Preliminary comparison of behavioral and biochemical effects of chronic transcranial magnetic stimulation and electroconvulsive shock in the rat

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.

Transcranial magnetic stimulation and ketamine: implications for combined treatment in depression

Drug-resistant mental disorders, particularly treatment-resistant depression, pose a significant medical and social problem. To address this challenge, modern psychiatry is constantly exploring the use of novel treatment methods, including biological treatments, such as transcranial magnetic stimulation (TMS), and novel rapid-acting antidepressants, such as ketamine. While both TMS and ketamine demonstrate high effectiveness in reducing the severity of depressive symptoms, some patients still do not achieve the desired improvement. Recent literature suggests that combining these two methods may yield even stronger and longer-lasting results. This review aims to consolidate knowledge in this area and elucidate the potential mechanisms of action underlying the increased efficacy of combined treatment, which would provide a foundation for the development and optimization of future treatment protocols.

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.

Mouse repeated electroconvulsive seizure (ECS) does not reverse social stress effects but does induce behavioral and hippocampal changes relevant to electroconvulsive therapy (ECT) side-effects in the treatment of depression

Electroconvulsive therapy (ECT) is an effective treatment for depression, but can have negative side effects including amnesia. The mechanisms of action underlying both the antidepressant and side effects of ECT are not well understood. An equivalent manipulation that is conducted in experimental animals is electroconvulsive seizure (ECS). Rodent studies have provided valuable insights into potential mechanisms underlying the antidepressant and side effects of ECT. However, relatively few studies have investigated the effects of ECS in animal models with a depression-relevant manipulation such as chronic stress. In the present study, mice were first exposed to chronic social stress (CSS) or a control procedure for 15 days followed by ECS or a sham procedure for 10 days. Behavioral effects were investigated using an auditory fear conditioning (learning) and expression (memory) test and a treadmill-running fatigue test. Thereafter, immunohistochemistry was conducted on brain material using the microglial marker Iba-1 and the cholinergic fibre marker ChAT. CSS did not increase fear learning and memory in the present experimental design; in both the control and CSS mice ECS reduced fear learning and fear memory expression. CSS induced the expected fatigue-like effect in the treadmill-running test; ECS induced increased fatigue in CSS and control mice. In CSS and control mice ECS induced inflammation in hippocampus in terms of increased expression of Iba-1 in radiatum of CA1 and CA3. CSS and ECS both reduced acetylcholine function in hippocampus as indicated by decreased expression of ChAT in several hippocampal sub-regions. Therefore, CSS increased fatigue and reduced hippocampal ChAT activity and, rather than reversing these effects, a repeated ECS regimen resulted in impaired fear learning-memory, increased fatigue, increased hippocampal Iba-1 expression, and decreased hippocampal ChAT expression. As such, the current model does not provide insights into the mechanism of ECT antidepressant function but does provide evidence for pathophysiological mechanisms that might contribute to important ECT side-effects.

Improvement of spatial learning by facilitating large-conductance calcium-activated potassium channel with transcranial magnetic stimulation in Alzheimer's disease model mice

Transcranial magnetic stimulation (TMS) is fragmentarily reported to be beneficial to Alzheimer's patients. Its underlying mechanism was investigated. TMS was applied at 1, 10 or 15 Hz daily for 4 weeks to young Alzheimer's disease model mice (3xTg), in which intracellular soluble amyloid-β is notably accumulated. Hippocampal long-term potentiation (LTP) was tested after behavior. TMS ameliorated spatial learning deficits and enhanced LTP in the same frequency-dependent manner. Activity of the large conductance calcium-activated potassium (Big-K; BK) channels was suppressed in 3xTg mice and recovered by TMS frequency-dependently. These suppression and recovery were accompanied by increase and decrease in cortical excitability, respectively. TMS frequency-dependently enhanced the expression of the activity-dependently expressed scaffold protein Homer1a, which turned out to enhance BK channel activity. Isopimaric acid, an activator of the BK channel, magnified LTP. Amyloid-β lowering was detected after TMS in 3xTg mice. In 3xTg mice with Homer1a knocked out, amyloid-β lowering was not detected, though the TMS effects on BK channel and LTP remained. We concluded that TMS facilitates BK channels both Homer1a-dependently and -independently, thereby enhancing hippocampal LTP and decreasing cortical excitability. Reduced excitability contributed to amyloid-β lowering. A cascade of these correlated processes, triggered by TMS, was likely to improve learning in 3xTg mice.

Effects of electroconvulsive seizures on depression-related behavior, memory and neurochemical changes in Wistar and Wistar-Kyoto rats

BACKGROUND

Investigations in healthy outbred rat strains have shown a potential role for brain-derived neurotrophic factor (BDNF) and the hypothalamic-pituitary-adrenal (HPA) axis in the antidepressant and memory side effects of electroconvulsive therapy (ECT, or ECS in animals). The Wistar-Kyoto (WKY) rat strain is used as a genetic model of depression yet no studies to date have directly compared the impact of ECS on the WKY strain to its healthy outbred control (Wistar).

OBJECTIVE

The objective of this study is to examine behavioral (antidepressant and retrograde memory) and neurochemical (BDNF and HPA axis) changes immediately (1day) and at a longer delay (7days) after repeated ECS (5 daily administrations) in WKY and Wistar rats.

METHODS

Male Wistar and WKY rats received 5days of repeated ECS or sham treatment and were assessed 1 and 7days later for 1) depression-like behavior and mobility; 2) retrograde memory; and 3) brain BDNF protein, brain corticotropin-releasing factor (CRF) and plasma corticosterone levels.

RESULTS

Both strains showed the expected antidepressant response and retrograde memory impairments at 1day following ECS, which were sustained at 7days. In addition, at 1day after ECS, Wistar and WKY rats showed similar elevations in brain BDNF and extra-hypothalamic CRF and no change in plasma corticosterone. At 7days after ECS, Wistar rats showed sustained elevations of brain BDNF and CRF, whereas WKY rats showed a normalization of brain BDNF, despite sustained elevations of brain CRF.

