Transcranial magnetic stimulation downregulates beta-adrenoreceptors in rat cortex

Better than treated as usual: Transcranial magnetic stimulation augmentation in selective serotonin reuptake inhibitor-refractory obsessive-compulsive disorder, mini-review and pilot open-label trial

OBJECTIVE

1 Hz repetitive transcranial magnetic stimulation (rTMS) over the supplementary motor area has been shown to be effective in a subset of obsessive-compulsive disorder (OCD) subjects, yet these results are still to be confirmed. This preliminary study compares the efficacy of augmentation with 1 Hz rTMS over the supplementary motor area and the usual augmentation treatment (TAU; treated as usual) with antipsychotics in a sample of selective serotonin reuptake inhibitor (SSRI)-refractory OCD patients.

METHOD

Fifty SSRI-refractory OCD patients consecutively admitted were studied: 25 were treated with a three-week trial of 1Hz, bilateral rTMS over the supplementary motor area and 25 with antipsychotic drugs. Yale-Brown Obsessive-Compulsive Scale (Y-BOCS; primary outcome measure), Hamilton Depression and Hamilton Anxiety scales were administered at first, second and third week of treatment.

RESULTS

Y-BOCS showed a statistically significant time effect from the baseline to the third week, with a 68% of responders (Y-BOCS score reduction of ⩾ 25%), in comparison with 24.0% in the TAU group. In the rTMS group, 17.6% of patients achieved remission.

CONCLUSIONS

1 Hz rTMS over the supplementary motor area appeared to be effective in approximately 2/3 of SSRI-refractory OCD subjects, whereas in the TAU group only 1/4 of subjects were responders. The supplementary motor area might be a new target area to be further explored with neuromodulation for OCD treatment.

Transcranial magnetic stimulation in neurology: what we have learned from randomized controlled studies

Background.  Initially developed to excite peripheral nerves, magnetic stimulation was quickly recognized as a valuable tool to noninvasively activate the cerebral cortex. The subsequent discovery that repetitive transcranial magnetic stimulation (rTMS) could have long-lasting effects on cortical excitability spawned a broad interest in the use of this technique as a new therapeutic method in a variety of neuropsychiatric disorders. Although the current outcomes from initial trials include some conflicting results, initial evidence supports that rTMS might have a therapeutic value in different neurologic conditions. Methods.  We reviewed the results of clinical trials of rTMS on four different disorders: stroke, Parkinson's disease, chronic refractory pain, and epilepsy. We reviewed randomized, controlled studies only in order to obtain the strongest evidence for the clinical effects of rTMS. Results.  An extensive literature review revealed 32 articles that met our criteria. From these studies, we found evidence for the therapeutic efficacy of rTMS, particularly in the relief of chronic pain and motor neurorehabilitation in single hemisphere stroke patients. Repetitive TMS also seems to have a therapeutic effect on motor function in Parkinson's disease, but the evidence is somewhat confounded by the uncontrolled variability of multiple factors. Lastly, only two randomized, sham-controlled studies have been performed for epilepsy; although evidence indicates rTMS may reduce seizure frequency in patients with neocortical foci, more research is needed to confirm these initial findings. Conclusions.  There is mounting evidence for the efficacy of rTMS in the short-term treatment of certain neurologic conditions. More long-term research is needed in order to properly evaluate the effects of this method in a clinical setting.

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.

An open label pilot study of transcranial magnetic stimulation for pregnant women with major depressive disorder

OBJECTIVE

Despite the data that major depressive disorder (MDD) is common during pregnancy and that pregnant women prefer nonmedication treatment options, there is a paucity of research examining alternative treatments for this special population. We present the results of an open label pilot study examining treatment with transcranial magnetic stimulation (TMS) in pregnant women with MDD.

METHODS

Ten women with MDD in the second or third trimester of pregnancy were treated with 20 sessions of 1-Hz TMS at 100% of motor threshold (MT) to the right dorsolateral prefrontal cortex. The total study dose was 6000 pulses. Antenatal monitoring was performed during treatment sessions 1, 10, and 20.

