Chronic repetitive transcranial magnetic stimulation is antidepressant but not anxiolytic in rat models of anxiety and depression

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.

A mitochondrial nexus in major depressive disorder: Integration with the psycho-immune-neuroendocrine network

Nervous system processes, including cognition and affective state, fundamentally rely on mitochondria. Impaired mitochondrial function is evident in major depressive disorder (MDD), reflecting cumulative detrimental influences of both extrinsic and intrinsic stressors, genetic predisposition, and mutation. Glucocorticoid 'stress' pathways converge on mitochondria; oxidative and nitrosative stresses in MDD are largely mitochondrial in origin; both initiate cascades promoting mitochondrial DNA (mtDNA) damage with disruptions to mitochondrial biogenesis and tryptophan catabolism. Mitochondrial dysfunction facilitates proinflammatory dysbiosis while directly triggering immuno-inflammatory activation via released mtDNA, mitochondrial lipids and mitochondria associated membranes (MAMs), further disrupting mitochondrial function and mitochondrial quality control, promoting the accumulation of abnormal mitochondria (confirmed in autopsy studies). Established and putative mechanisms highlight a mitochondrial nexus within the psycho-immune neuroendocrine (PINE) network implicated in MDD. Whether lowering neuronal resilience and thresholds for disease, or linking mechanistic nodes within the MDD pathogenic network, impaired mitochondrial function emerges as an important risk, a functional biomarker, providing a therapeutic target in MDD. Several treatment modalities have been demonstrated to reset mitochondrial function, which could benefit those with MDD.

Meta-analysis of cognitive and behavioral tests in leptin- and leptin receptor-deficient mice

Leptin is a hormone produced by adipocytes that regulates food intake and metabolism. Leptin-related gene-deficient mice, such as db/db and ob/ob mice, are widely used to study diabetes and its related diseases. However, broad effects of leptin appear to cause variability in behavioral test results. We performed a meta-analysis of major behavioral tests in db/db and ob/ob mice. These mice exhibited significant impairments in the Morris water maze, forced swim, novel object recognition, Y-maze, tail suspension, and light-dark box tests, whereas the elevated plus maze and open field tests did not reveal significant changes. We also performed correlation and regression analyses between the animals' performances and the experimental protocols and conditions. The memory-related tests were characterized by the correlations of their results with animal age, while the performances in the elevated plus-maze and forced swim tests were affected by the width of the devices used. In conclusion, db/db and ob/ob mice mainly exhibit memory deficits and depression-like behavior, although experimenters should be aware of animal age and device size in conducting experiments.

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.

Evaluation of the neuroprotective effects of electromagnetic fields and coenzyme Q10 on hippocampal injury in mouse

Electromagnetic fields (EMFs) are reported to interfere with chemical reactions involving free radical production. Coenzyme Q10 (CoQ10) is a strong antioxidant with some neuroprotective activities. The purpose of this study was to examine and compare the neuroprotective effects of EMF and CoQ10 in a mouse model of hippocampal injury. Hippocampal injury was induced in mature female mice (25-30 g), using an intraperitoneal injection of trimethyltin hydroxide (TMT; 2.5 mg/kg). The experimental groups were exposed to EMF at a frequency of 50 Hz and intensity of 5.9 mT for 7 hr daily over 1 week or treated with CoQ10 (10 mg/kg) for 2 weeks following TMT injection. A Morris water maze apparatus was used to assess learning and spatial memory. Nissl staining and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) tests were also performed for the histopathological analysis of the hippocampus. Antiapoptotic genes were studied, using the Western blot technique. The water maze test showed memory improvement following treatment with CoQ10 and coadministration of CoQ10 + EMF. The Nissl staining and TUNEL tests indicated a decline in necrotic and apoptotic cell count following treatment with CoQ10 and coadministration of CoQ10 + EMF. The Western blot study indicated the upregulation of antiapoptotic genes in treatment with CoQ10, as well as coadministration. Also, treatment with EMF had no significant effects on reducing damage induced by TMT in the hippocampus. According to the results, EMF had no significant neuroprotective effects in comparison with CoQ10 on hippocampal injury in mice. Nevertheless, coadministration of EMF and CoQ10 could improve the neuroprotective effects of CoQ10.

Quetiapine and repetitive transcranial magnetic stimulation ameliorate depression-like behaviors and up-regulate the proliferation of hippocampal-derived neural stem cells in a rat model of depression: The involvement of the BDNF/ERK signal pathway

Quetiapine (QUE) and repetitive transcranial magnetic stimulation (rTMS) have been considered to be possible monotherapies for depression or adjunctive therapies for the treatment of the resistant depression, but the underlying mechanisms remain unclear. The present study aimed to assess the effects of combined QUE and rTMS treatment on depressive-like behaviors, hippocampal proliferation, and the in vivo and in vitro expressions of phosphorylated extracellular signal-regulated protein kinase (pERK1/2) and brain-derived neurotrophic factor (BDNF) in male Sprague-Dawley rats. The administration of QUE and rTMS was determined not only to reverse the depressive-like behaviors of rats exposed to chronic unpredictable stress (CUS) but also to restore the protein expressions of pERK1/2 and BDNF and cell proliferation in the hippocampus. Additionally, QUE and rTMS promoted the proliferation and increased the expression of pERK1/2 and BDNF in hippocampal-derived neural stem cells (NSCs), and these effects were abolished by U0126. Taken together, these results suggest that the antidepressive-like effects of QUE and rTMS might be related to the activation of the BDNF/ERK signaling pathway and the up-regulation of cell proliferation in the hippocampus.

