Chronic repetitive transcranial magnetic stimulation induces subsensitivity of presynaptic serotonergic autoreceptor activity in rat brain

Effects of bilateral sequential theta-burst stimulation on 5-HT1A receptors in the dorsolateral prefrontal cortex in treatment-resistant depression: a proof-of-concept trial

Theta-burst stimulation (TBS) represents a brain stimulation technique effective for treatment-resistant depression (TRD) as underlined by meta-analyses. While the methodology undergoes constant refinement, bilateral stimulation of the dorsolateral prefrontal cortex (DLPFC) appears promising to restore left DLPFC hypoactivity and right hyperactivity found in depression. The post-synaptic inhibitory serotonin-1A (5-HT1A) receptor, also occurring in the DLPFC, might be involved in this mechanism of action. To test this hypothesis, we performed PET-imaging using the tracer [carbonyl-11C]WAY-100635 including arterial blood sampling before and after a three-week treatment with TBS in 11 TRD patients compared to sham stimulation (n = 8 and n = 3, respectively). Treatment groups were randomly assigned, and TBS protocol consisted of excitatory intermittent TBS to the left and inhibitory continuous TBS to the right DLPFC. A linear mixed model including group, hemisphere, time, and Hamilton Rating Scale for Depression (HAMD) score revealed a 3-way interaction effect of group, time, and HAMD on specific distribution volume (VS) of 5-HT1A receptor. While post-hoc comparisons showed no significant changes of 5-HT1A receptor VS in either group, higher 5-HT1A receptor VS after treatment correlated with greater difference in HAMD (r = -0.62). The results of this proof-of-concept trial hint towards potential effects of TBS on the distribution of the 5-HT1A receptor. Due to the small sample size, all results must, however, be regarded with caution.

Genetics of nonpharmacological treatments of depression

Nonpharmacological antidepressant treatments are effective and well tolerated in selected patients. However, response is heterogeneous and validated biomarkers would be precious to aid treatment choice. We searched Pubmed, Scopus, and Google Scholar until May 2022 for original articles evaluating the association of genetic variables with the efficacy of nonpharmacological treatments for major depressive episodes. Most studies analyzed small sample sizes using the candidate gene approach, leading to poorly replicated findings that need to be interpreted cautiously. The few available methylome-wide and genome-wide association studies (GWASs) considered only electroconvulsive therapy (ECT) and cognitive-behavioral therapy in small samples, providing interesting findings by using polygenic risk scores. A deeper knowledge of the genetic factors implicated in treatment response may lead to a better understanding of the neurobiological mechanisms of nonpharmacological therapies for depression, and depression itself. Future GWAS are going to expand their sample size, thanks to consortia such as the gen-ECT-ic consortium.

Non-Invasive Brain Stimulation Effects on Biomarkers of Tryptophan Metabolism: A Scoping Review and Meta-Analysis

Abnormal activation of the kynurenine and serotonin pathways of tryptophan metabolism is linked to a host of neuropsychiatric disorders. Concurrently, noninvasive brain stimulation (NIBS) techniques demonstrate high therapeutic efficacy across neuropsychiatric disorders, with indications for modulated neuroplasticity underlying such effects. We therefore conducted a scoping review with meta-analysis of eligible studies, conforming with the PRISMA statement, by searching the PubMed and Web of Science databases for clinical and preclinical studies that report the effects of NIBS on biomarkers of tryptophan metabolism. NIBS techniques reviewed were electroconvulsive therapy (ECT), transcranial magnetic stimulation (TMS), and transcranial direct current stimulation (tDCS). Of the 564 search results, 65 studies were included with publications dating back to 1971 until 2022. The Robust Bayesian Meta-Analysis on clinical studies and qualitative analysis identified general null effects by NIBS on biomarkers of tryptophan metabolism, but moderate evidence for TMS effects on elevating serum serotonin levels. We cannot interpret this as evidence for or against the effects of NIBS on these biomarkers, as there exists several confounding methodological differences in this literature. Future controlled studies are needed to elucidate the effects of NIBS on biomarkers of tryptophan metabolism, an under-investigated question with substantial implications to clinical research and practice.

Effect of adjunctive intermittent theta-burst repetitive transcranial magnetic stimulation as a prophylactic treatment in migraine patients: A double-blind sham-controlled study

BACKGROUND

The left dorsolateral prefrontal cortex (DLPFC) seems to exert a bilateral control of chronic pain states such as migraine. Repetitive transcranial magnetic stimulation (rTMS) is known to modulate brain excitability, neurotransmitters, and endogenous opioids involved in pathophysiology of migraine.

AIM

This study was designed to assess the efficacy of adjunctive intermittent theta-burst stimulation (iTBS) to the left DLPFC, as a prophylactic treatment in migraine.

MATERIALS AND METHODS

The study was a double-blind, sham-controlled experiment. Patients with migraine were allotted to active (n = 20) or sham (n = 21) rTMS, respectively. Each patient received ten sessions of iTBS over the left DLPFC. Patients were rated at baseline and at 2, 4, 6, and 12 weeks after receiving the treatment. Scores were obtained from the headache diary and by applying the Migraine Disability Assessment Scale (MIDAS).

RESULTS

There was a significant decrease in frequency, duration, and severity of migraine in the active group than the sham group over the study period. The effect was more pronounced during the initial 2 weeks. The MIDAS score reduced significantly in the active group than the sham group at 12 weeks. There were no significant adverse effects observed during the entire period of study.

CONCLUSION

Compared to sham stimulation, adjunctive active iTBS over the left DLPFC was safe and effective in reducing the frequency, duration, and severity of migraine headache and in reducing disability associated with the illness.

Personalized TMS: role of RNA genotyping

Purpose

Noninvasive brain stimulation (NIBS) such a transcranial magnetic stimulation, intermittent theta burst stimulation, transcranial direct current stimulation and electroconvulsive therapy have emerged as an efficacious and well-tolerated therapy for treatment-resistant psychiatric disorders. While novel NIBS techniques are an exciting addition to the current repertoire of neuropsychiatric therapies, their success is somewhat limited by the wide range of treatment responses seen among treated patients.

Design/methodology/approach

In this study, the authors will review the studies on relevant genetic polymorphisms and discuss the role of RNA genotyping in personalizing NIBS.