RESULTS

Seven of ten (70%) subjects responded (decrease ≥50% in Hamilton Depression Rating Scale [HDRS-17] scores). No adverse pregnancy or fetal outcomes were observed. All infants were admitted to the well baby nursery and were discharged with the mother. Mild headache was the only common adverse event and was reported by 4 of 10 (40%) subjects.

CONCLUSIONS

TMS appears to be a promising treatment option for pregnant women who do not wish to take antidepressant medications.

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.

Carbonic anhydrase I, II, and VI, blood plasma, erythrocyte and saliva zinc and copper increase after repetitive transcranial magnetic stimulation

INTRODUCTION

Repetitive transcranial magnetic stimulation (rTMS) has been used to treat symptoms from many disorders; biochemical changes occurred with this treatment. Preliminary studies with rTMS in patients with taste and smell dysfunction improved sensory function and increased salivary carbonic anhydrase (CA) VI and erythrocyte CA I, II. To obtain more information about these changes after rTMS, we measured changes in several CA enzymes, proteins, and trace metals in their blood plasma, erythrocytes, and saliva.

METHODS

Ninety-three patients with taste and smell dysfunction were studied before and after rTMS in an open clinical trial. Before and after rTMS, we measured erythrocyte CA I, II and salivary CA VI, zinc and copper in parotid saliva, blood plasma, and erythrocytes, and appearance of novel salivary proteins by using mass spectrometry.

RESULTS

After rTMS, CA I, II and CA VI activity and zinc and copper in saliva, plasma, and erythrocytes increased with significant sensory benefit. Novel salivary proteins were induced at an m/z value of 21.5K with a repetitive pattern at intervals of 5K m/z.

CONCLUSIONS

rTMS induced biochemical changes in specific enzymatic activities, trace metal concentrations, and induction of novel salivary proteins, with sensory improvement in patients with taste and smell dysfunction. Because patients with several neurologic disorders exhibit taste and smell dysfunction, including Parkinson disease, Alzheimer disease, and multiple sclerosis, and because rTMS improved their clinical symptoms, the biochemical changes we observed may be relevant not only in our patients with taste and smell dysfunction but also in patients with neurologic disorders with these sensory abnormalities.

Neurostimulatory and ablative treatment options in major depressive disorder: a systematic review

INTRODUCTION

Major depressive disorder is one of the most disabling and common diagnoses amongst psychiatric disorders, with a current worldwide prevalence of 5-10% of the general population and up to 20-25% for the lifetime period.

HISTORICAL PERSPECTIVE

Nowadays, conventional treatment includes psychotherapy and pharmacotherapy; however, more than 60% of the treated patients respond unsatisfactorily, and almost one fifth becomes refractory to these therapies at long-term follow-up.

NONPHARMACOLOGICAL TECHNIQUES

Growing social incapacity and economic burdens make the medical community strive for better therapies, with fewer complications. Various nonpharmacological techniques like electroconvulsive therapy, vagus nerve stimulation, transcranial magnetic stimulation, lesion surgery, and deep brain stimulation have been developed for this purpose.

DISCUSSION

We reviewed the literature from the beginning of the twentieth century until July 2009 and described the early clinical effects and main reported complications of these methods.

rTMS treatment for depression in Parkinson's disease increases BOLD responses in the left prefrontal cortex

