Neuron-specific deletion of VEGF or its receptor Flk-1 occludes the antidepressant-like effects of desipramine and fluoxetine in mice.

Vascular endothelial growth factor (VEGF) signaling is known to be involved in the antidepressant-like effects of conventional antidepressants, such as desipramine (DMI), a tricyclic antidepressant, and fluoxetine (FLX), a selective serotonin reuptake inhibitor; however, the precise role of neuronal VEGF signaling in mediating these effects remains unclear. Using mice with excitatory neuron-specific deletion of VEGF and its receptor, fetal liver kinase 1 (Flk-1) in the forebrain, we examined the effects of forebrain excitatory neuron-specific deletion of VEGF or Flk-1 on the antidepressant-like effects of repeated DMI and chronic FLX administration in the forced swim test (FST). Repeated intraperitoneal (i.p.) injections of DMI (10, 10, and 20 mg/kg at 24, 4, and 1 h before the FST, respectively) significantly decreased immobility in control mice; however, this effect was completely blocked in mice with neuron-specific VEGF or Flk-1 deletion. Although chronic treatment with FLX (18 mg/kg/day, i.p.) did not impact immobility in control mice 1 day after the 22nd injection, immobility was significantly reduced 1 day after the preswim and the 23rd FLX injection. However, in mice with neuron-specific Flk-1 deletion, chronic FLX treatment significantly increased immobility in the preswim and failed to produce antidepressant-like effects. Collectively, these findings indicate that neuronal VEGF-Flk-1 signaling contributes to the antidepressant-like actions of conventional antidepressants.

Epigenome-wide association study of posttraumatic stress disorder identifies novel loci in U.S. military veterans.

Posttraumatic stress disorder (PTSD) is a chronic and disabling psychiatric disorder prevalent in military veterans. Epigenetic mechanisms have been implicated in the etiology of PTSD, with DNA methylation being the most studied to identify novel molecular biomarkers associated with this disorder. We performed one of the largest single-sample epigenome-wide association studies (EWAS) of PTSD to date. Our sample included 1135 male European-American U.S. veterans who participated in the National Health and Resilience in Veterans Study (NHRVS). DNA was collected from saliva samples and the Illumina HumanMethylation EPIC BeadChip was used for the methylation analysis. PTSD was assessed using the PTSD Checklist. An EWAS was conducted using linear regression adjusted for age, cell-type proportions, first 10 principal components, and smoking status. After Bonferroni correction, we identified six genome-wide significant (GWS) CpG sites associated with past-month PTSD and three CpGs with lifetime PTSD (prange = 10-10-10-8). These CpG sites map to genes involved in immune function, transcription regulation, axonal guidance, cell signaling, and protein binding. Among these, SENP7, which is involved in transcription regulation and has been linked to risk-taking behavior and alcohol consumption in genome-wide association studies, replicated in an independent veteran cohort and was downregulated in medial orbitofrontal cortex of PTSD postmortem brain tissue. These findings suggest potential epigenetic biomarkers of PTSD that may help inform the pathophysiology of this disorder in veterans and other trauma-affected populations.

Hippocampal mitogen-activated protein kinase phosphatase-1 regulates behavioral and systemic effects of chronic corticosterone administration.