CONCLUSIONS

The model of 5 daily ECS was effective at eliciting behavioral and neurochemical changes in both strains. A temporal association was observed between brain CRF levels, but not BDNF, and measures of antidepressant effectiveness of ECS and retrograde memory impairments suggesting that extra-hypothalamic CRF may be a potential important contributor to these behavioral effects after repeated ECS/ECT.

Translational neuromodulation: approximating human transcranial magnetic stimulation protocols in rats

OBJECTIVE

Transcranial magnetic stimulation (TMS) is a well-established clinical protocol with numerous potential therapeutic and diagnostic applications. Yet, much work remains in the elucidation of TMS mechanisms, optimization of protocols, and in development of novel therapeutic applications. As with many technologies, the key to these issues lies in the proper experimentation and translation of TMS methods to animal models, among which rat models have proven popular. A significant increase in the number of rat TMS publications has necessitated analysis of their relevance to human work. We therefore review the essential principles for the approximation of human TMS protocols in rats as well as specific methods that addressed these issues in published studies.

MATERIALS AND METHODS

We performed an English language literature search combined with our own experience and data. We address issues that we see as important in the translation of human TMS methods to rat models and provide a summary of key accomplishments in these areas.

RESULTS

  An extensive literature review illustrated the growth of rodent TMS studies in recent years. Current advances in the translation of single, paired-pulse, and repetitive stimulation paradigms to rodent models are presented. The importance of TMS in the generation of data for preclinical trials is also highlighted.

CONCLUSIONS

Rat TMS has several limitations when considering parallels between animal and human stimulation. However, it has proven to be a useful tool in the field of translational brain stimulation and will likely continue to aid in the design and implementation of stimulation protocols for therapeutic and diagnostic applications.

Selectively bred rodents as models of depression and anxiety

Stress related diseases such as depression and anxiety have a high degree of co morbidity, and represent one of the greatest therapeutic challenges for the twenty-first century. The present chapter will summarize existing rodent models for research in psychiatry, mimicking depression- and anxiety-related diseases. In particular we will highlight the use of selective breeding of rodents for extremes in stress-related behavior. We will summarize major behavioral, neuroendocrine and neuronal parameters, and pharmacological interventions, assessed in great detail in two rat model systems: The Flinders Sensitive and Flinders Resistant Line rats (FSL/FRL model), and rats selectively bred for high (HAB) or low (LAB) anxiety related behavior (HAB/LAB model). Selectively bred rodents also provide an excellent tool in order to study gene and environment interactions. Although it is generally accepted that genes and environmental factors determine the etiology of mental disorders, precise information is limited: How rigid is the genetic disposition? How do genetic, prenatal and postnatal influences interact to shape adult disease? Does the genetic predisposition determine the vulnerability to prenatal and postnatal or adult stressors? In combination with modern neurobiological methods, these models are important to elucidate the etiology and pathophysiology of anxiety and affective disorders, and to assist in the development of new treatment paradigms.

Increase in cortical pyramidal cell excitability accompanies depression-like behavior in mice: a transcranial magnetic stimulation study

Clinical evidence suggests that cortical excitability is increased in depressives. We investigated its cellular basis in a mouse model of depression. In a modified version of forced swimming (FS), mice were initially forced to swim for 5 consecutive days and then were treated daily with repetitive transcranial magnetic stimulation (rTMS) or sham treatment for the following 4 weeks without swimming. On day 2 through day 5, the mice manifested depression-like behaviors. The next and last FS was performed 4 weeks later, which revealed a 4 week maintenance of depression-like behavior in the sham mice. In slices from the sham controls, excitability in cingulate cortex pyramidal cells was elevated in terms of membrane potential and frequencies of spikes evoked by current injection. Depolarized resting potential was shown to depend on suppression of large conductance calcium-activated potassium (BK) channels. This BK channel suppression was confirmed by measuring spike width, which depends on BK channels. Chronic rTMS treatment during the 4 week period significantly reduced the depression-like behavior. In slices obtained from the rTMS mice, normal excitability and BK channel activity were recovered. Expression of a scaffold protein Homer1a was reduced by the FS and reversed by rTMS in the cingulate cortex. Similar recovery in the same behavioral, electrophysiological, and biochemical features was observed after chronic imipramine treatment. The present study demonstrated that manifestation and disappearance of depression-like behavior are in parallel with increase and decrease in cortical neuronal excitability in mice and suggested that regulation of BK channels by Homer1a is involved in this parallelism.

Paroxetine pretreatment does not change the effects induced in the rat cortical beta-adrenergic receptor system by repetitive transcranial magnetic stimulation and electroconvulsive shock

Repetitive transcranial magnetic stimulation (rTMS) has been proposed as a clinically effective antidepressant treatment, but meta-analysis suggests that its efficacy is marginal. We investigated whether the administration of rTMS together with paroxetine would enhance its effects on the beta-adrenergic system of the rat. We compared our results with the effects of electroconvulsive shock therapy (ECS). The experiment was performed for 12 d on male Wistar rats that received a physical treatment of either rTMS (B=1.4 T, f=10 Hz, 300 s) or ECS (I=130 mA, f=50 Hz, t=500 ms), preceded by sterile water or paroxetine (10 mg/kg i.p. 30 min earlier). All rats were decapitated 24 h after the final treatment. Cyclic AMP (cAMP) was measured in cortical slices prelabelled with [3H]adenine and stimulated with noradrenaline. beta-adrenoceptor parameters (Bmax and KD) were assessed in the P2 fraction of cortical homogenates using [3H]CGP 12177 as a ligand. ECS resulted in down-regulation of both the cAMP response and beta-adrenoceptor density, while rTMS depressed only the responsiveness of the cAMP-generating system. Paroxetine, which was only effective in dampening the cAMP response, did not change the effects of either physical treatment. The data suggest that any possible interaction between paroxetine and rTMS or ECS does not involve the beta-adrenergic mechanisms.

Anxiolytic effects of transcranial magnetic stimulation--an alternative treatment option in anxiety disorders?