The mechanisms underlying the effects of antidepressant treatment in patients with Parkinson's disease (PD) are unclear. The neural changes after successful therapy investigated by neuroimaging methods can give insights into the mechanisms of action related to a specific treatment choice. To study the mechanisms of neural modulation of repetitive transcranial magnetic stimulation (rTMS) and fluoxetine, 21 PD depressed patients were randomized into only two active treatment groups for 4 wk: active rTMS over left dorsolateral prefrontal cortex (DLPFC) (5 Hz rTMS; 120% motor threshold) with placebo pill and sham rTMS with fluoxetine 20 mg/d. Event-related functional magnetic resonance imaging (fMRI) with emotional stimuli was performed before and after treatment - in two sessions (test and re-test) at each time-point. The two groups of treatment had a significant, similar mood improvement. After rTMS treatment, there were brain activity decreases in left fusiform gyrus, cerebellum and right DLPFC and brain activity increases in left DLPFC and anterior cingulate gyrus compared to baseline. In contrast, after fluoxetine treatment, there were brain activity increases in right premotor and right medial prefrontal cortex. There was a significant interaction effect between groups vs. time in the left medial prefrontal cortex, suggesting that the activity in this area changed differently in the two treatment groups. Our findings show that antidepressant effects of rTMS and fluoxetine in PD are associated with changes in different areas of the depression-related neural network.

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.

Changes to somatosensory detection and pain thresholds following high frequency repetitive TMS of the motor cortex in individuals suffering from chronic pain

Research has shown that transcranial magnetic stimulation (TMS) results in a transient reduction in the experience of chronic pain. The present research aimed to investigate whether a single session of high frequency TMS is able to change the sensory thresholds of individuals suffering from chronic pain. Detection and pain thresholds for cold and heat sensations were measured before and after 20Hz repetitive TMS (rTMS) administered over the motor cortex. A significant decrease in temperature for cold detection and pain thresholds and a significant increase in temperature for heat pain thresholds were evident following a single session of rTMS. In contrast, no change in detection and pain thresholds was obtained following sham rTMS. The finding that rTMS can have a direct effect on sensory thresholds in individuals suffering from chronic pain has implications for the therapeutic use of rTMS in the relief of chronic pain.

Transcranial magnetic stimulation as a therapeutic tool in psychiatry

Transcranial magnetic stimulation (TMS) is a patient-friendly stimulation technique of the brain with interesting perspectives. In clinical psychiatry, limited data are available on activity in psychosis and anxiety, but much research has been done in depression. Major concerns on published papers are the inconsistency of used parameter settings, the restraint numbers of patients in randomised trials, the lack of real sham controlled studies and the quasi inexistent reproducibility of results. The most stringent meta-analysis of TMS in affective disorders found a modest, statistically significant antidepressant effect after 2 weeks of daily treatment of high frequency repetitive left dorsolateral prefrontal cortex stimulation. Although most results are rather weak and not convincing enough to promote TMS as evidence-based antidepressive therapy, they show a measurable action that should not be ignored. Preclinical and clinical effects were observed analysing heterogeneous data, and results comparing TMS to electroconvulsive therapy (ECT) in affective disorders are encouraging. Efforts should continue with emphasis on increasing homogeneity and reproducibility in data. Further refinement of stimulation parameters should be established, so that new and large double-blind, long-term, sham-controlled trials can bring us to better understanding and standardising TMS procedure, finally leading to definitive conclusions about its efficacy in psychiatry.

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.

Transcranial magnetic stimulation treatment for epilepsy: can it also improve depression and vice versa?

Comorbidity with depression is an important determinant of the quality of life for patients with epilepsy. Antidepressant medications can effectively treat depression in epileptic patients, but drug-drug interactions and epileptogenic effects of these drugs pose therapeutic challenges. The mood-stabilizing effects of antiepileptic medications may not be sufficient to treat depression. Therefore, treatments that alleviate the burden of depression without increasing seizure risk or, better yet, with the possibility of improving seizure control are worth exploring. Neuroimaging techniques, such as functional magnetic resonance imaging, are providing novel insights into the pathophysiology of depression in epilepsy. For example, there appears to be prominent brain prefrontal hypoactivity, which may be sustained by the hyperactivity of the seizure focus. If so, neuromodulatory approaches that suppress epileptic focus hyperactivity and concurrently enhance prefrontal activity may be ideally suited. Indeed, vagus nerve stimulation has been shown to yield simultaneous antiseizure and mood effects. Another neuromodulatory technique, transcranial magnetic stimulation (TMS), can also modulate brain activity, but in a noninvasive, painless, and focal manner. Depending on the stimulation parameters, it is possible to enhance or reduce activity in the targeted brain region. Furthermore, TMS has been shown to be effective in treating depression, and preliminary data suggest that this treatment may also be effective for epilepsy treatment. This article reviews these data and explores further the question of whether depression and epilepsy can be simultaneously treated with TMS for optimal therapeutic impact.

