Effects of rTMS on Hippocampal Endocannabinoids and Depressive-like Behaviors in Adolescent Rats

Repetitive transcranial magnetic stimulation (rTMS) for depressive-like symptoms in rodent animal models

Repetitive transcranial magnetic stimulation (rTMS) emerged as a non-invasive brain stimulation technique in the treatment of psychiatric disorders. Both preclinical and clinical studies as well as systematic reviews provide a heterogeneous picture, particularly concerning the stimulation protocols used in rTMS. Here, we present a review of rTMS effects in rodent models of depressive-like symptoms with the aim to identify the most relevant factors that lead to an increased therapeutic success. The influence of different factors, such as the stimulation parameters (stimulus frequency and intensity, duration of stimulation, shape and positioning of the coil), symptom severity and individual characteristics (age, species and genetic background of the rodents), on the therapeutic success are discussed. Accumulating evidence indicates that rTMS ameliorates a multitude of depressive-like symptoms in rodent models, most effectively at high stimulation frequencies (≥5 Hz) especially in adult rodents with a pronounced pathological phenotype. The therapeutic success of rTMS might be increased in the future by considering these factors and using more standardized stimulation protocols.

Alterations in plasma endocannabinoid concentrations among individuals with major depression treated with electroconvulsive therapy

The role of the endocannabinoid system (ECS) in depression and suicidality has recently emerged. The purpose of the study was to identify changes in plasma endocannabinoid concentrations of several endocannabinoids and correlate them with depressive symptoms and suicidality in patients with severe major depression undergoing electroconvulsive therapy (ECT). The study included 17 patients that were evaluated in four visits at different stages of therapy. At each visit depression, anxiety and suicidality symptoms were assessed and blood samples collected. Several endocannabinoid concentrations increased following six sessions of ECT, as 2-AG (p < 0.05) and LEA (p < 0.01), and following twelve sessions of ECT, as 2-AG (p < 0.05), AEA (p < 0.05), LEA (p < 0.05) and DH-Gly (p < 0.05). Endocannabinoids also correlated with symptoms of depression, anxiety and suicidality at baseline and at the sixth ECT session. Finally, we found one endocannabinoid, l-Gly, that differentiated between remitted and not-remitted patients at the seventh and thirteenth ECT sessions (p < 0.05). Our findings suggest that depression is markedly related to imbalance of the endocannabinoid system, and further regulated by ECT. Plasma endocannabinoids could be promising biomarkers for detection of depression response and remission.

Reversing valproic acid-induced autism-like behaviors through a combination of low-frequency repeated transcranial magnetic stimulation and superparamagnetic iron oxide nanoparticles

Transcranial magnetic stimulation (TMS) is a neurostimulation device used to modulate brain cortex activity. Our objective was to enhance the therapeutic effectiveness of low-frequency repeated TMS (LF-rTMS) in a rat model of autism spectrum disorder (ASD) induced by prenatal valproic acid (VPA) exposure through the injection of superparamagnetic iron oxide nanoparticles (SPIONs). For the induction of ASD, we administered prenatal VPA (600 mg/kg, I.P.) on the 12.5th day of pregnancy. At postnatal day 30, SPIONs were injected directly into the lateral ventricle of the brain. Subsequently, LF-rTMS treatment was applied for 14 consecutive days. Following the treatment period, behavioral analyses were conducted. At postnatal day 60, brain tissue was extracted, and both biochemical and histological analyses were performed. Our data revealed that prenatal VPA exposure led to behavioral alterations, including changes in social interactions, increased anxiety, and repetitive behavior, along with dysfunction in stress coping strategies. Additionally, we observed reduced levels of SYN, MAP2, and BDNF. These changes were accompanied by a decrease in dendritic spine density in the hippocampal CA1 area. However, LF-rTMS treatment combined with SPIONs successfully reversed these dysfunctions at the behavioral, biochemical, and histological levels, introducing a successful approach for the treatment of ASD.

The Story of Ferumoxytol: Synthesis Production, Current Clinical Applications, and Therapeutic Potential

Ferumoxytol, approved by the U.S. Food and Drug Administration in 2009, is one of the intravenous iron oxide nanoparticles authorized for the treatment of iron deficiency in chronic kidney disease and end-stage renal disease. With its exceptional magnetic properties, catalytic activity, and immune activity, as well as good biocompatibility and safety, ferumoxytol has gained significant recognition in various biomedical diagnoses and treatments. Unlike most existing reviews on this topic, this review primarily focuses on the recent clinical and preclinical advances of ferumoxytol in disease treatment, spanning anemia, cancer, infectious inflammatory diseases, regenerative medicine application, magnetic stimulation for neural modulation, etc. Additionally, the newly discovered mechanisms associated with the biological effects of ferumoxytol are discussed, including its magnetic, catalytic, and immunomodulatory properties. Finally, the summary and future prospects concerning the treatment and application of ferumoxytol-based nanotherapeutics are presented.

CB1 Receptor Silencing Attenuates Ketamine-Induced Hyperlocomotion Without Compromising Its Antidepressant-Like Effects

Introduction: The antidepressant properties of ketamine have been extensively demonstrated in experimental and clinical settings. However, the psychotomimetic side effects still limit its wider use as an antidepressant. It was recently observed that endocannabinoids are inolved in ketamine induced reward properties. As an increase in endocannabinoid signaling induces antidepressant effects, this study aimed to investigate the involvement of cannabinoid type 1 receptors (CB1R) in the antidepressant and psychostimulant effects induced by ketamine. Methods: We tested the effects of genetic and pharmacological inhibition of CB1R in the hyperlocomotion and antidepressant-like properties of ketamine. The effects of ketamine (10-20 mg/kg) were assessed in the open-field and the forced swim tests (FSTs) in CB1R knockout (KO) and wild-type (WT) mice (male and female), and mice pre-treated with rimonabant (CB1R antagonist, 3-10 mg/kg). Results: We found that the motor hyperactivity elicited by ketamine was impaired in CB1R male and female KO mice. A similar effect was observed upon pharmacological blockade of CB1R in WT mice. However, genetic CB1R deletion did not modify the antidepressant effect of ketamine in male mice submitted to the FST. Surprisingly, pharmacological blockade of CB1R induced an antidepressant-like effect in both male and female mice, which was not further potentiated by ketamine. Conclusions: Our results support the hypothesis that CB1R mediate the psychostimulant side effects induced by ketamine, but not its antidepressant properties.

High-frequency repetitive transcranial magnetic stimulation regulates neural oscillations of the hippocampus and prefrontal cortex in mice by modulating endocannabinoid signalling

BACKGROUND

Neural oscillations play a role in the antidepressant effects of repetitive transcranial magnetic stimulation (rTMS). However, the effects of high-frequency rTMS on the neural oscillations of the medial prefrontal cortex (mPFC) and hippocampus (HPC) and its molecular mechanism have not been fully clarified.

METHODS

The depressive-like behaviours, local field potentials (LFPs) of the ventral HPC (vHPC)-mPFC, and alternations of endocannabinoid system (ECS) in the HPC and mPFC were observed after rTMS treatment. Meanwhile, depressive-like behaviours and LFPs were also observed after cannabinoid type-1 receptor (CB1R) antagonist AM281 or monoacylglycerol lipase inhibitor JZL184 injection. Moreover, the antidepressant effect of rTMS was further assessed in glutamatergic-CB1R and gamma-amino butyric acid (GABA)-ergic -CB1R knockout mice.

RESULTS

Alternations of endocannabinoids and energy value and synchronisation of mPFC-vHPC, especially the decrease of theta oscillation induced by CUMS, were alleviated by rTMS. JZL184 has similar effects to rTMS and AM281 blocked the effects of rTMS. GABAergic-CB1R deletion inhibited CUMS-induced depressive-like behaviours whereas Glutaminergic-CB1R deletion dampened the antidepressant effects of rTMS.

LIMITATIONS

The immediate effect of rTMS on field-potential regulation was not observed. Moreover, the role of region-specific regulation of the ECS in the antidepressant effect of rTMS was unclear and the effects of cell-specific CB1R knockout on neuronal oscillations of the mPFC and vHPC should be further investigated.

CONCLUSION

Endocannabinoid system mediated the antidepressant effects and was involved in the regulation of LFP in the vHPC-mPFC of high-frequency rTMS.

Hippocampal CB1 receptor mediates antidepressant-like effect of synthetic cannabinoid-HU210 in acute despair reaction model in mice

Growing evidence suggests that stress may contribute to the pathophysiology of depression. The alleviation of depressive symptoms is one of the most attractive medical applications of cannabis. Here, we investigated the antidepressant-like actions of synthetic cannabinoid-HU210 in acute despair response and explored the possible underlying mechanisms. Acute stress, induced by forced-swimming, induced depression-like behavior in the sucrose preference test (SPT). HU-210 (50 μg/kg) displayed anti-depressant like effect in the forced swim test in naïve mice and decreased depression-like behavior in the SPT, induced by forced swim stress. Pretreatment with AM251, an inhibitor of CB1R or inhibition of long-term depression (LTD) at hippocampal CA3-CA1 synapses by Tat-GluR2 attenuated the antidepressant like action of HU-210. These results indicate that HU210 produces antidepressant-like effects in acute stress and its underlying mechanism may be related to CB1R activation and hence hippocampal LTD production invivo. Synthetic cannabis or cannabis-related drugs may be used as an early intervention after acute stress exposure to prevent or at least reduce depression-like behaviors.

Repetitive transcranial magnetic stimulation (rTMS) for post-stroke sleep disorders: a systematic review of randomized controlled trials

OBJECTIVE

Survivors of stroke often experience post-stroke sleep disorders (PSSDs), but pharmacotherapy risks adverse side effects. Transcranial magnetic stimulation (TMS) is potentially a nonpharmacotherapeutic option. This meta-analysis investigated the effects of rTMS to treat PSSD.

METHODS

Databases were searched for randomized controlled trials (RCTs) of rTMS to treat PSSD, conducted in accordance with the PRISMA 2020 guidelines. Risk-of-bias assessments were performed using the Cochrane risk-of-bias tool. A meta-analysis of the following indexes was performed using RevMan 5.4 software: Pittsburgh sleep quality index; effective rate of sleep improvement; Hamilton Anxiety Rating Scale (for mood); and National Institute of Health Stroke Scale (NIHSS, stroke severity). Mean differences (MDs) and confidence intervals (CIs) were calculated.

RESULTS

The meta-analysis included 17 RCTs, with 1411 patients overall. The indexes indicated that rTMS could improve the sleep quality, mood, and stroke severity of patients with PSSD: Pittsburgh sleep quality index (12 studies; MD =  - 2.51, 95% CI [- 3.24, - 1.79], P < 0.00001); effective rate of sleep improvement (7 studies; MD = 4.03, 95% CI [2.43, 6.68], P < 0.0001); Hamilton Anxiety Rating Scale (2 studies; MD =  - 4.05, 95% CI [- 4.77, - 3.32], P < 0.00001); and NIHSS (2 studies; MD = -2.71, 95% CI [- 3.36, - 2.06], P < 0.00001).

CONCLUSION

The results suggest that rTMS may have positive effects on the sleep quality, mood, and stroke severity of patients with PSSD.

Rapid treatments for depression: Endocannabinoid system as a therapeutic target

Current first-line treatments for major depressive disorder (MDD), i.e., antidepressant drugs and psychotherapy, show delayed onset of therapeutic effect as late as 2-3 weeks or more. In the clinic, the speed of beginning of the actions of antidepressant drugs or other interventions is vital for many reasons. Late-onset means that depression, its related disability, and the potential danger of suicide remain a threat for some patients. There are some rapid-acting antidepressant interventions, such as sleep deprivation, ketamine, acute exercise, which induce a significant response, ranging from a few hours to maximally one week, and most of them share a common characteristic that is the activation of the endocannabinoid (eCB) system. Activation of this system, i.e., augmentation of eCB signaling, appears to have anti-depressant-like actions. This article puts the idea forward that the activation of eCB signaling represents a critical mechanism of rapid-acting therapeutic interventions in MDD, and this system might contribute to the development of novel rapid-acting treatments for MDD.