In contrast to major depression, only few studies are available so far on the effects of repetitive transcranial magnetic stimulation (rTMS) in anxiety disorders. In order to summarise available data concerning the putative anxiolytic action of repetitive rTMS, a systematic literature review was carried out. Although interpretation of the results is difficult because of a large variety of used treatment protocols and the lack of a placebo-controlled design in the majority of studies, there is evidence for anxiolytic action of rTMS both from preclinical trials and studies in humans. Based on the idea of interhemispheric imbalance and/or deficits in cortico-limbic control as a model for human anxiety, inhibitory rTMS of the prefrontal cortex has been shown to exert beneficial effects in a number of studies in healthy subjects, patients with PTSD and panic disorder. However, to further elucidate the putative anxiolytic action of rTMS in patients with anxiety disorders future studies have to be conducted addressing in particular the limitations of the studies mentioned above.

Repetitive transcranial magnetic stimulation does not influence immunological HL-60 cells and neuronal PC12 cells

BACKGROUND

Transcranial magnetic stimulation (TMS) is a non-invasive method used in medical applications such as brain mapping or as a therapeutic tool in neurological and psychiatric disorders because it can stimulate defined regions of the brain without anaesthesia.

METHODS

The action of repetitive transcranial magnetic stimulation (rTMS) on HL-60 and PC12 cells has been investigated. The cells have been stimulated in vitro with different number of pulses (75 - 1250), different intensities (10, 20 and 40%) and different frequencies (0.25, 1 and 10 Hz) by using a double coil (2x70 mm) connected to the 'Magstim rapid'. At selected time points after treatment the following endpoints have been determined: viability, cyclic AMP (cAMP) and heat shock protein 72 (Hsp72) (HL-60 cells), and viability, cAMP, dopamine and noradrenaline (PC12 cells). Viability was measured with the alamarBlue assay, whereas cAMP, Hsp72, dopamine and noradrenaline were determined with enzyme-linked immunosorbent assay (ELISA).

RESULTS

In both cell lines viability was not influenced by rTMS treatment, the same was true for the cytosolic cAMP concentration. In HL-60 cells rTMS treatment did not change the Hsp72 content, also a protective effect of rTMS treatment on cell viability before toxic H(2)O(2) treatment was not observed. After high potassium treatment the release of the two neurotransmitters dopamine and noradrenaline in PC12 cells was enhanced 15- and 5-fold, respectively, but after rTMS treatment no change in the release of the two neurotransmitters was observed.

CONCLUSIONS

In two mammalian cell lines rTMS treatment in a variety of exposure conditions does not influence any of the measured parameters.

Sex differences in antidepressant-like effect of chronic repetitive transcranial magnetic stimulation in rats

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive neurophysiological technique. Pre-clinical and clinical studies supported that rTMS might have antidepressant effects. However, whether antidepressant effect of chronic rTMS is gender-dependent is still unknown. In this study, male and female Wistar rats received 10-day rTMS (4 trains of 15 Hz; 200 stimuli/day; 1.0 T) or control condition, and then were subjected to the forced-swim test (FST). We found that female rats consistently showed higher activity levels than males in FST and revealed the significant effects of gender and rTMS as well as the interaction of gender and rTMS. The result suggested the antidepressant-like effects of chronic rTMS on behavioral components in FST are gender-dependent. The gender discrepancy related to rTMS should not be neglected in antidepressant treatment of rTMS.

Repetitive transcranial magnetic stimulation protects hippocampal plasticity in an animal model of depression

Despite its therapeutic success in treating mood-related disorders, little is known about the mechanism by which repetitive transcranial magnetic stimulation (rTMS) alters physiological responses of neurons. Using the forced swim test (FST) in rats as a model of depression, we tested the protective effect of rTMS on synaptic plasticity, specifically, on the induction of hippocampal long-term potentiation (LTP). Male Sprague-Dawley rats were subjected to FST to induce immobility, a behavioral symptom of depression. They were subsequently treated with one of the three conditions: rTMS (rTMS: 1000 stimuli at 10Hz), sham rTMS (SHAM: acoustic stimulation only), or an antidepressant drug, fluoxetine (FLX: 10mg/kg, i.p.) for 7 days. There was a significant difference in immobility time between rTMS and SHAM groups after 7 days of treatment, but not after a single day. Following the second swim test on day 7, they were anesthetized and LTP was induced in vivo in the perforant path-dentate gyrus synapses. Another group (NAIVE) that had received no prior treatment was used as a control for LTP. The SHAM or FLX group exhibited little signs of LTP induction. On the contrary, the rTMS and NAIVE group showed a significant increase in field excitatory postsynaptic potentials after LTP induction. These results show that rTMS has an antidepressant-like effect after a relatively short period of treatment, and this effect might be mediated by a cellular process that can potentially reverse the impaired synaptic efficacy caused by the forced swim procedure.

Rapid-rate transcranial magnetic stimulation of animal auditory cortex impairs short-term but not long-term memory formation

Bilateral rapid-rate transcranial magnetic stimulation (rTMS) of gerbil auditory cortex with a miniature coil device was used to study short-term and long-term effects on discrimination learning of frequency-modulated tones. We found previously that directional discrimination of frequency modulation (rising vs. falling) relies on auditory cortex processing and that formation of its memory depends on local protein synthesis. Here we show that, during training over 5 days, certain rTMS regimes contingent on training had differential effects on the time course of learning. When rTMS was applied several times per day, i.e. four blocks of 5 min rTMS each followed 5 min later by a 3-min training block and 15-min intervals between these blocks (experiment A), animals reached a high discrimination performance more slowly over 5 days than did controls. When rTMS preceded only the first two of four training blocks (experiment B), or when prolonged rTMS (20 min) preceded only the first block, or when blocks of experiment A had longer intervals (experiments C and D), no significant day-to-day effects were found. However, in experiment A, and to some extent in experiment B, rTMS reduced the within-session discrimination performance. Nevertheless the animals learned, as demonstrated by a higher performance the next day. Thus, our results indicate that rTMS treatments accumulate over a day but not strongly over successive days. We suggest that rTMS of sensory cortex, as used in our study, affects short-term memory but not long-term memory formation.