Clinical reports indicate a bidirectional relationship between mental illness and chronic systemic diseases. However, brain mechanisms linking chronic stress and development of mood disorders to accompanying peripheral organ dysfunction are still not well characterized in animal models. In the current study, we investigated whether activation of hippocampal mitogen-activated protein kinase phosphatase-1 (MKP-1), a key factor in depression pathophysiology, also acts as a mediator of systemic effects of stress. First, we demonstrated that treatment with the glucocorticoid receptor (GR) agonist dexamethasone or acute restraint stress (ARS) significantly increased Mkp-1 mRNA levels within the rat hippocampus. Conversely, administration of the GR antagonist mifepristone 30 min before ARS produced a partial blockade of Mkp-1 upregulation, suggesting that stress activates MKP-1, at least in part, through upstream GR signaling. Chronic corticosterone (CORT) administration evoked comparable increases in hippocampal MKP-1 protein levels and produced a robust increase in behavioral emotionality. In addition to behavioral deficits, chronic CORT treatment also produced systemic pathophysiological effects. Elevated levels of renal inflammation protein markers (NGAL and IL18) were observed suggesting tissue damage and early kidney impairment. In a rescue experiment, the effects of CORT on development of depressive-like behaviors and increased NGAL and IL18 protein levels in the kidney were blocked by CRISPR-mediated knockdown of hippocampal Mkp-1 prior to CORT exposure. In sum, these findings further demonstrate that MKP-1 is necessary for development of enhanced behavioral emotionality, while also suggesting a role in stress mechanisms linking brain dysfunction and systemic illness such as kidney disease.

Antibodies From Children With PANDAS Bind Specifically to Striatal Cholinergic Interneurons and Alter Their Activity.

OBJECTIVE: Pediatric obsessive-compulsive disorder (OCD) sometimes appears rapidly, even overnight, often after an infection. Pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections, or PANDAS, describes such a situation after infection with Streptococcus pyogenes. PANDAS may result from induced autoimmunity against brain antigens, although this remains unproven. Pilot work suggests that IgG antibodies from children with PANDAS bind to cholinergic interneurons (CINs) in the striatum. CIN deficiency has been independently associated with tics in humans and with repetitive behavioral pathology in mice, making it a plausible locus of pathology. The authors sought to replicate and extend earlier work and to investigate the cellular effects of PANDAS antibodies on cholinergic interneurons. METHODS: Binding of IgG to specific neurons in human and mouse brain slices was evaluated ex vivo after incubation with serum from 27 children with rigorously characterized PANDAS, both at baseline and after intravenous immunoglobulin (IVIG) treatment, and 23 matched control subjects. Binding was correlated with symptom measures. Neural activity after serum incubation was assessed in mouse slices using molecular markers and electrophysiological recording. RESULTS: IgG from children with PANDAS bound to CINs, but not to several other neuron types, more than IgG from control subjects, in three independent cohorts of patients. Post-IVIG serum had reduced IgG binding to CINs, and this reduction correlated with symptom improvement. Baseline PANDAS sera decreased activity of striatal CINs, but not of parvalbumin-expressing GABAergic interneurons, and altered their electrophysiological responses, in acute mouse brain slices. Post-IVIG PANDAS sera and IgG-depleted baseline sera did not alter the activity of striatal CINs. CONCLUSIONS: These findings provide strong evidence for striatal CINs as a critical cellular target that may contribute to pathophysiology in children with rapid-onset OCD symptoms, and perhaps in other conditions.

Role of BDNF in the pathophysiology and treatment of depression: Activity-dependent effects distinguish rapid-acting antidepressants.

The pathophysiology and treatment of depression have been the focus of intense research and while there is much that remains unknown, modern neurobiological approaches are making progress. This work demonstrates that stress and depression are associated with atrophy of neurons and reduced synaptic connectivity in brain regions such as the hippocampus and prefrontal cortex that contribute to depressive behaviors, and conversely that antidepressant treatment can reverse these deficits. The role of neurotrophic factors, particularly brain-derived neurotrophic factor (BDNF), has been of particular interest as these factors play a key role in activity-dependent regulation of synaptic plasticity. Here, we review the literature demonstrating that exposure to stress and depression decreases BDNF expression in the hippocampus and PFC and conversely that antidepressant treatment can up-regulate BDNF in the adult brain and reverse the effects of stress. We then focus on rapid-acting antidepressants, particularly the NMDA receptor antagonist ketamine, which produces rapid synaptic and antidepressant behavioral actions that are dependent on activity-dependent release of BDNF. This rapid release of BDNF differs from typical monoaminergic agents that require chronic administration to produce a slow induction of BDNF expression, consistent with the time lag for the therapeutic action of these agents. We review evidence that other classes of rapid-acting agents also require BDNF release, demonstrating that this is a common, convergent downstream mechanism. Finally, we discuss evidence that the actions of ketamine are also dependent on another growth factor, vascular endothelial growth factor (VEGF) and its complex interplay with BDNF.