The antidepressant and anxiolytic effects of cannabinoids in chronic unpredictable stress: a preclinical systematic review and meta-analysis

Neuroscience research presents contradictory evidence in support of both the protective and destructive effects of cannabinoids in depression. Therefore, this systematic review and meta-analysis summarizes the existing preclinical literature on the effects of cannabinoid administration in the chronic unpredictable stress model of depression in order to evaluate the effects of cannabinoids and identify gaps in the literature. After protocol registration (PROSPERO #CRD42020219986), we systematically searched Scopus, Embase, Psychology & Behavioral Sciences Collection, APA PsychINFO, PubMed, CINAHL Complete, and ProQuest Dissertations & Theses Global from the earliest record of the databases, February 1964, to November 2020 for articles that met inclusion criteria (e.g., rodent subjects and administration of a cannabinoid. A total of 26 articles were included representing a sample size estimate of 1132 rodents with the majority of articles administering daily intraperitoneal injections during chronic unpredictable stress. These articles were evaluated using a modified SYRCLE's risk-of-bias tool. For each continuous behavioral measure, the standardized mean difference was calculated between cannabinoid and vehicle groups in rodents subjected to chronic unpredictable stress. The effects of cannabinoids on depressive-like behavior was evaluated using a multilevel mixed-effects model with effect size weights nested within control groups. Cannabinoid administration moderately improved the pooled negative effects of chronic unpredictable stress on anhedonia, learned helplessness, novelty suppressed feeding, time in the anxiogenic context, and entries into the anxiogenic context. Although the interpretations are limited, these findings suggest that with further investigation, cannabinoids may be a viable long-term treatment for stress-related psychopathologies such as depression.

A Framework for Developing Translationally Relevant Animal Models of Stress-Induced Changes in Eating Behavior

Stress often affects eating behaviors, leading to increased eating in some individuals and decreased eating in others. Identifying physiological and psychological factors that determine the direction of eating responses to stress has been a major goal of epidemiological and clinical studies. However, challenges of standardizing the stress exposure in humans hinder efforts to uncover the underlying mechanisms. The issue of what determines the direction of stress-induced feeding responses has not been directly addressed in animal models, but assays that combine stress with a feeding-related task are commonly used as readouts of other behaviors, such as anxiety. Sex, estrous cyclicity, circadian cyclicity, caloric restriction, palatable diets, elevated body weight, and properties of the stressors similarly influence feeding behavior in humans and rodent models. Yet, most rodent studies do not use conditions that are most relevant for studying feeding behavior in humans. This review proposes a conceptual framework for incorporating these influences to develop reproducible and translationally relevant assays to study effects of stress on food intake. Such paradigms have the potential to uncover links between emotional eating and obesity as well as to the etiology of eating disorders.

The Effects of Repetitive Transcranial Magnetic Stimulation on Cognitive Impairment and the Brain Lipidome in a Cuprizone-Induced Mouse Model of Demyelination

The protective effects of repetitive transcranial magnetic stimulation (rTMS) on myelin integrity have been extensively studied, and growing evidence suggests that rTMS is beneficial in improving cognitive functions and promoting myelin repair. However, the association between cognitive improvement due to rTMS and changes in brain lipids remains elusive. In this study, we used the Y-maze and 3-chamber tests, as well as a mass spectrometry-based lipidomic approach in a CPZ-induced demyelination model in mice to assess the protective effects of rTMS on cuprizone (CPZ)-induced cognitive impairment and evaluate changes in lipid composition in the hippocampus, prefrontal cortex, and striatum. We found that CPZ induced cognitive impairment and remarkable changes in brain lipids, specifically in glycerophospholipids. Moreover, the changes in lipids within the prefrontal cortex were more extensive, compared to those observed in the hippocampus and striatum. Notably, rTMS ameliorated CPZ-induced cognitive impairment and partially normalized CPZ-induced lipid changes. Taken together, our data suggest that rTMS may reverse cognitive behavioral changes caused by CPZ-induced demyelination by modulating the brain lipidome, providing new insights into the therapeutic mechanism of rTMS.

Targeting 2-arachidonoylglycerol signalling in the neurobiology and treatment of depression

The endocannabinoid 2-arachidonoylglycerol (2-AG) is an atypical neurotransmitter synthesized on demand in response to a wide range of stimuli, including exposure to stress. Through the activation of cannabinoid receptors, 2-AG can interfere with excitatory and inhibitory neurotransmission in different brain regions and modulate behavioural, endocrine and emotional components of the stress response. Exposure to chronic or intense unpredictable stress predisposes to maladaptive behaviour and is one of the main risk factors involved in developing mood disorders, such as major depressive disorder (MDD). In this review, we describe the molecular mechanisms involved in 2-AG signalling in the brain of healthy and stressed animals and discuss how such mechanisms could modulate stress adaptation and susceptibility to depression. Furthermore, we review preclinical evidence indicating that the pharmacological modulation of 2-AG signalling stands as a potential new therapeutic target in treating MDD. Particular emphasis is given to the pharmacological augmentation of 2-AG levels by monoacylglycerol lipase (MAGL) inhibitors and the modulation of CB2 receptors.

