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

Ketamine - An Imperfect Wonder Drug?

Ketamine is a potent sedative and dissociative anesthetic agent that has been used clinically for over 50 years since it was first developed in the 1960 s as an alternative to phencyclidine (PCP). When compared to PCP, ketamine exhibited a much lower incidence of severe side effects, including hallucinations, leading to its increased popularity in clinical practice. Ketamine was initially used as an anesthetic agent, especially in emergency medicine and in surgical procedures where rapid induction and recovery was necessary. However, over the last few decades, ketamine was found to have additional clinically useful properties making it effective in the treatment of a variety of other conditions. Presently, ketamine has a wide range of clinical uses beyond anesthesia including management of acute and chronic pain, as well as treatment of psychiatric disorders such as major depression. In addition to various clinical uses, ketamine is also recognized as a common drug of abuse sought for its hallucinogenic and sedative effects. This review focuses on exploring the different clinical and non-clinical uses of ketamine and its overall impact on patient care.

ER stress in mouse serotonin neurons triggers a depressive phenotype alleviated by ketamine targeting eIF2α signaling

Depression is a devastating mood disorder that causes significant disability worldwide. Current knowledge of its pathophysiology remains modest and clear biological markers are lacking. Emerging evidence from human and animal models reveals persistent alterations in endoplasmic reticulum (ER) homeostasis, suggesting that ER stress-related signaling pathways may be targets for prevention and treatment. However, the neurobiological basis linking the pathways involved in depression-related ER stress remains unknown. Here, we report that an induced model of ER stress in mouse serotonin (5-HT) neurons is associated with reduced Egr1-dependent 5-HT cellular activity and 5-HT neurotransmission, resulting in neuroplasticity deficits in forebrain regions and a depressive-like phenotype. Ketamine administration engages downstream eIF2α signaling to trigger rapid neuroplasticity events that rescue the depressive-like effects. Collectively, these data identify ER stress in 5-HT neurons as a cellular pathway involved in the pathophysiology of depression and show that eIF2α is critical in eliciting ketamine's fast antidepressant effects.

Possible role of exercise therapy on depression: Effector neurotransmitters as key players

About 280 million people suffer from depression as the most common neurological disorder and the most common cause of death worldwide. Exercise with serotonin released in the brain by the 5-HT3-IGF-1 mechanism can lead to antidepressant effects. Swimming exercise has antidepressant effects by increasing the sensitivity of serotonin 5-HT2 receptors and postsynaptic 5-HT1A receptors, increasing 5-HT and 5HIAA levels, increasing TPH and serotonin, and decreasing inflammatory levels of IFN-γ and TNF-α. Anaerobic and aerobic exercises increase beta-endorphin, enkephalin, and dynorphin and have antidepressant effects. Exercise by increasing dopamine, D1R, and D2R leads to the expression of BDNF and activation of TrkB and has antidepressant behavior. Exercise leads to a significant increase in GABAAR (γ2 and α2 subunits) and reduces neurodegenerative disorders caused by GABA imbalance through anti-inflammatory pathways. By increasing glutamate and PGC1α and reducing glutamatergic neurotoxicity, exercise enhances neurogenesis and synaptogenesis and prevents neurodegeneration and the onset of depression. Irisin release during exercise shows an important role in depression by increasing dopamine, BDNF, NGF, and IGF-1 and decreasing inflammatory mediators such as IL-6 and IL-1β. In addition, exercise-induced orexin and NPY can increase hippocampal neurogenesis and relieve depression. After exercise, the tryptophan to large neutral amino acids (TRP/LNAA) ratio and the tryptophan to branched-chain amino acids (BCAA) ratio increase, which may have antidepressant effects. The expression of M5 receptor and nAChR α7 increases after exercise and significantly increases dopamine and acetylcholine and ameliorates depression. It appears that during exercise, muscarinic receptors can reduce depression through dopamine in the absence of acetylcholine. Therefore, exercise can be used to reduce depression by affecting neurotransmitters, neuromodulators, cytokines, and/or neurotrophins.

Impact of Stress on Brain Morphology: Insights into Structural Biomarkers of Stress-related Disorders

Exposure to acute and chronic stress has a broad range of structural effects on the brain. The brain areas commonly targeted in the stress response models include the hippocampus, the amygdala, and the prefrontal cortex. Studies in patients suffering from the so-called stress-related disorders -embracing post-traumatic stress, major depressive and anxiety disorders- have fairly replicated animal models of stress response -particularly the neuroendocrine and the inflammatory models- by finding alterations in different brain areas, even in the early neurodevelopment. Therefore, this narrative review aims to provide an overview of structural neuroimaging findings and to discuss how these studies have contributed to our knowledge of variability in response to stress and the ulterior development of stress-related disorders. There are a gross number of studies available but neuroimaging research of stress-related disorders as a single category is still in its infancy. Although the available studies point at particular brain circuitries involved in stress and emotion regulation, the pathophysiology of these abnormalities -involving genetics, epigenetics and molecular pathways-, their relation to intraindividual stress responses -including personality characteristics, self-perception of stress conditions…-, and their potential involvement as biomarkers in diagnosis, treatment prescription and prognosis are discussed.

Neurotrophin Crosstalk in the Etiology and Treatment of Neuropsychiatric and Neurodegenerative Disease

This article reviews the current progress in our understanding of the mechanisms by which growth factors, including brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF), and select neurotrophin-regulated gene products, such as VGF (non-acronymic) and VGF-derived neuropeptides, function in the central nervous system (CNS) to modulate neuropsychiatric and neurodegenerative disorders, with a discussion of the possible therapeutic applications of these growth factors to major depressive disorder (MDD) and Alzheimer’s disease (AD). BDNF and VEGF levels are generally decreased regionally in the brains of MDD subjects and in preclinical animal models of depression, changes that are associated with neuronal atrophy and reduced neurogenesis, and are reversed by conventional monoaminergic and novel ketamine-like antidepressants. Downstream of neurotrophins and their receptors, VGF was identified as a nerve growth factor (NGF)- and BDNF-inducible secreted protein and neuropeptide precursor that is produced and trafficked throughout the CNS, where its expression is greatly influenced by neuronal activity and exercise, and where several VGF-derived peptides modulate neuronal activity, function, proliferation, differentiation, and survival. Moreover, levels of VGF are reduced in the CSF of AD subjects, where it has been repetitively identified as a disease biomarker, and in the hippocampi of subjects with MDD, suggesting possible shared mechanisms by which reduced levels of VGF and other proteins that are similarly regulated by neurotrophin signaling pathways contribute to and potentially drive the pathogenesis and progression of co-morbid neuropsychiatric and neurodegenerative disorders, particularly MDD and AD, opening possible therapeutic windows.

Functional near-infrared spectroscopy during the verbal fluency task of English-Speaking adults with mood disorders: A preliminary study

Functional near-infrared spectroscopy (fNIRS) provides a direct and objective assessment of cerebral cortex function. It may be used to determine neurophysiological differences between psychiatric disorders with overlapping symptoms, such as major depressive disorder (MDD) and bipolar disorder (BD). Therefore, this preliminary study aimed to compare fNIRS signals during the verbal fluency task (VFT) of English-speaking healthy controls (HC), patients with MDD and patients with BD. Fifteen HCs, 15 patients with MDD and 15 patients with BD were recruited. Groups were matched for age, gender, ethnicity and education. Relative oxy-haemoglobin and deoxy-haemoglobin changes in the frontotemporal cortex was monitored with a 52-channel fNIRS system. Integral values of the frontal and temporal regions were derived as a measure cortical haemodynamic response magnitude. Both patient groups had lower frontal and temporal region integral values than HCs, and patients with MDD had lower frontal region integral value than patients with BD. Moreover, patients could be differentiated from HCs using the frontal and temporal integral values, and patient groups could be differentiated using the frontal region integral values. VFT performance, clinical history and symptom severity were not associated with integral values. These results suggest that prefrontal cortex haemodynamic dysfunction occurs in mood disorders, and it is more extensive in MDD than BD. The fNIRS-VFT paradigm may be a potential tool for differentiating MDD from BD in clinical settings, and these findings need to be verified in a larger sample of English-speaking patients with mood disorders.

