Repetitive transcranial magnetic stimulation (rTMS) is increasingly used as a treatment for neurological and psychiatric disorders. Although the induced field is focused on a target region during rTMS, adjacent areas also receive stimulation at a lower intensity and the contribution of this perifocal stimulation to network-wide effects is poorly defined. Here, we examined low-intensity rTMS (LI-rTMS)-induced changes on a model neural network using the visual systems of normal (C57Bl/6J wild-type, n = 22) and ephrin-A2A5^−/− (n = 22) mice, the latter possessing visuotopic anomalies. Mice were treated with LI-rTMS or sham (handling control) daily for 14 d, then fluorojade and fluororuby were injected into visual cortex. The distribution of dorsal LGN (dLGN) neurons and corticotectal terminal zones (TZs) was mapped and disorder defined by comparing their actual location with that predicted by injection sites. In the afferent geniculocortical projection, LI-rTMS decreased the abnormally high dispersion of retrogradely labeled neurons in the dLGN of ephrin-A2A5^−/− mice, indicating geniculocortical map refinement. In the corticotectal efferents, LI-rTMS improved topography of the most abnormal TZs in ephrin-A2A5^−/− mice without altering topographically normal TZs. To investigate a possible molecular mechanism for LI-rTMS-induced structural plasticity, we measured brain derived neurotrophic factor (BDNF) in the visual cortex and superior colliculus after single and multiple stimulations. BDNF was upregulated after a single stimulation for all groups, but only sustained in the superior colliculus of ephrin-A2A5^−/− mice. Our results show that LI-rTMS upregulates BDNF, promoting a plastic environment conducive to beneficial reorganization of abnormal cortical circuits, information that has important implications for clinical rTMS.

Exposure to man-made electromagnetic fields (EMFs), which increasingly pollute our environment, have consequences for human health about which there is continuing ignorance and debate. Whereas there is considerable ongoing concern about their harmful effects, magnetic fields are at the same time being applied as therapeutic tools in regenerative medicine, oncology, orthopedics, and neurology. This paradox cannot be resolved until the cellular mechanisms underlying such effects are identified. Here, we show by biochemical and imaging experiments that exposure of mammalian cells to weak pulsed electromagnetic fields (PEMFs) stimulates rapid accumulation of reactive oxygen species (ROS), a potentially toxic metabolite with multiple roles in stress response and cellular ageing. Following exposure to PEMF, cell growth is slowed, and ROS-responsive genes are induced. These effects require the presence of cryptochrome, a putative magnetosensor that synthesizes ROS. We conclude that modulation of intracellular ROS via cryptochromes represents a general response to weak EMFs, which can account for either therapeutic or pathological effects depending on exposure. Clinically, our findings provide a rationale to optimize low field magnetic stimulation for novel therapeutic applications while warning against the possibility of harmful synergistic effects with environmental agents that further increase intracellular ROS. Repetitive low-intensity magnetic stimulation has been used in the treatment of disease for over 50 years. Associated benefits have included alleviation of depression, memory loss, and symptoms of Parkinson disease, as well as accelerated bone and wound healing and the treatment of certain cancers, independently of surgery or drugs. However, the cellular mechanisms underlying these effects remain unclear. Here, we demonstrate that repetitive magnetic field exposure in human cells stimulates production of biological stress response chemicals known as reactive oxygen species (ROS). At moderate doses, we find that reactive oxygen actively stimulates cellular repair and stress response pathways, which might account for the observed therapeutic effects to repetitive magnetic stimulation. We further show that this response requires the function of a well-characterized, evolutionarily conserved flavoprotein receptor known as cryptochrome, which has been implicated in magnetic sensing in organisms ranging from plants to flies, including migratory birds. We conclude that exposure to weak magnetic fields induces the production of ROS in human cells and that this process requires the presence of the cryptochrome receptor.