Transcranial magnetic stimulation and chronic pain: current status

OBJECTIVE

To examine evidence suggesting a potential role for transcranial magnetic stimulation (TMS) in the treatment of chronic pain.

CONCLUSION

Chronic pain is characterized by brain changes that can reasonably be presumed to be associated with hyperalgesia, as occurs with neuropathic changes in the periphery. TMS has the ability to induce plastic changes in the cortex at the site of stimulation and at connected sites, including the spinal cord. It also has the ability to influence the experience of experimental/acute pain. In studies of TMS in chronic pain, there is some evidence that temporary relief can be achieved in a proportion of sufferers. Chronic pain is common. Current treatments are often ineffective and complicated by side-effects. Work to this point is encouraging, but systematic assessment of stimulation parameters is necessary if TMS is to achieve a role in the treatment of chronic pain. Maintenance TMS is currently provided in relapsing major depression and may be a useful model in chronic pain management.

Anxiolytic suppression of repetitive transcranial magnetic stimulation-induced anxiety in the rats

Repetitive transcranial magnetic stimulation (rTMS) is effective for treatment of several psychiatric disorders such as depression and anxiety disorder. However, some reports suggest that rTMS induced anxiety in normal volunteers. Consistent with this observation, we have reported that chronic rTMS induces anxiety in normal rats which was suppressed by chronic treatment, but not acute paroxetine treatment. The current study evaluates rTMS as animal model of anxiety by investigating the effect of rTMS on anxiety behaviors and the ability of standard anxiolytics to block expression of these behaviors. We found that 10-day rTMS induced anxiety in normal rats, as evidenced by expression of anxiety behaviors in the elevated plus-maze. This anxiety was suppressed by acute treatment with diazepam, alprazolam, or buspirone suggesting that chronic rTMS treatment provides a good animal model for anxiety.

Transcranial magnetic stimulation effects on one-trial learning and response to anxiogenic stimuli in adult male rats

Transcranial magnetic stimulation (TMS) is a relatively new technique for inducing small, localized, and reversible changes in living brain tissue and has been suggested to have antidepressant properties in humans and animal models of depression. Memory function generally has been found to be unaffected by TMS, although some studies have raised the possibility of memory interference from TMS. Additionally, there have been indirect indications that TMS may possess anxiolytic features. This study examines the effects of TMS in animal models of one-trial learning and anxiety. In this study, short-term treatment with TMS compared with identically handled animals not given TMS in adult rats resulted in no significant differences in memory as assessed both by a one-time learning paradigm and by components of an elevated-plus maze task, that TMS does not impair memory as assessed by these tasks. In addition, no changes were found in anxiety-like behavior on the elevated plus maze task. In summary, these findings support previous reports that TMS does not interfere with memory function. There was no evidence of an anxiolytic response from TMS in rats as assessed by the elevated plus maze test.

Repetitive transcranial magnetic stimulation : does it have potential in the treatment of depression?

Transcranial magnetic stimulation (TMS) has become a major research tool in experimental clinical neurophysiology as a result of its potential to noninvasively and focally stimulate cortical brain regions. Currently, studies are being conducted to investigate whether repetitive TMS (rTMS)-mediated modulation of cortical function may also provide a therapeutic approach in neurological and psychiatric disorders. Preclinical findings have shown that prefrontal rTMS can modulate the function of fronto-limbic circuits, which is reversibly altered in major depression. rTMS has also been found to exert effects on neurotransmitter systems involved in the pathophysiology of major depression (e.g. stimulates subcortical dopamine release and acts on the hypothalamic pituitary adrenal axis, which is dysregulated in depression). To date, numerous open and controlled clinical trials with widely differing stimulation parameters have explored the antidepressant potential of rTMS. Though conducted with small sample sizes, the majority of the controlled trials demonstrated significant antidepressant effects of active rTMS compared with a sham condition. Effect sizes, however, varied from modest to substantial, and the patient selection focused on therapy-resistant cases. Moreover, the average treatment duration was approximately 2 weeks, which is short compared with other antidepressant interventions. Larger multicentre trials, which would be mandatory to demonstrate the antidepressant effectiveness of rTMS, have not been conducted to date.A putative future application of rTMS may be the treatment of patients who did not tolerate or did not respond to antidepressant pharmacotherapy before trying more invasive strategies such as electroconvulsive therapy and vagus nerve stimulation. Theoretically, rTMS may be also applied early in the course of disease in order to speed up and increase the effects of antidepressant pharmacotherapy. However, this application has not been a focus of clinical trials to date. Research efforts should be intensified to further investigate the effectiveness of rTMS as an antidepressant intervention and to test specific applications of the technique in the treatment of depressive episodes.

Putative common pathways in therapeutic brain stimulation for affective disorders

Brain stimulation methods in the treatment of affective disorder are electroconvulsive therapy (ECT), transcranial magnetic stimulation (TMS), vagus nerve stimulation (VNS), and deep brain stimulation (DBS). Clinically, ECT is considered the strongest remedy in the treatment of severe depression, especially depression with psychotic features, and in the elderly. TMS, despite positive reports, is somewhat more controversial. VNS has, so far, only been used in treatment-resistant depression with limited results. DBS may be of potential use in rare cases of treatment-resistant cases of affective disorder. This article highlights the similarities and differences between the four stimulation methods. The main difference is the seizures necessary in ECT. A stronger involvement of the hippocampus following experimental seizures compared with effects in that region induced by TMS and VNS might explain the consistent findings of the superiority of ECT in the most severe cases of affective disorder.