Lithium augmentation of ketamine increases insulin signaling and antidepressant-like active stress coping in a rodent model of treatment-resistant depression

Lithium, a mood stabilizer and common adjunctive treatment for refractory depression, shares overlapping mechanisms of action with ketamine and enhances the duration of ketamine's antidepressant actions in rodent models at sub-therapeutic doses. Yet, in a recent clinical trial, lithium co-treatment with ketamine failed to improve antidepressant outcomes in subjects previously shown to respond to ketamine alone. The potential for lithium augmentation to improve antidepressant outcomes in ketamine nonresponders, however, has not been explored. The current study examined the behavioral, molecular and metabolic actions of lithium and ketamine co-treatment in a rodent model of antidepressant resistance. Male Wistar rats were administered adrenocorticotropic hormone (ACTH; 100 µg/day, i.p. over 14 days) and subsequently treated with ketamine (10 mg/kg; 2 days; n = 12), lithium (37 mg/kg; 2 days; n = 12), ketamine + lithium (10 mg/kg + 37 mg/kg; 2 days; n = 12), or vehicle saline (0.9%; n = 12). Rats were subjected to open field (6 min) and forced swim tests (6 min). Peripheral blood and brain prefrontal cortical (PFC) tissue was collected one hour following stress exposure. Western blotting was used to determine the effects of treatment on extracellular signal-regulated kinase (ERK); mammalian target of rapamycin (mTOR), phospho kinase B (Akt), and glycogen synthase kinase-3ß (GSK3ß) protein levels in the infralimbic (IL) and prelimbic (PL) subregions of the PFC. Prefrontal oxygen consumption rate (OCR) and extracellular acidification rates (ECAR) were also determined in anterior PFC tissue at rest and following stimulation with brain-derived neurotrophic factor (BDNF) and tumor necrosis factor α (TNFα). Blood plasma levels of mTOR and insulin were determined using enzyme-linked immunosorbent assays (ELISAs). Overall, rats receiving ketamine+lithium displayed a robust antidepressant response to the combined treatment as demonstrated through significant reductions in immobility time (p < 0.05) and latency to immobility (p < 0.01). These animals also had higher expression of plasma mTOR (p < 0.01) and insulin (p < 0.001). Tissue bioenergetics analyses revealed that combined ketamine+lithium treatment did not significantly alter the respiratory response to BDNF or TNFα. Animals receiving both ketamine and lithium had significantly higher phosphorylation (p)-to-total expression ratios of mTOR (p < 0.001) and Akt (p < 0.01), and lower ERK in the IL compared to control animals. In contrast, pmTOR/mTOR levels were reduced in the PL of ketamine+lithium treated animals, while pERK/ERK expression levels were elevated. Taken together, these data demonstrate that lithium augmentation of ketamine in antidepressant nonresponsive animals improves antidepressant-like behavioral responses under stress, together with peripheral insulin efflux and region-specific PFC insulin signaling.

Stress Diminishes BDNF-stimulated TrkB Signaling, TrkB-NMDA Receptor Linkage and Neuronal Activity in the Rat Brain

Exposure to intense or repeated stressors can lead to depression or post-traumatic stress disorder (PTSD). Neurological changes induced by stress include impaired neurotrophin signaling, which is known to influence synaptic integrity and plasticity. The present study used an ex vivo approach to examine the impact of acute or repeated stress on BDNF-stimulated TrkB signaling in hippocampus (HIPPO) and prefrontal cortex (PFC). Rats in an acute multiple stressor group experienced five stressors in one day whereas rats in a repeated unpredictable stressor group experienced 20 stressors across 10 days. After stress exposure, slices were incubated with vehicle or BDNF, followed by immunoprecipitation and immunoblot assays to assess protein levels, activation states and protein-protein linkage associated with BDNF-TrkB signaling. Three key findings are (1) exposure to stressors significantly diminished BDNF-stimulated TrkB signaling in HIPPO and PFC such that reductions in TrkB activation, diminished recruitment of adaptor proteins to TrkB, reduced activation of downstream signaling molecules, disruption of TrkB-NMDAr linkage, and changes in basal and BDNF-stimulated Arc expression were observed. (2) After stress, BDNF stimulation enhanced TrkB-NMDAr linkage in PFC, suggestive of compensatory mechanisms in this region. (3) We discovered an uncoupling between TrkB signaling, TrkB-NMDAr linkage and Arc expression in PFC and HIPPO. In addition, a robust surge in pro-inflammatory cytokines was observed in both regions after repeated exposure to stressors. Collectively, these data provide therapeutic targets for future studies that investigate how to reverse stress-induced downregulation of BDNF-TrkB signaling and underscore the need for functional studies that examine stress-related TrkB-NMDAr activities in PFC.

Brain derived neurotrophic factor deficiency exacerbates inflammation-induced anhedonia in mice

Brain-derived neurotrophic factor (BDNF) is implicated in the pathology of major depression and influences the inflammatory response. Prolonged immune system activation can cause depression symptoms, and individuals with low BDNF expression may be vulnerable to inflammation-induced depression. We tested the hypothesis that BDNF deficient mice are vulnerable to the induction of depressive-like behavior following peripheral immune challenge. BDNF heterozygous (BDNF+/-) or wild-type (BDNF+/+) littermate mice were injected intraperitoneally (i.p.) with endotoxin (lipopolysaccharide, LPS) to trigger an acute pro-inflammatory response. After resolution of the acute sickness response, central expression of inflammatory genes, kynurenine metabolites, and depressive-like behaviors across multiple dimensions (symptoms) were measured. BDNF+/- mice displayed an exaggerated neuroinflammatory response following peripheral immune challenge. Pro-inflammatory cytokines interleukin-1β (IL-1β), tumor necrosis factor α (TNFα) and interleukin-6 (IL-6) were overexpressed in BDNF+/- mice relative to BDNF+/+ littermate control mice. While behavioral despair and anxiety-like behavior was not different between genotypes, LPS-induced anhedonia-like behavior was significantly more pronounced in BDNF+/- mice relative to BDNF+/+ mice. The kynurenine pathway mediates the many depressive-like behavioral effects of peripheral LPS, and similar to pro-inflammatory cytokine gene expression, indoleamine 2,3-dioxygenase (IDO) expression and kynurenine metabolism was exaggerated in BDNF+/- mice. Genetic BDNF deficiency results in a dysregulated neuroinflammatory and metabolic response to peripheral immune challenge and in a specific vulnerability to the development of inflammation-induced anhedonia.

BDNF Impact on Biological Markers of Depression-Role of Physical Exercise and Training

Depression is the most common and devastating psychiatric disorder in the world. Its symptoms, especially during the pandemic, are observed in all age groups. Exercise training (ET) is well known as a non-pharmacological strategy to alleviate clinical depression. The brain-derived neurotrophic factor (BDNF) is one of the biological factors whose expression and secretion are intensified in response to ET. BDNF is also secreted by contracted skeletal muscle that likely exerts para-, auto- and endocrine effects, supporting the crosstalk between skeletal muscle and other distant organs/tissues, such as the nervous system. This finding suggests that they communicate and work together to induce improvements on mood, cognition, and learning processes as BDNF is the main player in the neurogenesis, growth, and survival of neurons. Therefore, BDNF has been recognized as a therapeutic factor in clinical depression, especially in response to ET. The underlying mechanisms through which ET impacts depression are varied. The aim of this review was to provide information of the biological markers of depression such as monoamines, tryptophan, endocannabinoids, markers of inflammatory processes (oxidative stress and cytokines) stress and sex hormones and their relationship to BDNF. In addition, we reviewed the effects of ET on BNDF expression and how it impacts depression as well as the potential mechanisms mediating this process, providing a better understanding of underlying ET-related mechanisms in depression.

