Peripheral insulin-like growth factor-I produces antidepressant-like behavior and contributes to the effect of exercise

Association between insulin resistance and serum insulin-like growth factor 1 levels in patients with non-remitting major depressive disorder

BACKGROUND

Major depressive disorder (MDD) is linked to an increased risk of diabetes; however, the underlying pathomechanism remains unknown. Although insulin-like growth factor 1 (IGF-1) is involved in the pathogenesis of both insulin resistance (IR) and MDD, no studies have investigated the relationship between IGF-1 and IR in patients with MDD.

METHODS

We recruited 120 patients with MDD (84 non-remitting patients and 36 remitting patients) and 99 control participants. Blood samples were collected after overnight fasting to investigate associations between serum and clinical factors, such as serum IGF-1 levels and homeostasis model assessment-insulin resistance (HOMA-IR).

RESULTS

Serum IGF-1 levels were higher in patients with non-remitting MDD than in control participants and patients with remitting MDD (P = 0.001 and P = 0.007, respectively). There were no significant differences in HOMA-IR between the three groups. HOMA-IR was positively correlated with serum IGF-1 levels in patients with non-remitting MDD (R = 0.355; P= 0.001) but not in control participants or patients with remitting MDD. A stepwise multiple regression analysis with various clinical factors revealed a positive association of serum IGF-1 levels and body mass index with HOMA-IR in patients with non-remitting MDD.

LIMITATIONS

This is a cross-sectional study and therefore we cannot draw firm conclusions about causal associations.

CONCLUSIONS

Serum IGF-1 levels may play a role in IR in patients with MDD who fail to achieve remission. Further studies, including longitudinal studies, are needed to determine the relationship between high serum IGF-1 levels and subsequent IR and diabetes risk.

Synergism of Carbamoylated Erythropoietin and Insulin-like Growth Factor-1 in Immediate Early Gene Expression

Trophic factors are secreted proteins that can modulate neuronal integrity, structure, and function. Previous preclinical studies have shown synergistic effects on decreasing apoptosis and improving behavioral performance after stroke when combining two such trophic factors, erythropoietin (EPO) and insulin-like growth factor-1 (IGF-1). However, EPO can elevate the hematocrit level, which can be life-threatening for non-anemic individuals. A chemically engineered derivative of EPO, carbamoylated EPO (CEPO), does not impact hematological parameters but retains neurotrophic effects similar to EPO. To obtain insight into CEPO and IGF-1 combination signaling, we examined immediate early gene (IEG) expression after treatment with CEPO, IGF-1, or CEPO + IGF-1 in rat pheochromocytoma (PC-12) cells and found that combining CEPO and IGF-1 produced a synergistic increase in IEG expression. An in vivo increase in the protein expression of Npas4 and Nptx2 was also observed in the rat hippocampus. We also examined which kinase signaling pathways might be mediating these effects and found that while AKT inhibition did not alter the pattern of IEG expression, both ERK and JAK2 inhibition significantly decreased IEG expression. These results begin to define the molecular effects of combining CEPO and IGF-1 and indicate the potential for these trophic factors to produce positive, synergistic effects.

Role of neurotrophic and growth factors in the rapid and sustained antidepressant actions of ketamine

The neurotrophic hypothesis of depression proposes that reduced levels of brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) contribute to neuronal atrophy or loss in the prefrontal cortex (PFC) and hippocampus and impaired hippocampal adult neurogenesis, which are associated with depressive symptoms. Chronic, but acute, treatment with typical monoaminergic antidepressants can at least partially reverse these deficits, in part via induction of BDNF and/or VEGF expression, consistent with their delayed onset of action. Ketamine, an N-methyl-d-aspartate receptor antagonist, exerts rapid and sustained antidepressant effects. Rodent studies have revealed that ketamine rapidly increases BDNF and VEGF release and/or expression in the PFC and hippocampus, which in turn increases the number and function of spine synapses in the PFC and hippocampal neurogenesis. Ketamine also induces the persistent release of insulin-like growth factor 1 (IGF-1) in the PFC of male mice. These neurotrophic effects of ketamine are associated with its rapid and sustained antidepressant effects. In this review, we first provide an overview of the neurotrophic hypothesis of depression and then discuss the role of BDNF, VEGF, IGF-1, and other growth factors (IGF-2 and transforming growth factor-β1) in the antidepressant effects of ketamine and its enantiomers. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

Serum cortisol and insulin-like growth factor 1 levels in major depressive disorder and schizophrenia

The pathophysiology underlying major depressive disorder (MDD) and schizophrenia is related to endocrine system functions and includes changes in the blood levels of cortisol and insulin-like growth factor 1 (IGF-1). However, these hormones have not been investigated simultaneously in patients with MDD and schizophrenia. We investigated the differences in serum cortisol and IGF-1 levels among patients with MDD and schizophrenia and controls. We included 129 patients with MDD, 71 patients with schizophrenia, and 71 healthy volunteers. Blood tests were performed between 6:00 am and 11:00 am after fasting. Serum cortisol levels were significantly higher in patients with schizophrenia than in patients with MDD and controls. Serum cortisol levels were significantly higher in patients with MDD than in controls. Serum IGF-1 levels were higher in both patient groups than in controls, whereas there was no significant difference between patients with MDD and schizophrenia. Both cortisol and IGF-1 levels were positively correlated with the Hamilton Rating Scale for Depression score in patients with MDD, whereas cortisol level was positively correlated and IGF-1 level was negatively correlated with the Brief Psychiatric Rating Scale score in patients with schizophrenia. The differences in the level of these hormones suggest pathophysiological differences between these disorders.

Antidepressant-like effects of trophic factor receptor signaling

A significant body of research has demonstrated that antidepressants regulate neurotrophic factors and that neurotrophins themselves are capable of independently producing antidepressant-like effects. While brain derived neurotrophic factor (BDNF) remains the best studied molecule in this context, there are several structurally diverse trophic factors that have shown comparable behavioral effects, including basic fibroblast growth factor (FGF-2), insulin-like growth factor 1 (IGF-1) and vascular endothelial growth factor (VEGF). In this review we discuss the structural and biochemical signaling aspects of these neurotrophic factors with antidepressant activity. We also include a discussion on a cytokine molecule erythropoietin (EPO), widely known and prescribed as a hormone to treat anemia but has recently been shown to function as a neurotrophic factor in the central nervous system (CNS).

Effects of Exercise Training on the Autonomic Nervous System with a Focus on Anti-Inflammatory and Antioxidants Effects

Studies show that the autonomic nervous system (ANS) has an important impact on health in general. In response to environmental demands, homeostatic processes are often compromised, therefore determining an increase in the sympathetic nervous system (SNS)’s functions and a decrease in the parasympathetic nervous system (PNS)’s functions. In modern societies, chronic stress associated with an unhealthy lifestyle contributes to ANS dysfunction. In this review, we provide a brief introduction to the ANS network, its connections to the HPA axis and its stress responses and give an overview of the critical implications of ANS in health and disease—focused specifically on the immune system, cardiovascular, oxidative stress and metabolic dysregulation. The hypothalamic–pituitary–adrenal axis (HPA), the SNS and more recently the PNS have been identified as regulating the immune system. The HPA axis and PNS have anti-inflammatory effects and the SNS has been shown to have both pro- and anti-inflammatory effects. The positive impact of physical exercise (PE) is well known and has been studied by many researchers, but its negative impact has been less studied. Depending on the type, duration and individual characteristics of the person doing the exercise (age, gender, disease status, etc.), PE can be considered a physiological stressor. The negative impact of PE seems to be connected with the oxidative stress induced by effort.