PTSD is associated with neuroimmune suppression: evidence from PET imaging and postmortem transcriptomic studies.

Despite well-known peripheral immune activation in posttraumatic stress disorder (PTSD), there are no studies of brain immunologic regulation in individuals with PTSD. [11C]PBR28 Positron Emission Tomography brain imaging of the 18-kDa translocator protein (TSPO), a microglial biomarker, was conducted in 23 individuals with PTSD and 26 healthy individuals-with or without trauma exposure. Prefrontal-limbic TSPO availability in the PTSD group was negatively associated with PTSD symptom severity and was significantly lower than in controls. Higher C-reactive protein levels were also associated with lower prefrontal-limbic TSPO availability and PTSD severity. An independent postmortem study found no differential gene expression in 22 PTSD vs. 22 controls, but showed lower relative expression of TSPO and microglia-associated genes TNFRSF14 and TSPOAP1 in a female PTSD subgroup. These findings suggest that peripheral immune activation in PTSD is associated with deficient brain microglial activation, challenging prevailing hypotheses positing neuroimmune activation as central to stress-related pathophysiology.

Neuron-specific deletion of VEGF or its receptor Flk-1 impairs recognition memory.

Vascular endothelial growth factor (VEGF, also known as VEGF-A) is a pleiotropic factor which is expressed by neurons, astrocytes and perivascular macrophages, as well as endothelial cells, in the brain. Recently, VEGF signaling has been implicated in learning and memory, and several clinical and preclinical studies demonstrate that VEGF inhibitors induce cognitive impairment. However, the role of endogenous neuronal VEGF signaling in recognition memory remains unclear. Recently, we have developed mice with forebrain excitatory neuron-specific deletion of VEGF or its receptor, fetal liver kinase 1 (Flk-1) by crossing Camk2a-Cre mice with Vegfaflox/flox and Flk-1flox/flox mice, respectively. Using these conditional knockout mice, the present study addressed the influence of forebrain excitatory neuron-specific deletion of VEGF or Flk-1 on recognition memory in the novel object recognition test. The results show that both short-term (2 h) and long-term (24 h) recognition memory are impaired by neuron-specific deletion of either Flk-1 or VEGF. These findings indicate the physiological importance of endogenous neuronal VEGF-Flk-1 signaling in recognition memory. In addition, the current results also suggest that the impairment of neuronal VEGF-Flk-1 signaling can be a cause of anti-VEGF chemotherapy-induced cognitive impairment.

Neurotrophic mechanisms underlying the rapid and sustained antidepressant actions of ketamine.

Clinical and preclinical studies have demonstrated that depression, one of the most common psychiatric illnesses, is associated with reduced levels of neurotrophic factors, including brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF), contributing to neuronal atrophy in the prefrontal cortex (PFC) and hippocampus, and reduced hippocampal adult neurogenesis. Conventional monoaminergic antidepressants can block/reverse, at least partially, these deficits in part via induction of BDNF and/or VEGF, although these drugs have significant limitations, notably a time lag for therapeutic response and low response rates. Recent studies reveal that ketamine, an N-methyl-d-aspartate receptor antagonist produces rapid (within hours) and sustained (up to a week) antidepressant actions in both patients with treatment-resistant depression and rodent models of depression. Rodent studies also demonstrate that ketamine rapidly increases BDNF and VEGF release and/or expression in the medial PFC (mPFC) and hippocampus, leading to increase in the number and function of spine synapses in the mPFC and enhancement of hippocampal neurogenesis. These neurotrophic effects of ketamine are associated with the antidepressant effects of this drug. Together, these findings provide evidence for a neurotrophic mechanism underlying the rapid and sustained antidepressant actions of ketamine and pave the way for the development of rapid and more effective antidepressants with fewer side effects than ketamine.