Hemodynamic Response to Three Types of Urban Spaces before and after Lockdown during the COVID-19 Pandemic

(1) Background: Prolonged lockdowns with stay-at-home orders have been introduced in many countries since the outbreak of the COVID-19 pandemic. They have caused a drastic change in the everyday lives of people living in urbanized areas, and are considered to contribute to a modified perception of the public space. As research related to the impact of COVID-19 restrictions on mental health and well-being emerges, the associated longitudinal changes of brain hemodynamics in healthy adults remain largely unknown. (2) Methods: this study examined the hemodynamic activation patterns of the prefrontal and occipital cortices of 12 participants (5 male, Mage = 47.80, SDage = 17.79, range 25 to 74, and 7 female, Mage = 39.00, SDage = 18.18, range 21 to 65) passively viewing videos from three urban sites in Singapore (Urban Park, Neighborhood Landscape and City Center) at two different time points-T1, before the COVID-19 pandemic and T2, soon after the lockdown was over. (3) Results: We observed a significant and marginally significant decrease in average oxyhemoglobin (Oxy-Hb) over time for each of the visual conditions. For both green spaces (Urban Park and Neighborhood Landscape), the decrease was in the visual cortex, while for the City Center with no green elements, the marginal decrease was observed in the visual cortex and the frontal eye fields. (4) Conclusions: The results suggest that the COVID-19-related lockdown experienced by urban inhabitants may have contributed to decreased brain hemodynamics, which are further related to a heightened risk of mental health disorders, such as depression or a decline in cognitive functions. Moreover, the busy City Center scenes induced a hemodynamic pattern associated with stress and anxiety, while urban green spaces did not cause such an effect. Urban green scenes can be an important factor to offset the negative neuropsychological impact of busy urban environments post-pandemic.

Emerging role of microRNAs in major depressive disorder and its implication on diagnosis and therapeutic response

BACKGROUND

Major depressive disorder (MDD) is a serious and common psychiatric disorder with a high prevalence in the population. Although great advances have been made, its pathogenesis is still unclear and a validated biomarker for diagnosis or therapeutic response remains unidentified. This review aims at summarizing the functional role of miRNAs in MDD pathogenesis and their potential as biomarkers for MDD diagnosis and antidepressant response.

METHODS

We performed a bibliographic research on the main databases (PubMed, Google Scholar and Web of Science) using the terms "microRNAs", "major depressive disorder", "synaptic plasticity", "biomarker", "antidepressant treatment", in order to find studies that propose the role of microRNAs in MDD pathogenesis and their potential as biomarkers for MDD diagnosis and antidepressant response.

RESULTS

microRNAs (miRNAs), a class of small noncoding RNAs, act as key regulators of synaptic plasticity in MDD pathogenesis. Growing researches provide the evidence for peripheral miRNAs as potential biomarkers for MDD diagnosis and antidepressant response. These results suggest that targeting miRNAs directly could be therapeutically beneficial for MDD and miRNAs are potential biomarkers of MDD and its treatment.

LIMITATIONS

The role of miRNAs in MDD pathogenesis needs further investigation. Whether miRNAs in peripheral tissues truly represent brain-derived miRNAs is still unclear at the present time. Moreover, only a few blood miRNAs alterations are consistent across studies.

CONCLUSIONS

Overall, miRNAs act key regulators of synaptic plasticity in MDD pathogenesis and hold significant promise as biomarkers or therapeutic targets for MDD, but further research is still needed.

Repeated fluoxetine treatment induces transient and long-term astrocytic plasticity in the medial prefrontal cortex of normal adult rats

Fluoxetine (Flx)-induced neuronal plasticity plays an important role in the effective treatment of depression and mood disorders. It is less understood whether repeated Flx treatment induces astrocytic plasticity that outlasts the presence of the drug in the body. We showed previously that Flx-induced neuronal plasticity in the medial prefrontal cortex (mPFC) persisted up to 20 days after the treatment. In this study, adult rats were subjected to a 15-day repeated Flx treatment at a daily dose of 20 mg/kg body weight. Astrocytic metabolites and markers were assessed in the mPFC at day 1 (d1) and day 20 (d20) after the treatment. Significant transient reductions in the concentrations of astrocytic metabolites taurine and myo-inositol and the expressions of glial fibrillary acidic protein (GFAP) and aquaporin-4 (AQP4) were observed in the mPFC of Flx-treated rats at d1, which recovered to the control levels at d20. Further, Flx treatment resulted in long-lasting changes in Kir4.1 expression in the mPFC, which remained downregulated at d20. The expression of 5-HT_1A receptor in the mPFC of Flx-treated rats was downregulated at d1 but became upregulated at d20. In summary, repeated Flx treatment induces both transient and long-term astrocytic plasticity in the mPFC of adult rats. The changes observed at d1 are consistent with disturbed water homeostasis and astrocytic de-maturation in the mPFC. The persistent changes in the expressions of Kir4.1 and 5-HT_1A at d20, presumably of the astrocytic origin, might have contributed to the long-term neurotrophic effects of repeated Flx treatment in the mPFC.

Serotonin receptor 4 in the hippocampus modulates mood and anxiety

Serotonin receptor 4 (5-HT₄R) plays an important role in regulating mood, anxiety, and cognition, and drugs that activate this receptor have fast-acting antidepressant (AD)-like effects in preclinical models. However, 5-HT₄R is widely expressed throughout the central nervous system (CNS) and periphery, making it difficult to pinpoint the cell types and circuits underlying its effects. Therefore, we generated a Cre-dependent 5-HT₄R knockout mouse line to dissect the function of 5-HT₄R in specific brain regions and cell types. We show that the loss of functional 5-HT₄R specifically from excitatory neurons of hippocampus led to robust AD-like behavioral responses and an elevation in baseline anxiety. 5-HT₄R was necessary to maintain the proper excitability of dentate gyrus (DG) granule cells and cell type-specific molecular profiling revealed a dysregulation of genes necessary for normal neural function and plasticity in cells lacking 5-HT₄R. These adaptations were accompanied by an increase in the number of immature neurons in ventral, but not dorsal, dentate gyrus, indicating a broad impact of 5-HT₄R loss on the local cellular environment. This study is the first to use conditional genetic targeting to demonstrate a direct role for hippocampal 5-HT₄R signaling in modulating mood and anxiety. Our findings also underscore the need for cell type-based approaches to elucidate the complex action of neuromodulatory systems on distinct neural circuits.

Potential antidepressant-like effect of piperazine derivative LQFM212 in mice: Role of monoaminergic pathway and brain-derived neurotrophic factor

Major depression disorder (MDD) is one of the most widespread and debilitating psychiatric diseases and may be associated with other mental disorders such as anxiety. Despite advances in neurobiology studies, currently no established mechanism can explain all facets of MDD, and available drugs often show therapeutic delay for clinical effectiveness and response rates in patients are around 50 %. Previous activities of piperazine derivatives on CNS are indicators of its therapeutic potential for treating mental disorders. In this regard, we have previously shown that the piperazine derivative 2,6-di-tert-butyl-4-((4-(2-hydroxyethyl)piperazin-1-yl)methyl)phenol (LQFM212) has anxiolytic-like activity which involves serotonergic pathway, nicotinic receptors and BZD-site of GABA_A receptor, without cognitive impairments. Herein, was evaluated the potential antidepressant-like effect of LQFM212 on forced swimming test (FST) after a single dose of 54 μmol/kg and after repeated treatment for 15 days in mice. Pretreatment with WAY-100635, PCPA, prazosin, SCH-23390, sulpiride or AMPT reversed the antidepressant-like effect on FST, suggesting that monoaminergic pathway contributes for effects of LQFM212. Furthermore, repeated treatment with LQFM212 increased hippocampal BDNF levels dosed by ELISA kit. In assessment of possible adverse effects, repeated treatment with LQFM212 did not alter the body weight of the animals, glutathione levels in the liver, and serum levels of AST, ALT, urea, and creatinine. Taken together, the results showed that LQFM212 has an antidepressant-like effect that involves monoaminergic pathway and increased BDNF levels. This compound represents promising candidate for prototype of psychoactive drugs for treatment of anxiety and depression disorders since these pathological conditions may exist in comorbidities.

