Very important research into spinal cord injury nerve regeneration by Ron Meyor a great scientist who I admire very much.
Meyor severed the optic nerve of fish and frog and showed that nerve regeneration occurs in both species. He compared this to mammals, where nerve regeneration of the optic nerve does not occur. What Meyor missed, is that in both fish and frog, the nerve pathway to regeneration remains constant. In other words, the fish and frog remain upright so that the angle from the eye to the brain is inline with the direction of gravity and it's influence on circulation in the optic nerve.
Mammals on the other hand, like ourselves, continually change their posture so while the nerves still grow, the gravitational signals and the driving force for growth confuses the nerve endings sending them in all directions.
Meyor then removes the nerves from the mammals and shows in a special culture dish that the mammalian nerves do grow in what appears to be an inclined culture dish, which he refers to as "special circumstances" The nerve is observed to grow past a horizontally placed nerve, unable to make a connection. A simple way to test this in a laboratory would be to have rats with damaged spinal cords in wheeled wire frames, so they can move around freely but remain in the upright position with their spines at an angle down at 5 degrees.
But wait, we don't need to do animals studies any more. The recent breakthrough seen in Brazil and elsewhere, where patients with spinal cord injuries are provided with a vertical device that enables them to remain upright and mobile for longer periods has shown that nerves do regenerate and connections are made to restore sensitivity, bowel and bladder control and mobility.
I rest my case !!!!!
Short Video Clip Ronald Meyor's Research: