Intraocular spinal cord transplantation: Model for studies of growth, differentiation and synaptic organization

The repair process after a spinal cord injury has long been knwon to be insignificant or insufficient for substantial structural or functional restitution in animals and man in both adult and immature individuals. Transplantation of embyronic spinal cord or brain stem enhances endogenous sprouting in the spinal cord and reconstitutes brain stem inputs to spinal neurons, respectively. However, the mechanisms governing sprouting and structural regeneration, as well as functional restitution with or without morphological regrowth in the spinal cord, are largely unknown. A model system that allows in vivo studies of differentiation, growth and regenerative processes, and avoids some of the complicating factors of posttraumatic degeneration, is the intraocular transplantation technique. It also allows the isolation of small fragments of embryonic brain or spinal cord from the test. Some examples of how the versatile intraocular technique can be used for studies of growth, innervation, and synaptic specificity in the spinal cord will be reviewed. The ultimate goal of intraocular spinal cord grafting is to better understand and characterize growth of and into spinal cord tissue, so that the spontaneous repair process after spinal cord injuries can be optimized and possible growth-promoting factors or substitutes, or both, such as fetal cells, can maximize the structural and functional restitution of the injured spinal cord.