Corticosterone as a Potential Confounding Factor in Delineating Mechanisms Underlying Ketamine's Rapid Antidepressant Actions

Recent research into the rapid antidepressant effect of subanesthetic doses of ketamine have identified a series of relevant protein cascades activated within hours of administration. Prior to, or concurrent with, these activation cascades, ketamine treatment generates dissociative and psychotomimetic side effects along with an increase in circulating glucocorticoids. In rats, we observed an over 3-fold increase in corticosterone levels in both serum and brain tissue, within an hour of administration of low dose ketamine (10 mg/kg), but not with (2R, 6R)-hydroxynorketamine (HNK) (10 mg/kg), a ketamine metabolite shown to produce antidepressant-like action in rodents without inducing immediate side-effects. Hippocampal tissue from ketamine, but not HNK, injected animals displayed a significant increase in the expression of sgk1, a downstream effector of glucocorticoid receptor signaling. To examine the role conscious sensation of ketamine's side effects plays in the release of corticosterone, we assessed serum corticosterone levels after ketamine administration while under isoflurane anesthesia. Under anesthesia, ketamine failed to increase circulating corticosterone levels relative to saline controls. Concurrent with its antidepressant effects, ketamine generates a release of glucocorticoids potentially linked to disturbing cognitive side effects and the activation of distinct molecular pathways which should be considered when attempting to delineate the molecular mechanisms of its antidepressant function.

Pharmacological basis of the anxiolytic and antidepressant properties of Silexan®, an essential oil from the flowers of lavender

Silexan®, a proprietary essential oil manufactured by steam distillation from Lavandula angustifolia flowers showed pronounced anxiolytic effects in patients with subthreshold anxiety disorders and was also efficacious in patients with Generalized Anxiety disorder (GAD). Moreover, evidences for antidepressant-like properties of Silexan® have been observed in anxious patients suffering from comorbid depressive symptoms and in patients with mixed anxiety-depression disorder (ICD-10 F41.2). In accordance with the clinical data Silexan® is active in several behavioral models in rodents at rather low concentrations indicating potent anxiolytic and antidepressive properties. As possible mechanism of action a moderate inhibition of voltage dependent calcium channels (VDCC) has been found showing some similarities to the anxiolytic drug pregabalin. However, while pregabalin mainly inhibits P/Q-type channels by binding to a modulatory subunit, Silexan® moderately inhibits mainly T-type and N-type channels and to some extent P/Q-type channels. Unlike pregabalin Silexan® is free of hypnotic or sedative side effects and seems to be devoid of any abuse potential. With respect to its specific antidepressant like properties Silexan® improves several aspects of neuroplasticity which seems to be the common final pathway of all antidepressant drugs. As a potential mechanism of its effects on neuroplasticity an activation of the transcription factor CREB via activation of intracellular signaling kinases like PKA and MAPK has been found. Since the concentrations of Silexan® needed to inhibit VDCC function and to improve neuroplasticity are quite similar, the effects of Silexan® on PKA or MAPK could constitute a common intracellular signaling cascade leading to VDCC modulation as well as CREB activation and improved neuroplasticity.

Dietary Exposure to Excess Saturated Fat During Early Life Alters Hippocampal Gene Expression and Increases Risk for Behavioral Disorders in Adulthood

Purpose

Maternal and postnatal diets result in long-term changes in offspring brain and behavior; however, the key mediators of these developmental changes are not well-defined. In this study, we investigated the impact of maternal and post-weaning high-fat diets on gene expression of key components mediating hippocampal synaptic efficacy. In addition, we evaluated the risk for impaired stress-coping and anxiety-like behaviors in adult offspring exposed to obesogenic diets during early life.

Methods

Dams were fed a control (C) or high-fat (HF) diet prior to mating, pregnancy, and lactation. Male offspring from control chow and high-fat fed dams were weaned to control chow or HF diets. The forced swim test (FST) and the elevated-plus maze (EPM) were used to detect stress-coping and anxiety-like behavior, respectively. Real-time RT-PCR and ELISA were used to analyze hippocampal expression of genes mediating synaptic function.

Results

Animals fed a HF diet post-weaning spent more time immobile in the FST. Swimming time was reduced in response to both maternal and post-weaning HF diets. Both maternal and post-weaning HF diets contributed to anxiety-like behavior in animals exposed to the EPM. Maternal and post-weaning HF diets were associated with a significant decrease in mRNA and protein expression for hippocampal GDNF, MAP2, SNAP25, and synaptophysin. Hippocampal mRNA expression of key serotonergic and glutamatergic receptors also exhibited differential responses to maternal and post-weaning HF diets. Hippocampal serotonergic receptor 5HT1A mRNA was reduced in response to both the maternal and post-weaning diet, whereas, 5HT2A receptor mRNA expression was increased in response to the maternal HF diet. The glutamate AMPA receptor subunit, GluA1, mRNA expression was significantly reduced in response to both diets, whereas no change was detected in GluA2 subunit mRNA expression.

Conclusion

These data demonstrate that the expression of genes mediating synaptic function are differentially affected by maternal and post-weaning high-fat diets. The post-weaning high-fat diet clearly disturbs both behavior and gene expression. In addition, although the transition to control diet at weaning partially compensates for the adverse effects of the maternal HF diet, the negative consequence of the maternal HF diet is exacerbated by continuing the high-fat diet post-weaning. We present evidence to support the claim that these dietary influences increase the risk for anxiety and impaired stress-coping abilities in adulthood.

Validating a functional near-infrared spectroscopy diagnostic paradigm for Major Depressive Disorder

Reduced haemodynamic response in the frontotemporal cortices of patients with major depressive disorder (MDD) has been demonstrated using functional near-infrared spectroscopy (fNIRS). Most notably, changes in cortical oxy-haemoglobin during a Japanese phonetic fluency task can differentiate psychiatric patients from healthy controls (HC). However, this paradigm has not been validated in the English language. Therefore, the present work aimed to distinguish patients with MDD from HCs, using haemodynamic response measured during an English letter fluency task. One hundred and five HCs and 105 patients with MDD took part in this study. NIRS signals during the verbal fluency task (VFT) was acquired using a 52-channel system, and changes in oxy-haemoglobin in the frontal and temporal regions were quantified. Depression severity, psychosocial functioning, pharmacotherapy and psychiatric history were noted. Patients with MDD had smaller changes in oxy-haemoglobin in the frontal and temporal cortices than HCs. In both regions of interest, oxy-haemoglobin was not associated with any of the clinical variables studied. 75.2% and 76.5% of patients with MDD were correctly classified using frontal and temporal region oxy-haemoglobin, respectively. Haemodynamic response measured by fNIRS during an English letter fluency task is a promising biomarker for MDD.

Effects of Zuojin pill on depressive behavior and gastrointestinal function in rats with chronic unpredictable mild stress: Role of the brain-gut axis

ETHNOPHARMACOLOGICAL RELEVANCE

Zoujin pill (ZJP), a medication used to treat gastrointestinal disorders since the 15th Century in China, have been reported to exert anti-depressant effects in various models.

STUDY AIM

To assess the effects of ZJP on gastrointestinal function and depressive behavior in rats under chronic unpredictable mild stress (CUMS), and to examine the underlying mechanisms related to brain-gut axis.

METHODS

The rats suffered the stressor once daily for 5 weeks. ZJP (0.6 and 1.2 g/kg) and fluoxetine (15 mg/kg) as positive control were administered to the rats through gastric intubation once daily for 5 consecutive weeks. The anti-depression effects were compared by performing sucrose preference tests and open field tests. Gastrointestinal motility was investigated by determining the gastrointestinal transit rate and by electrogastrogram. The serum levels of the gastrointestinal hormone (GAS, MOT, VIP, SP), inflammatory cytokine (IL-1β, IL-6; , TNFα) and glucagon-like peptide-1 (GLP-1) were assayed by enzyme-linked immunosorbent assay. For monoamine neurotransmitters (NE, 5-HT, DA), the levels were determined by high-performance liquid chromatography and electrochemical detection in conjunction, which was applied on the samples taken from the hypothalamus, hippocampus, and striatum.