Neurotrophic and Antidepressant Actions of Brain-Derived Neurotrophic Factor Require Vascular Endothelial Growth Factor.

BACKGROUND: Activity-dependent release of brain-derived neurotrophic factor (BDNF) in the medial prefrontal cortex (mPFC) is essential for the rapid and sustained antidepressant actions of ketamine, and a recent study shows a similar requirement for vascular endothelial growth factor (VEGF). Since BDNF is reported to stimulate VEGF expression and/or release in neuroblastoma cells, the present study tested the hypothesis that the actions of BDNF are mediated by VEGF. METHODS: The role of VEGF in the antidepressant behavioral actions of BDNF was tested by intra-mPFC coinfusion of a VEGF neutralizing antibody and by neuron-specific deletion of VEGF. The influence of BDNF on the release of VEGF and the role of VEGF in the neurotrophic actions of BDNF were determined in rat primary cortical neurons. The role of BDNF in the behavioral and neurotrophic actions of VEGF was also determined. RESULTS: The results show that the rapid and sustained antidepressant-like actions of intra-mPFC BDNF are blocked by coinfusion of a VEGF neutralizing antibody, and that neuron-specific mPFC deletion of VEGF blocks the antidepressant-like actions of BDNF. Studies in primary cortical neurons demonstrate that BDNF stimulates the release of VEGF and that BDNF induction of dendrite complexity is blocked by a selective VEGF-fetal liver kinase 1 receptor antagonist. Surprisingly, the results also show reciprocal interactions, indicating that the behavioral and neurotrophic actions of VEGF are dependent on BDNF. CONCLUSIONS: These findings indicate that the antidepressant-like and neurotrophic actions of BDNF require VEGF signaling, but they also demonstrate reciprocal interdependence for BDNF in the actions of VEGF.

Role of Neuronal VEGF Signaling in the Prefrontal Cortex in the Rapid Antidepressant Effects of Ketamine.

OBJECTIVE: The N-methyl-d-aspartate receptor antagonist ketamine produces rapid and sustained antidepressant actions even in patients with treatment-resistant depression. Vascular endothelial growth factor (VEGF) has been implicated in the effects of conventional monoamine-based antidepressants, but the role of VEGF in the rapid antidepressant actions of ketamine remains unclear. The authors examined whether neuronal VEGF signaling in the medial prefrontal cortex (mPFC) mediates the rapid antidepressant actions of ketamine. METHODS: The authors used a combination of approaches, including conditional, neuron-specific knockout of VEGF or its receptor, Flk-1; antibody neutralization; viral-mediated knockdown of Flk-1; and pharmacological inhibitors. Further in vitro and in vivo experiments were performed to examine whether neuronal VEGF signaling was required for the neurotrophic and synaptogenic actions of ketamine that underlie its behavioral actions. RESULTS: The behavioral actions of systemic ketamine are blocked by forebrain excitatory neuron-specific deletion of either VEGF or Flk-1 or by intra-mPFC infusion of a VEGF neutralizing antibody. Moreover, intra-mPFC infusions of VEGF are sufficient to produce rapid ketamine-like behavioral actions, and these effects are blocked by neuron-specific Flk-1 deletion. The results also show that local knockdown of Flk-1 in mPFC excitatory neurons in adulthood blocks the behavioral effects of systemic ketamine. Moreover, inhibition of neuronal VEGF signaling blocks the neurotrophic and synaptogenic effects of ketamine. CONCLUSIONS: Together, these findings indicate that neuronal VEGF-Flk-1 signaling in the mPFC plays an essential role in the antidepressant actions of ketamine.

