title: Biphasic monopolar electrical stimulation induces rapid and directed galvanotaxis in adult subependymal neural precursors.
abstract: BACKGROUND
  Following injury such as stroke, adult mammalian subependymal neural precursor cells (NPCs) are induced to proliferate and migrate toward the lesion site where they differentiate into neural cells, albeit with limited efficacy. We are interested in enhancing this migratory ability of NPCs with the long-term goal of promoting neural repair. Herein we build on our previous studies demonstrating that direct current electric fields (DCEFs) promote rapid and cathode-directed migration of undifferentiated adult NPCs (but not differentiated phenotypes) - a phenomenon known as galvanotaxis. While galvanotaxis represents a promising strategy to promote NPC recruitment to lesion sites, stimulation of neural tissue with DCEFs is not a clinically-viable strategy due to the associated accumulation of charge and toxic byproducts. Balanced biphasic waveforms prevent the accumulation of charge and thus are outside of the limitations of DCEFs. In this study, we investigated the effects of balanced biphasic electrical stimulation on the migratory behaviour of undifferentiated subependymal NPCs and their differentiated progeny.
  
  
  METHODS
  NPCs were isolated from the subependymal zone of adult mouse brains and cultured in a NPC colony-forming assay to form neurospheres. Neurospheres were plated onto galvanotaxis chambers in conditions that either promoted maintenance in an undifferentiated state or promoted differentiation into mature phenotypes. Chambers containing cells were then time-lapse imaged in the presence of either biphasic monopolar, or biphasic bipolar electrical stimulation, or in the complete absence of electrical stimulation. Single cell migration was subsequently tracked and the cells' magnitude of velocity, directedness and tortuosity were quantified.
  
  
  RESULTS
  We demonstrate, for the first time, the use of balanced biphasic electric fields to induce galvanotaxis of NPCs. Undifferentiated adult mouse subependymal NPCs exposed to biphasic monopolar stimulation undergo rapid and directed migration toward the cathode. In contrast, both biphasic bipolar stimulation and the lack of electrical stimulation produced non-directed migration of NPCs. Notably, NPCs induced to differentiate into mature phenotypes prior to exposure to electrical stimulation do not migrate in the presence or absence of biphasic stimulation.
  
  
  CONCLUSIONS
  We purport that balanced biphasic stimulation represents a clinically-viable technique for mobilizing NPCs that may be integrated into strategies for promoting endogenous neurorepair.
authors.affiliation: Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Room 407, M5S 3G9, Toronto, Ontario, Canada. robert.babona.pilipos@mail.utoronto.ca.
authors.forename: Robart
authors.initials: R
authors.lastname: Babona-Pilipos
authors.affiliation: Department of Chemical Engineering, University of Waterloo, Waterloo, ON, Canada. atpritch@uwaterloo.ca.
authors.forename: Alex
authors.initials: A
authors.lastname: Pritchard-Oh
authors.affiliation: Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Room 407, M5S 3G9, Toronto, Ontario, Canada. milos.popovic@utoronto.ca.|Lyndhurst Centre, Toronto Rehabilitation Institute, University Health Network, Toronto, ON, Canada. milos.popovic@utoronto.ca.
authors.forename: Milos R
authors.initials: MR
authors.lastname: Popovic
authors.affiliation: Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Room 407, M5S 3G9, Toronto, Ontario, Canada. cindi.morshead@utoronto.ca.|Department of Surgery, University of Toronto, 1 King's College Circle, Room 1156, M5S 1A8, Toronto, ON, Canada. cindi.morshead@utoronto.ca.|Department of Rehabilitation Science, University of Toronto, 160 College Street, Room 1006, Toronto, ON, Canada. cindi.morshead@utoronto.ca.
authors.forename: Cindi M
authors.initials: CM
authors.lastname: Morshead
mesh_terms: D000818:Animals; D001921:Brain / Q000166:cytology / Q000378:metabolism; D002465:Cell Movement; D002478:Cells, Cultured; D004558:Electric Stimulation / Q000379:methods*; D008297:Male; D051379:Mice; D058953:Neural Stem Cells / Q000166:cytology* / Q000378:metabolism; D055495:Neurogenesis / Q000502:physiology*; D009474:Neurons / Q000166:cytology* / Q000378:metabolism; D014945:Wound Healing / Q000502:physiology*