Findings

Genome studies have revealed several genetic polymorphisms that may contribute for the heterogeneity of treatment response to NIBS where the presence of certain single nucleotide polymorphisms (SNPs) are associated with responders versus nonresponders.

Originality/value

Historically, mental illnesses have been arguably some of the most challenging disorders to study and to treat because of the degree of biological variability across affected individuals, the role of genetic and epigenetic modifications, the diversity of clinical symptomatology and presentations and the interplay with environmental factors. In lieu of these challenges, there has been a push for personalized medicine in psychiatry that aims to optimize treatment response based on one's unique characteristics.

Association of the loudness dependence of auditory evoked potentials with clinical changes to repetitive transcranial magnetic stimulation in patients with depression

BACKGROUND

Although the application of repetitive transcranial magnetic stimulation (rTMS) for treatment of depression has been well investigated, there are few biological predictors of clinical outcomes to rTMS treatment. Previous studies have suggested that the loudness dependence of auditory evoked potentials (LDAEP) can be used as a predictor of response to antidepressant treatment. However, little is known about the association between rTMS and LDAEP. The present study aimed to investigate whether baseline LDAEP is associated with clinical changes to rTMS treatment in patients with major depressive disorder (MDD), and to explore the effect of high-frequency rTMS on LDAEP.

METHODS

Thirty patients were randomized to receive 15 sessions of active (n = 15) or sham rTMS (n = 15). LDAEP and clinical measures of depression were assessed before and after 10 Hz rTMS treatment for 15 days.

RESULTS

Baseline LDAEP was associated with changes in scores on the Hamilton Rating Scale for Depression. There were no significant effects of rTMS on LDAEP. Patients with high LDAEP exhibited more favorable clinical changes than those with low LDAEP following treatment with rTMS.

LIMITATIONS

The sample was relatively small, and the participants were not divided into responders and non-responders group due to small sample. An influence of medication has not been controlled.

CONCLUSIONS

Our findings suggest that high baseline LDAEP may be associated with favorable clinical changes to rTMS treatment in patients with MDD. Further studies are required to replicate and validate the potential use of LDAEP as a predictor of clinical changes to rTMS treatment.

The 5-HT1B receptor - a potential target for antidepressant treatment

Major depressive disorder (MDD) is the leading cause of disability worldwide. The serotonin hypothesis may be the model of MDD pathophysiology with the most support. The majority of antidepressants enhance synaptic serotonin levels quickly, while it usually takes weeks to discern MDD treatment effect. It has been hypothesized that the time lag between serotonin increase and reduction of MDD symptoms is due to downregulation of inhibitory receptors such as the serotonin 1B receptor (5-HT1BR). The research on 5-HT1BR has previously been hampered by a lack of selective ligands for the receptor. The last extensive review of 5-HT1BR in the pathophysiology of depression was published 2009, and based mainly on findings from animal studies. Since then, selective radioligands for in vivo quantification of brain 5-HT1BR binding with positron emission tomography has been developed, providing new knowledge on the role of 5-HT1BR in MDD and its treatment. The main focus of this review is the role of 5-HT1BR in relation to MDD and its treatment, although studies of 5-HT1BR in obsessive-compulsive disorder, alcohol dependence, and cocaine dependence are also reviewed. The evidence outlined range from animal models of disease, effects of 5-HT1B receptor agonists and antagonists, case-control studies of 5-HT1B receptor binding postmortem and in vivo, with positron emission tomography, to clinical studies of 5-HT1B receptor effects of established treatments for MDD. Low 5-HT1BR binding in limbic regions has been found in MDD patients. When 5-HT1BR ligands are administered to animals, 5-HT1BR agonists most consistently display antidepressant-like properties, though it is not yet clear how 5-HT1BR is best approached for optimal MDD treatment.

Dorsolateral prefrontal transcranial magnetic stimulation in patients with major depression locally affects alpha power of REM sleep

Sleep alterations are among the most important disabling manifestation symptoms of Major Depression Disorder (MDD). A critical role of sleep importance is also underlined by the fact that its adjustment has been proposed as an objective marker of clinical remission in MDD. Repetitive transcranial magnetic stimulation (rTMS) represents a relatively novel therapeutic tool for the treatment of drug-resistant depression. Nevertheless, besides clinical evaluation of the mood improvement after rTMS, we have no clear understanding of what are the neurophysiological correlates of such treatment. One possible marker underlying the clinical outcome of rTMS in MDD could be cortical changes on wakefulness and sleep activity. The aim of this open-label study was to evaluate the efficacy of a sequential bilateral rTMS treatment over the dorsolateral prefrontal cortex (DLPFC) to improve the mood in MDD patients, and to determine if rTMS can induce changes on the sleep structure, and if those changes can be used as a surrogate marker of the clinical state of the patient. Ten drug-resistant depressed patients participated to ten daily sessions of sequential bilateral rTMS with a low-frequency TMS (1 Hz) over right-DLPFC and a subsequent high-frequency (10 Hz) TMS over left-DLPFC. The clinical and neurophysiological effects induced by rTMS were evaluated, respectively by means of the Hamilton Depression Rating Scale (HDRS), and by comparing the sleep pattern modulations and the spatial changes of EEG frequency bands during both NREM and REM sleep, before and after the real rTMS treatment. The sequential bilateral rTMS treatment over the DLPFC induced topographical-specific decrease of the alpha activity during REM sleep over left-DLPFC, which is significantly associated to the clinical outcome. In line with the notion of a left frontal hypoactivation in MDD patients, the observed local decrease of alpha activity after rTMS treatment during the REM sleep suggests that alpha frequency reduction could be considered as a marker of up-regulation of cortical activity induced by rTMS, as well as a surrogate neurophysiological correlate of the clinical outcome.

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.

High-frequency rTMS treatment increases white matter FA in the left middle frontal gyrus in young patients with treatment-resistant depression

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is an effective treatment for treatment-resistant depression (TRD), but its therapeutic mechanisms are unclear. White matter abnormalities are thought to cause network dysfunction underlying TRD. Diffusion tensor imaging (DTI) is an ideal tool for examining neural connections and the integrity of white matter. Few studies have used DTI to investigate the impact of rTMS on alterations of whiter matter in TRD.