The anxiolytic effects of cannabidiol in chronically stressed mice are mediated by the endocannabinoid system: Role of neurogenesis and dendritic remodeling.

Repeated injections of cannabidiol (CBD), the major non-psychotomimetic compound present in the Cannabis sativa plant, attenuate the anxiogenic effects induced by Chronic Unpredictable Stress (CUS). The specific mechanisms remain to be fully understood but seem to involve adult hippocampal neurogenesis and recruitment of endocannabinoids. Here we investigated for the first time if the behavioral and pro-neurogenic effects of CBD administered concomitant the CUS procedure (14 days) are mediated by CB1, CB2 or 5HT1A receptors, as well as CBD effects on dendritic remodeling and on intracellular/synaptic signaling (fatty acid amide hydrolase - FAAH, Akt, GSK3ß and the synaptic proteins Synapsin Ia/b, mGluR1 and PSD95). After 14 days, CBD injections (30 mg/kg) induced anxiolytic responses in stressed animals in the elevated plus-maze and novelty suppressed feeding tests, that were blocked by pre-treatment with a CB1 (AM251, 0.3 mg/kg) or CB2 (AM630, 0.3 mg/kg), but not by a 5HT1A (WAY100635, 0.05 mg/kg) receptor antagonist. Golgi staining and immunofluorescence revealed that these effects were associated with an increase in hippocampal neurogenesis and spine density in the dentate gyrus of the hippocampus. AM251 and AM630 abolished the effects of CBD on spines density. However, AM630 was more effective in attenuating the pro-neurogenic effects of CBD. CBD decreased FAAH and increased p-GSK3ß expression in stressed animals, which was also attenuated by AM630. These results indicate that CBD prevents the behavioral effects caused by CUS probably due to a facilitation of endocannabinoid neurotransmission and consequent CB1/CB2 receptors activation, which could recruit intracellular/synaptic proteins involved in neurogenesis and dendritic remodeling.

Stress-Induced Neuronal Colony Stimulating Factor 1 Provokes Microglia-Mediated Neuronal Remodeling and Depressive-like Behavior.

BACKGROUND: Chronic stress exposure causes neuronal atrophy and synaptic deficits in the medial prefrontal cortex (PFC), contributing to development of anxiety- and depressive-like behaviors. Concomitantly, microglia in the PFC undergo morphological and functional changes following stress exposure, suggesting that microglia contribute to synaptic deficits underlying behavioral consequences. METHODS: Male and female mice were exposed to chronic unpredictable stress (CUS) to examine the role of neuron-microglia interactions in the medial PFC during development of anxiety- and depressive-like behaviors. Thy1-GFP-M mice were used to assess microglia-mediated neuronal remodeling and dendritic spine density in the medial PFC. Viral-mediated knockdown of neuronal colony stimulating factor 1 (CSF1) was used to modulate microglia function and behavioral consequences after CUS. RESULTS: CUS promoted anxiety- and depressive-like behaviors that were associated with increased messenger RNA levels of CSF1 in the PFC. Increased CSF1 messenger RNA levels were also detected in the postmortem dorsolateral PFC of individuals with depression. Moreover, microglia isolated from the frontal cortex of mice exposed to CUS show elevated CSF1 receptor expression and increased phagocytosis of neuronal elements. Notably, functional alterations in microglia were more pronounced in male mice compared with female mice. These functional changes in microglia corresponded with reduced dendritic spine density on pyramidal neurons in layer 1 of the medial PFC. Viral-mediated knockdown of neuronal CSF1 in the medial PFC attenuated microglia-mediated neuronal remodeling and prevented behavioral deficits caused by CUS. CONCLUSIONS: These findings revealed that stress-induced elevations in neuronal CSF1 provokes microglia-mediated neuronal remodeling in the medial PFC, contributing to synaptic deficits and development of anxiety- and depressive-like behavior.