Should transcranial magnetic stimulation research in children be considered minimal risk?

OBJECTIVE

Transcranial magnetic stimulation (TMS) is a neurophysiologic technique with research applications. Institutional Review Boards (IRBs) must carefully consider potential risks and possible benefits in research involving children. The purpose of this study is to provide concise information for investigators and IRBs about the safety of single and paired pulse TMS research in children.

METHODS

This paper has 4 sections: (I) Regulations governing research in children are reviewed and applied to the use of TMS. (II) Energy imparted by TMS is assessed in terms of theoretical biological risks to human subjects. (III) Through MEDLINE review, the empirical evidence of risk from TMS is assessed. Reported adverse events, including issues related to risk of seizures and of hearing loss, are summarized. (IV) Safety data are presented from a study of TMS in children with Tourette Syndrome.

RESULTS

No published or empirical evidence was found to suggest that single or paired pulse TMS is associated with more than minimal risk in children.

CONCLUSIONS

IRBs may consider well-designed studies using single and paired pulse TMS protocols similar to those described in this study as bearing minimal risk to children.

SIGNIFICANCE

This manuscript may be useful as a reference to IRBs and TMS investigators.

Mechanisms and the current state of transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) is unique among the current brain stimulation techniques because it is relatively non-invasive. TMS markedly differs from vagus nerve stimulation, deep brain stimulation and magnetic seizure therapy, all of which require either an implanted prosthesis or general anesthesia, or both. Since its rebirth in its modern form in 1985, TMS has already shown potential usefulness in at least three important domains-as a basic neuroscience research instrument, as a potential clinical diagnostic tool, and as a therapy for several different neuropsychiatric conditions. The TMS scientific literature has now expanded beyond what a single summary article can adequately cover. This review highlights several new developments in combining TMS with functional brain imaging, using TMS as a psychiatric therapy, potentially using TMS to enhance performance, and finally recent advances in the core technology of TMS. TMS' ability to non-invasively and focally stimulate the brain of an awake human is proving to be a most important development for neuroscience in general, and neuropsychiatry in particular.

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.

Transcranial magnetic stimulation

TMS is a powerful new tool with extremely interesting research and therapeutic potentials. Further understanding of the ways by which TMS changes neuronal function, especially as a function of its use parameters, will improve its ability to answer neuroscience questions as well as to treat diseases. Because of its noninvasiveness, it does not readily fit under the umbrella of neurosurgery. Nevertheless, it is important for neurosurgeons to be aware of TMS, because findings from TMS studies will have implications for neurosurgical approaches like DBS and VNS. Indeed, it is possible to think of using TMS as a potential noninvasive initial screening tool to identify whether perturbation of a circuit has short-term clinical effects. In the example of chronic refractory depression or OCD, which is generally a chronic illness, it might then follow that rather than having daily or weekly TMS for the rest of their lives, patients would have DBS electrodes implanted in the same circuit. Whatever road the future takes, TMS is an important new tool that will likely be of interest to neurosurgeons over the next 20 years and perhaps even longer.