METHOD

30 young treatment-resistant unipolar depression patients (19 males and 11 females) were enrolled in a double-blind, randomized high-frequency (15 Hz) rTMS treatment study. Seventeen patients were treated with real stimulation, and 13 were treated with sham stimulation. White-matter fractional anisotropy (FA) was evaluated using voxel-based analysis (VBA) of FA maps derived from DTI before and after treatment. Twenty-five age- and gender-matched subjects were examined as a control group.

RESULTS

In an exploratory VBA method, clusters of fifty voxels or greater that survived a family-wise error (FWE)-corrected threshold of p<0.05 were considered significant. The results revealed significantly reduced FA in the left middle frontal gyrus, with peak coordinates [-18 46 -14] in TRD patients. This reduced FA was significantly improved after active rTMS treatment, but not sham stimulation. FA increases were correlated with decreased depressive symptoms.

LIMITATIONS

This study requires replication and further clarification in a larger patient population, and optimization of stimulation locations and methods.

CONCLUSIONS

These results suggest that the efficacy of rTMS on TRD is related to increased white-matter FA in the left middle frontal gyrus.

Role of COMT, 5-HT(1A) , and SERT genetic polymorphisms on antidepressant response to Transcranial Magnetic Stimulation

BACKGROUND

Transcranial Magnetic Stimulation (TMS) is an effective technique in the treatment of depression, specifically in drug-resistant patients. However, there is little data available on the influence of genetic variables on TMS response.

METHODS

We analyzed the role of three genetic polymorphisms that affected the antidepressant response: serotonin transporter promoter region (SERTPR) polymorphism, 5-HT(1A) serotonergic receptor promoter region polymorphism (rs6295), and the coding region of COMT gene polymorphism (rs4680). Ninety patients with a major depressive drug-resistant episode due to a Major Depressive Disorder or to a Bipolar Disorder were included in our study. Patients underwent high frequency TMS, focused on the left prefrontal cortex, for 2 weeks. At study completion, the response rate was 45.5%. Effects of gene polymorphisms on clinical improvement were analyzed with an analysis of variance with each gene (SERTPR, 5-HT(1A) , and COMT) as factors and the Hamilton Rating Scale for Depression variation from baseline to the end of the treatment as a dependent variable.

RESULTS

We found a significant model in which three factors were not significant (diagnosis, COMT, and SERTPR), whereas factor 5-HT(1A) showed a significant influence on the outcome, with patients with C/C genotype showing a greater improvement than G/G and C/G and no difference between G/G and C/G.

CONCLUSION

According to our data, 5-HT(1A) polymorphism may play a role in influencing TMS response. The effect of COMT and SERTPR did not reach statistical significance. The analysis of these and other candidate genes in larger samples could help explain genetic influence on TMS response.

The role of serotonin receptor subtypes in treating depression: a review of animal studies

RATIONALE

Serotonin reuptake inhibitors (SSRIs) are effective in treating depression. Given the existence of different families and subtypes of 5-HT receptors, multiple 5-HT receptors may be involved in the antidepressant-like behavioral effects of SSRIs.

OBJECTIVE

Behavioral pharmacology studies investigating the role of 5-HT receptor subtypes in producing or blocking the effects of SSRIs were reviewed.

RESULTS

Few animal behavior tests were available to support the original development of SSRIs. Since their development, a number of behavioral tests and models of depression have been developed that are sensitive to the effects of SSRIs, as well as to other types of antidepressant treatments. The rationale for the development and use of these tests is reviewed. Behavioral effects similar to those of SSRIs (antidepressant-like) have been produced by agonists at 5-HT(1A), 5-HT(1B), 5-HT(2C), 5-HT(4), and 5-HT(6) receptors. Also, antagonists at 5-HT(2A), 5-HT(2C), 5-HT(3), 5-HT(6), and 5-HT(7) receptors have been reported to produce antidepressant-like responses. Although it seems paradoxical that both agonists and antagonists at particular 5-HT receptors can produce antidepressant-like effects, they probably involve diverse neurochemical mechanisms. The behavioral effects of SSRIs and other antidepressants may also be augmented when 5-HT receptor agonists or antagonists are given in combination.

CONCLUSIONS

The involvement of 5-HT receptors in the antidepressant-like effects of SSRIs is complex and involves the orchestration of stimulation and blockade at different 5-HT receptor subtypes. Individual 5-HT receptors provide opportunities for the development of a newer generation of antidepressants that may be more beneficial and effective than SSRIs.

Higher serotonin 1A binding in a second major depression cohort: modeling and reference region considerations

BACKGROUND

Serotonin 1A receptors (5-HT(1A)) are implicated in major depressive disorder (MDD). We previously reported higher 5-HT(1A) binding potential (BP(F)) in antidepressant naive MDD subjects compared with control subjects, while other studies report lower BP(ND). Discrepancies can be related to differences in study population or methodology. We sought to replicate our findings in a novel cohort and determine whether choice of reference region and outcome measure could explain discrepancies.

METHODS

Nine new control subjects and 22 new not recently medicated (NRM) MDD subjects underwent positron emission tomography. BP(F) and BP(ND) were determined using a metabolite and free fraction corrected arterial input function. BP(ND) was also determined using cerebellar gray matter (CGM) and cerebellar white matter (CWM) reference regions as input functions.

RESULTS

BP(F) was higher in the new NRM cohort (p = .037) compared with new control subjects, comparable to the previous cohort (p = .04). Cohorts were combined to examine the reference region and outcome measure. BP(F) was higher in the NRM compared with control subjects (p = .0001). Neither BP(ND) using CWM (p = .86) nor volume of distribution (V(T)) (p = .374) differed between groups. When CGM was used, the NRM group had lower 5-HT(1A) BP(ND) compared with control subjects (p = .03); CGM V(T) was higher in NRM compared with control subjects (p = .007).

CONCLUSIONS

Choice of reference region and outcome measure can produce different 5-HT(1A) findings. Higher 5-HT(1A) BP(F) in MDD was found with the method with fewest assumptions about nonspecific binding and a reference region without receptors.

SSRI response in depression may be influenced by SNPs in HTR1B and HTR1A

OBJECTIVES

Desensitization of serotonin 1A (HTR1A) and 1B (HTR1B) autoreceptors has been proposed to be involved in the delayed onset of response to selective serotonin reuptake inhibitors (SSRIs). Variations in gene expression in these genes may thus affect SSRI response.