Peripheral endocannabinoid serum level in association with repetitive transcranial magnetic stimulation (rTMS) treatment in patients with major depressive disorder

Repetitive transcranial magnetic stimulation (rTMS) is an effective and well tolerable biological intervention in major depressive disorder (MDD) contributing to rapid symptom improvement. Molecular mechanisms underpinning the therapeutic effects of rTMS have still not been clarified. Recently published animal data implicated relevant associations with changes in endocannabinoid (eCB) brain levels during rTMS treatment, human studies, however, have not been published. In our study we assessed the detailed phenotypic spectrum of MDD and serum 2-arachidnoylglycerol (2-AG) and anandamide (AEA) levels in 18 patients with treatment-resistant depression before, immediately following, and two weeks after completion of a 10-day rTMS treatment. We found significant associations between serum 2-AG level changes from pretreatment to 2 weeks after treatment and symptom reduction. The greater the increase of 2-AG levels, the greater the improvement of depressive (p = 0.031), anxious (p = 0.007) and anhedonia symptoms (p = 0.047). Here we report for the first time a significant association of human circulating eCB and antidepressant effect of rTMS. Our data may indicate that direct stimulation of targeted brain areas can rapidly alleviate depressive complaints via activation of the eCB system.

Magnetic brain stimulation using iron oxide nanoparticle-mediated selective treatment of the left prelimbic cortex as a novel strategy to rapidly improve depressive-like symptoms in mice

Magnetic brain stimulation has greatly contributed to the advancement of neuroscience. However, challenges remain in the power of penetration and precision of magnetic stimulation, especially in small animals. Here, a novel combined magnetic stimulation system (c-MSS) was established for brain stimulation in mice. The c-MSS uses a mild magnetic pulse sequence and injection of superparamagnetic iron oxide (SPIO) nanodrugs to elevate local cortical susceptibility. After imaging of the SPIO nanoparticles in the left prelimbic (PrL) cortex in mice, we determined their safety and physical characteristics. Depressive-like behavior was established in mice using a chronic unpredictable mild stress (CUMS) model. SPIO nanodrugs were then delivered precisely to the left PrL cortex using in situ injection. A 0.1 T magnetic field (adjustable frequency) was used for magnetic stimulation (5 min/session, two sessions daily). Biomarkers representing therapeutic effects were measured before and after c-MSS intervention. Results showed that c-MSS rapidly improved depressive-like symptoms in CUMS mice after stimulation with a 10 Hz field for 5 d, combined with increased brain-derived neurotrophic factor (BDNF) and inactivation of hypothalamic-pituitary-adrenal (HPA) axis function, which enhanced neuronal activity due to SPIO nanoparticle-mediated effects. The c-MSS was safe and effective, representing a novel approach in the selective stimulation of arbitrary cortical targets in small animals, playing a bioelectric role in neural circuit regulation, including antidepressant effects in CUMS mice. This expands the potential applications of magnetic stimulation and progresses brain research towards clinical application.

Transcranial direct current stimulation (tDCS) produce anti-anxiety response in acute stress exposure rats via activation of amygdala CB1R

Anxiety is one of the most common mental disorders worldwide. Currently, the main anti-anxiety drugs, selective serotonin/noradrenalin reuptake inhibitors (SSRIs/SNRIs), are always associated with delayed onset of action and low therapeutic response rate. Benzodiazepines can produce rapid effects, but their long-term use may result in severe adverse reaction and drug dependence. Transcranial direct current stimulation (tDCS) is one of the noteworthy noninvasive brain stimulation techniques and is expected to be a new choice of anti-anxiety therapy. However, the underlying mechanism remains unclear. In our recent published study, we have observed the important role of endogenous cannabinoid in the pathophysiology and treatment of anxiety. Here we verified the anti-anxiety effects of tDCS in the acute stress exposure rats, and investigated the possible role of amygdala cannabinoid receptor 1 (CB1R) activation in the anti-anxiety response of tDCS. Forced swimming exposure produced anxiety-like behaviors, which can be reversed by tDCS treatment. tDCS increased the time spent in the center without affection of locomotor activity in open field test (OFT) and elevated the number of entries into open arm and time spent in open arm in elevated plus maze test (EPMT). However, Inhibition of CB1R function by AM251 intraperitoneal injection or CB1R knockdown in amygdala produced the negative effects on the anti-anxiety action of tDCS. In conclusion, tDCS may play an anti-anxiety role at least partly via activation of amygdala CB1R, which provides a theoretical basis for the clinical application of tDCS in the treatment of anxiety disorder.

