These spinal cord motor neurons have been filled with an orange colored reaction product generated from an enzyme - horseradish peroxidase - that was delivered by an intraneural route. The enzyme was conjugated to wheat germ agglutinin (WGA) - a natural but non-physiological ATF (axonal transport facilitator). The complex is injected in to muscle, taken up into the nerve endings, and transported in transport vesicles. These vesicles do not destroy or digest the enzyme and it remains functional when this histological staining procedure was carried out days later. Note that the interiors of the cell bodies and their processes make up only a small fraction of the spinal cord interior.