CELLS OF THE NERVOUS SYSTEM AND ELECTRICAL STIMULATION - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 602

18.5.6.1 Stimulation Methodology 626

18.5.6.2 Signal Selection 626

18.5.6.3 Electrode Material 627

18.5.6.4 Changes in Hydrogen Concentration 627

18.5.7 Cellular Response to Electric Field In Vitro 628

18.6 Neurons in Electric Fields 629

18.6.1 Axon Guidance 629

18.6.2 Cellular Level Changes Due to EFs 630

18.6.3 Receptor Accumulation and Autoregulation 631

18.6.4 Calcium 633

18.7 Neural Progenitor Cells and Electric Fields 633

18.8 Conclusions 634

Acknowledgments 634

Dedication 634

References 635

18.1 OVERVIEW

A potential cell-based therapy for Alzheimer's disease, spinal cord injury and
other non-treatable damage to the central nervous system (CNS) is the use of
neural progenitor cells (NPCs). To exploit the therapeutic potential of NPCs, sci-
entists must fi rst learn how to control the differentiation and proliferation of
NPCs. NPC characterization in vivo can be cumbersome due to the myriad of
stimulants found in the neurogenic niche. Thus, the identifi cation of stimulants
that affect NPC differentiation and proliferation is best performed in vitro .
Examples of such cues are soluble and insoluble proteins secreted by other cells,
membrane-bound signaling proteins, and topography. One additional consider-
ation is the electric gradient that is present in the developing and adult nervous
system. In the developing nervous system, a rostral to caudal electric fi eld guides
growth and development of the nervous system. At this time there are also neural
progenitor cells present, which are differentiating into the cells that make up the
nervous system. Yet, the effect of electrical stimulation on neural progenitor cells
is yet to be studied. So this chapter focuses on recent studies that may give an
inkling of the relationship between electrical stimulation and the proliferation,
growth and differentiation of neural progenitor cells. Briefl y, the main subjects
covered in this text are the effect of electric fi elds on neurons, the use of electrical
stimulation to improve spinal cord injury, and the complexity of investigating
electrical stimulation of cells in vitro .

18.2 CELLS IN THE NERVOUS SYSTEM

The central nervous system (CNS) is comprised of two types of cells, neurons and
glia. There exist 10 to 50 times more glial cells than neurons in the CNS of verte-
brates. Glial cells provide support and structure to the CNS; insulate axons with
myelin; perform housekeeping duties regularly and during injury; guide migrating