Safety aspects of chronic low-frequency transcranial magnetic stimulation based on localized proton magnetic resonance spectroscopy and histology of the rat brain

Because repetitive transcranial magnetic stimulation (rTMS) is capable of inducing lasting alterations of cortical excitability, it represents a promising therapeutic tool in several neuropsychiatric disorders. However, rTMS, especially when applied chronically, may cause harmful effects in the stimulated tissue. To study the safety of chronic rTMS we used a novel small stimulation coil, which was specially designed to treat rats, and investigated brain tissue using in vivo localized proton magnetic resonance spectroscopy (MRS) and post mortem histological analysis. Histology was based on a modified stereology method in combination with immunohistochemistry applying antibodies against OX-6, OX-42, ED, and GFAP to detect any microglial and/or astrocytic activation 48 h after the last TMS session. Conscious rats were treated with a daily suprathreshold rTMS regimen of 1000 stimuli applied on 5 consecutive days at a frequency of 1 Hz. In comparison with control animals receiving magnetic stimulation over the lumbar spine, quantitative evaluations of cerebral metabolite concentrations by proton MRS revealed no significant alterations of N-acetyl-aspartate, creatine and phosphocreatine, choline-containing compounds, myo-inositol, glucose and lactate after chronic rTMS. Similarly to the in vivo results, post mortem histology revealed no changes in microglial and astrocytic activation after rTMS. In conclusion, these data provide support for the safety of chronic rTMS. However, they do not exclude acute changes on neurotransmitters systems or other physiologic responses during or directly after the rTMS treatment.

Duration of transcranial magnetic stimulation effects on the neuroendocrine stress response and coping behavior of adult male rats

BACKGROUND

Transcranial magnetic stimulation (TMS) is a relatively novel, noninvasive method of altering cerebral electrophysiological activity that produces localized and reversible changes in brain tissue. TMS has been shown to have antidepressant properties in both human trials and animal models. Additionally, TMS may alter hypothalamic-pituitary-adrenal (HPA) function resulting in a normalized dexamethasone suppression test in some depressed subjects and an attenuated stress-induced increase in adrenocorticotropic hormone (ACTH) and a possibly lowered basal corticosterone (CORT) concentration in rats. This research was undertaken to investigate the duration of these behavioral and neuroendocrine effects of TMS in rats.

METHODS

In this study, serum ACTH, CORT, testosterone, and luteinizing hormone (LH) concentrations following and immobility parameters during a forced-swim test in adult male rats were evaluated immediately and 1, 3, 5, 7, and 14 days subsequent to a 10-day course of once-daily TMS or sham application.

RESULTS

TMS animals had significantly higher ACTH and CORT concentrations immediately following the 10-day course of TMS compared to sham controls. Higher CORT concentrations (numerically but not statistically) were displayed by TMS-treated animals 1 and 3 days after the 10-day application course, although there were no significant differences between TMS and sham groups for ACTH or CORT levels 1, 3, 5, 7, and 14 days following application of sham or TMS. No significant differences were found between groups for serum testosterone and LH levels at any given collection time point. Immobility time, a measure of coping ability that is predictive of human antidepressant response, was significantly decreased (i.e., time spent actively swimming was significantly increased) immediately after the 10-day course of TMS. Thereafter, a nonsignificant numerical trend at 1 and 3 days after TMS application for immobility times between the TMS and control groups was observed (TMS<control values). No significant differences in immobility between TMS and control animals were found at subsequent time points.

CONCLUSIONS

The present findings suggest that the HPA stress axis is significantly altered immediately following a 10-day course of TMS in that a significant increase in ACTH and CORT levels in TMS-treated animals corresponded to a significant decrease in immobility times in the forced-swim test compared to control values. Finally, based upon the obtained results, the TMS effects in rats appear to be of relatively short duration.

Chronic psychosocial stress and concomitant repetitive transcranial magnetic stimulation: effects on stress hormone levels and adult hippocampal neurogenesis

BACKGROUND

Repetitive transcranial magnetic stimulation is increasingly used as a therapeutic tool in psychiatry and has been demonstrated to attenuate the activity of the stress hormone system. Stress-induced structural remodeling in the adult hippocampus may provide a cellular basis for understanding the impairment of neural plasticity in depressive illness. Accordingly, reversal of structural remodeling might be a desirable goal for antidepressant therapy. The present study investigated the effect of chronic psychosocial stress and concomitant repetitive transcranial magnetic stimulation treatment on stress hormone regulation and hippocampal neurogenesis.

METHODS

Adult male rats were submitted to daily psychosocial stress and repetitive transcranial magnetic stimulation (20 Hz) for 18 days. Cell proliferation in the dentate gyrus was quantified by using BrdU immunohistochemistry, and both the proliferation rate of progenitors and the survival rate of BrdU-labeled cells were evaluated. To characterize the activity of the hypothalamic-pituitary-adrenocortical system, plasma corticotropin and corticosterone concentrations were measured.

RESULTS

Chronic psychosocial stress resulted in a significant increase of stress hormone levels and potently suppressed the proliferation rate and survival of the newly generated hippocampal granule cells. Concomitant repetitive transcranial magnetic stimulation treatment normalized the stress-induced elevation of stress hormones; however, despite the normalized activity of the hypothalamic-pituitary-adrenocortical system, the decrement of hippocampal cell proliferation was only mildly attenuated by repetitive transcranial magnetic stimulation, while the survival rate of BrdU-labeled cells was further suppressed by the treatment.

CONCLUSIONS

These results support the notion that attenuation of the hypothalamic-pituitary-adrenocortical system is an important mechanism underlying the clinically observed antidepressant effect of repetitive transcranial magnetic stimulation, whereas this experimental design did not reveal beneficial effects of repetitive transcranial magnetic stimulation on adult hippocampal neurogenesis.

Effects of different frequencies of transcranial magnetic stimulation (TMS) on the forced swim test model of depression in rats

BACKGROUND

Repetitive transcranial magnetic stimulation has been demonstrated in humans as well as in animal models to have an antidepressant effect, but the optimal frequency of stimulation is not known. We examined this question in a rat model of depression.

METHODS

Young male Sprague-Dawley rats were allocated to two placebo (restraint and sham transcranial magnetic stimulation), one active control (imipramine), and four transcranial magnetic stimulation groups at 1, 5, 15 and 25 Hz and 1000 stimuli each. The Porsolt Swim Test was performed on day 1 (experiment 1). In an extension (experiment 2), the treatments were repeated on days 2 through 5, and the Swim Test repeated on days 3, 5, and 7.

RESULTS

After one treatment session, all transcranial magnetic stimulation groups had significantly reduced immobility times compared with sham stimulation (p =.000), but the higher frequencies (15 and 25 Hz) did not differ significantly from lower (1 and 5 Hz) frequencies. After three sessions, all transcranial magnetic stimulation groups were different from placebo, and the rapid transcranial magnetic stimulation groups had lower immobility times than the slow transcranial magnetic stimulation groups (p =.035). After five sessions, only 15- and 25-Hz groups were different from control, and on day 7, only the 25-Hz group had reduced immobility. There was an overall difference between fast and slow transcranial magnetic stimulation (p =.010), and 1 Hz was different from the other three transcranial magnetic stimulation conditions (p =.016).

CONCLUSIONS

Repetitive transcranial magnetic stimulation reduces immobility time in the Forced Swim Test model of depression, suggesting an antidepressant effect, which is evident at a range (1-25 Hz) of frequencies. With repeated administration, the findings suggest that the antidepressant effect of the higher frequencies, as for imipramine, is likely to be sustained, although the model used for this (i.e., repeating the Swim Test) requires further validation.

Transcranial magnetic stimulation (TMS) effects on testosterone, prolactin, and corticosterone in adult male rats

BACKGROUND

Transcranial magnetic stimulation is a relatively new technique for inducing small, localized, and reversible changes in living brain tissue. Although transcranial magnetic stimulation generally results in no immediate changes in plasma corticosterone, prolactin, and testosterone, it normalizes the dexamethasone suppression test in some depressed subjects and has been shown to attenuate stress-induced increases in adrenocorticotropic hormone in rats.

METHODS

In this study, serum corticosterone and testosterone concentrations were assayed in male rats immediately and 3, 6, 9, 12, 24, and 48 hours following a single transcranial magnetic stimulation or sham application. Serum prolactin concentrations were determined immediately and 2 hours following a one-time application of either transcranial magnetic stimulation or sham.

RESULTS

Transcranial magnetic stimulation animals displayed significantly lower corticosterone concentrations at 6 and 24 hours following a single application compared with sham-control values. Transcranial magnetic stimulation also resulted in lower corticosterone concentrations numerically but not statistically in transcranial magnetic stimulation animals immediately after application (p =.089). No significant differences were found between groups for serum prolactin or testosterone levels at any given collection time point.

CONCLUSIONS

These findings 1) suggest that transcranial magnetic stimulation alters the hypothalamic-pituitary-adrenal stress axis and 2) provide time-course data for the implications of the hormonal mechanism that may be involved in the actions of transcranial magnetic stimulation.

Effect of repetitive transcranial magnetic stimulation on forced swimming test

Repetitive transcranial magnetic stimulation (rTMS) and electroconvulsive shock (ECS) have been shown to affect mood in health and disease. Evidence to date has demonstrated an antidepressant potential for rTMS and electroconvulsive therapy (ECT). The present experiment, aimed at comparing the effects of ECS and rTMS in rats, employed one test used for screening of antidepressant activity: the forced swimming test (FST). In this study, the authors investigated whether chronic rTMS influenced active behavior in the rat FST, similar to ECS. Male Wistar rats received rTMS treatment daily, for 10 days as is commonly used for ECT treatment. Control rats received sham treatment by placing the stimulation coil in a perpendicular position to the rat's head. Passing a current through earclip electrodes for 1 s induced ECS. The control animals were treated identically, but current was not applied. The FST was carried out 24 h after the last rTMS or ECS. The immobility time in the FST was not significantly affected by rTMS and ECS for 1 day. The immobility time in the FST was significantly shortened at rTMS and ECS for 10 days. Chronic treatment with rTMS, similar to chronic treatment with ECS, decreased the immobility time in the FST. These results indicate that chronic treatment with rTMS might have antidepressant effect similar to chronic treatment with ECS.

Transcranial magnetic stimulation in the treatment of mood disorder: a review and comparison with electroconvulsive therapy

OBJECTIVE

To review repetitive transcranial magnetic stimulation (rTMS) as a mode of therapy for depression.

METHOD

The following aspects of rTMS were reviewed and compared with electroconvulsive therapy (ECT): history, basic principles, technical considerations, possible mode of action, safety, adverse effects, and effects on mood in both healthy individuals and those suffering from bipolar disorder (BD) or depression.

RESULTS

rTMS may selectively increase or decrease neuronal activity over discrete brain regions. As a result of this focused intervention with TMS, the potential for unwanted side effects is substantially reduced, compared with ECT. In open trials, rTMS and ECT are reported to be equally efficacious for patients having depression without psychosis, but the therapeutic benefits reported in double-blind sham-rTMS controlled trials are more modest.

CONCLUSION

The antidepressant and antimanic effects of rTMS depend on technical considerations such as stimulus frequency, intensity, and magnetic coil placement, which may not yet be optimized. Biological heterogeneity among the patients treated with rTMS may also contribute to differing efficacy across clinical trials. rTMS may possess tremendous potential as a treatment for mood disorder, but this has not yet been realized. rTMS must still be regarded as an experimental intervention requiring further refinement.

Therapeutic application of repetitive transcranial magnetic stimulation: a review

Transcranial magnetic stimulation (TMS), a non-invasive means of electrically stimulating neurons in the human cerebral cortex, is able to modify neuronal activity locally and at distant sites when delivered in series or trains of pulses. Data from stimulation of the motor cortex suggest that the type of effect on the excitability of the cortical network depends on the frequency of stimulation. These data, as well as results from studies in rodents, have been generalized across brain areas and species to provide rationales for using repetitive TMS (rTMS) to treat various brain disorders, most notably depression. Research into clinical applications for TMS remains active and has the potential to provide useful data, but, to date, the results of blinded, sham-controlled trials do not provide clear evidence of beneficial effects that replace or even match the effectiveness of conventional treatments in any disorder. In this review, we discuss the clinical and scientific bases for using rTMS as treatment, and review the results of trials in psychiatric and neurological disorders to date.

Transcranial magnetic stimulation as a therapeutic tool in psychiatry: what do we know about the neurobiological mechanisms?