Mechanisms and state of the art of transcranial magnetic stimulation

In 1985, Barker et al. built a transcranial magnetic stimulation (TMS) device with enough power to stimulate dorsal roots in the spine. They quickly realized that this machine could likely also noninvasively stimulate the superficial cortex in humans. They waited a while before using their device over a human head, fearing that the TMS pulse might magnetically "erase the hard-drive" of the human brain. Almost 10 years later, in 1994, an editorial in this journal concerned whether TMS might evolve into a potential antidepressant treatment. In the intervening years, there has been an explosion of basic and clinical research with and about TMS. Studies are now uncovering the mechanisms by which TMS affects the brain. It does not "erase the hard-drive" of the brain, and it has many demonstrated research and clinical uses. This article reviews the major recent advances with this interesting noninvasive technique for stimulating the brain, critically reviewing the data on whether TMS has anticonvulsant effects or modulates cortical-limbic loops.

Depression as a spreading adjustment disorder of monoaminergic neurons: a case for primary implication of the locus coeruleus

A model for the pathophysiology of depression is discussed in the context of other existing theories. The classic monoamine theory of depression suggests that a deficit in monoamine neurotransmitters in the synaptic cleft is the primary cause of depression. More recent elaborations of the classic theory also implicitly include this postulate, other theories of depression frequently prefer to depart from the monoamine-based model altogether. We suggest that the primary defect emerges in the regulation of firing rates in brainstem monoaminergic neurons, which brings about a decrease in the tonic release of neurotransmitters in their projection areas, an increase in postsynaptic sensitivity, and concomitantly, exaggerated responses to acute increases in the presynaptic firing rate and transmitter release. It is proposed that the initial defect involves, in particular, the noradrenergic innervation from the locus coeruleus (LC). Dysregulation of the LC projection activities may lead in turn to dysregulation of serotonergic and dopaminergic neurotransmission. Failure of the LC function could explain the basic impairments in the processing of novel information, intensive processing of irrational beliefs, and anxiety. Concomitant impairments in the serotonergic neurotransmission may contribute to the mood changes and reduction in the mesotelencephalic dopaminergic activity to loss of motivation, and anhedonia. Dysregulation of CRF and other neuropeptides such as neuropeptide Y, galanin and substance P may reinforce the LC dysfunction and thus further weaken the adaptivity to stressful stimuli.

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.

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.

Chronic repetitive transcranial magnetic stimulation enhances c-fos in the parietal cortex and hippocampus

Repetitive transcranial magnetic stimulation (rTMS) is a novel non-invasive method with anti-depressant properties. However, the mechanism of activation on the cellular level is unknown. Twelve hours after the last chronic rTMS treatment (14 days, once per day, 20 Hz, 10 s, 75% machine output, the transcription factor c-fos was markedly increased in neurons in layers I-IV and VI of the parietal cortex and in few scattered neurons in the hippocampus of Sprague-Dawley rats. The cortical activation was not blocked by the NMDA antagonist MK-801. The increase of c-fos was not paralleled by an increased glial response and activation of cortical growth factors. Thus, it is concluded that chronic rTMS differentially activates parietal cortical layers and this might be involved in mediating anti-depressant activity in other brain areas.

Magnetic field desensitizes 5-HT(1B) receptor in brain: pharmacological and functional studies

It was previously suggested that exposure to magnetic fields (MFs) could generate dysfunction of the CNS. The physiological manifestations described lead us to postulate that these symptoms might be related to a dysfunction of the serotonergic system and particularly of the 5-HT(1B) receptors. Accordingly, MFs could modify the conformation of these receptors altering their functional activities. In rat brain membrane preparations, we showed that the affinity constant of 5-HT for 5-HT(1B) receptors was modified under exposure to MFs since K(d) varied from 4.7+/-0.5 to 12+/-3 nM in control and exposed (2.5 mT) membranes, respectively. This effect was intensity-dependent (the sigmoidal dose-response curve was characterized by an EI(50) of 662+/-69 microT and a maximal increase of 321+/-13% of the control K(d)), reversible, temperature-dependent and specific to the 5-HT(1B) receptors. Similar results have also been obtained with the human 5-HT(1B) receptors. In parallel assays, the functional activity of 5-HT(1B) receptors was investigated. The capacity of a 5-HT(1B) agonist to inhibit the cAMP production was reduced by 37% (53.7+/-3.5% to 33.7+/-4.1%) following exposure to MFs and the cellular activity of the receptors (inhibition of the synaptosomal release of 5-HT) also was markedly reduced (66.5+/-3.2% to 28.5+/-4.2%). These results clearly show that in in vitro assays, MF specifically interacts with 5-HT(1B) receptors, inducing structural changes of the protein that result in a functional desensitization of the receptors. Thus, in vivo, exposure to MFs may lead to physiological changes, particularly in the field of mood disorders where the 5-HT system is strongly involved.