Cilostazol as an adjunctive treatment in major depressive disorder: a pilot randomized, double-blind, and placebo-controlled clinical trial

BACKGROUND

Cilostazol, a phosphodiesterase-3 inhibitor, has been reported to improve depressive-like behavior in experimental studies of depression. We investigated the safety and efficacy of cilostazol combination therapy with sertraline in treating patients with major depressive disorder (MDD) in a 6-week, parallel, randomized controlled trial.

METHOD

Among patients referred to the outpatient clinic of a tertiary hospital, those with a diagnosis of MDD with moderate to severe severity (a score of >19 on the Hamilton depression rating scale (HAM-D)) were enrolled. A total of 54 MDD patients aged 18-65 years were randomly assigned to either the cilostazol (100 mg daily) or the placebo group. Both groups received sertraline 100 mg per day similarly. Changes in HAM-D at weeks 2, 4, and 6 were the primary outcome. Participants and outcome assessors were blinded.

RESULTS

At week 6, patients in the cilostazol group had significantly lower HAM-D score (p value= 0.015). General linear model repeated-measure analysis showed significant effect for treatment in improving MDD severity (p value <0.001). The remission rate at the study endpoint and number of responders at week 4 were significantly higher in the cilostazol group (p value= 0.047, p value= 0.032, respectively). The cilostazol group demonstrated a significantly shorter time to response. No significant difference was observed in treatment response at the study endpoint, and there were no serious adverse effects.

CONCLUSION

Our study supports safety and efficacy of cilostazol in treating MDD patients.

TRIAL REGISTRATION

This trial was registered at the Iranian registry of clinical trials (IRCT: www.irct.ir ; registration number: IRCT20090117001556N130).

Association of growth hormone deficiency (GHD) with anxiety and depression: experimental data and evidence from GHD children and adolescents

Anxiety and depression are among the commonest emotional problems in children and young adolescents. They are encountered with even higher prevalence in children and adults with growth hormone deficiency (GHD). Alterations in the somatotropic axis, as observed in both GH/IGF1 deficiency and excess, can produce permanent changes in brain tissue structure. The growth hormone/insulin-like growth factor 1 (GH/IGF1) axis seems to exert a regulatory effect on brain function and neurogenesis, especially in the hippocampus, a brain region associated with mental and emotional disorders, such as depression and anxiety. There is evidence from animal models of the possible interrelationship of the endocrine system with the pathogenesis of emotional disorders. Moreover, clinical data support the association of GHD and mood disorders, which are often reversed by GH replacement therapy. However, the causal relationship and the mechanism underlying this association are to date obscure and remain to be clarified. The present review reports experimental data from animal models regarding the role of GH/IGF1 in emotional disorders and focuses on clinical data on the presence of these disorders in children with GHD and their response to GH therapy.

Adult Neurogenesis and Antidepressant Treatment: The Surprise Finding by Ron Duman and the Field 20 Years Later

Of Duman's many influential findings, the finding that long-term treatment with antidepressant drugs produces an increase in neurogenesis in the subgranular zone of the adult hippocampus may be one of the most enduring and far-reaching. This novel discovery and his decades of continued research in the field led to a new hypothesis about the mechanism of action of antidepressants, providing a critical step in our understanding of the neurotrophic hypothesis of depression and synaptic plasticity. It is now accepted that antidepressant treatments can oppose and even reverse the effects of stress on the brain and on newly born hippocampal cells, possibly via neurotrophic factors, which Duman had continued to explore. Furthermore, ablation studies have shown preclinically that hippocampal neurogenesis may be necessary for some of the clinical effects of antidepressant drugs. Duman's laboratory continued to interrogate neurotrophins and synaptic plasticity, demonstrating that newer clinically approved antidepressant compounds also affect neurogenesis and synaptic plasticity. In this review, we summarize Duman's original findings and discuss the current state of the field of neurogenesis with respect to animal models and human studies and the implications of those findings on the field of drug discovery.

Childhood trauma and insulin-like growth factors in amniotic fluid: An exploratory analysis of 79 women

BACKGROUND

Perinatal stress has adverse effects on fetal outcome, yet the effect of early maternal trauma on fetal outcome has scarcely been studied. We investigated effects of maternal childhood trauma and current environment on important regulators of prenatal growth, fetal insulin-like growth factor (IGF)-1 and IGF-2 in amniotic fluid and assessed the impact of IGFs on newborn anthropometrics.

METHODS

79 pregnant women in their second trimester who underwent amniocentesis (15.9 ± 0.9 weeks of gestational age) and their newborns at birth were analyzed. Maternal childhood trauma was assessed using the childhood trauma questionnaire (CTQ) and current environment was operationalized by assessing maternal psychosocial, physical health and endocrine measurements in amniotic fluid.

RESULTS

In this exploratory analysis of 79 pregnant women, maternal childhood trauma, defined as reporting at least low scores on any of the CTQ subscales, negatively correlated with fetal IGF-1 (M_ln = 3.48 vs. 2.98; p = 0.012) and IGF-2 (Mdn_ln = 4.99 vs. 4.70; p = 0.002). Trauma severity, defined as the overall trauma score, negatively correlated with fetal IGF-2 (r = -0.24; p = 0.037). From trauma subscales, maternal sexual abuse correlated with fetal IGF-1 (r = -0.32; p = 0.006) and IGF-2 (r = -0.39; p = 0.001). Maternal BMI negatively correlated with fetal IGF-1 (r = -0.26; p = 0.023) and IGF-2 (r = -0.29; p = 0.011). Newborn anthropometrics were operationalized by length, weight, sex, gestational age, length/gestational age and weight/gestational age at birth. Fetal weight at birth associated with a trend with fetal IGF-1 when controlling for BMI. Maternal hypothalamus-pituitary-adrenal axis activity and maternal exercise did not contribute significantly to predicting fetal IGFs. Maternal childhood trauma (β = -0.27; p = 0.011) and BMI (β = -0.24; p = 0.026) remained significantly associated with fetal IGF-1. Maternal childhood trauma (β = -0.32; p = 0.003), maternal BMI (β = -0.30; p = 0.005) and maternal sexual abuse (β = -0.22; p = 0.049) remained significantly associated with fetal IGF-2 and with a trend with fetal IGF-1 (β = -0.21; p = 0.076) when excluding women with gestational diabetes.

CONCLUSION

Maternal childhood trauma and BMI associate negatively with fetal IGF-1 and IGF-2 in amniotic fluid. Controlling for maternal BMI, fetal weight at birth remains associated with a trend with fetal IGF-1. The presented data suggests that childhood trauma can affect endocrine measurements of the developing next generation, providing a mechanism by which adverse maternal life events are transmitted to the next generation.

