Enhancing Spinal Cord Regeneration In Situ with Applied Electric Fields

Abstract

The first unambiguous demonstration of enhanced spinal cord nerve regeneration in the living animal was carried out in a primitive fish, the ammocoete larvae of the lamprey (Borgens et al. 1981). This investigation utilized the special characteristics of the lamprey brain and spinal cord. In this animal, individually identifiable giant nerve cells in the brain (Müller and Mauthner cells) give rise to descending nerve fibers that are also identifiable in the spinal cord as part of the descending reticulospinal system (Rovainen 1967, 1974). Since the lamprey is an Agnathan, a primitive cartilaginous fish, there is no bony vertebral column surrounding and protecting the spinal cord: the cord and brain is easy for the investigator to surgically expose. Therefore, the fish system provides some of the same advantages as nerve fibers in culture where the investigator can describe the regeneration or growth of specific individual and identifiable nerve cells. The cell bodies of lamprey reticulospinal neurons are giant (~100 µm in diameter) and so are their spinal cord axons (~30 µm), making them easy to fill with intracellular dyes from a micropipette and to identify at any location within the brain and spinal cord (Wood and Cohen 1979; Borgens 1981) (Fig. 20).