Beta-hydroxybutyrate, an endogenic NLRP3 inflammasome inhibitor, attenuates stress-induced behavioral and inflammatory responses.

Neuro-inflammation has been shown to play a critical role in the development of depression. Beta-hydroxybutyrate (BHB) is a ketone body and has recently been reported to exert anti-inflammatory effects via inhibition of NLRP3 inflammasome. Here, we investigated the potential antidepressant and anti-inflammatory effects of BHB on rats exposed to acute and chronic stress. We examined the influence of repeated BHB administration on depressive and anxiety behaviors in a rodent model of chronic unpredictable stress (CUS). Additionally, the influence of acute immobilization (IMM) stress and single BHB administration on hippocampal interleukin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α) were assessed. Repeated administration of BHB attenuated CUS-induced depressive- and anxiety-related behaviors. IMM stress increased levels of IL-1ß in the hippocampus, while a single pre-administration of BHB attenuated this increase. Although no effect was observed on hippocampal TNF-α levels after 1 h of IMM stress, a single BHB pre-administration reduced hippocampal TNF-α. Our previous report showed that the release of IL-1ß and TNF-α caused by stress is tightly regulated by NLRP3 inflammasome. These findings demonstrate that BHB exerts antidepressant-like effects, possibly by inhibiting NLRP3-induced neuro-inflammation in the hippocampus, and that BHB may be a novel therapeutic candidate for the treatment of stress-related mood disorders.

Stress induces equivalent remodeling of hippocampal spine synapses in a simulated postpartum environment and in a female rat model of major depression.

Stress and withdrawal of female reproductive hormones are known risk factors of postpartum depression. Although both of these factors are capable of powerfully modulating neuronal plasticity, there is no direct electron microscopic evidence of hippocampal spine synapse remodeling in postpartum depression. To address this issue, hormonal conditions of pregnancy and postpartum period were simulated in ovariectomized adult female Sprague-Dawley rats (n=76). The number of hippocampal spine synapses and the depressive behavior of rats in an active escape task were investigated in untreated control, hormone-withdrawn 'postpartum', simulated proestrus, and hormone-treated 'postpartum' animals. After 'postpartum' withdrawal of gonadal steroids, inescapable stress caused a loss of hippocampal spine synapses, which was related to poor escape performance in hormone-withdrawn 'postpartum' females. These responses were equivalent with the changes observed in untreated controls that is an established animal model of major depression. Maintaining proestrus levels of ovarian hormones during 'postpartum' stress exposure did not affect synaptic and behavioral responses to inescapable stress in simulated proestrus animals. By contrast, maintaining pregnancy levels of estradiol and progesterone during 'postpartum' stress exposure completely prevented the stress-induced loss of hippocampal spine synapses, which was associated with improved escape performance in hormone-treated 'postpartum' females. This protective effect appears to be mediated by a muted stress response as measured by serum corticosterone concentrations. In line with our emerging 'synaptogenic hypothesis' of depression, the loss of hippocampal spine synapses may be a novel perspective both in the pathomechanism and in the clinical management of postpartum affective illness.

Cacna1c in the Prefrontal Cortex Regulates Depression-Related Behaviors via REDD1.

The CACNA1C gene that encodes the L-type Ca2+ channel (LTCC) Cav1.2 subunit has emerged as a candidate risk gene for multiple neuropsychiatric disorders including bipolar disorder, major depressive disorder, and schizophrenia, all marked with depression-related symptoms. Although cacna1c heterozygous (HET) mice have been previously reported to exhibit an antidepressant-like phenotype, the molecular and circuit-level dysfunction remains unknown. Here we report that viral vector-mediated deletion of cacna1c in the adult prefrontal cortex (PFC) of mice recapitulates the antidepressant-like effect observed in cacna1c HET mice using the sucrose preference test (SPT), forced swim test (FST), and tail suspension test (TST). Molecular studies identified lower levels of REDD1, a protein previously linked to depression, in the PFC of HET mice, and viral-mediated REDD1 overexpression in the PFC of these HET mice reversed the antidepressant-like effect in SPT and TST. Examination of downstream REDD1 targets found lower levels of active/phosphorylated Akt (S473) with no change in mTORC1 phosphorylation. Examination of the transcription factor FoxO3a, previously linked to depression-related behavior and shown to be regulated in other systems by Akt, revealed higher nuclear levels in the PFC of cacna1c HET mice that was further increased following REDD1-mediated reversal of the antidepressant-like phenotype. Collectively, these findings suggest that REDD1 in cacna1c HET mice may influence depression-related behavior via regulation of the FoxO3a pathway. Cacna1c HET mice thus serve as a useful mouse model to further study cacna1c-associated molecular signaling and depression-related behaviors relevant to human CACNA1C genetic variants.

Psychological Stress Activates the Inflammasome via Release of Adenosine Triphosphate and Stimulation of the Purinergic Type 2X7 Receptor.

BACKGROUND: The mechanisms underlying stress-induced inflammation that contribute to major depressive disorder are unknown. We examine the role of the adenosine triphosphate (ATP)/purinergic type 2X7 receptor (P2X7R) pathway and the NLRP3 (nucleotide-binding, leucine-rich repeat, pyrin domain containing 3) inflammasome in interleukin (IL)-1ß and depressive behavioral responses to stress. METHODS: The influence of acute restraint stress on extracellular ATP, glutamate, IL-1ß, and tumor necrosis factor alpha in hippocampus was determined by microdialysis, and the influence of acute restraint stress on the NLRP3 inflammasome was determined by western blot analysis. The influence of P2X7R antagonist administration on IL-1ß and tumor necrosis factor alpha and on anxiety and depressive behaviors was determined in the chronic unpredictable stress rodent model. The role of the NLRP3 inflammasome was determined by analysis of Nlrp3 null mice. RESULTS: Acute restraint stress rapidly increased extracellular ATP, an endogenous agonist of P2X7R; the inflammatory cytokine IL-1ß; and the active form of the NLRP3 inflammasome in the hippocampus. Administration of a P2X7R antagonist completely blocked the release of IL-1ß and tumor necrosis factor alpha, another stress-induced cytokine, and activated NLRP3. Moreover, P2X7R antagonist administration reversed the anhedonic and anxiety behaviors caused by chronic unpredictable stress exposure, and deletion of the Nlrp3 gene rendered mice resistant to development of depressive behaviors caused by chronic unpredictable stress. CONCLUSIONS: These findings demonstrate that psychological "stress" is sensed by the innate immune system in the brain via the ATP/P2X7R-NLRP3 inflammasome cascade, and they identify novel therapeutic targets for the treatment of stress-related mood disorders and comorbid illnesses.

Rapid antidepressant actions of scopolamine: Role of medial prefrontal cortex and M1-subtype muscarinic acetylcholine receptors.

Clinical studies demonstrate that scopolamine, a non-selective muscarinic acetylcholine receptor (mAchR) antagonist, produces rapid therapeutic effects in depressed patients, and preclinical studies report that the actions of scopolamine require glutamate receptor activation and the mechanistic target of rapamycin complex 1 (mTORC1). The present study extends these findings to determine the role of the medial prefrontal cortex (mPFC) and specific muscarinic acetylcholine receptor (M-AchR) subtypes in the actions of scopolamine. The administration of scopolamine increases the activity marker Fos in the mPFC, including the infralimbic (IL) and prelimbic (PrL) subregions. Microinfusions of scopolamine into either the IL or the PrL produced significant antidepressant responses in the forced swim test, and neuronal silencing of IL or PrL blocked the antidepressant effects of systemic scopolamine. The results also demonstrate that the systemic administration of a selective M1-AChR antagonist, VU0255035, produced an antidepressant response and stimulated mTORC1 signaling in the PFC, similar to the actions of scopolamine. Finally, we used a chronic unpredictable stress model as a more rigorous test of rapid antidepressant actions and found that a single dose of scopolamine or VU0255035 blocked the anhedonic response caused by CUS, an effect that requires the chronic administration of typical antidepressants. Taken together, these findings indicate that mPFC is a critical mediator of the behavioral actions of scopolamine and identify the M1-AChR as a therapeutic target for the development of novel and selective rapid-acting antidepressants.