Transcranial magnetic stimulation (TMS) in controlled treatment studies: are some "sham" forms active?

BACKGROUND

Carefully designed controlled studies are essential in further evaluating the therapeutic efficacy of transcranial magnetic stimulation (TMS) in psychiatric disorders. A major methodological concern is the design of the "sham" control for TMS. An ideal sham would produce negligible cortical stimulation in conjunction with a scalp sensation akin to real treatment. Strategies employed so far include alterations in the position of the stimulating coil, but there has been little systematic study of their validity. In this study, we investigated the effects of different coil positions on cortical activation and scalp sensation.

METHODS

In nine normal subjects, single TMS pulses were administered at a range of intensities with a "figure eight" coil held in various positions over the left primary motor cortex. Responses were measured as motor-evoked potentials in the right first dorsal interosseus muscle. Scalp sensation to TMS with the coil in various positions over the prefrontal area was also assessed.

RESULTS

None of the coil positions studied met the criteria for an ideal sham. Arrangements associated with a higher likelihood of scalp sensation were also more likely to stimulate the cortex.

CONCLUSIONS

The choice of a sham for TMS involves a trade-off between effective blinding and truly inactive "stimulation." Further research is needed to develop the best sham condition for a range of applications.

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.

Repetitive transcranial magnetic stimulation: perspectives for application in the treatment of bipolar and unipolar disorders

OBJECTIVES

Transcranial magnetic stimulation (TMS) affects the brain by non-invasively stimulating the cerebral cortex and inducing electrical currents in neurons. The powerful magnetic field acts as a vector that passes across the scalp and the skull, and then converts into an electrical energy within the brain. Originally used in neurophysiology, TMS has since been applied in a variety of neuropsychiatric conditions, including mood disorders. Imaging studies in mood-disordered patients have pointed to dysfunctional limbic and prefrontal cortex activity. TMS researchers have thus postulated that dorsolateral prefrontal cortex (DLPFC) stimulation might change brain activity both locally and in paralimbic areas through transynaptic connections, and alter mood.

METHODS

We will describe the technology of TMS, its applications to date, and explore its mechanisms of action.

RESULTS

Several clinical trials have demonstrated TMS effects on mood in health and disease. There is a growing consensus that TMS has antidepressant effects, although little is known about the role played by a variety of stimulation parameters such as the intensity or frequency of stimulation. One study has found an antimanic effect of right prefrontal TMS.

CONCLUSION

TMS is relatively safe; however, much more research is needed before TMS can be integrated into routine clinical practice.

Improvement of depression following transcranial magnetic stimulation

Psychiatry as a field was transformed by the discovery and introduction of electroconvulsive therapy (ECT) as a treatment in the early part of this century. ECT demonstrated that depression was a disease of the brain and that it could be treated with a direct brain intervention. Psychiatry's evolution continued in 1958 with the discovery of the antidepressant activity of the monoamine oxidase inhibitors. Interestingly, although the area of neuropsychopharmacology has continued to advance, the realm of physical somatic interventions in psychiatry has lagged behind. With perhaps the exception of light therapy, there were no advances in somatic interventions in psychiatry. However, in 1985, Barker et al. developed a brief high intensity electromagnet capable of depolarizing cortical neurons, called transcranial magnetic stimulation (TMS). There has been much interest in the past 10 years in whether TMS might have antidepressant actions, similar to ECT but without causing a seizure and with no apparent cognitive side effects. This review examines the basic principles underlying TMS, and describes how TMS differs from electrical stimulation and the other uses of magnets.