Although the organization of neuronal circuitry is shaped by activity patterns, the capacity to modify and/or optimize the structure and function of whole projection pathways using external stimuli is poorly defined. We investigate whether neuronal activity induced by pulsed magnetic fields (PMFs) alters brain structure and function. We delivered low‐intensity PMFs to the posterior cranium of awake, unrestrained mice (wild‐type and ephrin‐A2A5 ^‐/‐ ) that have disorganized retinocollicular circuitry and associated visuomotor deficits. Control groups of each genotype received sham stimulation. Following daily stimulation for 14 d, we measured biochemical, structural (anterograde tracing), and functional (electrophysiology and behavior) changes in the retinocollicular projection. PMFs induced BDNF, GABA, and nNOS expression in the superior colliculus and retina of wild‐type and ephrin‐A2A5 ^‐/‐ mice. Furthermore, in ephrin‐A2A5 ^‐/‐ mice, PMFs corrected abnormal neuronal responses and selectively removed inaccurate ectopic axon terminals to improve structural and functional organization of their retinocollicular projection and restore normal visual tracking behavior. In contrast, PMFs did not alter the structure or function of the normal projection in wild‐type mice. Sham PMF stimulation had no effect on any mice. Thus, PMF‐induced biochemical changes are congruent with its capacity to facilitate beneficial reorganization of abnormal neural circuits without disrupting normal connectivity and function.—Rodger, J., Mo, C., Wilks, T., Dunlop, S. A., Sherrard, R. M. Transcranial pulsed magnetic field stimulation facilitates reorganization of abnormal neural circuits and corrects behavioral deficits without disrupting normal connectivity. FASEB J. 26, 1593‐1606 (2012). www.fasebj.org

Neuronal maturation during development is a multistep process regulated by transcription factors. The transcription factor RORα (retinoic acid-related orphan receptor α) is necessary for early Purkinje cell (PC) maturation but is also expressed throughout adulthood. To identify the role of RORα in mature PCs, we used Cre-lox mouse genetic toolsin vivothat delete it specifically from PCs between postnatal days 10–21. Up to 14 d of age, differences between mutant and control PCs were not detectable: both were mono-innervated by climbing fibers (CFs) extending along their well-developed dendrites with spiny branchlets. By week 4, mutant mice were ataxic, some PCs had died, and remaining PC soma and dendrites were atrophic, with almost complete disappearance of spiny branchlets. The innervation pattern of surviving RORα-deleted PCs was abnormal with several immature characteristics. Notably, multiple functional CF innervation was reestablished on these mature PCs, simultaneously with the relocation of CF contacts to the PC soma and their stem dendrite. This morphological modification of CF contacts could be induced even later, using lentivirus-mediated depletion ofrorafrom adult PCs. These data show that the late postnatal expression of RORα cell-autonomously regulates the maintenance of PC dendritic complexity, and the CF innervation status of the PC (dendritic vs somatic contacts, and mono-innervation vs multi-innervation). Thus, the differentiation state of adult neurons is under the control of transcription factors; and in their absence, adult neurons lose their mature characteristics and acquire some characteristics of an earlier developmental stage.

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by significant impairment in reciprocal social interactions and communication coupled with stereotyped, repetitive behaviors and restricted interests. Although genomic and functional studies are beginning to reveal some of the genetic complexity and underlying pathobiology of ASD, the consistently reported male bias of ASD remains an enigma. We have recently proposed that retinoic acid-related orphan receptor alpha (RORA), which is reduced in the brain and lymphoblastoid cell lines of multiple cohorts of individuals with ASD and oppositely regulated by male and female hormones, might contribute to the sex bias in autism by differentially regulating target genes, including CYP19A1 (aromatase), in a sex-dependent manner that can also lead to elevated testosterone levels, a proposed risk factor for autism. In this study, we examine sex differences in RORA and aromatase protein levels in cortical tissues of unaffected and affected males and females by re-analyzing pre-existing confocal immunofluorescence data from our laboratory. We further investigated the expression of RORA and its correlation with several of its validated transcriptional targets in the orbital frontal cortex and cerebellum as a function of development using RNAseq data from the BrainSpan Atlas of the Developing Human Brain. In a pilot study, we also analyzed the expression of Rora and the same transcriptional targets in the cortex and cerebellum of adult wild-type male and female C57BL/6 mice. Our findings suggest that Rora/RORA and several of its transcriptional targets may exhibit sexually dimorphic expression in certain regions of the brain of both mice and humans. Interestingly, the correlation coefficients between Rora expression and that of its targets are much higher in the cortex of male mice relative to that of female mice. A strong positive correlation between the levels of RORA and aromatase proteins is also seen in the cortex of control human males and females as well as ASD males, but not ASD females. Based on these studies, we suggest that disruption of Rora/RORA expression may have a greater impact on males, since sex differences in the correlation of RORA and target gene expression indicate that RORA-deficient males may experience greater dysregulation of genes relevant to ASD in certain brain regions during development.