METHODS

Here, we test this hypothesis in two samples from the Sequenced Treatment Alternatives to Relieve Depression (STAR*D), and show evidence for involvement of several genetic variants alone and in interaction. Initially, three functional single nucleotide polymorphisms (SNPs) in the HTR1B gene and in the HTR1A gene were analyzed in 153 depressed patients treated with citalopram. The 16-item Quick Inventory of Depressive Symptomatology Clinician scores were evaluated over time with respect to genetic variation.

RESULTS

Individuals homozygous for the -1019 G allele (rs6295) in HTR1A showed the higher baseline 16-item Quick Inventory of Depressive Symptomatology Clinician scores (P=0.033), and by 12 weeks had a significantly lower response rate (P=0.005). HTR1B haplotypes were estimated according to the previously reported in-vitro expression levels. Individuals who were homozygous for the high-expression haplotype showed significantly slower response to citalopram (P=0.034). We then analyzed more SNPs in the extended overall STAR*D sample. Although we could not directly test the same functional SNPs, we found that homozygotes for the G allele at rs1364043 in HTR1A (P=0.045) and the C allele of rs6298 in HTR1B showed better response to citalopram over time (P=0.022). Test for interaction between rs6298 in HTR1B and rs1364043 in HTR1A was significant (overall P=0.032).

CONCLUSION

Our data suggest that an enhanced capacity of HTR1B or HTR1A transcriptional activity may impair desensitization of the autoreceptors during SSRI treatment.

Role of serotonergic gene polymorphisms on response to transcranial magnetic stimulation in depression

Transcranial magnetic stimulation (TMS) has been extensively studied as a treatment for Major Depression. However, no data are available about the role of genetic variables on the response to this treatment. We analysed the role of two polymorphisms that influence the response to antidepressants: the polymorphisms of the serotonin transporter promoter region (SERTPR) and of the 5-HT(1A) serotonergic receptor promoter region (-1019C/G). Ninety-nine patients from two double-blind, randomised, sham-controlled TMS trials were enrolled. There was a significant influence (p=0.016) of the SERTPR polymorphism on treatment outcome, without differences between active and sham stimulation. Conversely, there was a significant (p=0.014) interaction between 5-HT(1A) genotype and type of stimulation: C/C patients showed a higher difference between active and sham stimulation, indicating that these patients benefited more by TMS than C/G and G/G subjects. Our sample has not the power to control for the possible influence of different medications on these results.

Nonpharmacological, somatic treatments of depression: electroconvulsive therapy and novel brain stimulation modalities

Until recently, a review of nonpharmacological, somatic treatments of psychiatric disorders would have included only electroconvulsive therapy (ECT). This situation is now changing very substantially. Although ECT remains the only modality in widespread clinical use, several new techniques are under investigation. Their principal indication in the psychiatric context is the treatment of major depression, but other applications are also being studied. All the novel treatments involve brain stimulation, which is achieved by different technological methods. The treatment closest to the threshold of clinical acceptability is transcranial magnetic stimulation (TMS). Although TMS is safe and relatively easy to administer, its efficacy has still to be definitively established. Other modalities, at various stages of research development, include magnetic seizure therapy (MST), deep brain stimulation (DBS), and vagus nerve stimulation (VNS). We briefly review the development and technical aspects of these treatments, their potential role in the treatment of major depression, adverse effects, and putative mechanism of action. As the only one of these treatment modalities that is in widespread clinical use, more extended consideration is given to ECT Although more than half a century has elapsed since ECT was first introduced, it remains the most effective treatment for major depression, with efficacy in patients refractory to antidepressant drugs and an acceptable safety profile. Although they hold considerable promise, the novel brain stimulation techniques reviewed here will be need to be further developed before they achieve clinical acceptability.

Safety and efficacy of repetitive transcranial magnetic stimulation in the treatment of depression: a critical appraisal of the last 10 years

Depression is a common and debilitating illness, for which alternative treatments are urgently needed. Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive and relatively painless experimental technique of altering brain physiology. The authors critically review the evidence for the efficacy, safety and tolerability of rTMS in the treatment of depression based on published data over the last decade. They also discuss studies which have examined relevant clinical, demographic, methodological, and technical parameters that might be implicated in optimizing the antidepressant efficacy of this technique. rTMS depression trials conducted through early 2006 are included in this review, which focuses mainly on the results of published sham-controlled studies, literature reviews and meta-analyses. Trials published so far have been characterized by the use of a great variety of stimulation parameters, study designs, questionable sham controls, small sample sizes and heterogeneously depressed populations, all of which have made comparisons between studies difficult. Meta-analyses of 2-week rTMS sham-controlled studies support, for the most part, the antidepressant effects of rTMS which are statistically superior to sham. However, the degree of clinical improvement remains small, although greater efficacy has been shown with longer treatment courses and predictors of response to rTMS are progressively being identified. rTMS is a promising antidepressant treatment with overall minor adverse effects. Because the clinical efficacy of rTMS as an antidepressant remains questionable, further systematic, large-scale multicenter studies comparing rTMS to a sham and/or to an antidepressant medication along with more stringent stimulation parameters are warranted in order to identify patient populations most likely to benefit and treatment parameters most likely to optimize its antidepressant efficacy.

Exposure to AC and DC magnetic fields induces changes in 5-HT1B receptor binding parameters in rat brain membranes

The binding properties of the G-protein coupled receptor (GPCR) serotonin 5-HT1B receptor were studied under exposure to AC (50 and 400 Hz) and DC magnetic fields (MF) in rat brain membranes. This was an attempt at replicating the positive findings of Massot et al. In saturation experiments using [3H]5-HT, 1-h exposures at 1.1 mT(rms) 50 Hz caused statistically significant increases in both the K(D) and B(max) binding parameters, from 1.74 +/- 0.3 to 4.51 +/- 0.86 nM and from 1428 +/- 205 to 2137 +/- 399 CPM, respectively, in good agreement with previous results. Exposure of the membranes at 400 Hz 0.675 mT(rms) did not elicit a larger increase in K(D) in spite of a much larger induced current density. DC fields (1.1 and 11 mT) had a lesser effect compared to AC fields at low values of K(Dsham), but decreased the affinity at higher values of K(Dsham). Modeling of the receptor-ligand-G protein interactions using the extended ternary complex model yielded good fits for all our data and that of Massot et al., showing that the AC field may act by decreasing the ability of the G-protein to alter the ligand-receptor affinity. The hypothesis is that the bipolar nature of the AC field explains the different nature of the effects observed with AC and DC exposures. These findings constitute one of the few documented pieces of evidence for cell-free effects of DC and extremely low frequency (ELF) AC MFs in the mT range.

