Testing of photolytic uncaging with intraspinal fiber optics as a basis for motor neuroprostheses

Recently, methods have been developed that can 'cage' neurotransmitters, limiting their ability to bind with a receptor and rendering them biologically inert until photolytic uncaging. We explored uncaging of glutamate with implanted fiber optics as a stimulation technology. The spinal cord was bathed in caged glutamate at different concentrations, and a photolysis unit projected brief, spatially concentrated bursts of light into the lumbar spinal cord. Forces generated at the ankle were measured in 3 dimensions. Responses were tested at discrete depths in the lumbar cord, with the strongest responses located in the 900 to 1100 μm range. Our results indicate feasibility of this approach for engineering a prosthesis. The advantage of this technology is that excitation, inhibition, and modulation of spinal circuits can be controlled. This technique, when used in a paralyzed individual, would allow greater freedom of movement and independence.