Neuronal galvanotropism: An investigation of mechanisms and application

Amy Melisa Palmer, Purdue University

Abstract

The process of neurite outgrowth is a well-explored aspect of neuronal development and repair. For two decades applied electric fields have been used to manipulate neurite outgrowth in cultures. Here we report the findings of exploring mechanisms of neuronal galvanotropism, using Xenopus laevis spinal neurite cultures. Also, we report the results of using neuronal galvanotropism to augment nerve regeneration in the leech, Hirudo medicinalis. Several mechanisms for neuronal galvanotropism have been considered and here we look at two: calcium and cyclic nucleotides. Using calcium chelators, we reduced extracellular levels of calcium to less than 1μM and disrupted intracellular gradients of calcium. Under both conditions, we were still able to measure a turning response of the neurites in culture to 100 mV/mm electric fields. We conclude that neither calcium nor the cyclic nucleotides directly mediates neuronal galvanotropism in Xenopus spinal neurites. Since the beginning of studies on neuronal galvanotropism, it has been suggested that this phenomenon may be a useful therapy for nerve repair in CNS neurons following damage or injury. Here we considered the leech nervous system as a model to study neuronal galvanotropism in regeneration. We suggest that the application of small electric fields would enhance regeneration in the leech. Using steady and slowly alternating current, we assess the effects of exogenous current on regeneration. Using both techniques, we did not detect a difference in regeneration with or without electric field application by electrophysiological techniques. Further, histological methods did not show any significant growth of neurites in response to the electric field. We conclude that under the parameters used here, electric field application does not enhance regeneration in Hirudo medicinalis. We suggest that while neurites in culture respond to electric fields, the mechanism of this response may not be similar to the mechanisms neurons use to respond to other guidance cues. Similarly, we suggest that the use of electric field for nerve regeneration requires further study to optimize and understand various parameters of this technique.

Degree

Ph.D.

Advisors

Robinson, Purdue University.

Subject Area

Neurosciences

COinS