Sensation Plasticity

Can we fix spinal cord injuries without repairing the physical damage?

MRI-Spine-9238

A paper published this week in Nature suggests we can. Scientists proposed the possibility of recovering some motor control functions despite severe damages in the spinal cord. The study used a combination of serotonergic agonists (drugs which enhance the abilities of Serotonin to activate Postsynaptic Receptors, most likely by blocking its reuptake), electrical stimulations, and physiological training on paralyzed rats. The results were groundbreaking and certainly encouraging; paralyzed rats were able to recover substantial motor abilities, especially when measured in respect to stepping.

The study titled, “Transformation of nonfunctional spinal circuits into functional states after the loss of brain input”, was conducted at the David Geffen School of Medicine at the University of California, Los Angeles.

Source: Cedars Sinai Health System

Although the results were remarkable, numerous studies in the past which used embryonic stem cell also had modest successes. What is the breakthrough in science in this study? The P.I. – Principal Investigator of the study, Dr. Reggie Edgerton explained the implications of his research in an interview with the New York Times earlier today.

Dr. Edgerton explains that “The most novel thing is that it’s demonstrating, in the rat, that there are neuro-networks within the lumbar-sacral spinal cord capable of full weight-bearing and relatively coordinated stepping without any input from the brain”. In other words, although the connection between spinal cord and the brain is critical for motor functions, the neuro-network in the sensory system (spinal cord) has the capabilities to control the stepping.

More specifically, Dr. Edgerton explains that a lot of our movements are automatic; we don’t have to think about the particular action that we are performing. For example, when we trip, our reflexes correct the stepping pattern much faster than what our brain can handle (there is not enough time for the sensory system to send the information to the brain, and back). As a result the initial reaction is simply controlled and carried out by the lower sensory system (peripheral nervous system) – the spinal cord. In a sense, the spinal cord is capable of interpreting complicated perceptions without the brain. However the brain will still receive the sensory information after the reflex and the connection from the spinal cord to the brain is still critical in carrying out movement.

In the case of a spinal cord injury, the sensory information can no longer be send to the brain – the central nervous system, but that sensory information is still available to the spinal circuitry. Our nervous system contains many redundancies so there is a good possibility that peripheral nervous system can take over the basic motor functions completely given the right environment.

The important implication of the study is that perhaps using the correct combination of pharmacological agents, and training we can activate the spinal circuitry to take over the brain’s role in controlling motor movement. In addition, this study shows that it is possible to restore motor function without repairing the physical damage between the brain and the spinal circuitry, if the physical link is repaired using stem cell therapy, the results could be even more promising.

For further information, you can read the research paper at:

http://www.nature.com/neuro/journal/vaop/ncurrent/full/nn.2401.html

You can catch the entire Q and A interview from the New York Times at:

http://well.blogs.nytimes.com/2009/09/21/paralyzed-rats-walk-again-raising-hope-for-spinal-cord-patients/

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