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

Transcranial magnetic stimulation (TMS) has been proposed as a treatment for depression and anxiety disorders. While the antidepressant effect has been modelled in animals, there have been few attempts to examine a possible anxiolytic effect of repetitive TMS (rTMS) in animal models. We administered 18 days of rTMS to male Sprague-Dawley rats. On days 10 through 18, rats were tested in several anxiety models (social interaction, emergence, elevated plus-maze, and predator odor avoidance) and in the forced swim test. No group differences were apparent on any of the anxiety models, while TMS produced an antidepressant effect in the forced swim test. Interestingly, on day 1 of the forced swim test, the home cage control group displayed increased swimming behaviour compared with sham-treated animals, suggesting an observable level of stress may have accompanied sham treatment. The results from the forced swim test suggested that TMS had modest antidepressant properties, but it did not show anxiolytic properties in the models examined. The study also suggested that stress associated with handling should be taken into account in the interpretation of TMS studies in animals.

Antidepressant-like effects of cranial stimulation within a low-energy magnetic field in rats

BACKGROUND

Evidence suggests that a novel type of magnetic resonance imaging (MRI) scan called echo planar magnetic resonance spectroscopic imaging (EP-MRSI) has mood-elevating actions in humans during the depressive phases of bipolar disorder. We examined whether a low-energy component of EP-MRSI (low-field magnetic stimulation [LFMS]) has antidepressant-like, locomotor-stimulating, or amnestic effects in rats.

METHODS

We examined the effects of LFMS on immobility in the forced swim test (FST) and activity within an open field in separate groups of rats. After exposure to forced swimming, rats received LFMS (three 20-min sessions at 1.5 G/cm and .75 V/m) before behavioral testing. We also examined the effects of LFMS on fear conditioning (FC), a learning paradigm that also involves exposure to stressful conditions.

RESULTS

Low-field magnetic stimulation reduced immobility in the FST, an antidepressant-like effect qualitatively similar to that of standard antidepressants. Low-field magnetic stimulation did not alter locomotor activity or FC.

CONCLUSIONS

Low-field magnetic stimulation has antidepressant-like effects in rats that seem unrelated to locomotor-activating or amnestic effects. These findings raise the possibility that electromagnetic fields can affect the brain biology and might have physiologic consequences that offer novel approaches to therapy for psychiatric disorders. These same consequences might render MRI-based scans more invasive than previously appreciated.

5-HT1A receptors, gene repression, and depression: guilt by association

The serotonin system is implicated in major depression and suicide and is negatively regulated by somatodendritic 5-HT1A autoreceptors. Desensitization of 5-HT1A autoreceptors is implicated in the 2- to 3-week latency for antidepressant treatments. Alterations in 5-HT1A receptor levels are reported in depression and suicide, and gene knockout of the 5-HT1A receptor results in an anxiety phenotype, suggesting that abnormal transcriptional regulation of this receptor gene may underlie these disorders. The 5-HT1A receptor gene is negatively regulated in neurons by repressors including REST/NRSF, Freud-1, NUDR/Deaf-1, and Hes5. The association with major depression, suicide, and panic disorder of a new functional 5-HT1A polymorphism at C(-1019)G that selectively blocks repression of the 5-HT1A autoreceptor by NUDR further suggests a causative role for altered regulation of this receptor in predisposition to mental illness. The authors review evidence that altered transcription of the 5-HT1A receptor can affect the serotonin system and limbic and cortical areas, leading to predisposition to depression.

rTMS of the prefrontal cortex in the treatment of chronic migraine: a pilot study

A recent fMRI study showed that dorsolateral prefrontal cortex (DLPFC) exerts an inhibitory control on pain pathways in humans. We investigated whether high-frequency rTMS over left DLPFC could ameliorate chronic migraine. Treatment consisted of 12 rTMS sessions, delivered in alternate days over left DLPFC. Sham rTMS was used as placebo. Eleven patients were randomly assigned to the rTMS (n=6) or to the placebo (n=5) treatment. Measures of attack frequency, headache index, number of abortive medications (outcome measures) were recorded in the month before, during and in the month after treatment. Subjects treated by rTMS showed a significant reduction of the outcome measures during and in the month after the treatment as compared to the month before treatment. No significant differences in the outcome measures were observed in the placebo group. High-frequency rTMS over left DLPFC was able to ameliorate chronic migraine. This is in agreement with the suggested role of DLPFC in pain control.

Repetitive transcranial magnetic stimulation: A possible novel therapeutic approach to eating disorders

The two most common eating disorders, anorexia nervosa and bulimia nervosa, are characterized by aberrant eating patterns and disturbances in body image. Treatment involves combining individual, behavioural, group, and family therapies, possibly with medications. Studies have found that medication, chiefly antidepressants, could be of help in bulimia nervosa but the evidence is weaker for use in anorexia nervosa. Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive technique that briefly stimulates or depresses cortical areas within the brain. It has been used in the treatment of various psychiatric disorders, especially major depression, which is a condition that patients with eating disorders often experience as a significant comorbidity. Given that both disorders may share a common pathogenesis, this report proposes that rTMS may represent an alternative strategy for the treatment of eating disorders. Other evidence that supports this notion comes from animal studies that show that rTMS can change feeding behaviours and central neurotransmitters related to the regulation of eating behaviours. Further investigation into the dose, duration and type of rTMS stimulus is needed to verify the efficacy of this intervention in eating disorders.

Antidepressive Stimulationsverfahren

Affective disorders, especially major depression, are the most common psychiatric disorders. Although well treatable, a number of patients do not or do not sufficiently respond to antidepressant pharmacotherapy. Therefore there is a need for safe and efficient alternative therapeutic strategies. Neurostimulatory therapies such as electroconvulsive therapy, repetitive transcranial magnetic stimulation, and vagus nerve stimulation belong to these alternatives. In this article we review their mechanisms of action and summarize efficacy and adverse effects.