The effect of repetitive transcranial magnetic stimulation on fear extinction in rats

Facilitating fear extinction is clinically important to improve the efficacy of current exposure therapies for the treatment of anxiety disorders, such as post-traumatic stress disorder (PTSD). The aim of this study was to determine if repeated transcranial magnetic stimulation (rTMS) facilitates fear extinction in rats, especially when paired with exposure to a conditioned stimulus (CS). Thirty-five rats were conditioned to a tone CS by pairing the tone with an electric foot shock as an aversive unconditioned stimulus (US). We assessed the effects of 10 Hz rTMS before fear extinction (experiment 1) and rTMS paired with CS during extinction (experiment 2) on the following day. Fear responses of the rats were estimated using the level of freezing upon tone stimulus and were compared between the rTMS and corresponding sham groups. The rats treated with rTMS before fear extinction showed no difference in freezing time when compared with the sham group. However, the rats treated with rTMS paired with CS during extinction showed significantly less freezing behavior than the sham group, and this enhancement of fear extinction remained after 24 h without further stimulation. This finding suggests that high-frequency rTMS paired with trauma-reminding stimuli enhances fear extinction and that rTMS in conjunction with exposure therapy is potentially useful for facilitating extinction memory in the treatment of PTSD.

Is rTMS an effective therapeutic strategy that can be used to treat anxiety disorders?

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive procedure whereby a pulsed magnetic field stimulates electrical activity in the brain. Anxiety disorders are the most common of all mental health problems for which effective, mechanism-based treatments remain elusive. Consequently, more advanced non-invasive therapeutic methods are required. A possible method to modulate brain activity and potentially viable for use in clinical practice is rTMS. Here, we focus on the main findings of rTMS from animal models of anxiety and the experimental advances of rTMS that may become a viable clinical application to treat anxiety disorders, one of the most common causes of disability in the workplace in the world. Key advances in combining rTMS with neuroimaging technology may aid such future developments. This article is part of a Special Issue entitled 'Anxiety and Depression'.

A rat model for measuring the effectiveness of transcranial direct current stimulation using fMRI

Transcranial direct current stimulation (tDCS) is one of the noteworthy noninvasive brain stimulation techniques, but the mechanism of its action remains unclear. With the aim of clarifying the mechanism, we developed a rat model and measured its effectiveness using fMRI. Carbon fiber electrodes were placed on the top of the head over the frontal cortex as the anode and on the neck as the cathode. The stimulus was 400- or 40-μA current applied for 10 min after a baseline recording under an anesthetized condition. The 400-μA stimulation significantly increased signal intensities in the frontal cortex and nucleus accumbens. This suggests anodal tDCS over the frontal cortex induces neuronal activation in the frontal cortex and in its connected brain region.

Site-specific antidepressant effects of repeated subconvulsive electrical stimulation: potential role of brain-derived neurotrophic factor

BACKGROUND

Electroconvulsive therapy (ECT) is a very effective treatment for major depression. This method involves robust nonfocal stimulation of the brain and can normalize both neurochemical alterations and depressive behavior in animal models. We hypothesized that short stimulation sessions of specific reward-related brain sites might induce similar effects.

METHODS

In the present study we compared behavioral and neurochemical effects produced by ECT and by repeated stimulation of reward-related brain sites, in a widely used rat model for depressive behavior induced by chronic mild stress (CMS). Different groups of rats received 10 sessions of either electroconvulsive shocks or subconvulsive electrical stimulation (SCES) of specific brain sites with an implanted electrode. The SCES temporal parameters were similar to those used in transcranial magnetic stimulation studies in humans. A battery of behavioral tests and measurements of brain-derived neurotrophic factor (BDNF) levels were used to assess the effectiveness of these treatments relative to sham treatments.

RESULTS

Repeated SCES of either the nucleus accumbens (NAC) or the ventral but not the dorsal prelimbic cortex (PLC) reversed the main behavioral deficit and the reduction of BDNF levels in the hippocampus that were induced by CMS. The ECT was more effective because it also normalized a behavioral deficit associated with anxiety but produced a learning and memory impairment.

CONCLUSIONS

This study implicates the ventral PLC and the NAC in the pathophysiology of depressive behavior and suggests that local intermittent SCES can induce an antidepressant effect similar to that of ECT, without the cognitive impairment caused by the convulsive treatment.