title: Cellular and molecular changes to cortical neurons following low intensity repetitive magnetic stimulation at different frequencies.
abstract: BACKGROUND
  Repetitive transcranial magnetic stimulation is increasingly used as a treatment for neurological dysfunction. Therapeutic effects have been reported for low intensity rTMS (LI-rTMS) although these remain poorly understood.
  
  
  OBJECTIVE
  Our study describes for the first time a systematic comparison of the cellular and molecular changes in neurons in vitro induced by low intensity magnetic stimulation at different frequencies.
  
  
  METHODS
  We applied 5 different low intensity repetitive magnetic stimulation (LI-rMS) protocols to neuron-enriched primary cortical cultures for 4 days and assessed survival, and morphological and biochemical change.
  
  
  RESULTS
  We show pattern-specific effects of LI-rMS: simple frequency pulse trains (10 Hz and 100 Hz) impaired cell survival, while more complex stimulation patterns (theta-burst and a biomimetic frequency) did not. Moreover, only 1 Hz stimulation modified neuronal morphology, inhibiting neurite outgrowth. To understand mechanisms underlying these differential effects, we measured intracellular calcium concentration during LI-rMS and subsequent changes in gene expression. All LI-rMS frequencies increased intracellular calcium, but rather than influx from the extracellular milieu typical of depolarization, all frequencies induced calcium release from neuronal intracellular stores. Furthermore, we observed pattern-specific changes in expression of genes related to apoptosis and neurite outgrowth, consistent with our morphological data on cell survival and neurite branching.
  
  
  CONCLUSIONS
  Thus, in addition to the known effects on cortical excitability and synaptic plasticity, our data demonstrate that LI-rMS can change the survival and structural complexity of neurons. These findings provide a cellular and molecular framework for understanding what low intensity magnetic stimulation may contribute to human rTMS outcomes.
authors.affiliation: School of Animal Biology, University of Western Australia, Perth, Australia; Sorbonne Universités, UPMC Univ Paris 06 & CNRS, IBPS-B2A UMR 8256 Biological Adaptation and Ageing, Paris, France.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Grehl
authors.affiliation: School of Anatomy, Physiology and Human Biology, University of Western Australia, Perth, Australia.
authors.forename: Helena M
authors.initials: HM
authors.lastname: Viola
authors.affiliation: School of Animal Biology, University of Western Australia, Perth, Australia.
authors.forename: Paula I
authors.initials: PI
authors.lastname: Fuller-Carter
authors.affiliation: Telethon Institute for Child Health Research, Centre for Child Health Research, University of Western Australia, Perth, Australia.
authors.forename: Kim W
authors.initials: KW
authors.lastname: Carter
authors.affiliation: School of Animal Biology, University of Western Australia, Perth, Australia.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Dunlop
authors.affiliation: School of Anatomy, Physiology and Human Biology, University of Western Australia, Perth, Australia.
authors.forename: Livia C
authors.initials: LC
authors.lastname: Hool
authors.affiliation: School of Anatomy, Physiology and Human Biology, University of Western Australia, Perth, Australia; Sorbonne Universités, UPMC Univ Paris 06 & CNRS, IBPS-B2A UMR 8256 Biological Adaptation and Ageing, Paris, France.
authors.forename: Rachel M
authors.initials: RM
authors.lastname: Sherrard
authors.affiliation: School of Animal Biology, University of Western Australia, Perth, Australia. Electronic address: jennifer.rodger@uwa.edu.au.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Rodger
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002470:Cell Survival / Q000502:physiology*; D002540:Cerebral Cortex / Q000378:metabolism / Q000502:physiology*; D004574:Electromagnetic Fields; D015870:Gene Expression; D051379:Mice; D016501:Neurites / Q000502:physiology; D009473:Neuronal Plasticity; D009474:Neurons / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D061251:Primary Cell Culture; D050781:Transcranial Magnetic Stimulation
chemical_list: D002118:Calcium
keywords: Calcium signaling; Cortical neurons; Pulsed magnetic fields; Repetitive transcranial magnetic stimulation; rTMS