Effects of triiodothyronine and fluoxetine on 5-HT1A and 5-HT1B autoreceptor activity in rat brain: regional differences

The thyroid hormone triiodothyronine (T3) augments and accelerates the effects of antidepressant drugs. Although the majority of studies showing this have used tricyclics, a few studies have shown similar effects with the selective serotonin re-uptake inhibitor (SSRI) fluoxetine. In this study we investigated the effects of fluoxetine (5 mg/kg), T3 (20 microg/kg) and the combination of these drugs, each administered daily for 7 days, on serotonergic function in the rat brain, using in vivo microdialysis. Fluoxetine alone induced a trend towards desensitization of 5-HT1A autoreceptors as shown by a reduction in the effect of 8-OH-DPAT to lower 5-HT levels in frontal cortex, and desensitized 5-HT1B autoreceptors in frontal cortex. The combination of fluoxetine and T3 induced desensitization of 5-HT1B autoreceptors in hypothalamus. Since there is evidence linking hypothalamic function and depression, we suggest that this effect may partly account for the therapeutic efficacy of the combination of an SSRI and T3.

Effects of acute repetitive transcranial magnetic stimulation on extracellular serotonin concentration in the rat prefrontal cortex

Repetitive transcranial magnetic stimulation (rTMS) changes the function of the cortex. This study clarified the effects of acute rTMS treatment on extracellular serotonin (5-HT) concentrations in the rat prefrontal cortex (PFC) by using in vivo microdialysis methods. Each rat received acute rTMS treatment of the frontal brain at 500 stimuli from twenty trains applied at 25 Hz for 1 s at 1-min intervals between trains. Sham-treated rats received the same handling procedure and sound of the stimulator. Sham treatment increased the extracellular 5-HT levels compared with the non-treated group. However, rTMS treatment using the stimulation intensity of 110% motor threshold eliminated the increase in 5-HT levels induced by the sham treatment. Acute rTMS treatment of the frontal brain is related to the serotonergic neuronal system in the rat PFC, and it may have therapeutic implications for emotional disorders.

Differential effects of the novel antidepressant agomelatine (S 20098) versus fluoxetine on 5-HT1A receptors in the rat brain

Agomelatine (S 20098) is a novel antidepressant drug with melatonin receptor agonist and 5-HT(2C) receptor antagonist properties, but actual mechanisms underlying its antidepressant action are unknown. Because functional desensitization of 5-HT(1A) autoreceptors in the dorsal raphe nucleus (DRN) occurs after chronic administration of several classes of antidepressants, we investigated whether this adaptive change could also be induced by agomelatine. Neither acute nor chronic treatment with agomelatine (10 mg/kg i.p. for 14 days or 50 mg/kg i.p. for 21 days) changed the density of 5-HT(1A) receptors and their coupling with G proteins in the DRN and the hippocampus in rats. Moreover, these treatments did not affect the basal electrophysiological characteristics and the responses to 5-HT(1A) receptor stimulation of DRN and hippocampal neurons in brain slices. Parallel experiments with melatonin (10 mg/kg i.p. for 14 days) and fluoxetine (5 mg/kg i.p. for 14 days) as reference compounds showed that the former was unable to affect 5-HT(1A) receptors whereas the latter decreased both the 5-HT(1A) receptor-mediated [(35)S]GTP-gamma-S binding and the potency of ipsapirone, a 5-HT(1A) receptor agonist, to inhibit neuronal firing in the DRN. These data indicate that the antidepressant action of agomelatine is not mediated through the same mechanisms as SSRIs or tricyclics.

Chronic fluoxetine-induced desensitization of 5-HT1A and 5-HT1B autoreceptors: regional differences and effects of WAY-100635

Desensitization of 5-HT(1A) and 5-HT(1B) autoreceptors is thought to be the mechanism underlying the therapeutic effects of fluoxetine and other selective serotonin reuptake inhibitors when these are administered chronically. The blockade of 5-HT(1A) autoreceptors occurring on administration of a selective serotonin reuptake inhibitor together with a 5-HT(1A) autoreceptor antagonist is responsible for the acute increase in 5-hydroxytryptamine (serotonin, 5-HT) levels observed under these circumstances. The effects of repeated administration of selective serotonin reuptake inhibitors together with 5-HT(1A) receptor antagonists have not been widely studied. In this work, we found that the effects of fluoxetine (5 mg/kg, i.p., daily for 12 days) to desensitize 5-HT(1B) autoreceptors in the frontal cortex, as measured by the effect of the locally administered 5-HT(1B) receptor agonist, 3-(1,2,5,6-tetrahydropyrid-4-yl)pyrrolo[3,2-b]pyrid-5-one (CP 93129), and to desensitize 5-HT(1A) autoreceptors as measured by the action of the 5-HT(1A) receptor agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT; 50 microg/kg, s.c.) to reduce 5-HT levels in cortex, were prevented by concomitant administration of the 5-HT(1A) receptor antagonist, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide (WAY-100635; 0.3 mg/kg, s.c.). 5-HT(1B) receptor activity in the hypothalamus, as measured by the effects of locally administered CP 93129, and 5-HT(1A) autoreceptor activity, as determined by the effects of subcutaneous 8-OH-DPAT to reduce 5-HT levels in hypothalamus, were not altered either by fluoxetine alone or by fluoxetine in the presence of WAY-100635. The data suggest that the regulation of extracellular levels of 5-HT in the cortex and hypothalamus is subject to different autoregulatory mechanisms.

Repetitive transcranial magnetic stimulation improves open field locomotor recovery after low but not high thoracic spinal cord compression-injury in adult rats

Electromagnetic fields are able to promote axonal regeneration in vitro and in vivo. Repetitive transcranial magnetic stimulation (rTMS) is used routinely in neuropsychiatric conditions and as an atraumatic method to activate descending motor pathways. After spinal cord injury, these pathways are disconnected from the spinal locomotor generator, resulting in most of the functional deficit. We have applied daily 10 Hz rTMS for 8 weeks immediately after an incomplete high (T4-5; n = 5) or low (T10-11; n = 6) thoracic closed spinal cord compression-injury in adult rats, using 6 high- and 6 low-lesioned non-stimulated animals as controls. Functional recovery of hindlimbs was assessed using the BBB locomotor rating scale. In the control group, the BBB score was significantly better from the 7th week post-injury in animals lesioned at T4-5 compared to those lesioned at T10-11. rTMS significantly improved locomotor recovery in T10-11-injured rats, but not in rats with a high thoracic injury. In rTMS-treated rats, there was significant positive correlation between final BBB score and grey matter density of serotonergic fibres in the spinal segment just caudal to the lesion. We propose that low thoracic lesions produce a greater functional deficit because they interfere with the locomotor centre and that rTMS is beneficial in such lesions because it activates this central pattern generator, presumably via descending serotonin pathways. The benefits of rTMS shown here suggest strongly that this non-invasive intervention strategy merits consideration for clinical trials in human paraplegics with low spinal cord lesions.

