKanren-predicted compound 1NM-PP1 led to decreased MEK activity. Upregulation of TRKB signaling by mediKanren-predicted valproic acid led to subsequent increase of mTor activity. Overall, our results provide further characterization of the pathogenicity of these two variants in the NTRK2 gene. Indeed, Y434C is the first patient-specific NTRK2 variant with demonstrated hypermorphic activity. Furthermore, we observed that variants Y434C and T720I result in distinct functional consequences that require distinct therapeutic strategies. These data suggest the possibility that unique mutations within different regions of the NTRK2 gene results in separate clinical presentations, representing distinct genetic disorders requiring unique therapeutics.

Impact of Early Life Stress on Reward Circuit Function and Regulation

Early life stress - including experience of child maltreatment, neglect, separation from or loss of a parent, and other forms of adversity - increases lifetime risk of mood, anxiety, and substance use disorders. A major component of this risk may be early life stress-induced alterations in motivation and reward processing, mediated by changes in the nucleus accumbens (NAc) and ventral tegmental area (VTA). Here, we review evidence of the impact of early life stress on reward circuit structure and function from human and animal models, with a focus on the NAc. We then connect these results to emerging theoretical models about the indirect and direct impacts of early life stress on reward circuit development. Through this review and synthesis, we aim to highlight open research questions and suggest avenues of future study in service of basic science, as well as applied insights. Understanding how early life stress alters reward circuit development, function, and motivated behaviors is a critical first step toward developing the ability to predict, prevent, and treat stress-related psychopathology spanning mood, anxiety, and substance use disorders.

H3K9me2 regulation of BDNF expression in the hippocampus and medial prefrontal cortex is involved in the depressive-like phenotype induced by maternal separation in male rats

BACKGROUND

Early life stress (ELS) induces a depressive-like phenotype and increases the risk of depression. Brain-derived neurotrophic factor (BDNF) has been confirmed to be involved in the pathophysiology of depression. However, the mechanism by which ELS alters the epigenetic regulation of BDNF and changes susceptibility to depression has not been fully clarified.

METHODS

The present study used maternal separation (MS) and chronic unpredicted mild stress (CUMS) to establish an MS animal model and a depressive animal model. We assessed depressive-like behaviours, including anhedonia, locomotor activity, anxiety-like behaviour, and spatial memory, using the sucrose preference test, the open field test, the elevated plus maze test, and the Morris water maze test. We also investigated BDNF and H3K9me2 expression in the hippocampus and medial prefrontal cortex (mPFC) by immunohistochemistry, western blotting, and qPCR analysis. Additionally, we used Unc0642, a small molecule inhibitor of histone methyltransferase (G9a), as an intervention.

RESULTS

The results showed that CUMS induced depressive-like behaviours in rats and resulted in increased H3K9me2 expression and decreased BDNF expression in the hippocampus and mPFC. More importantly, adult MS rats experiencing CUMS had more severe depressive behaviours, had higher expression of H3K9me2 in the hippocampus and mPFC, and had lower expression of BDNF in the hippocampus and mPFC. In addition, administration of the G9a inhibitor reversed most of the changes.

CONCLUSIONS

Our study suggests that ELS changed BDNF and H3K9me2 expression in the rat brain, resulting in a depressive-like phenotype.

Effect of Early Life Stress on the Epigenetic Profiles in Depression

Depression is one of the most common mental disorders and has caused an overwhelming burden on world health. Abundant studies have suggested that early life stress may grant depressive-like phenotypes in adults. Childhood adversities that occurred in the developmental period amplified stress events in adulthood. Epigenetic-environment interaction helps to explain the role of early life stress on adulthood depression. Early life stress shaped the epigenetic profiles of the HPA axis, monoamine, and neuropeptides. In the context of early adversities increasing the risk of depression, early life stress decreased the activity of the glucocorticoid receptors, halted the circulation and production of serotonin, and reduced the molecules involved in modulating the neurogenesis and neuroplasticity. Generally, DNA methylation, histone modifications, and the regulation of non-coding RNAs programmed the epigenetic profiles to react to early life stress. However, genetic precondition, subtypes of early life stress, the timing of epigenetic status evaluated, demographic characteristics in humans, and strain traits in animals favored epigenetic outcomes. More research is needed to investigate the direct evidence for how early life stress-induced epigenetic changes contribute to the vulnerability of depression.