Potential therapeutic properties of repetitive transcranial magnetic stimulation (rTMS) have been suggested in several psychiatric disorders such as depression, mania, obsessive-compulsive disorder, posttraumatic stress disorder and schizophrenia. By inducing electric currents in brain tissue via a time-varying strong magnetic field, rTMS has the potential to either directly or trans-synaptically modulate neuronal circuits thought to be dysfunctional in these psychiatric disorders. However, in order to optimize rTMS for therapeutic use, it is necessary to understand the neurobiological mechanisms involved, particularly the nature of the changes induced and the brain regions affected. Compared to the growing number of clinical studies on its putative therapeutic properties, the studies on the basic mechanisms of rTMS are surprisingly scarce. rTMS currently still awaits clinical routine administration although,there is compelling evidence that it causes changes in neuronal circuits as reflected by behavioural changes and decreases in the activity of the hypothalamic-pituitary-adrenocortical system. Both alterations suggest regional changes in neurotransmitter/neuromodulator release, transsynaptic efficiency, signaling pathways and in gene transcription. Together, these changes are, in part, reminiscent of those accompanying antidepressant drugs.

Transcranial magnetic stimulation: no effect on mood with single pulse during learned helplessness

1. Transcranial Magnetic Stimulation (TMS) is suggested to be an effective tool in the treatment of depression. However, the methodology most suitable for clinical application remains unclear. 2. The effect of TMS was tested in a double-blind and placebo-controlled setting on 18 healthy subjects. At the same time an established learned helplessness paradigm was applied to induce dysphoria, which consisted of unsolvable anagrams. 3. Sixty 0.5 Hz stimuli were administered at an intensity of 130% of the subject's motor threshold after the subjects were exposed to the learned helplessness situation. Using a vertically positioned coil, the stimuli were applied to the right or to the left frontal cortex, or on the occipital cortex as a placebo condition. 4. Although dysphoria was successfully induced by unsolvable anagrams, TMS on either of the two frontal locations did not influence mood. This lack of effect may be due to the stimulation characteristics employed here (low TMS intensity, and low frequency). On the other hand, the findings may reflect the neurobiological difference between experimentally induced sad mood and clinical depression.

Animal models of the mechanisms of action of repetitive transcranial magnetic stimulation (RTMS): comparisons with electroconvulsive shock (ECS)

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive means of brain stimulation with a broad range of basic neuroscience and potential future clinical applications. Recent animal studies have shed some light on the mechanisms of action of rTMS, and broadened our understanding of how this intervention affects brain functioning acutely and chronically. Differences in the physical properties of magnetic and electrical stimulation result in marked disparities in the amount and distribution of electrical current induced in the brain; nevertheless, rTMS shares many of the behavioral and biochemical actions of electroconvulsive shock (ECS) and other antidepressant treatments. rTMS reduces immobility in the Porsolt swim task and enhances apomorphine-induced stereotypy, as does ECS. Although rTMS can induce a seizure when given at high enough doses, most studies have found subconvulsive levels of rTMS to be anticonvulsant. rTMS acutely modulates dopamine and serotonin content and turnover rates. Chronic rTMS modulates cortical beta-adrenergic receptors, reduces frontal cortex 5-HT2 receptors, increases 5-hydroxytryptamine1A receptors in frontal cortex and cingulate, and increases N-methyl-D-aspartate receptors in the ventromedial hypothalamus, basolateral amygdala, and parietal cortex. More work will be needed to clarify and explore the mechanism behind the early suggestions that rTMS may exert long-term-potentiation-like or long-term-depression-like action on hippocampal activity. Finally, rTMS is emerging as yet another intervention, like ECS and other antidepressants, that can regulate gene expression and may have an impact on neuronal viability and synaptic plasticity.

Transcranial magnetic stimulation applications and potential use in chronic pain: studies in waiting

Transcranial magnetic stimulation (TMS) is a new technology which uses electromagnetic principles to produce small electrical currents in the cortex. Evidence indicates that TMS can produce plastic changes in the CNS which are observable at both the cellular and physiological levels. It is proposed that studies are justified to determine whether TMS can provide short-term or long-term relief in chronic pain.

Antidepressants: past, present and future

Since the discovery of first antidepressants in mid-1950's, the field has been intensively studied. Several new classes of compounds emerged and several hypotheses on the mechanism of their action were proposed. The novel antidepressants are either selective and reversible monoamine oxidase inhibitors, (e.g., moclobemide), or selective serotonin reuptake inhibitors (e.g., citalopram or paroxetine), or serotonin and noradrenaline reuptake inhibitors (e.g. , venlafaxine). Recently neuropeptides (e.g., thyrotropin-releasing hormone,TRH) or antagonists of neuropeptide receptors (e.g., tachykinin NK(1) receptor) undergo clinical tests. Several hypotheses proposed the predominant involvement of one or few neurotransmitter receptors in the mechanism of antidepressant action, but it is now assumed that several distinct receptor mechanisms' trigger different but converging intracellular signal cascades that activate transcription factors, which, in turn, promote the expression of genes encoding for proteins, that play a crucial role in restoring of neuronal functions involved in mood regulation.

Repetitive transcranial magnetic stimulation induces active coping strategies and attenuates the neuroendocrine stress response in rats

The effects of repetitive transcranial magnetic stimulation (rTMS) on various brain functions were investigated in adult male Wistar rats. The stimulation parameters were adjusted according to the results of accurate computer-assisted, magnetic resonance imaging-based reconstructions of the current density distributions induced by rTMS in the rat and human brain, ensuring comparable stimulation patterns in both cases. The animals were subjected to daily rTMS-treatment (three trains of 20 Hz; 2.5 s) for 8 weeks from the age of 4 weeks on. In the forced swim test these rats showed a more active stress coping strategy than the control rats. This was accompanied by a significantly attenuated stress-induced elevation of plasma ACTH concentrations. Pituitary changes accounting for the attenuation were ruled out by the corticotropin-releasing hormone test. Baseline concentrations of ACTH and corticosterone were indistinguishable in the two groups. No changes were found in the anxiety-related behavior of the rats on the elevated plus-maze or in behavior during the social interaction test. Accordingly, the binding characteristics of the benzodiazepine agonist [(3)H]flunitrazepam at the benzodiazepine/gamma-aminobutyric acid type A receptor complex were similar in the rTMS and control groups. In summary, chronic rTMS treatment of frontal brain regions in rats resulted in a change in coping strategy that was accompanied by an attenuated neuroendocrine response to stress, thus revealing parallels to the effects of antidepressant drug treatment.