Effects of chronic antidepressants and electroconvulsive shock on serotonergic neurotransmission in the rat hippocampus

The hippocampus may play a critical role in the pathophysiology and treatment of depression. There are two main lines of evidence for this: firstly, many of its functions correspond to those altered in depression, and secondly, many hippocampal functions are regulated by the serotonergic (5-HT) system, which is a common target of antidepressant treatments. Chronic effects of antidepressants and electroconvulsive shock (ECS) have been studied by various methods using electrophysiology, in vivo microdialysis or ex vivo neurochemical measurements. The aim of the current review is to point out possible correlations between these studies based on different methods and to suggest neurochemical mechanisms that result in the observed changes in hippocampal physiology and neurogenesis. These changes in hippocampal neurochemistry are reviewed and compared with the abnormalities associated with stress, corticosterone or depression.

Effects of repetitive transcranial magnetic stimulation on behavioral and neurochemical changes in rats during an elevated plus-maze test

In transcranial magnetic stimulation (TMS) the regional electrical activity in the brain is influenced by a pulsed magnetic field. The rapidly changed magnetic field produces electrical currents that activate neurons. Repetitive TMS (rTMS) treatment can cause functional changes in the cortex. The present study clarified the effects of rTMS treatment on behavioral changes in rats, focusing on anxiety by using an elevated plus-maze (plus-maze) test. The effects of rTMS treatment on neurochemical changes during the plus-maze test were investigated by determining the extracellular levels of serotonin (5-HT) and dopamine (DA) in the prefrontal cortex by using in vivo microdialysis. Each rat received rTMS of the frontal brain for 3 days, during which 125 stimuli from five trains in a day were applied at 25 Hz for 1 s with 2-min intervals between trains. Three-day series of (chronic) rTMS treatment caused significant increases in the time spent in open arms and the number of entries into open arms of the plus-maze compared with non-treated and sham-treated rats, which were not observed in 1-day series of (acute) rTMS treatment. Chronic rTMS treatment suppressed the increases in 5-HT levels induced by the plus-maze test, but did not influence the elicited DA levels. These data suggest that chronic rTMS treatment of the frontal brain has anxiolytic effects in rats, which are related to the 5-HTergic neuronal system.

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.

The combined dexamethasone-CRH test before and after repetitive transcranial magnetic stimulation (rTMS) in major depression

BACKGROUND

Hypothalamic-pituitary-adrenocortical (HPA) dysregulation assessed by the combined dexamethasone corticotropin releasing hormone test (DEX/CRH test) has been demonstrated to normalize after successful antidepressant pharmacotherapy. Here, we investigated whether repetitive transcranial magnetic stimulation (rTMS) also leads to a normalization of HPA system activity in depressed patients.

METHODS

Thirty-seven medication free patients suffering from a major depressive episode (DSM-IV) underwent a DEX/CRH test before and after 13 daily sessions of left prefrontal rTMS in an open trial.

RESULTS

There was an overshoot of CRH-induced cortisol release that was not affected by rTMS treatment. Postdexamethasone cortisol levels prior to CRH challenge decreased in responders after rTMS treatment, whereas no change of CRH-induced adrenocorticotropic hormone (ACTH) and cortisol release in responders or nonresponders was observed.

CONCLUSIONS

The persisting HPA system hyperactivity after rTMS suggests a high risk for relapse and therefore argues for an immediate maintenance therapy in patients responding to this treatment.

Alcohol reduces prefrontal cortical excitability in humans: a combined TMS and EEG study

The effects of alcohol (0.8 g/kg) on the prefrontal cortex were studied in nine healthy subjects using the technique of transcranial magnetic stimulation (TMS) combined with electroencephalography (EEG). A total of 120 magnetic pulses were delivered with a figure-of-eight coil to the left prefrontal cortex at the rate of 0.4-0.7 Hz. The EEG was recorded simultaneously with 60 scalp electrodes (41 electrodes were used for analysis); the TMS-evoked activation was estimated by the area under the global mean field amplitude (GMFA) time curve. TMS caused changes in EEG activity lasting up to 270 ms poststimulus. Alcohol decreased GMFA at 30-270 ms poststimulus (713+/-303 vs 478+/-142 microV ms; p=0.007). Alcohol-induced differences were most pronounced at anterior electrodes. These results suggest that alcohol reduces the excitability in the prefrontal cortex.

Effects of antidepressant pharmacotherapy after repetitive transcranial magnetic stimulation in major depression: an open follow-up study

An increasing number of clinical studies demonstrates antidepressant effects of repetitive transcranial magnetic stimulation (rTMS). However, limited data are available so far concerning the stability of these effects and the efficacy of subsequent maintenance therapy. Therefore, we examined whether antidepressant pharmacotherapy can stabilize clinical improvement after rTMS monotherapy. Twenty-six drug-free patients suffering from a major depressive episode (DSM-IV criteria) participated in an open rTMS trial over two weeks (10-13 sessions, 10 Hz, left prefrontal stimulation at 100% motor threshold intensity). Subsequently, the patients were followed up during standardized antidepressant pharmacotherapy with mirtazapine for a further 4 weeks. The interval between the last rTMS and the first day of pharmacotherapy varied between one and five days. After two weeks of rTMS monotherapy 39% of the patients responded to rTMS by at least 50% reduction in their Hamilton Rating Scale for Depression (HRSD) scores. Treatment interruption after rTMS resulted in a significant increase in the HRSD score of rTMS responders. The degree of the deterioration was dependent on the length of interval without treatment. However, this deterioration was reverted and the further clinical course stabilized by subsequent mirtazapine treatment. The overall response rate after rTMS and mirtazapine treatment (alone or in combination) was 77%. Our results suggest that (1) antidepressant pharmacotherapy is able to further improve the clinical response to rTMS and (2) that responders to rTMS monotherapy should receive subsequent psychopharmalogical treatment without interruption in order to avoid a deterioration of symptoms.