RESULTS

The depression-like symptoms among rats under CUMS were significantly relieved by ZJP administration (0.6 and 1.2 g/kg). Gastrointestinal motility was also improved by restoring gastric electrical rhythm and promoting gastrointestinal propulsion. The ZJP at 0.6 g/kg dosage obviously up-regulated 5-HT and DA levels in hippocampus. The ZJP at 1.2 g/kg dosage could increase 5-HT and DA levels in hypothalamus, striatum, and hippocampus, while down-regulated the NE level in hypothalamus and hippocampus. ZJP also reversed the alterations in serum gastrointestinal hormones. Furthermore, treatment with ZJP significantly reduced levels of IL-1β, IL-6 and TNF-α and increased serum GLP-1 compared with the CUMS group. Fluoxetine also exerted similar anti-depressant effects in the absence of effects on gastrointestinal motility and the levels of serum hormone, inflammatory cytokine and GLP-1.

CONCLUSION

ZJP imposed anti-depressant and gastrointestinal regulating functions in rats under CUMS, suggesting potential clinical application. .

New insights into the cellular activities of Fndc5/Irisin and its signaling pathways

Fndc5, a well-defined myokine and also identified as an adipokine, has a critical role in modulation of metabolism and protection against obesity. These important functions are mediated by irisin, a secretory peptide produced from proteolytic processing of Fndc5. The other beneficial physiological effects of irisin are alleviation of oxidative stress, neuroprotective effects, and anti-inflammatory properties and associated anti-metastatic effects. Fndc5/irisin exerts its biological effects through several intracellular signaling pathways. The major signaling pathway is thought to be MAPK signaling pathways which are involved in neural differentiation, browning of white adipocytes, as well as osteoblast proliferation and differentiation. Other essential functions of Fndc5/irisin are mediated through additional pathways including AMPK pathway, PI3K/AKT, and STAT3/Snail. Thorough understanding of the mechanisms of irisin actions are essential in order to develop Fndc5/irisin for therapeutic purposes. In the present review, we focus on the current knowledge of the signaling pathways that elicit irisin actions.

Obsessive-compulsive disorder and growth factors: A comparative review

The goal of this article is to clarify the role of various growth factors in the establishment and progression of obsessive-compulsive disorder (OCD). OCD is a chronic mental disorder with recurrent intrusive thoughts and/or repetitive compulsive behaviors that increase during stressful periods. Growth and neurotrophic factors may be contributing factors in the pathophysiology of OCD. Many of them are synthesized and released within the central nervous system and act as trophic agents in neurons; some of them are involved in brain growth, development, neurogenesis, myelination and plasticity, while others take part in the protection of the nervous system following brain injuries. This paper attempts to identify all articles investigating the relationship between OCD and neurotrophic and growth factors, in both animal and human studies, with a focus on adult brain studies. Based on the PubMed and Scopus and Science Direct search tools, the available articles and studies are reviewed. Out of 230 records in total, the ones related to our review topic were taken into account to further understand the pathophysiological mechanism(s) of OCD, providing methods to improve its symptoms via the modification of neurotrophins and growth factor imbalances.

Relationship between VEGF-related gene polymorphisms and brain morphology in treatment-naïve patients with first-episode major depressive disorder

Vascular endothelial growth factor (VEGF) is involved in the development of major depressive disorder (MDD). Recently, a genome-wide association study has revealed that four VEGF-related single nucleotide polymorphisms (SNPs) (i.e., rs4416670, rs6921438, rs6993770 and rs10738760) were independently associated with circulating VEGF levels. The current study investigated the relationship between brain volume and these four SNPs in first-episode drug-naïve MDD patients. A total of 38 first-episode drug-naïve MDD patients and 39 healthy subjects (HS) were recruited and underwent high-resolution T1-weighted imaging. Blood samples were collected from all the participants for serum VEGF assays and VEGF-related SNPs genotyping. Genotype-diagnosis interactions related to whole-brain cortical thickness and hippocampal subfield volumes were evaluated for the four SNPs. The results revealed a genotype-diagnosis interaction only for rs6921438 (i.e., the MDD patients and HS with the G/G genotype versus the MDD patients and HS with A-carrier genotype) in the subiculum of the left hippocampus (p < 0.05), and not the other SNPs. There was a volume reduction in the left subiculum of G/G genotype patients compared with the other groups. The "hypochondriasis" scores of the HAMD-17 scale were significantly higher in the G/G genotype patients than the A-carrier genotype patients. The association was observed between VEGF-related SNP rs6921438 and subiculum atrophy in first-episode drug-naïve MDD patients.

Reduced vascular endothelial growth factor levels in the cerebrospinal fluid in patients with treatment resistant major depression and the effects of electroconvulsive therapy-A pilot study

BACKGROUND

Several lines of evidence are pointing towards an involvement of the vascular endothelial growth factor (VEGF) in the pathophysiology of depression. There are studies analyzing blood levels of VEGF in patients with depression compared to controls, but a data on cerebrospinal fluid (CSF) levels of VEGF in patients with depression are lacking.

METHOD

CSF VEGF levels were measured in patients (n = 12) with a severe, treatment-resistant depressive episode before and after the antidepressant treatment by a course of electroconvulsive therapy (ECT) and compared to age- and sex-matched controls (n = 20).

RESULTS

The patients with depression showed lower mean VEGF levels in the CSF prior to ECT than the controls (p = 0.041). Regarding the patients, CSF VEGF concentration at baseline and after the complete ECT treatment did not differ from each other (p = 0.78).

LIMITATIONS

Major limitations of this study are the small sample size and that data from corresponding serum levels cannot be provided. Another limitation is that the controls were not completely healthy, as they were recruited from a memory clinic with subjective complaints. The timing of the second sample might have been suboptimal, when taking into account that there might be an on-going phase of re-equilibrating after ECT.

CONCLUSIONS

CSF VEGF concentrations were lower in a clinical sample of patients with treatment-resistant depression compared with matched controls. Additionally, no change in CSF VEGF levels during a course of ECT could be detected.

International Union of Basic and Clinical Pharmacology CIV: The Neurobiology of Treatment-resistant Depression: From Antidepressant Classifications to Novel Pharmacological Targets

Major depressive disorder is one of the most prevalent and life-threatening forms of mental illnesses and a major cause of morbidity worldwide. Currently available antidepressants are effective for most patients, although around 30% are considered treatment resistant (TRD), a condition that is associated with a significant impairment of cognitive function and poor quality of life. In this respect, the identification of the molecular mechanisms contributing to TRD represents an essential step for the design of novel and more efficacious drugs able to modify the clinical course of this disorder and increase remission rates in clinical practice. New insights into the neurobiology of TRD have shed light on the role of a number of different mechanisms, including the glutamatergic system, immune/inflammatory systems, neurotrophin function, and epigenetics. Advances in drug discovery processes in TRD have also influenced the classification of antidepressant drugs and novel classifications are available, such as the neuroscience-based nomenclature that can incorporate such advances in drug development for TRD. This review aims to provide an up-to-date description of key mechanisms in TRD and describe current therapeutic strategies for TRD before examining novel approaches that may ultimately address important neurobiological mechanisms not targeted by currently available antidepressants. All in all, we suggest that drug targeting different neurobiological systems should be able to restore normal function but must also promote resilience to reduce the long-term vulnerability to recurrent depressive episodes.

Reduced serum VGF levels were reversed by antidepressant treatment in depressed patients

OBJECTIVES

VGF, a non-acronymic neuropeptide, is important in the pathogenesis of major depressive disorder (MDD) and in the functioning and efficacy of some antidepressant drugs. In this study we assessed whether serum VGF levels change in MDD patients and if antidepressant treatments can restore these changes.

METHODS

We measured serum VGF concentrations using sandwich ELISA in drug-free MDD patients before treatment began (n = 26) and at 8 weeks after antidepressant treatment (n = 26) with escitalopram and duloxetine, two common antidepressants. The severity of depression was assessed with the 17-item Hamilton Depression Rating Scale (HDRS).

RESULTS

VGF serum levels were significantly lower in MDD patients compared to controls (P = .002), even after controlling for the effects of age and education (P = .037), and they were reversed by 8 weeks of drug treatment (P < .0001). Both escitalopram and duloxetine restored the decreased serum VGF levels (P < .05). We observed no correlation between VGF levels and HDRS scores in pre-treatment MDD patients (P = .879).

