Yes, it’s possible. I assume “so many of them” is mostly a matter of very, very difficult details of precision surgery and such. I see no particular reason to assume it would require a dramatic breakthrough, instead of (a very large number of) incremental improvements.
It should be noted that this is not actually connecting neuron fibers. This is providing empty myelin sheath, with the nerve cells within dead and destroyed due to being cut off from their cell bodies. When the living ends of a cut nerve fiber on the end that contains the cell body are left undisturbed, a subset of them send out growth cones that wander out from the cut. If theres nothing there they dont do much but if a bunch of open ends of myelin sheaths are brought up next to them they will find sheaths and grow through them at something like a millimeter per day to the positions of the former nerve endings of the grafted nerve. You can string together multiple cut nerve fragments in fact, if a nerve is damaged in multiple places due to trauma.
The fibers are not going to grow to their original destinations, and your brain needs to relearn what the heck its controlling or feeling once the fibers grow the long distance through the nerve, but they can regrow and people can and do relearn how to use the remapped fibers. You can even transfer/remap which nerves control what within an individual: see http://nerve.wustl.edu/nd_transfer.php .
Notably, this happens automatically in the peripheral nervous system but usually not the central nervous system. All the attempts do do so in the spinal cord itself, a CNS tissue, have relied on weird interventions and are by no means reliably successful and have never involved tissue from two organisms to my knowledge.
Motor neuron fibers would need to grow from the brain down through the spine, and sensory fibers would need to grow from the spine up into the brain itself. That is not a process that I would expect to go nearly as well in an adult compared to during initial development.
I’m very surprised that this has been done with dogs and rats, but as I did expect the nerves did not join and the result is a quadriplegic.
Is it even possible in theory for nerves of two originally different organisms to join? And so many of them?
Yes, it’s possible. I assume “so many of them” is mostly a matter of very, very difficult details of precision surgery and such. I see no particular reason to assume it would require a dramatic breakthrough, instead of (a very large number of) incremental improvements.
It should be noted that this is not actually connecting neuron fibers. This is providing empty myelin sheath, with the nerve cells within dead and destroyed due to being cut off from their cell bodies. When the living ends of a cut nerve fiber on the end that contains the cell body are left undisturbed, a subset of them send out growth cones that wander out from the cut. If theres nothing there they dont do much but if a bunch of open ends of myelin sheaths are brought up next to them they will find sheaths and grow through them at something like a millimeter per day to the positions of the former nerve endings of the grafted nerve. You can string together multiple cut nerve fragments in fact, if a nerve is damaged in multiple places due to trauma.
The fibers are not going to grow to their original destinations, and your brain needs to relearn what the heck its controlling or feeling once the fibers grow the long distance through the nerve, but they can regrow and people can and do relearn how to use the remapped fibers. You can even transfer/remap which nerves control what within an individual: see http://nerve.wustl.edu/nd_transfer.php .
Notably, this happens automatically in the peripheral nervous system but usually not the central nervous system. All the attempts do do so in the spinal cord itself, a CNS tissue, have relied on weird interventions and are by no means reliably successful and have never involved tissue from two organisms to my knowledge.
Motor neuron fibers would need to grow from the brain down through the spine, and sensory fibers would need to grow from the spine up into the brain itself. That is not a process that I would expect to go nearly as well in an adult compared to during initial development.