Transcranial magnetic stimulation induces increases in extracellular levels of dopamine and glutamate in the nucleus accumbens

Transcranial magnetic stimulation (TMS) is a non-invasive approach used for stimulating the human brain. Repetitive stimulation over the prefrontal cortex has proven effective in the treatment of major depression, however the mechanism of the antidepressant action is unknown. Since the nucleus accumbens is a major region implicated in reward circuitry and depressive disorders, we used the microdialysis technique to study some of the neurochemical changes induced in that region during and after acute TMS. Magnetic stimulation was applied over the frontal or the caudal cortex of the rat brain using a special coil design and microdialysis samples were collected before, during and after the stimulation session. The extracellular levels of both dopamine and glutamate in the nucleus accumbens were increased during the stimulation while the extracellular levels of acetylcholine were not affected. Stimulation over the caudal cortex caused a greater increase in dopamine levels than the stimulation over the frontal cortex, while such difference was not observed for glutamate levels. The changes in dopamine and glutamate extracellular levels in the nucleus accumbens may play a role in the antidepressant effect of TMS and it is therefore suggested that the effect of stimulation over caudal cortical sites on depressive patients will be examined.

DNA variation and psychopharmacology of the human serotonin receptor 1B (HTR1B) gene

One of the neurotransmitter serotonin's receptors, HTR1B, is of interest for many neuropsychiatric traits, illnesses and treatments for multiple reasons, especially its tissue distribution, pharmacological profile and findings from mice lacking the receptor, along with reasons generally implicating serotonin. Eight mutation scans have uncovered sixteen polymorphisms in the coding sequence and surrounding 5'- and 3'-untranslated regions and much is now known of the distribution of these polymorphisms in various ethnic groups and their linkage disequilibrium relationships. Thus far, evidence exists that the uncommon missense T371G (Phe124Cys) and the common promoter region A-161T polymorphisms may exhibit functional effects and possibly that the common synonymous G861C (or more likely a variant in linkage disequilibrium with G861C) does as well. From the eighteen reported population-based case control studies of HTR1B to multiple disorders, several facts stand out. There exists preliminary evidence for association of G861C with i) antisocial alcoholism in the Finnish; ii) alcoholism in the presence of inactive aldehyde dehydrogenase 2 in the Japanese; iii) a history of suicide attempts in European-American personality disorder patients; and iv) minimum lifetime body mass index in Canadian bulimia nervosa patients. From the three reported family-based case control studies of HTR1B to various disorders, one provides preliminary evidence for association of G861C with obsessive compulsive disorder. Although many association studies have been completed, positive results should still be considered preliminary. As these preliminary reports are tested for replication with larger, more powerful samples, there should be increased clarity as to which findings remain robust; in some cases this will require the application of meta-analytic techniques.

Effects of repetitive transcranial magnetic stimulation on visual evoked potentials in migraine

Between attacks, migraine patients are characterized by potentiation instead of habituation of stimulation-evoked cortical responses. It is debated whether this is due to increased or decreased cortical excitability. We have studied the changes in visual cortex excitability by recording pattern-reversal visual evoked potentials (PR-VEP) after low- and high-frequency repetitive transcranial magnetic stimulation (rTMS), known respectively for their inhibitory and excitatory effect on the cortex. In 30 patients (20 migraine without, 10 with aura) and 24 healthy volunteers, rTMS of the occipital cortex was performed with a focal figure-of-eight magnetic coil (Magstim). Nine hundred pulses were delivered randomly at 1 or 10 Hz in two separate sessions. Stimulus intensity was set to the phosphene threshold or to 110% of the motor threshold if no phosphenes were elicited. Before and after rTMS, PR-VEP were averaged sequentially in six blocks of 100zztieresponses during uninterrupted 3.1 Hz stimulation. In healthy volunteers, PR-VEP amplitude was significantly decreased in the first block after 1 Hz rTMS and the habituation normally found in successive blocks after sustained stimulation was significantly attenuated. In migraine patients, 10 Hz rTMS was followed by a significant increase of first block PR-VEP amplitude and by a reversal to normal habituation of the potentiation (or dishabituation) characteristic of the disorder. This effect was similar in both forms of migraine and lasted for at least 9 min. There were no significant changes of PR-VEP amplitudes after 1 Hz rTMS in migraineurs and after 10 Hz rTMS in healthy volunteers, nor after sham stimulation. The recovery of a normal PR-VEP habituation pattern after high-frequency rTMS is probably due to activation of the visual cortex and the dishabituation in healthy volunteers to cortical inhibition. We conclude, therefore, that the deficient interictal PR-VEP habituation in migraine is due to a reduced, and not to an increased, pre-activation excitability level of the visual cortex.

Effects of chronically administered venlafaxine on 5-HT receptor activity in rat hippocampus and hypothalamus

The effects of chronic administration of the mixed serotonin [5-hydroxytryptamine (5-HT)]/norepinephrine re-uptake inhibitor venlafaxine (5 mg/kg daily by osmotic minipump for 28 days) on the sensitivity of somatodendritic 5-HT(1A) autoreceptors on serotonergic neurons innervating the hypothalamus, and on 5-HT(1B) autoreceptors in both hypothalamus and hippocampus, were determined using in vivo microdialysis in freely moving rats. Venlafaxine induced a reduction in sensitivity of 5-HT(1B) autoreceptors in hypothalamus, but did not affect the sensitivity of 5-HT(1A) autoreceptors, or of 5-HT(1B) autoreceptors in hippocampus. The corticosterone and oxytocin responses to the 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT, 0.05 or 0.2 mg/kg), a measure of postsynaptic 5-HT(1A) receptor activity in the hypothalamus, were reduced in animals administered 5 or 10 mg/kg venlafaxine daily by intraperitoneal injection for 21 days. This desensitization of post-synaptic 5- HT(1A) receptors in the hypothalamus may be a consequence of increased 5-HT levels induced by desensitization of the presynaptic 5-HT(1B) receptors. These results taken together with those of previous studies suggest that the hypothalamus might be an important site of drug action, and that venlafaxine has an overall mechanism similar to that of selective serotonin re-uptake inhibitors.

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.