Recovering from depression with repetitive transcranial magnetic stimulation (rTMS): a systematic review and meta-analysis of preclinical studies

Repetitive transcranial magnetic stimulation (rTMS) has gained growing interest for the treatment of major depression (MDD) and treatment-resistant depression (TRD). Most knowledge on rTMS comes from human studies as preclinical application has been problematic. However, recent optimization of rTMS in animal models has laid the foundations for improved translational studies. Preclinical studies have the potential to help identify optimal stimulation protocols and shed light on new neurobiological-based rationales for rTMS use. To assess existing evidence regarding rTMS effects on depressive-like symptoms in rodent models, we conducted a comprehensive literature search in accordance with PRISMA guidelines (PROSPERO registration number: CRD42019157549). In addition, we conducted a meta-analysis to determine rTMS efficacy, performing subgroup analyses to examine the impact of different experimental models and neuromodulation parameters. Assessment of the depressive-like phenotype was quite homogeneous whilst rTMS parameters among the 23 included studies varied considerably. Most studies used a stress-induced model. Overall, results show a largely beneficial effect of active rTMS compared to sham stimulation, as reflected in the statistically significant recovery of both helplessness (SDM 1.34 [1.02;1.66]) and anhedonic (SDM 1.87 [1.02;2.72]) profiles. Improvement of the depressive-like phenotype was obtained in all included models and independently of rTMS frequency. Nonetheless, these results have limited predictive value for TRD patients as only antidepressant-sensitive models were used. Extending rTMS studies to other MDD models, corresponding to distinct endophenotypes, and to TRD models is therefore crucial to test rTMS efficacy and to develop cost-effective protocols, with the potential of yielding faster clinical responses in MDD and TRD.

Differential effect of interferon-alpha treatment on AEA and 2-AG levels

The endocannabinoid (eCB) system is one of the key players in immunoregulation, and reduced activity of the eCB system has been linked with depressive-like behaviours in animal studies and depression in clinical samples. There is a well-established link between immune activation and depression, such as following the administration of the pro-inflammatory cytokine, interferon-α (IFN-α), used to treat hepatitis C viral (HCV) infection. However, the role of peripheral endocannabinoids (eCBs), anandamide (AEA) and 2-arachidonoylglycerol (2-AG), following immunotherapy with IFN-α and in IFN-α -induced depression, have not been examined yet. In this study, we investigated whether circulating AEA and 2-AG were modified by treatment with IFN-α and whether they were involved in the development of IFN-α-induced depression. We also explored whether circulating eCBs were associated with peripheral cytokines during and after IFN-α treatment. We measured serum concentrations of AEA and 2-AG using High Performance Liquid Chromatography with Tandem Mass Spectrometry, and serum concentrations of cytokines using Meso Scale Discovery electrochemiluminescence V-PLEX assay, in 70 patients with HCV infection and 41 healthy subjects. We assessed HCV patients at baseline, IFN-α-treatment weeks (TW) 4 and 24, end of treatment (END) and at six months follow-up (FU). We assessed depression using M.I.N.I. International Neuropsychiatric Interview. We found a different pattern of change in peripheral AEA and 2-AG during and after IFN-α treatment. Whilst 2-AG increased earlier in immunotherapy (TW4), remained elevated throughout treatment, and reduced at six months follow-up (FU), AEA increased later in treatment (TW24) and remained elevated six months post-treatment. We also found that baseline levels of AEA were lower in HCV patients compared with healthy controls, whereas there were no differences in 2-AG levels. Interestingly, AEA, but not 2-AG, was significantly, negatively correlated with interleukin (IL)-2 and IL-17a at six months follow-up. We did not find any difference in both eCBs between patients with and without IFN-α-induced depression, at any time point. Our findings suggest that AEA and 2-AG are involved in different stages of immunoregulation following IFN-α treatment, where AEA might be involved in chronic inflammation. Lack of association between peripheral eCBs and IFN-α-induced depression suggests that different biological mechanisms may underpin inflammation-induced depression compared with classic "psychiatric" depression, or that any changes in the eCB system in depression may not be captured by peripheral AEA and 2-AG.

Mechanisms of repetitive transcranial magnetic stimulation for anti-depression: Evidence from preclinical studies

This review summarizes the anti-depressant mechanisms of repetitive transcranial magnetic stimulation in preclinical studies, including anti-inflammatory effects mediated by activation of nuclear factor-E2-related factor 2 signaling pathway, anti-oxidative stress effects, enhancement of synaptic plasticity and neurogenesis via activation of the endocannabinoid system and brain derived neurotrophic factor signaling pathway, increasing the content of monoamine neurotransmitters via inhibition of Sirtuin 1/monoamine oxidase A signaling pathway, and reducing the activity of the hypothalamic-pituitary-adrenocortical axis. We also discuss the shortcomings of transcranial magnetic stimulation in preclinical studies such as inaccurate positioning, shallow depth of stimulation, and difficulty in elucidating the neural circuit mechanism up- and down-stream of the stimulation target brain region.

Neuroprotective efficacy of different levels of high-frequency repetitive transcranial magnetic stimulation in mice with CUMS-induced depression: Involvement of the p11/BDNF/Homer1a signaling pathway

High-frequency repetitive transcranial magnetic stimulation (HF-rTMS) is widely used to treat depression. However, the underlying mechanism has not been identified, and there is uncertainty regarding the optimal choice of stimulus parameters, especially stimulus frequency. Our previous study in mice demonstrated that 10-Hz HF-rTMS ameliorated depression by inducing expression of Homer1a and reducing excitability of cortical pyramidal cells. The aims of this study were to compare the effects of 15-Hz and 25-Hz HF-rTMS in a model of chronic unpredictable mild stress (CUMS)-induced depression and investigate its possible molecular mechanism. Male C57BL/6J mice were treated with CUMS for 28 days followed by 15-Hz and 25-Hz rTMS for 4 weeks. The sucrose preference, open field, forced swimming, and tail suspension tests were used to evaluate depression-like behaviors. Immunostaining was performed to measure neuronal loss and neurogenesis. Apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining. Expression of synapse-related proteins and the effects of HF-rTMS on the signaling pathway were examined using Western blot. The results showed that both 15-Hz and 25-Hz rTMS had significant antidepressant effects; 15-Hz rTMS seemed to be more effective than 25-Hz rTMS in preventing neuronal loss and promoting neurogenesis, while 25-Hz rTMS was superior to 15-Hz rTMS in facilitating synaptic plasticity. We also found that 15-Hz and 25-Hz rTMS markedly increased expression of p11, BDNF, Homer1a, and p-trkB proteins. These findings suggest that 15-Hz and 25-Hz HF-rTMS could exert neuroprotective effects to different degrees via multiple perspectives, which at least in part involve the p11/BDNF/Homer1a pathway.

Repetitive Transcranial Magnetic Stimulation Elicits Antidepressant- and Anxiolytic-like Effect via Nuclear Factor-E2-related Factor 2-mediated Anti-inflammation Mechanism in Rats

Repetitive transcranial magnetic stimulation (rTMS) treatment is widely accepted as an evidence-based treatment option for depression and anxiety. However, the underlying mechanism of this treatment maneuver has not been clearly understood. The chronic unpredictable mild stress (CUMS) procedure was used to establish depression and anxiety-like behavior in rats. The rTMS was performed with a commercially available stimulator for seven consecutive days, and then depression and anxiety-like behaviors were subsequently measured. The expression of nuclear factor-E2-related factor 2 (Nrf2) was measured by western-blot, and the level of tumor necrosis factor-α (TNF-α), inducible nitric oxide synthase (iNOS), interleukin-1β (IL-1β), and interleukin-6 (IL-6) was measured with Enzyme-linked immunesorbent assay (ELISA) analyzing kits. Furthermore, a small interfering RNA was employed to knockdown Nrf2, after which the neurobehavioral assessment, Nrf2 nuclear expression, and the amount of inflammation factors were evaluated. Application of rTMS exhibited a significant antidepressant and anxiolytic-like effect, which was associated with the increased Nrf2 nuclear translocation and reduced level of TNF-α, iNOS, IL-1β, and IL-6 in the hippocampus. Following Nrf2 silencing, the antidepressant and anxiolytic-like effect produced by rTMS was abolished. Moreover, the elevated Nrf2 nuclear translocation, and the reduced production of TNF-α, iNOS, IL-1β, and IL-6 in hippocampus mediated by rTMS, were reversed by Nrf2 knockdown. Together, these results reveal that the Nrf2-induced anti-inflammation effect is crucial in regulating antidepressant-related behaviors produced by rTMS.

Endocannabinoid System Components as Potential Biomarkers in Psychiatry

The high heterogeneity of psychiatric disorders leads to a lack of diagnostic precision. Therefore, the search of biomarkers is a fundamental aspect in psychiatry to reach a more personalized medicine. The endocannabinoid system (ECS) has gained increasing interest due to its involvement in many different functional processes in the brain, including the regulation of emotions, motivation, and cognition. This article reviews the role of the main components of the ECS as biomarkers in certain psychiatric disorders. Studies carried out in rodents evaluating the effects of pharmacological and genetic manipulation of cannabinoid receptors or endocannabinoids (eCBs) degrading enzymes were included. Likewise, the ECS-related alterations occurring at the molecular level in animal models reproducing some behavioral and/or neuropathological aspects of psychiatric disorders were reviewed. Furthermore, clinical studies evaluating gene or protein alterations in post-mortem brain tissue or in vivo blood, plasma, and cerebrospinal fluid (CSF) samples were analyzed. Also, the results from neuroimaging studies using positron emission tomography (PET) or functional magnetic resonance (fMRI) were included. This review shows the close involvement of cannabinoid receptor 1 (CB1r) in stress regulation and the development of mood disorders [anxiety, depression, bipolar disorder (BD)], in post-traumatic stress disorder (PTSD), as well as in the etiopathogenesis of schizophrenia, attention deficit hyperactivity disorder (ADHD), or eating disorders (i.e. anorexia and bulimia nervosa). On the other hand, recent results reveal the potential therapeutic action of the endocannabinoid tone manipulation by inhibition of eCBs degrading enzymes, as well as by the modulation of cannabinoid receptor 2 (CB2r) activity on anxiolytic, antidepressive, or antipsychotic associated effects. Further clinical research studies are needed; however, current evidence suggests that the components of the ECS may become promising biomarkers in psychiatry to improve, at least in part, the diagnosis and pharmacological treatment of psychiatric disorders.

Repetitive high-frequency transcranial magnetic stimulation reverses depressive-like behaviors and protein expression at hippocampal synapses in chronic unpredictable stress-treated rats by enhancing endocannabinoid signaling

The anti-depressant effect of repetitive transcranial magnetic stimulation (rTMS), a clinically-useful treatment for depression, is associated with changes to the endocannabinoid system (ECS). However, it is currently unknown whether different frequencies of rTMS alter the ECS differently. To test this, rats exposed to chronic unpredictable stress (CUS) were treated with rTMS at two different frequencies (5 (high) or 1 Hz (low), 1.26 Tesla) for 7 consecutive days. Twenty-four hours after the final rTMS treatment, we evaluated depressive-like behaviors and the expression of several synaptic proteins and ECS-related proteins in the hippocampus. In addition, we knocked-down diacylglycerol lipase alpha (DAGLα) and cannabinoid type 1 receptor (CB1R), two important components of the ECS, and measured depressive-like behaviors and synaptic protein expression following rTMS. Furthermore, we measured the expression levels of several components of the ECS system in hippocampal-derived astrocytes and neurons exposed to repetitive magnetic stimulation (rMS) with different parameters (5 or 1 Hz, 0.84 or 1.26 Tesla). Interestingly, we found that only high-frequency rTMS ameliorated depressive-like behaviors and normalized the expression of hippocampal synaptic proteins in CUS-treated rats; this effect was eliminated by knockdown of DAGLα or CB1R. Moreover, we found that rMS at 5 Hz increased the expression of DAGLα and CB1R in hippocampal astrocytes and neurons. Collectively, our results suggest that high-frequency rTMS exerts its anti-depressant effect by up-regulating DAGLα and CB1R.