Vascular endothelial growth factor receptor 3 controls neural stem cell activation in mice and humans.

Neural stem cells (NSCs) continuously produce new neurons within the adult mammalian hippocampus. NSCs are typically quiescent but activated to self-renew or differentiate into neural progenitor cells. The molecular mechanisms of NSC activation remain poorly understood. Here, we show that adult hippocampal NSCs express vascular endothelial growth factor receptor (VEGFR) 3 and its ligand VEGF-C, which activates quiescent NSCs to enter the cell cycle and generate progenitor cells. Hippocampal NSC activation and neurogenesis are impaired by conditional deletion of Vegfr3 in NSCs. Functionally, this is associated with compromised NSC activation in response to VEGF-C and physical activity. In NSCs derived from human embryonic stem cells (hESCs), VEGF-C/VEGFR3 mediates intracellular activation of AKT and ERK pathways that control cell fate and proliferation. These findings identify VEGF-C/VEGFR3 signaling as a specific regulator of NSC activation and neurogenesis in mammals.

Overexpression of human GATA-1 and GATA-2 interferes with spine formation and produces depressive behavior in rats.

Functional consequences to which vertebrate GATA transcription factors contribute in the adult brain remain largely an open question. The present study examines how human GATA-1 and GATA-2 (hGATA-1 and hGATA-2) are linked to neuronal differentiation and depressive behaviors in rats. We investigated the effects of adeno-associated viral expression of hGATA-1 and hGATA-2 (AAV-hGATA1 and AAV-hGATA2) in the dentate gyrus (DG) of the dorsal hippocampus on dendrite branching and spine number. We also examined the influence of AAV-hGATA1 and AAV-hGATA2 infusions into the dorsal hippocampus on rodent behavior in models of depression. Viral expression of hGATA-1 and hGATA-2 cDNA in rat hippocampal neurons impaired dendritic outgrowth and spine formation. Moreover, viral-mediated expression of hGATA-1 and hGATA-2 in the dorsal hippocampus caused depressive-like deficits in the forced swim test and learned helplessness models of depression, and decreased the expression of several synapse-related genes as well as spine number in hippocampal neurons. Conversely, shRNA knockdown of GATA-2 increased synapse-related gene expression, spine number, and dendrite branching. The results demonstrate that hGATA-1 and hGATA-2 expression in hippocampus is sufficient to cause depressive like behaviors that are associated with reduction in spine synapse density and expression of synapse-related genes.

Depression and treatment response: dynamic interplay of signaling pathways and altered neural processes.

Since the 1960s, when the first tricyclic and monoamine oxidase inhibitor antidepressant drugs were introduced, most of the ensuing agents were designed to target similar brain pathways that elevate serotonin and/or norepinephrine signaling. Fifty years later, the main goal of the current depression research is to develop faster-acting, more effective therapeutic agents with fewer side effects, as currently available antidepressants are plagued by delayed therapeutic onset and low response rates. Clinical and basic science research studies have made significant progress towards deciphering the pathophysiological events within the brain involved in development, maintenance, and treatment of major depressive disorder. Imaging and postmortem brain studies in depressed human subjects, in combination with animal behavioral models of depression, have identified a number of different cellular events, intracellular signaling pathways, proteins, and target genes that are modulated by stress and are potentially vital mediators of antidepressant action. In this review, we focus on several neural mechanisms, primarily within the hippocampus and prefrontal cortex, which have recently been implicated in depression and treatment response.