Peripheral Markers of Depression

Major Depressive Disorder (MDD) is a leading cause of disability worldwide, creating a high medical and socioeconomic burden. There is a growing interest in the biological underpinnings of depression, which are reflected by altered levels of biological markers. Among others, enhanced inflammation has been reported in MDD, as reflected by increased concentrations of inflammatory markers-C-reactive protein, interleukin-6, tumor necrosis factor-α and soluble interleukin-2 receptor. Oxidative and nitrosative stress also plays a role in the pathophysiology of MDD. Notably, increased levels of lipid peroxidation markers are characteristic of MDD. Dysregulation of the stress axis, along with increased cortisol levels, have also been reported in MDD. Alterations in growth factors, with a significant decrease in brain-derived neurotrophic factor and an increase in fibroblast growth factor-2 and insulin-like growth factor-1 concentrations have also been found in MDD. Finally, kynurenine metabolites, increased glutamate and decreased total cholesterol also hold promise as reliable biomarkers for MDD. Research in the field of MDD biomarkers is hindered by insufficient understanding of MDD etiopathogenesis, substantial heterogeneity of the disorder, common co-morbidities and low specificity of biomarkers. The construction of biomarker panels and their evaluation with use of new technologies may have the potential to overcome the above mentioned obstacles.

Differential impact of stress and environmental enrichment on corticolimbic circuits

Stress exposure can produce profound changes in physiology and behavior that can impair health and well-being. Of note, stress exposure is linked to anxiety disorders and depression in humans. The widespread impact of these disorders warrants investigation into treatments to mitigate the harmful effects of stress. Pharmacological treatments fail to help many with these disorders, so recent work has focused on non-pharmacological alternatives. One of the most promising of these alternatives is environmental enrichment (EE). In rodents, EE includes social, physical, and cognitive stimulation for the animal, in the form of larger cages, running wheels, and toys. EE successfully reduces the maladaptive effects of various stressors, both as treatment and prophylaxis. While we know that EE can have beneficial effects under stress conditions, the morphological and molecular mechanisms underlying these behavioral effects are still not well understood. EE is known to alter neurogenesis, dendrite development, and expression of neurotrophic growth factors, effects that vary by type of enrichment, age, and sex. To add to this complexity, EE has differential effects in different brain regions. Understanding how EE exerts its protective effects on morphological and molecular levels could hold the key to developing more targeted pharmacological treatments. In this review, we summarize the literature on the morphological and molecular consequences of EE and stress in key emotional regulatory pathways in the brain, the hippocampus, prefrontal cortex, and amygdala. The similarities and differences among these regions provide some insight into stress-EE interaction that may be exploited in future efforts toward prevention of, and intervention in, stress-related diseases.

Enhancement of Hippocampal Plasticity by Physical Exercise as a Polypill for Stress and Depression: A Review

Generation of newborn neurons that form functional synaptic connections in the dentate gyrus of adult mammals, known as adult hippocampal neurogenesis, has been suggested to play critical roles in regulating mood, as well as certain forms of hippocampus-dependent learning and memory. Environmental stress suppresses structural plasticity including adult neurogenesis and dendritic remodeling in the hippocampus, whereas physical exercise exerts opposite effects. Here, we review recent discoveries on the potential mechanisms concerning how physical exercise mitigates the stressrelated depressive disorders, with a focus on the perspective of modulation on hippocampal neurogenesis, dendritic remodeling and synaptic plasticity. Unmasking such mechanisms may help devise new drugs in the future for treating neuropsychiatric disorders involving impaired neural plasticity.

Evidence-based umbrella review of 162 peripheral biomarkers for major mental disorders

The literature on non-genetic peripheral biomarkers for major mental disorders is broad, with conflicting results. An umbrella review of meta-analyses of non-genetic peripheral biomarkers for Alzheimer's disease, autism spectrum disorder, bipolar disorder (BD), major depressive disorder, and schizophrenia, including first-episode psychosis. We included meta-analyses that compared alterations in peripheral biomarkers between participants with mental disorders to controls (i.e., between-group meta-analyses) and that assessed biomarkers after treatment (i.e., within-group meta-analyses). Evidence for association was hierarchically graded using a priori defined criteria against several biases. The Assessment of Multiple Systematic Reviews (AMSTAR) instrument was used to investigate study quality. 1161 references were screened. 110 met inclusion criteria, relating to 359 meta-analytic estimates and 733,316 measurements, on 162 different biomarkers. Only two estimates met a priori defined criteria for convincing evidence (elevated awakening cortisol levels in euthymic BD participants relative to controls and decreased pyridoxal levels in participants with schizophrenia relative to controls). Of 42 estimates which met criteria for highly suggestive evidence only five biomarker aberrations occurred in more than one disorder. Only 15 meta-analyses had a power >0.8 to detect a small effect size, and most (81.9%) meta-analyses had high heterogeneity. Although some associations met criteria for either convincing or highly suggestive evidence, overall the vast literature of peripheral biomarkers for major mental disorders is affected by bias and is underpowered. No convincing evidence supported the existence of a trans-diagnostic biomarker. Adequately powered and methodologically sound future large collaborative studies are warranted.

Acute Sprint Interval Exercise Increases Both Cognitive Functions and Peripheral Neurotrophic Factors in Humans: The Possible Involvement of Lactate

There is increasing attention to sprint interval exercise (SIE) training as a time-efficient exercise regime. Recent studies, including our own (Kujach et al., 2018), have shown that acute high-intensity intermittent exercise can improve cognitive function; however, the neurobiological mechanisms underlying the effect still remain unknown. We thus examined the effects of acute SIE on cognitive function by monitoring the peripheral levels of growth and neurotrophic factors as well as blood lactate (LA) as potential mechanisms. Thirty-six young males participated in the current study and were divided into two groups: SIE (n = 20; mean age: 21.0 ± 0.9 years) and resting control (CTR) (n = 16; mean age: 21.7 ± 1.3 years). The SIE session consisted of 5 min of warm-up exercise and six sets of 30 s of all-out cycling exercise followed by 4.5 min of rest on a cycling-ergometer. Blood samples to evaluate the changes of serum concentrations of brain-derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1), vascular endothelial growth factor (VEGF), and blood LA were obtained at three time points: before, immediately after, and 60 min after each session. A Stroop task (ST) and trail making test (TMT) parts A and B were used to assess cognitive functions. Acute SIE shortened response times for both the ST and TMT A and B. Meanwhile, the peripheral levels of BDNF, IGF-1, and VEGF were significantly increased after an acute bout of SIE compared to those in CTR. In response to acute SIE, blood LA levels significantly increased and correlated with increased levels of BDNF, IGF-1, and VEGF. Furthermore, cognitive function and BDNF are found to be correlated. The current results suggest that SIE could have beneficial effects on cognitive functions with increased neuroprotective factors along with peripheral LA concentration in humans.

Neuroendocrine drivers of risk and resilience: The influence of metabolism & mitochondria

The manifestation of risk versus resilience has been considered from varying perspectives including genetics, epigenetics, early life experiences, and type and intensity of the challenge with which the organism is faced. Although all of these factors are central to determining risk and resilience, the current review focuses on what may be a final common pathway: metabolism. When an organism is faced with a perturbation to the environment, whether internal or external, appropriate energy allocation is essential to resolving the divergence from equilibrium. This review examines the potential role of metabolism in the manifestation of stress-induced neural compromise. In addition, this review details the current state of knowledge on neuroendocrine factors which are poised to set the tone of the metabolic response to a systemic challenge. The goal is to provide an essential framework for understanding stress in a metabolic context and appreciation for key neuroendocrine signals.