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.

Changes in 5-HT1A and NMDA binding sites by a single rapid transcranial magnetic stimulation procedure in rats

The effects of a single rapid-rate transcranial magnetic stimulation (rTMS) exposure on neurotransmitter binding sites in the rat brain 24 h after the stimulation were examined. Quantification by in vitro-autoradiography showed no differences for 3H-paroxetine binding (5-HT uptake sites) between rTMS-treated, sham and control animals. In contrast, the number of 5-HT1A binding sites (labeled with 3H-8-OH-DPAT) were selectively increased in the rTMS-group with significantly higher BMAX values in the frontal cortex, the cingulate cortex, and the anterior olfactory nucleus. A non-specific increase in NMDA binding sites (labeled with 125I-MK-801) in rTMS and sham animals was observed in the hippocampal formation. A selective increase of these binding sites after rTMS was detected in the ventromedial hypothalamus, the basolateral amygdala and layers 5-6 of the parietal cortex. These findings imply that a single rTMS exposure can result in persistent effects on NMDA and 5-HT1A binding sites even 24 h after stimulation and therefore may be of relevance with respect to the therapeutic action of rTMS reported from clinical studies.

Long-term effects of transcranial magnetic stimulation on hippocampal reactivity to afferent stimulation

Transcranial magnetic stimulation (TMS) has become a promising treatment of affective disorders in humans, yet the neuronal basis of its long-lasting effects in the brain is still unknown. We studied acute and lasting effects of TMS on reactivity of the rat hippocampus to stimulation of the perforant path. Application of TMS to the brain of the anesthetized rat caused a dose-dependent transient increase in population spike (PS) response of the dentate gyrus to perforant path stimulation. In addition, TMS caused a marked decrease in inhibition and an increase in paired-pulse potentiation of reactivity to stimulation of the perforant path. Also, TMS suppressed the ability of fenfluramine (FFA), a serotonin releaser, to potentiate PS response to perforant path stimulation. Chronic TMS did not affect single population spikes but caused an increase in paired-pulse potentiation, which was still evident 3 weeks after the last of seven daily TMS treatments. After chronic TMS, FFA was ineffective in enhancing reactivity to perforant path stimulation, probably because it lost the ability to release serotonin. In addition, the beta adrenergic receptor agonist isoproterenol, which caused an increase in PS in the control rats, failed to do so in the TMS-treated rats. These results indicate that TMS produces a long-term reduction in efficacy of central modulatory systems.

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.

Transcranial magnetic stimulation as therapy for depression and other disorders

OBJECTIVE

To provide an overview of the progress and prospects of transcranial magnetic stimulation as a psychiatric therapy for depression.

METHOD

Published and unpublished studies of the usefulness of transcranial magnetic stimulation as a therapy for depression were assessed, and characterised in terms of a consistent measure of dosage. Additional information was obtained through correspondence, personal meetings and visits to facilities.

RESULTS

Transcranial magnetic stimulation, a means for inducing small regional currents in the brain, has been used in clinical neurology for some time, and can be used on conscious subjects with minimal side-effects. Early researchers noticed transient mood effects on people receiving this treatment, which prompted several inconclusive investigations of its effects on depressed patients. More recently, knowledge of functional abnormalities associated with depression has led to trials using repetitive transcranial magnetic stimulation to stimulate underactive left prefrontal regions, an approach which has produced short-term benefits for some subjects. The higher dosage delivered by high-frequency repetitive transcranial magnetic stimulation appears to produce greater benefits; scope exists for more conclusive studies based on extended treatment periods.

CONCLUSIONS

Repetitive transcranial magnetic stimulation is a promising technology. The reviewed evidence indicates that it may be useful in the treatment of depression, and perhaps other disorders which are associated with regional hypometabolism. Should repetitive transcranial magnetic stimulation prove an effective, non-invasive, drug-free treatment for depression, a range of disorders could be similarly treatable.