CONCLUSIONS

The results suggest that VGF may be implicated in the pathophysiology of MDD and in the mechanisms underlying the action of antidepressants, and serum VGF may be regarded as a trait parameter for MDD.

Cariprazine Exhibits Anxiolytic and Dopamine D3 Receptor-Dependent Antidepressant Effects in the Chronic Stress Model

Background

Cariprazine, a D3-preferring dopamine D2/D3 receptor partial agonist, is a new antipsychotic drug recently approved in the United States for the treatment of schizophrenia and bipolar mania. We recently demonstrated that cariprazine also has significant antianhedonic-like effects in rats subjected to chronic stress; however, the exact mechanism of action for cariprazine's antidepressant-like properties is not known. Thus, in this study we examined whether the effects of cariprazine are mediated by dopamine D3 receptors.

Methods

Wild-type and D3-knockout mice were exposed to chronic unpredictable stress for up to 26 days, treated daily with vehicle, imipramine (20 mg/kg), aripiprazole (1 and 5 mg/kg), or cariprazine (0.03, 0.1, 0.2, and 0.4 mg/kg), and tested in behavioral assays measuring anhedonia and anxiety-like behaviors.

Results

Results showed that cariprazine significantly attenuated chronic unpredictable stress-induced anhedonic-like behavior in wild-type mice, demonstrating potent antidepressant-like effects comparable with aripiprazole and the tricyclic antidepressant imipramine. This antianhedonic-like effect of cariprazine was not observed in D3-knockout mice, suggesting that the cariprazine antidepressant-like activity is mediated by dopamine D3 receptors. Moreover, cariprazine significantly reduced drinking latency in the novelty-induced hypophagia test in wild-type mice, further confirming its antianhedonic-like effect and showing that it also has anxiolytic-like activity.

Conclusions

In combination with previous studies, these results suggest that cariprazine has a unique pharmacological profile and distinct dopamine D3 receptor-dependent mechanism of action that may be beneficial in the treatment of schizophrenia, bipolar disorder, and major depressive disorder.

Functional Recovery in Major Depressive Disorder: Providing Early Optimal Treatment for the Individual Patient

Major depressive disorder is an often chronic and recurring illness. Left untreated, major depressive disorder may result in progressive alterations in brain morphometry and circuit function. Recent findings, however, suggest that pharmacotherapy may halt and possibly reverse those effects. These findings, together with evidence that a delay in treatment is associated with poorer clinical outcomes, underscore the urgency of rapidly treating depression to full recovery. Early optimized treatment, using measurement-based care and customizing treatment to the individual patient, may afford the best possible outcomes for each patient. The aim of this article is to present recommendations for using a patient-centered approach to rapidly provide optimal pharmacological treatment to patients with major depressive disorder. Offering major depressive disorder treatment determined by individual patient characteristics (e.g., predominant symptoms, medical history, comorbidities), patient preferences and expectations, and, critically, their own definition of wellness provides the best opportunity for full functional recovery.

MicroRNAs 146a/b-5 and 425-3p and 24-3p are markers of antidepressant response and regulate MAPK/Wnt-system genes

Antidepressants (ADs) are the most common treatment for major depressive disorder (MDD). However, only ∼30% of patients experience adequate response after a single AD trial, and this variability remains poorly understood. Here, we investigated microRNAs (miRNAs) as biomarkers of AD response using small RNA-sequencing in paired samples from MDD patients enrolled in a large, randomized placebo-controlled trial of duloxetine collected before and 8 weeks after treatment. Our results revealed differential expression of miR-146a-5p, miR-146b-5p, miR-425-3p and miR-24-3p according to treatment response. These results were replicated in two independent clinical trials of MDD, a well-characterized animal model of depression, and post-mortem human brains. Furthermore, using a combination of bioinformatics, mRNA studies and functional in vitro experiments, we showed significant dysregulation of genes involved in MAPK/Wnt signalling pathways. Together, our results indicate that these miRNAs are consistent markers of treatment response and regulators of the MAPK/Wnt systems.

Antidepressant drugs are the most common treatment for depressive episodes but only a fraction of patients experience adequate response. Here the authors find dysregulation of miRNAs in peripheral blood samples from depressed patients after antidepressant treatment, and show that the miRNAs are regulators of psychiatrically relevant signalling pathways.

The serum protein levels of the tPA-BDNF pathway are implicated in depression and antidepressant treatment

Evidence demonstrates that brain-derived neurotrophic factor (BDNF) has a pivotal role in the pathogenesis of major depressive disorder (MDD). Precursor-BDNF (proBDNF) and mature BDNF (mBDNF) have opposing biological effects in neuroplasticity, and the tissue-type plasminogen activator (tPA)/plasmin system is crucial in the cleavage processing of proBDNF to mBDNF. However, very little is known about the role of the tPA-BDNF pathway in MDD. We examined serum protein concentrations in the tPA-BDNF pathway, including tPA, BDNF, tropomyosin receptor kinase B (TrkB), proBDNF and p75NTR, obtained from 35 drug-free depressed patients before and after 8 weeks of escitalopram (mean 12.5 mg per day) or duloxetine (mean 64 mg per day) treatment and 35 healthy controls using sandwich ELISA (enzyme-linked immunosorbent assay) methods. Serum tPA and BDNF and the ratio of BDNF/proBDNF were significantly lower in the MDD patients than in controls, whereas TrkB, proBDNF and its receptor p75NTR were higher. After 8 weeks of treatment, tPA, BDNF and proBDNF and the BDNF/proBDNF ratio were reversed, but p75NTR was higher than baseline, and TrkB was not significantly changed. tPA, BDNF, TrkB, proBDNF and p75NTR all yielded fairly good or excellent diagnostic performance (area under the receiver operating characteristic curve (AUC) >0.8 or 0.9). Combination of these five proteins demonstrated much better diagnostic effectiveness (AUC: 0.977) and adequate sensitivity and specificity of 88.1% and 92.7%, respectively. Our results suggest that the tPA-BDNF lysis pathway may be implicated in the pathogenesis of MDD and the mechanisms underlying antidepressant therapeutic action. The combination of tPA, BDNF, TrkB, proBDNF and p75NTR may provide a diagnostic biomarker panel for MDD.

Ketamine and Imipramine Reverse Transcriptional Signatures of Susceptibility and Induce Resilience-Specific Gene Expression Profiles

BACKGROUND

Examining transcriptional regulation by antidepressants in key neural circuits implicated in depression and understanding the relation to transcriptional mechanisms of susceptibility and natural resilience may help in the search for new therapeutic agents. Given the heterogeneity of treatment response in human populations, examining both treatment response and nonresponse is critical.

METHODS

We compared the effects of a conventional monoamine-based tricyclic antidepressant, imipramine, and a rapidly acting, non-monoamine-based antidepressant, ketamine, in mice subjected to chronic social defeat stress, a validated depression model, and used RNA sequencing to analyze transcriptional profiles associated with susceptibility, resilience, and antidepressant response and nonresponse in the prefrontal cortex (PFC), nucleus accumbens, hippocampus, and amygdala.

RESULTS

We identified similar numbers of responders and nonresponders after ketamine or imipramine treatment. Ketamine induced more expression changes in the hippocampus; imipramine induced more expression changes in the nucleus accumbens and amygdala. Transcriptional profiles in treatment responders were most similar in the PFC. Nonresponse reflected both the lack of response-associated gene expression changes and unique gene regulation. In responders, both drugs reversed susceptibility-associated transcriptional changes and induced resilience-associated transcription in the PFC.

CONCLUSIONS

We generated a uniquely large resource of gene expression data in four interconnected limbic brain regions implicated in depression and its treatment with imipramine or ketamine. Our analyses highlight the PFC as a key site of common transcriptional regulation by antidepressant drugs and in both reversing susceptibility- and inducing resilience-associated molecular adaptations. In addition, we found region-specific effects of each drug, suggesting both common and unique effects of imipramine versus ketamine.

Serum Levels of Insulin-Like Growth Factor-1 and Obsessive-Compulsive Disorder: A Case-Control Study

BACKGROUND/AIMS

Recent findings suggest an involvement of insulin-like growth factor-1 (IGF-1) in the pathogenesis of many psychiatric disorders; however, there is a lack of data regarding IGF-1 in patients with obsessive-compulsive disorder (OCD). The aims of the present study were (1) to analyze putative alterations of IGF-1 serum content in patients with OCD compared to patients with major depressive disorder (MDD) and healthy controls, and (2) to analyze putative changes of IGF-1 levels during drug treatment in subjects with OCD compared to patients with MDD.

METHODS

We recruited 40 OCD patients, 37 MDD patients, and 43 healthy controls. All participants were adults. Serum IGF-1 levels were measured by the ELISA method on venous blood samples collected at baseline and after 10 ± 1 weeks of drug treatment.

RESULTS

IGF-1 levels were increased in OCD patients compared to controls (149.9 ± 60.2 vs. 121.2 ± 51.6 ng/ml; p = 0.040). No correlations were observed between baseline IGF-1 levels, clinical features, and response to treatment at follow-up in OCD or MDD patients. No changes in serum IGF-1 were observed after drug treatment.

CONCLUSION

Our results show for the first time that serum IGF-1 levels are altered in patients with OCD. Further research on the role of IGF-1 in OCD is warranted.

Biological hypotheses and biomarkers of bipolar disorder

The most common mood disorders are major depressive disorders and bipolar disorders (BD). The pathophysiology of BD is complex, multifactorial, and not fully understood. Creation of new hypotheses in the field gives impetus for studies and for finding new biomarkers for BD. Conversely, new biomarkers facilitate not only diagnosis of a disorder and monitoring of biological effects of treatment, but also formulation of new hypotheses about the causes and pathophysiology of the BD. BD is characterized by multiple associations between disturbed brain development, neuroplasticity, and chronobiology, caused by: genetic and environmental factors; defects in apoptotic, immune-inflammatory, neurotransmitter, neurotrophin, and calcium-signaling pathways; oxidative and nitrosative stress; cellular bioenergetics; and membrane or vesicular transport. Current biological hypotheses of BD are summarized, including related pathophysiological processes and key biomarkers, which have been associated with changes in genetics, systems of neurotransmitter and neurotrophic factors, neuroinflammation, autoimmunity, cytokines, stress axis activity, chronobiology, oxidative stress, and mitochondrial dysfunctions. Here we also discuss the therapeutic hypotheses and mechanisms of the switch between depressive and manic state.

Kinase-mediated signaling cascades in mood disorders and antidepressant treatment

Kinase-mediated signaling cascades regulate a number of different molecular mechanisms involved in cellular homeostasis, and are viewed as one of the most common intracellular processes that are robustly dysregulated in the pathophysiology of mood disorders such as depression. Newly emerged, rapid acting antidepressants are able to achieve therapeutic improvement, possibly in part, through stimulating activity of kinase-dependent signaling pathways. Thus, advancements in our understanding of how kinases may contribute to development and treatment of depression seem crucial. However, current investigations are limited to a single or small number of kinases and are unable to detect novel kinases. Here, we review fast developing kinome profiling approaches that allow identification of multiple kinases and kinase network connections simultaneously, analyze technical limitation and challenges, and discuss their future applications to mood disorders and antidepressant treatment.

Role of trophic factors GDNF, IGF-1 and VEGF in major depressive disorder: A comprehensive review of human studies

RATIONALE

The neurotrophin hypothesis of major depressive disorder (MDD) postulates that this illness results from aberrant neurogenesis in brain regions that regulates emotion and memory. Notwithstanding this theory has primarily implicated BDNF in the neurobiology of MDD. Recent evidence suggests that other trophic factors namely GDNF, VEGF and IGF-1 may also be involved.

PURPOSE

The present review aimed to critically summarize evidence regarding changes in GDNF, IGF-1 and VEGF in individuals with MDD compared to healthy controls. In addition, we also evaluated the role of these mediators as potential treatment response biomarkers for MDD.

METHODS

A comprehensive review of original studies studies measuring peripheral, central or mRNA levels of GDNF, IGF-1 or VEGF in patients with MDD was conducted. The PubMed/MEDLINE database was searched for peer-reviewed studies published in English through June 2nd, 2015.

RESULTS

Most studies reported a reduction in peripheral GDNF and its mRNA levels in MDD patients versus controls. In contrast, IGF-1 levels in MDD patients compared to controls were discrepant across studies. Finally, most studies reported high peripheral VEGF levels and mRNA expression in MDD patients compared to healthy controls.

CONCLUSIONS

GDNF, IGF-1 and VEGF levels and their mRNA expression appear to be differentially altered in MDD patients compared to healthy individuals, indicating that these molecules might play an important role in the pathophysiology of depression and antidepressant action of therapeutic interventions.

Comorbidity Factors and Brain Mechanisms Linking Chronic Stress and Systemic Illness

Neuropsychiatric symptoms and mental illness are commonly present in patients with chronic systemic diseases. Mood disorders, such as depression, are present in up to 50% of these patients, resulting in impaired physical recovery and more intricate treatment regimen. Stress associated with both physical and emotional aspects of systemic illness is thought to elicit detrimental effects to initiate comorbid mental disorders. However, clinical reports also indicate that the relationship between systemic and psychiatric illnesses is bidirectional, further increasing the complexity of the underlying pathophysiological processes. In this review, we discuss the recent evidence linking chronic stress and systemic illness, such as activation of the immune response system and release of common proinflammatory mediators. Altogether, discovery of new targets is needed for development of better treatments for stress-related psychiatric illnesses as well as improvement of mental health aspects of different systemic diseases.

Involvement of glutamatergic neurotransmission in the antidepressant-like effect of zinc in the chronic unpredictable stress model of depression

Stress and excessive glutamatergic neurotransmission have been implicated in the pathophysiology of depression. Therefore, this study was aimed at investigating the influence of zinc on depressive-like behavior induced by chronic unpredictable stress (CUS), on alterations in glutamate-induced toxicity and immunocontent of proteins involved in the control of glutamatergic neurotransmission in the hippocampus of mice. Mice were subjected to CUS procedure for 14 days. From the 8th to the 14th day, mice received zinc chloride (ZnCl2) (10 mg/kg) or fluoxetine (10 mg/kg, positive control) once a day by oral route. CUS caused a depressive-like behavior evidenced by the increased immobility time in the tail suspension test (TST), which was prevented by treatment with ZnCl2 or fluoxetine. Ex vivo exposure of hippocampal slices to glutamate (10 mM) resulted in a significant decrease on cell viability; however, neither CUS procedure nor drug treatments altered this reduction. No alterations in the immunocontents of GLT-1 and GFAP or p-Akt were observed in any experimental group. The ratio of p-Akt/AKT was also not altered in any group. However, Akt immunocontent was increased in stressed mice and in animals treated with ZnCl2 (stressed or non-stressed mice) and EAAC1 immunocontent was increased in stressed mice treated with ZnCl2, fluoxetine or vehicle and in non-stressed mice treated with ZnCl2 and fluoxetine. These findings indicate a robust effect of zinc in reversing behavioral alteration induced by CUS in mice, through a possible modulation of the glutamatergic neurotransmission, extending literature data regarding the mechanisms underlying its antidepressant-like action.

Fluoxetine exposure during adolescence increases preference for cocaine in adulthood

Currently, there is a high prevalence of antidepressant prescription rates within juvenile populations, yet little is known about the potential long-lasting consequences of such treatments, particularly on subsequent responses to drugs of abuse. To address this issue at the preclinical level, we examined whether adolescent exposure to fluoxetine (FLX), a selective serotonin reuptake inhibitor, results in changes to the sensitivity of the rewarding properties of cocaine in adulthood. Separate groups of male c57bl/6 mice were exposed to FLX (0 or 20 mg/kg) for 15 consecutive days either during adolescence (postnatal days [PD] 35–49) or adulthood (PD 65–79). Twenty-one days after FLX treatment, behavioral responsivity to cocaine (0, 2.5, 5, 10, or 20 mg/kg) conditioned place preference was assessed. Our data shows that mice pretreated with FLX during adolescence, but not during adulthood, display an enhanced dose-dependent preference to the environment paired with cocaine (5 or 10 mg/kg) when compared to age-matched saline pretreated controls. Taken together, our findings suggest that adolescent exposure to FLX increases sensitivity to the rewarding properties of cocaine, later in life.

Expression of the 5-HT1A serotonin receptor in the hippocampus is required for social stress resilience and the antidepressant-like effects induced by the nicotinic partial agonist cytisine

Nicotinic acetylcholine receptor (nAChR) blockers potentiate the effects of selective serotonin reuptake inhibitors (SSRIs) in some treatment-resistant patients; however, it is not known whether these effects are independent, or whether the two neurotransmitter systems act synergistically. We first determined that the SSRI fluoxetine and the nicotinic partial agonist cytisine have synergistic effects in a mouse model of antidepressant efficacy, whereas serotonin depletion blocked the effects of cytisine. Using a pharmacological approach, we found that the 5-HT1A agonist 8-OH-DPAT also potentiated the antidepressant-like effects of cytisine, suggesting that this subtype might mediate the interaction between the serotonergic and cholinergic systems. The 5-HT1A receptors are located both presynaptically and postsynaptically. We therefore knocked down 5-HT1A receptors in either the dorsal raphe (presynaptic autoreceptors) or the hippocampus (a brain area with high expression of 5-HT1A heteroreceptors sensitive to cholinergic effects on affective behaviors). Knockdown of 5-HT1A receptors in hippocampus, but not dorsal raphe, significantly decreased the antidepressant-like effect of cytisine. This study suggests that serotonin signaling through postsynaptic 5-HT1A receptors in the hippocampus is critical for the antidepressant-like effects of a cholinergic drug and begins to elucidate the molecular mechanisms underlying interactions between the serotonergic and cholinergic systems related to mood disorders.

Increased antidepressant sensitivity after prefrontal cortex glucocorticoid receptor gene deletion in mice

Our laboratory has previously shown that antidepressants regulate glucocorticoid receptor (GR) expression in the prefrontal cortex (PFC). To determine if PFC GR are involved in antidepressant effects on behavior or hypothalamic-pituitary-adrenocortical (HPA) axis activity, we treated floxed GR male mice with saline or 15 or 30 mg/kg/d imipramine after PFC injection of adeno-associated virus 2/9 vectors transducing expression of Cre recombinase, to knock-down GR (PFC-GRKD), or green fluorescent protein (PFC-GFP), to serve as a control. The pattern of virally transduced GR deletion, common to all imipramine treatment groups, included the infralimbic, prelimbic, and medial anterior cingulate cortex at its largest extent, but was confined to the prelimbic and anterior cingulate cortex at its smallest extent. PFC GR knock-down increased behavioral sensitivity to imipramine, with imipramine-treated PFC-GRKD but not PFC-GFP mice exhibiting significant decreases in depression-like immobility during forced swim. PFC GR deletion did not alter general locomotor activity. The 30 mg/kg dose of imipramine increased plasma corticosterone levels immediately after a 5-min forced swim, but PFC GR knock-down had no significant effect on plasma corticosterone under these experimental conditions. We conclude that PFC GR knock-down, likely limited to the medial prelimbic and anterior cingulate cortices, can increase behavioral sensitivity to antidepressants. These findings indicate a novel role for PFC GR in influencing antidepressant response.

Superior pattern processing is the essence of the evolved human brain

Humans have long pondered the nature of their mind/brain and, particularly why its capacities for reasoning, communication and abstract thought are far superior to other species, including closely related anthropoids. This article considers superior pattern processing (SPP) as the fundamental basis of most, if not all, unique features of the human brain including intelligence, language, imagination, invention, and the belief in imaginary entities such as ghosts and gods. SPP involves the electrochemical, neuronal network-based, encoding, integration, and transfer to other individuals of perceived or mentally-fabricated patterns. During human evolution, pattern processing capabilities became increasingly sophisticated as the result of expansion of the cerebral cortex, particularly the prefrontal cortex and regions involved in processing of images. Specific patterns, real or imagined, are reinforced by emotional experiences, indoctrination and even psychedelic drugs. Impaired or dysregulated SPP is fundamental to cognitive and psychiatric disorders. A broader understanding of SPP mechanisms, and their roles in normal and abnormal function of the human brain, may enable the development of interventions that reduce irrational decisions and destructive behaviors.

Physical activity and the endocannabinoid system: an overview

Recognized as a "disease modifier", physical activity (PA) is increasingly viewed as a more holistic, cost-saving method for prevention, treatment and management of human disease conditions. The traditional view that PA engages the monoaminergic and endorphinergic systems has been challenged by the discovery of the endocannabinoid system (ECS), composed of endogenous lipids, their target receptors, and metabolic enzymes. Indeed, direct and indirect evidence suggests that the ECS might mediate some of the PA-triggered effects throughout the body. Moreover, it is now emerging that PA itself is able to modulate ECS in different ways. Against this background, in the present review we shall discuss evidence of the cross-talk between PA and the ECS, ranging from brain to peripheral districts and highlighting how ECS must be tightly regulated during PA, in order to maintain its beneficial effects on cognition, mood, and nociception, while avoiding impaired energy metabolism, oxidative stress, and inflammatory processes.

Signaling mechanisms involved in the acute effects of estradiol on 5-HT clearance

Estradiol was found previously to have an antidepressant-like effect and to block the ability of selective serotonin reuptake inhibitors (SSRIs) to have an antidepressant-like effect. The antidepressant-like effect of estradiol was due to estrogen receptor β (ERβ) and/or GPR30 activation, whereas estradiol's blockade of the effect of an SSRI was mediated by ERα. This study focuses on investigating signaling pathways as well as interacting receptors associated with these two effects of estradiol. In vivo chronoamperometry was used to measure serotonin transporter (SERT) function. The effect of local application of estradiol or selective agonists for ERα (PPT) or ERβ (DPN) into the CA3 region of the hippocampus of ovariectomized (OVX) rats on 5-hydroxytryptamine (5-HT) clearance as well as on the ability of fluvoxamine to slow 5-HT clearance was examined after selective blockade of signaling pathways or that of interacting receptors. Estradiol- or DPN-induced slowing of 5-HT clearance mediated by ERβ was blocked after inhibition of MAPK/ERK1/2 but not of PI3K/Akt signaling pathways. This effect also involved interactions with TrkB, and IGF-1 receptors. Estradiol's or PPT's inhibition of the fluvoxamine-induced slowing of 5-HT clearance mediated by ERα, was blocked after inhibition of either MAPK/ERK1/2 or PI3K/Akt signaling pathways. This effect involved interactions with the IGF-1 receptor and with the metabotropic glutamate receptor 1, but not with TrkB. This study illustrates some of the signaling pathways required for the effects of estradiol on SERT function, and particularly shows that ER subtypes elicit different as well as common signaling pathways for their actions.

The serotonin-BDNF duo: developmental implications for the vulnerability to psychopathology

Serotonin (5-HT) and brain-derived neurotrophin factor (BDNF) are known to modulate behavioral responses to stress and to mediate the therapeutic efficacy of antidepressant agents through neuroplastic and epigenetic mechanisms. While the two systems interact at several levels, this scenario is complicated by a number of variants including brain region specificity, 5-HT receptor selectivity and timing. Based on recent insights obtained using 5-HT transporter (5-HTT) knockout rats we here set-out and discuss the crucial role of neurodevelopmental mechanisms and the contribution of transcription factors and epigenetic modifications to this interaction and its variants. 5-HTT knockout in rats, as well as the low activity short allelic variant of the serotonin transporter human polymorphism, consistently show reduced BDNF mRNA and protein levels in the hippocampus and in the prefrontal cortex. This starts during the second postnatal week, is preceded by DNA hypermethylation during the first postnatal week, and it is developmentally paralleled by reduced expression of key transcription factors. The reduced BDNF levels, in turn, affect 5-HT1A receptor-mediated intracellular signaling and thereby the serotonergic phenotype of the neurons. We propose that such a negative spiral of modifications may affect brain development and reduce its resiliency to environmental challenges during critical time windows, which may lead to phenotypic alterations that persist for the entire life. The characterization of 5-HT-BDNF interactions will eventually increase the understanding of mental illness etiology and, possibly, lead to the identification of novel molecular targets for drug development.