Central IGF-1 protects against features of cognitive and sensorimotor decline with aging in male mice

Disruptions in growth hormone/insulin-like growth factor-1 (GH/IGF-1) signaling have been linked to improved longevity in mice and humans. Nevertheless, while IGF-1 levels are associated with increased cancer risk, they have been paradoxically implicated with protection from other age-related conditions, particularly in the brain, suggesting that strategies aimed at selectively increasing central IGF-1 action may have favorable effects on aging. To test this hypothesis, we generated inducible, brain-specific (TRE-IGF-1 × Camk2a-tTA) IGF-1 (bIGF-1) overexpression mice and studied effects on healthspan. Doxycycline was removed from the diet at 12 weeks old to permit post-development brain IGF-1 overexpression, and animals were monitored up to 24 months. Brain IGF-1 levels were increased approximately twofold in bIGF-1 mice, along with greater brain weights, volume, and myelin density (P < 0.05). Age-related changes in rotarod performance, exercise capacity, depressive-like behavior, and hippocampal gliosis were all attenuated specifically in bIGF-1 male mice (P < 0.05). However, chronic brain IGF-1 failed to prevent declines in cognitive function or neurovascular coupling. Therefore, we performed a short-term intranasal (IN) treatment of either IGF-1 or saline in 24-month-old male C57BL/6 mice and found that IN IGF-1 treatment tended to reduce depressive (P = 0.09) and anxiety-like behavior (P = 0.08) and improve motor coordination (P = 0.07) and unlike transgenic mice improved motor learning (P < 0.05) and visuospatial and working memory (P < 0.05). These data highlight important sex differences in how brain IGF-1 action impacts healthspan and suggest that translational approaches that target IGF-1 centrally can restore cognitive function, a possibility that should be explored as a strategy to combat age-related cognitive decline.

The insulin-like growth factor-1 system in the adult mammalian brain and its implications in central maternal adaptation

Our knowledge on the bioavailability and actions of insulin-like growth factor-1 (IGF-1) has markedly expanded in recent years as novel mechanisms were discovered on IGF binding proteins (IGFBPs) and their ability to release IGF-1. The new discoveries allowed a better understanding of the endogenous physiological actions of IGF-1 and also its applicability in therapeutics. The focus of the present review is to summarize novel findings on the neuronal, neuroendocrine and neuroplastic actions of IGF-1 in the adult brain. As most of the new regulatory mechanisms were described in the periphery, their implications on brain IGF system will also be covered. In addition, novel findings on the effects of IGF-1 on lactation and maternal behavior are described. Based on the enormous neuroplastic changes related to the peripartum period, IGF-1 has great but largely unexplored potential in maternal adaptation of the brain, which is highlighted in the present review.

Neurotrophic factors and neuroplasticity pathways in the pathophysiology and treatment of depression

Depression is a major health problem with a high prevalence and a heavy socioeconomic burden in western societies. It is associated with atrophy and impaired functioning of cortico-limbic regions involved in mood and emotion regulation. It has been suggested that alterations in neurotrophins underlie impaired neuroplasticity, which may be causally related to the development and course of depression. Accordingly, mounting evidence suggests that antidepressant treatment may exert its beneficial effects by enhancing trophic signaling on neuronal and synaptic plasticity. However, current antidepressants still show a delayed onset of action, as well as lack of efficacy. Hence, a deeper understanding of the molecular and cellular mechanisms involved in the pathophysiology of depression, as well as in the action of antidepressants, might provide further insight to drive the development of novel fast-acting and more effective therapies. Here, we summarize the current literature on the involvement of neurotrophic factors in the pathophysiology and treatment of depression. Further, we advocate that future development of antidepressants should be based on the neurotrophin theory.

Voluntary exercise and depression-like behavior in rodents: are we running in the right direction?

Acute or chronic exposure to stress can increase the risk to develop major depressive disorder, a severe, recurrent and common psychiatric condition. Depression places an enormous social and financial burden on modern society. Although many depressed patients are treated with antidepressants, their efficacy is only modest, underscoring the necessity to develop clinically effective pharmaceutical or behavioral treatments. Exercise training produces beneficial effects on stress-related mental disorders, indicative of clinical potential. The pro-resilient and antidepressant effects of exercise training have been documented for several decades. Nonetheless, the underlying molecular mechanisms and the brain circuitries involved remain poorly understood. Preclinical investigations using voluntary wheel running, a frequently used rodent model that mimics aspects of human exercise training, have started to shed light on the molecular adaptations, signaling pathways and brain nuclei underlying the beneficial effects of exercise training on stress-related behavior. In this review, I highlight several neurotransmitter systems that are putative mediators of the beneficial effects of exercise training on mental health, and review recent rodent studies that utilized voluntary wheel running to promote our understanding of exercise training-induced central adaptations. Advancements in our mechanistic understanding of how exercise training induces beneficial neuronal adaptations will provide a framework for the development of new strategies to treat stress-associated mental illnesses.

Intermittent metabolic switching, neuroplasticity and brain health

During evolution, individuals whose brains and bodies functioned well in a fasted state were successful in acquiring food, enabling their survival and reproduction. With fasting and extended exercise, liver glycogen stores are depleted and ketones are produced from adipose-cell-derived fatty acids. This metabolic switch in cellular fuel source is accompanied by cellular and molecular adaptations of neural networks in the brain that enhance their functionality and bolster their resistance to stress, injury and disease. Here, we consider how intermittent metabolic switching, repeating cycles of a metabolic challenge that induces ketosis (fasting and/or exercise) followed by a recovery period (eating, resting and sleeping), may optimize brain function and resilience throughout the lifespan, with a focus on the neuronal circuits involved in cognition and mood. Such metabolic switching impacts multiple signalling pathways that promote neuroplasticity and resistance of the brain to injury and disease.

Salivary Gland Derived BDNF Overexpression in Mice Exerts an Anxiolytic Effect

Brain-derived neurotrophic factor (BDNF) is abundant in the hippocampus and plays critical roles in memory and synapse formation, as well as exerting antidepressant-like effects in psychiatric disorders. We previously reported that BDNF is expressed in salivary glands and affects blood BDNF content. However, the function of salivary BDNF remains unclear. The aim of this study was to generate transgenic mice overexpressing BDNF in the salivary glands. Hence, we used the Lama construct (hemagglutinin (HA)-tagged mouse Bdnf cDNA) to specifically express BDNF in mouse salivary glands. Compared with control mice, Bdnf-HA transgenic mice showed increased blood BDNF and expressed salivary BDNF-HA. Molecular analysis revealed enhanced hippocampal BDNF levels and activation of the BDNF receptor, tyrosine kinase B (TrkB), in transgenic mice. In both the open field and elevated-plus maze tests, transgenic mice showed anxiolytic-like behavioral effects compared with control or sialoadenectomized mice. Among downstream components of the BDNF-TrkB signaling pathway, metabolic activation of the γ-aminobutyric acid (GABA) synthetic pathway was found, including higher levels of the GABA synthetic enzyme, glutamate decarboxylase 1 (GAD1). Thus, we have established a transgenic mouse expressing BDNF in the parotid gland that may be useful to examine the hippocampal effects of salivary BDNF.

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.

Exercise increases mTOR signaling in brain regions involved in cognition and emotional behavior

Exercise can enhance learning and memory and produce resistance against stress-related psychiatric disorders such as depression and anxiety. In rats, these beneficial effects of exercise occur regardless of exercise controllability: both voluntary and forced wheel running produce stress-protective effects. The mechanisms underlying these beneficial effects of exercise remain unknown. The mammalian target of rapamycin (mTOR) is a translation regulator important for cell growth, proliferation, and survival. mTOR has been implicated in enhancing learning and memory as well as antidepressant effects. Moreover, mTOR is sensitive to exercise signals such as metabolic factors. The effects of exercise on mTOR signaling, however, remain unknown. The goal of the present study was to test the hypothesis that exercise, regardless of controllability, increases levels of phosphorylated mTOR (p-mTOR) in brain regions important for learning and emotional behavior. Rats were exposed to 6 weeks of either sedentary (locked wheel), voluntary, or forced wheel running conditions. At 6 weeks, rats were sacrificed during peak running and levels of p-mTOR were measured using immunohistochemistry. Overall, both voluntary and forced exercise increased p-mTOR-positive neurons in the medial prefrontal cortex, striatum, hippocampus, hypothalamus, and amygdala compared to locked wheel controls. Exercise, regardless of controllability, also increased numbers of p-mTOR-positive glia in the striatum, hippocampus, and amygdala. For both neurons and glia, the largest increase in p-mTOR positive cells was observed after voluntary running, with forced exercise causing a more modest increase. Interestingly, voluntary exercise preferentially increased p-mTOR in astrocytes (GFAP+), while forced running increased p-mTOR in microglia (CD11+) in the inferior dentate gyrus. Results suggest that mTOR signaling is sensitive to exercise, but subtle differences exist depending on exercise controllability. Increases in mTOR signaling could contribute to the beneficial effects of exercise on cognitive function and mental health.

Voluntary running improves depressive behaviours and the structure of the hippocampus in rats: A possible impact of myokines

This study investigated the impact of voluntary exercise on depressive behaviours, serum and hippocampal levels of myokines, and histopathological features of hippocampal formation in rats. Depressed rats were allowed to voluntarily run on a wheel for 3weeks. Locomotor activity was assessed by a forced swimming test and the myokine levels in sera and hippocampal homogenates were measured using Enzyme-linked Immunosorbent Assay. Brain sections were analysed for hippocampal structure and neuronal counts. Voluntary running produced significant increase in the distance moved by rats and significant decrease in immobility duration. After voluntary running, there were significant increases in serum and hippocampal brain-derived neurotrophic factor (BDNF) and macrophage migration inhibitory factor (MIF), significant increase in hippocampal vascular endothelial growth factor (VEGF), and significant decrease in serum interleukin-6 (IL-6). Significant correlation was detected between the serum levels of BDNF and MIF (r=0.276) as well as IL-6 (r=-0.340). In addition, significant correlation was observed between hippocampal BDNF levels and MIF (r=0.500) and VEGF levels (r=0.279). After voluntary running, there was significant decrease in number degenerated neurons in hippocampal areas and significant increase in number of healthy neurons in the upper limb of the dentate gyrus, but not in its lower limb, compared to depression group. This study showed the relation of myokines to the development and/or relief of depression, as well as the correlation between serum and hippocampal myokine levels. Attention should be paid to studying the biological effects of myokines on different hippocampal areas that could respond differently to treatments.

Insulin-like growth factor 1 and risk of depression in older people: the English Longitudinal Study of Ageing

Depressive disorders are a leading cause of disability in older age. Although the role of psychosocial and behavioural predictors has been well examined, little is known about the biological origins of depression. Findings from animal studies have implicated insulin-like growth factor 1 (IGF-1) in the aetiology of this disorder. A total of 6017 older adults (mean age of 65.7 years; 55% women) from the English Longitudinal Study of Ageing provided serum levels of IGF-1 (mean=15.9 nmol l(-1), s.d. 5.7) during a nurse visit in 2008. Depression symptoms were assessed in the same year and again in 2012 using the eight-item Center for Epidemiologic Studies Depression Scale. Self-reports of a physician-diagnosis of depression were also collected at both time points. In separate analyses for men and women, the results from both the cross-sectional and longitudinal analyses revealed a 'U'-shaped pattern of association, such that lower and higher levels of IGF-1 were associated with a slightly elevated risk of depression, whereas the lowest risk was seen around the median levels. Thus, in men, with the lowest quintile of IGF-1 as the referent, the age-adjusted odds ratios (95% confidence interval) of developing depression symptoms after 4 years of follow-up, for increasing quintiles of IGF-1, were: 0.51 (0.28-0.91), 0.50 (0.27-0.92), 0.63 (0.35-1.15) and 0.63 (0.35-1.13) (P-value for quadratic association 0.002). Some attenuation of these effects was apparent after adjustment for co-morbidity, socioeconomic status and health behaviours. In conclusion, in the present study of older adults, there was some evidence that moderate levels of IGF-1 levels conferred a reduced risk of depression.

Antidepressive and BDNF effects of enriched environment treatment across ages in mice lacking BDNF expression through promoter IV

Reduced promoter IV-driven expression of brain-derived neurotrophic factor (BDNF) is implicated in stress and major depression. We previously reported that defective promoter IV (KIV) caused depression-like behavior in young adult mice, which was reversed more effectively by enriched environment treatment (EET) than antidepressants. The effects of promoter IV-BDNF deficiency and EET over the life stages remain unknown. Since early-life development (ED) involves dynamic epigenetic processes, we hypothesized that EET during ED would provide maximum antidepressive effects that would persist later in life due to enhanced, long-lasting BDNF induction. We tested this hypothesis by determining EET effects across three life stages: ED (0-2 months), young adult (2-4 months), and old adult (12-14 months). KIV mice at all life stages showed depression-like behavior in the open-field and tail-suspension tests compared with wild-type mice. Two months of EET reduced depression-like behavior in ED and young adult, but not old adult mice, with the largest effect in ED KIV mice. This effect lasted for 1 month after discontinuance of EET only in ED mice. BDNF protein induction by EET in the hippocampus and frontal cortex was also the largest in ED mice and persisted only in the hippocampus of ED KIV mice after discontinuance of EET. No gender-specific effects were observed. The results suggest that defective promoter IV causes depression-like behavior, regardless of age and gender, and that EET during ED is particularly beneficial to individuals with promoter IV-BDNF deficiency, while additional treatment may be needed for older adults.

Sleep extension increases IGF-I concentrations before and during sleep deprivation in healthy young men

Sleep deprivation is known to suppress circulating trophic factors such as insulin-like growth factor (IGF)-I and brain-derived neurotrophic factor (BDNF). This experiment examined the effect of an intervention involving 6 nights of extended sleep before total sleep deprivation on this catabolic profile. In a randomized crossover design, 14 young men (age range: 26-37 years) were either in an extended (EXT; time in bed: 2100-0700 h) or habitual (HAB: 2230-0700 h) sleep condition, followed by 3 days in the laboratory with blood sampling at baseline (B), after 24 h of sleep deprivation (24h-SD), and after 1 night of recovery sleep (R). In the EXT condition compared with the HAB condition, free IGF-I levels were significantly higher at B, 24h-SD, and R (P < 0.001), and those of total IGF-I at B and 24h-SD (P < 0.05). EXT did not influence growth hormone, IGF binding protein 3, BDNF, insulin, and glucose levels. The only effect of 24 h of sleep deprivation was for insulin levels, which were significantly higher after R compared with B. In a healthy adult, additional sleep over 1 week increased blood concentrations of the anabolic factor IGF-I before and during 24 h of sleep deprivation and after the subsequent recovery night without effects on BDNF. With further research, these findings may prove to be important in guiding effective lifestyle modifications to limit physical or cognitive deficits associated with IGF-I decrease with age.

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)-1β and depressive behavioral responses to stress.

METHODS

The influence of acute restraint stress on extracellular ATP, glutamate, IL-1β, 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-1β 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-1β; and the active form of the NLRP3 inflammasome in the hippocampus. Administration of a P2X7R antagonist completely blocked the release of IL-1β 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.

Plasma insulin-like growth factor I levels are higher in depressive and anxiety disorders, but lower in antidepressant medication users

It has been postulated that many peripheral and (neuro)biological systems are involved in psychiatric disorders such as depression. Some studies found associations of depression and antidepressant treatment with insulin-like growth factor 1 (IGF-I) - a pleiotropic hormone affecting neuronal growth, survival and plasticity - but evidence is mixed. We therefore studied whether depressive and anxiety disorders were associated with plasma IGF-I, and explored the role of antidepressant medication in this association in a large observational study. The sample consisted of 2714 participants enrolled in The Netherlands Study of Depression and Anxiety, classified as healthy controls (n=602), antidepressant users (76 remitted and 571 with current depressive and/or anxiety disorder(s), n=647), persons having remitted depressive and/or anxiety disorder(s) without antidepressant use (n=502), and persons having current depressive and/or anxiety disorder(s) without antidepressant use (n=963). Associations with IGF-I concentrations were studied and adjusted for socio-demographic, health, and lifestyle variables. Relative to healthy controls, antidepressant-free individuals with current disorders had significantly higher IGF-I levels (Cohen's d=0.08, p=0.006), whereas antidepressant-free individuals with remitted disorders had a trend towards higher IGF-I levels (d=0.06, p=0.09). Associations were evident for depressive and for anxiety disorders. In contrast, antidepressant users had significantly lower IGF-I levels compared to healthy controls (d=-0.08, p=0.028). Our findings suggests that antidepressant medication use modifies the association between depressive/anxiety disorders and plasma IGF-I. These results corroborate with findings of some previous small-scale case-control and intervention studies. The higher IGF-I levels related to depression and anxiety might point to a compensatory mechanism to counterbalance the impaired neurogenesis, although future studies are needed to support this hypothesis.

Central monoaminergic systems are a site of convergence of signals conveying the experience of exercise to brain circuits involved in cognition and emotional behavior

Physical activity can enhance cognitive function and increase resistance against deleterious effects of stress on mental health. Enhanced cognitive function and stress resistance produced by exercise are conserved among vertebrates, suggesting that ubiquitous mechanisms may underlie beneficial effects of exercise. In the current review, we summarize the beneficial effects of exercise on cognitive function and stress resistance and discuss central and peripheral signaling factors that may be critical for conferring the effects of physical activity to brain circuits involved in cognitive function and stress. Additionally, it is suggested that norepinephrine and serotonin, highly conserved monoamines that are sensitive to exercise and able to modulate behavior in multiple species, could represent a convergence between peripheral and central exercise signals that mediate the beneficial effects of exercise. Finally, we offer the novel hypothesis that thermoregulation during exercise could contribute to the emotional effects of exercise by activating a subset of temperature-sensitive serotonergic neurons in the dorsal raphe nucleus that convey anxiolytic and stress-protective signals to forebrain regions. Throughout the review, we discuss limitations to current approaches and offer strategies for future research in exercise neuroscience.

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.

Is increased antidepressant exposure a contributory factor to the obesity pandemic?

Major depressive disorder (MDD) and obesity are both common heterogeneous disorders with complex aetiology, with a major impact on public health. Antidepressant prescribing has risen nearly 400% since 1988, according to data from the Centers for Disease Control and Prevention (CDC). In parallel, adult obesity rates have doubled since 1980, from 15 to 30 percent, while childhood obesity rates have more than tripled. Rising obesity rates have significant health consequences, contributing to increased rates of more than thirty serious diseases. Despite the concomitant rise of antidepressant use and of the obesity rates in Western societies, the association between the two, as well as the mechanisms underlying antidepressant-induced weight gain, remain under explored. In this review, we highlight the complex relationship between antidepressant use, MDD and weight gain. Clinical findings have suggested that obesity may increase the risk of developing MDD, and vice versa. Hypothalamic-pituitary-adrenal (HPA) axis activation occurs in the state of stress; concurrently, the HPA axis is also dysregulated in obesity and metabolic syndrome, making it the most well-understood shared common pathophysiological pathway with MDD. Numerous studies have investigated the effects of different classes of antidepressants on body weight. Previous clinical studies suggest that the tricyclics amitriptyline, nortriptyline and imipramine, and the serotonin norepinephrine reuptake inhibitor mirtazapine are associated with weight gain. Despite the fact that selective serotonin reuptake inhibitor (SSRI) use has been associated with weight loss during acute treatment, a number of studies have shown that SSRIs may be associated with long-term risk of weight gain; however, because of high variability and multiple confounds in clinical studies, the long-term effect of SSRI treatment and SSRI exposure on body weight remains unclear. A recently developed animal paradigm shows that the combination of stress and antidepressants followed by long-term high-fat diet results, long after discontinuation of antidepressant treatment, in markedly increased weight, in excess of what is caused by high-fat diet alone. On the basis of existing epidemiological, clinical and preclinical data, we have generated the testable hypothesis that escalating use of antidepressants, resulting in high rates of antidepressant exposure, might be a contributory factor to the obesity epidemic.

The Beneficial Impact of Antidepressant Drugs on Prenatal Stress-Evoked Malfunction of the Insulin-Like Growth Factor-1 (IGF-1) Protein Family in the Olfactory Bulbs of Adult Rats

Insulin-like growth factor-1 (IGF-1) promotes the growth, differentiation, and survival of both neurons and glial cells, and it is believed to exert antidepressant-like activity. Thus, disturbances in the IGF-1 system could be responsible for the course of depression. To date, there have been no papers showing the impact of chronic antidepressant treatment on the IGF-1 network in the olfactory bulb (OB) in an animal model of depression. Prenatal stress was used as model of depression. Twenty-four 3-month-old male offspring of control and stressed mothers were subjected to behavioral testing (forced swim test). The mRNA expression of IGF-1 and IGF-1 receptor (IGF-1R) and the protein level of IGF-1 and its phosphorylation, as well as the concentrations of IGF-binding proteins (IGFBP-2, -4, -3, and -6), were measured in OBs before and after chronic imipramine, fluoxetine, or tianeptine administration. Adult rats exposed prenatally to stressful stimuli displayed not only depression-like behavior but also decreased IGF-1 expression, dysregulation in the IGFBP network, and diminished mRNA expression, as well as IGF-1R phosphorylation, in the OB. The administration of antidepressants normalized most of the changes in the IGF-1 system of the OB evoked by prenatal stress. These results suggested a beneficial effect of chronic antidepressant drug treatment in the alleviation of IGF-1 family malfunction in OBs in an animal model of depression.

Insulin-Like Growth Factor I Produces an Antidepressant-Like Effect and Elicits N-Methyl-D-Aspartate Receptor Independent Long-Term Potentiation of Synaptic Transmission in Medial Prefrontal Cortex and Hippocampus

BACKGROUND

Growth factors play an important role in regulating neurogenesis and synapse formation and may be involved in regulating the antidepressant response to conventional antidepressants. To date, Insulin-like growth factor I (IGFI) is the only growth factor that has shown antidepressant properties in human clinical trials. However, its mechanism of action remains unclear.

METHODS

The antidepressant-like effect of a single IV dose of IGFI was determined using a chronic unpredictable stress paradigm in the rat Porsolt, sucrose preference, novelty-induced hypophagia, and ultrasonic vocalization models. The dependence of the medial prefrontal cortex for these effects was determined by direct medial prefrontal cortex injection followed by Porsolt testing as well as IGFI receptor activation in the medial prefrontal cortex following an optimal IV antidepressant-like dose of IGFI. The effect of IGFI on synaptic transmission and long-term potentiation (LTP) of synaptic strength was assessed in the hippocampus and medial prefrontal cortex. The dependence of these effects on IGFI and AMPA receptor activation and protein synthesis were also determined.

RESULTS

IGFI produced a rapid-acting and long-lasting antidepressant-like effect in each of the depression models. These effects were blocked by IGFI and AMPA receptor antagonists, and medial prefrontal cortex was localized. IGFI robustly increased synaptic strength in the hippocampus and medial prefrontal cortex and these effects were IGFI receptor and protein synthesis-dependent but N-methyl-d-aspartate receptor independent. IGFI also robustly facilitated hippocampal metaplasticity 24 hours postdosing.

CONCLUSIONS

These data support the conclusion that the antidepressant-like effects of IGFI are mediated by a persistent, LTP-like enhancement of synaptic strength requiring both IGFIR activation and ongoing protein synthesis.

Serum insulin-like growth factor 1 and late-life depression: a population-based study

OBJECTIVE

Serum insulin-like growth factor 1 (IGF-1) concentration decreases, while the prevalence of depressive symptoms increases with advancing age. Although basic research indicates a link between low IGF-1 concentration and depression, this has scarcely been investigated in humans. This study investigates whether lower IGF-1 concentrations are associated with prevalent and incident late-life depression over a 3-year period.

METHODS

The study included 1188 participants, aged ≥ 65 years, from the Longitudinal Aging Study Amsterdam (LASA), an ongoing, population-based cohort study. Depression was assessed at baseline and after three years using the Center for Epidemiological Studies-Depression Scale (CES-D) and the Diagnostic Interview Schedule (DIS), and categorized into minor depression and major depression (MDD). Serum IGF-1 concentration was determined at baseline. Associations were adjusted for relevant confounders.

RESULTS

Serum IGF-1 concentrations were within the normal range (mean 13.9 nmol/l, standard deviation 5.3 nmol/l). At baseline, in men, as compared to high concentrations, mid concentrations decreased the probability of prevalent minor depression (odds ratio [OR] = 0.35, 95% confidence interval [CI] = 0.15-0.82). In women, as compared to high concentrations, low concentrations tended to increase the probability of prevalent MDD (OR = 2.66, 95% CI = 0.89-7.89). At three-year follow-up, in men, no significant prospective associations were detected. In women, as compared to high concentrations, mid concentrations decreased the probability of incident minor depression (OR = 0.43, 95% CI = 0.19-0.95).

CONCLUSIONS

Several associations, which differed across the genders, were observed between IGF-1 and depression. Cross-sectional findings were not supported by longitudinal findings, which suggest that IGF-1 may not play an important predictive role in the development of depression in older persons over time. However, a more acute role of IGF-1 in current depression, as indicated by the cross-sectional results, may be possible. Further studies are needed to elucidate the complex relation between IGF-1 and late-life depression.

Galanin mediates features of neural and behavioral stress resilience afforded by exercise

Exercise promotes resilience to stress and increases galanin in the locus coeruleus (LC), but the question of whether changes in galanin signaling mediate the stress-buffering effects of exercise has never been addressed. To test the contributions of galanin to stress resilience, male Sprague Dawley rats received intracerebroventricular (ICV) cannulation for drug delivery and frontocortical cannulation for microdialysis, and were housed with or without a running wheel for 21d. Rats were acutely injected with vehicle or the galanin receptor antagonist M40 and exposed to a single session of either footshock or no stress. Other groups received galanin, the galanin receptor antagonist M40, or vehicle chronically for 21d prior to the stress session. Microdialysis sampling occurred during stress exposure and anxiety-related behavior was measured on the following day in the elevated plus maze. Dendritic spines were visualized by Golgi impregnation in medial prefrontal cortex (mPFC) pyramidal neurons and quantified. Exercise increased galanin levels in the LC. Under non-stressed conditions, anxiety-related behavior and dopamine levels were comparable between exercised and sedentary rats. In contrast, exposure to stress reduced open arm exploration in sedentary rats but not in exercise rats or those treated chronically with ICV galanin, indicating improved resilience. Both exercise and chronic, ICV galanin prevented the increased dopamine overflow and loss of dendritic spines observed after stress in sedentary rats. Chronic, but not acute M40 administration blocked the resilience-promoting effects of exercise. The results indicate that increased galanin levels promote features of resilience at both behavioral and neural levels.

A Review of Biomarkers in Mood and Psychotic Disorders: A Dissection of Clinical vs. Preclinical Correlates

Despite significant research efforts aimed at understanding the neurobiological underpinnings of mood (depression, bipolar disorder) and psychotic disorders, the diagnosis and evaluation of treatment of these disorders are still based solely on relatively subjective assessment of symptoms as well as psychometric evaluations. Therefore, biological markers aimed at improving the current classification of psychotic and mood-related disorders, and that will enable patients to be stratified on a biological basis into more homogeneous clinically distinct subgroups, are urgently needed. The attainment of this goal can be facilitated by identifying biomarkers that accurately reflect pathophysiologic processes in these disorders. This review postulates that the field of psychotic and mood disorder research has advanced sufficiently to develop biochemical hypotheses of the etiopathology of the particular illness and to target the same for more effective disease modifying therapy. This implies that a "one-size fits all" paradigm in the treatment of psychotic and mood disorders is not a viable approach, but that a customized regime based on individual biological abnormalities would pave the way forward to more effective treatment. In reviewing the clinical and preclinical literature, this paper discusses the most highly regarded pathophysiologic processes in mood and psychotic disorders, thereby providing a scaffold for the selection of suitable biomarkers for future studies in this field, to develope biomarker panels, as well as to improve diagnosis and to customize treatment regimens for better therapeutic outcomes.