Repetitive transcranial magnetic stimulation is as effective as electroconvulsive therapy in the treatment of nondelusional major depressive disorder: an open study

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS), a new method for the stimulation of the central nervous system, is being proposed as a potential new treatment in patients with major depressive disorder (MDD). We tested the hypothesis that rTMS would be as effective as electroconvulsive therapy (ECT) in patients with MDD.

METHODS

Forty patients with MDD referred for ECT were randomly assigned to either ECT or rTMS. Repetitive transcranial magnetic stimulation was performed at 90% power of the motor threshold. The stimulation frequency was 10 Hz for either 2 sec (first eight patients) or 6 sec (final 12 patients) for 20 trains. Patients were treated for up to 20 treatment days. Electroconvulsive therapy was performed according to standard protocols.

RESULTS

Overall patients responded best to ECT (chi(2) = 3.8, p <.05). Patients with MDD and psychosis responded significantly better to ECT (chi(2) = 9.2, p <. 01), whereas MDD patients without psychosis responded similarly to both treatments (chi(2) = 0.0, ns). The analysis of variance with repeated measures of clinical variables for the whole sample revealed significant treatment effects for both groups; however, interaction between group and treatment was seen only for the Global Assessment of Function and the Sleep assessment. When the psychosis-nonpsychosis grouping was considered, patients with psychosis responded dramatically better to ECT in all assessments, whereas those without psychosis responded similarly to both treatments.

CONCLUSIONS

Overall ECT was a more potent treatment for patients with MDD, this being particularly evident in patients with MDD and psychosis; however, in patients with MDD without psychosis the effects of rTMS were similar to those of ECT. The results we report are encouraging and support an important role for rTMS in the treatment of severe MDD; however, additional blinded studies are needed to precisely define this role.

Transcranial magnetic stimulation in the treatment of psychiatric disorders

Transcranial magnetic stimulation (TMS) is a new technology that applies the principles of electromagnetism to deliver an electrical field to the cerebral cortices. Well established in diagnostic electrophysiology, TMS is now being studied as a treatment for psychiatric disorders. Evidence suggests this technique is safe and acceptable to patients. The future may see the application of TMS in obsessive-compulsive disorder, post-traumatic stress disorder and mania. There is strong evidence that it will become an accepted treatment of depression.

Chronic treatment with repetitive transcranial magnetic stimulation inhibits seizure induction by electroconvulsive shock in rats

BACKGROUND

Studies in laboratory animals suggest that repetitive transcranial magnetic stimulation (rTMS) and electroconvulsive shock (ECS) increase seizure inhibition acutely. This study was designed to explore whether chronic rTMS would also have seizure inhibition properties.

METHODS

To this purpose we administered rTMS (Magstim Rapid) and sham rTMS twice daily (2.5 T, 4-sec train duration, 20 Hz) to two groups of 10 rats for 16 days. The rTMS coil was a 50-mm figure-8 coil held directly over the rat's head. Raters were blind to experimental groups. On days 11, 17, and 21 (5 days after the last rTMS) ECS was administered with a Siemens convulsator using three electrical charge levels. Variables examined were the presence or absence of seizures and seizure length (measured from the initiation of the tonic contraction until the end of the limb movement).

RESULTS

At day 11 rTMS had no effect on seizures, and both rTMS and sham rTMS animals convulsed equally. At day 17, however, rTMS-treated animals convulsed significantly less (both at presence/absence of seizures, and at seizure length) than sham rTMS animals. At day 21 the effects of rTMS had disappeared.

CONCLUSIONS

These findings suggest that rTMS administered chronically leads to changes in seizure threshold similar to those reported for ECS and ECT; however, these effects were short-lived.

Chronic repetitive transcranial magnetic stimulation alters beta-adrenergic and 5-HT2 receptor characteristics in rat brain

Repetitive transcranial magnetic stimulation (rTMS) has been shown to affect mood in health and disease. Evidence to date has demonstrated an antidepressant potential for low- and high-frequency rTMS treatment. In animal behavioral models of depression magnetic stimulation of the brain induced similar effects to those of electroconvulsive shock (ECS). In this study the effects of repeated rTMS on rat brain noradrenaline, dopamine, serotonin and their metabolites levels, as well as on beta-adrenergic and 5-HT2 receptor characteristics were studied. After 10 days of treatment, beta-adrenergic receptors were significantly up regulated in the frontal cortex, down regulated in the striatum and were unchanged in the hippocampus. 5-HT2 receptors were down regulated in the frontal cortex and were not changed in the other brain areas. No change in benzodiazepine receptors in the frontal cortex and cerebellum were demonstrated. These findings demonstrate specific and selective alterations induced by repeated rTMS, which are distinct from those induced by other antidepressant treatments. TMS therapeutic effects in humans and behavioral and biochemical effects in animal, suggest that TMS has a unique mechanism of action which requires further investigation.

Repetitive transcranial magnetic stimulation activates specific regions in rat brain

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive technique to induce electric currents in the brain. Although rTMS is being evaluated as a possible alternative to electroconvulsive therapy for the treatment of refractory depression, little is known about the pattern of activation induced in the brain by rTMS. We have compared immediate early gene expression in rat brain after rTMS and electroconvulsive stimulation, a well-established animal model for electroconvulsive therapy. Our result shows that rTMS applied in conditions effective in animal models of depression induces different patterns of immediate-early gene expression than does electroconvulsive stimulation. In particular, rTMS evokes strong neural responses in the paraventricular nucleus of the thalamus (PVT) and in other regions involved in the regulation of circadian rhythms. The response in PVT is independent of the orientation of the stimulation probe relative to the head. Part of this response is likely because of direct activation, as repetitive magnetic stimulation also activates PVT neurons in brain slices.