Effects of Physical Exercise on Neuroinflammation, Neuroplasticity, Neurodegeneration, and Behavior: What We Can Learn From Animal Models in Clinical Settings

Physical exercise is a cornerstone in the management of many neurodegenerative disorders, such as Parkinson's disease, dementia, and stroke. However, much of its beneficial effects on improving motor functions and cognition as well as decreasing neurodegeneration and neuroinflammation are not yet well understood. The obvious limitations of studying the protective mechanisms behind exercise, for example, brain plasticity and neurodegeneration, could be overcome by generating novel animal models of neurodegenerative disorders. In this narrative review, we discuss the beneficial effects of exercise performed in animal models of neurodegenerative disorders and how the results from animal studies can be used in clinical settings. From preclinical studies, the positive effects of exercise have been related to increased levels of neurotrophic factors, elevated expression of anti-inflammatory cytokines, and reduced levels of pro-inflammatory cytokines and activated microglia. It is clear that parameters influencing the effect of exercise, such as intensity, still remain to be investigated in animal studies in order to find the optimal program that can be translated into exercise interventions for patients with neurodegenerative diseases.

Food restriction does not relieve PTSD-like anxiety

We used the inescapable foot shock paradigm (IFS) in rats as an animal model for post-traumatic stress disorder (PTSD). Previously we showed that exercise reversed the enhanced stress sensitivity induced by IFS. From literature it is known that food restriction has antidepressant and anxiolytic effects. Since both treatments influence energy expenditure, we questioned whether food restriction reduces anxiety in the IFS model via a comparable, NPY dependent mechanism as enrichment. Anxiety of IFS-exposed animals was measured as change in locomotion and freezing after sudden silence in an open field test, before and after two weeks of food restriction. In addition a forced swim test (FST) was performed. Next, using qPCR, the expression of neuropeptide Y (NPY) and the neuropeptide Y1 receptor (Y1 receptor) was measured in the amygdala. Food restriction increased locomotion and decreased freezing behavior both in control and IFS animals. These effects were small. IFS-induced anxiety was not abolished after two weeks of food restriction. IFS did not influence immobility or the duration of swimming in the FST of animals fed ad libitum. However, food restriction increased swimming and decreased the duration of immobility in IFS-exposed animals. Y1 receptor expression in the basolateral amygdala decreased after both IFS and food restriction. Although food restriction seems to induce a general anxiolytic effect, it does not operate via enhanced Y1 receptor expression and has no effect on the more pathogenic anxiety induced by IFS.

Prenatal stress affects insulin-like growth factor-1 (IGF-1) level and IGF-1 receptor phosphorylation in the brain of adult rats

It has been shown that stressful events occurring in early life have a powerful influence on the development of the central nervous system. Insulin-like growth factor-1 (IGF-1) promotes the growth, differentiation and survival of both neurons and glial cells and is thought to exert antidepressant-like activity. Thus, it is possible that disturbances in the function of the IGF-1 system may be responsible for disturbances observed over the course of depression. Prenatal stress was used as a valid model of depression. Adult male offspring of control and stressed rat dams were subjected to behavioural testing (forced swim test). The level of IGF-1 in the blood and the expression of IGF-1, IGF-1R, and IRS-1/2 in the hippocampus and frontal cortex using RT-PCR, ELISA and western blotting were measured. In addition the effect of intracerebroventricularly administered IGF-1 and/or the IGF-1R receptor antagonist JB1 in the forced swim test was studied. Prenatally stressed rats showed depressive like behaviour, including increased immobility time as well as decreased mobility and climbing. Intracerebroventricular administration of IGF-1 reversed these effects in stressed animals, whereas concomitant administration of the IGF-1R antagonist JB1 completely blocked the effects. Biochemical analysis of homogenates from the hippocampus and frontal cortex revealed decreases in IGF-1 level and IGF-1R phosphorylation along with disturbances in IRS-1 phosphorylation. These findings reveal that prenatal stress alters IGF-1 signalling, which may contribute to the behavioural changes observed in depression.

The impact of prenatal stress on insulin-like growth factor-1 and pro-inflammatory cytokine expression in the brains of adult male rats: the possible role of suppressors of cytokine signaling proteins

Stress, inflammation and the reduced expression of neurotrophic factors are risk factors for depression. The objective of this study was to determine if prenatal stress affects IGF-1 - cytokine interactions by influencing suppressors of cytokine signaling (SOCS) in the brains of adult rats, in basal conditions and after acute lipopolysaccharide (LPS) treatment. We demonstrated that prenatal stress leads to depression-like behavior, decreased IGF-1, increased IL-1β, TNF-α and IFN-γ release and disturbed SOCS-1, SOCS-2 and SOCS-3 expression in the hippocampus and frontal cortex of adult offspring. Furthermore, prenatal stress enhances the brain response to LPS-evoked inflammatory challenges.

Faster, better, stronger: towards new antidepressant therapeutic strategies

Major depression is a highly prevalent disorder and is predicted to be the second leading cause of disease burden by 2020. Although many antidepressant drugs are currently available, they are far from optimal. Approximately 50% of patients do not respond to initial first line antidepressant treatment, while approximately one third fail to achieve remission following several pharmacological interventions. Furthermore, several weeks or months of treatment are often required before clinical improvement, if any, is reported. Moreover, most of the commonly used antidepressants have been primarily designed to increase synaptic availability of serotonin and/or noradrenaline and although they are of therapeutic benefit to many patients, it is clear that other therapeutic targets are required if we are going to improve the response and remission rates. It is clear that more effective, rapid-acting antidepressants with novel mechanisms of action are required. The purpose of this review is to outline the current strategies that are being taken in both preclinical and clinical settings for identifying superior antidepressant drugs. The realisation that ketamine has rapid antidepressant-like effects in treatment resistant patients has reenergised the field. Further, developing an understanding of the mechanisms underlying the rapid antidepressant effects in treatment-resistant patients by drugs such as ketamine may uncover novel therapeutic targets that can be exploited to meet the Olympian challenge of developing faster, better and stronger antidepressant drugs.

Prenatal stress leads to changes in IGF-1 binding proteins network in the hippocampus and frontal cortex of adult male rat

Depression is a mental disorder of still unknown origin. Currently, much attention is paid to the potential influence of disturbances in the functioning of neurotrophic factors on the onset of this disease. Insulin-like growth factor 1 (IGF-1) is one of the most important growth agents affecting processes that are crucial for brain development. To date, there are no data showing the impact of prenatal stress on the family of six IGF binding proteins (IGFBP 1-6) that regulate IGF-1 bioactivity. The goal of this study was to investigate whether the decreased expression of IGF-1 in the frontal cortex (FCx) and hippocampus (Hp) of adult male rats following a prenatal stress procedure is related to changes in the IGFBP family. Our results show that rats exposed prenatally to stressful stimuli displayed depression-like behavior based on sucrose preference and elevated plus maze tests. In both cases, in the adult rat brain structures that were examined after the prenatal stress procedure, the IGF-1 protein level was reduced. Moreover, we observed changes of varying degrees in the levels of IGFBPs in stressed animals. A decrease in IGFBP-2 and IGFBP-3 accompanied by an increase in the IGFBP-4 concentration in the Hp and the FCx was detected. There were no differences in IGFBP-1 and IGFBP-6 brain levels between the stressed and control animals, whereas IGFBP-5 concentration was decreased in the Hp of prenatally stressed animals. This study demonstrated that stress during pregnancy may lead not only to behavioral disturbances but also to a decrease in IGF-1 level and the dysregulation of the IGF-1 binding protein network in adult rat offspring.