The Nature of Human Spinal Cord Injury

What actually happens to nerves and nerve connections after human SCI? What cellular and molecular mechanisms create the damage? Following injury, is it possible for nerve pathways to be rewired? Can nerve pathways change after injury and do the changes improve recovery? Do rehabilitation interventions influence any rewiring that occurs?

These are questions that researchers hope to answer as they carry out human pathology and human neurophysiology studies to determine the nature of human spinal cord injury.

Pathology

Postmorten Human Spinal Cord. Boney fracture is causing pressure on spinalcord tissue (in white). Copyright 2004. The Miami Project to Cure Paralysis.

To increase the knowledge, Miami Project scientists use postmortem human spinal cords to microscopically analyze damaged spinal tissue and compare it to diagnostic Magnetic Resonance Imaging (MRI). Studies such as these help investigators define the nature of the cellular damage, which will guide scientists in developing future treatment strategies. The studies are also providing information that may improve the capabilities of diagnostic tools such as the MRI.

Miami Project scientists report:

• Some cell damage in human SCI may be caused by apoptosis, a programmed cell death. In a study of postmortem tissue, researchers found evidence of apoptosis in 14 of 15 injured human spinal cords. [Abstract]

• Schwann cells may migrate into the spinal cord after injury and produce an inhibitory protein, CSPG, that impairs spinal cord regeneration after injury. In 48% of the spinal cords examined, Schwann cells were present in the spinal cord and found to produce CSPG. [Abstract]

Neurophysiology
Neurophysiology is the study of the functions and activities of the nervous system. Miami Project scientists conduct neurophysiology studies in people with SCI to learn how the electrical and chemical connections are affected by the injury. These types of studies help them to gain an understanding of the nerve circuits that carry messages between the brain and the body to control movement and sensation.

In many people with SCI, some recovery of function does occur naturally, the amount varying from person to person and depending on the type and extent of injury. By performing neurophysiology tests on selected research volunteers, investigators hope to determine if natural motor recovery relates to changes in nerve circuitry. They are also interested in exploring the potential to use rehabilitation interventions to retrain the spinal cord to improve walking in persons with SCI. (See Improving Function and Fitness)

Research evidence suggests that the human spinal cord has the capacity to alter nerve circuits and connections even after injury. This characteristic, known as plasticity, allows existing circuits to be modified and new circuits and connections to be formed. Many questions still need to be answered about what happens to the neural circuitry after human SCI and whether positive changes in neurophysiological connections can be influenced by rehabilitation strategies. By conducting neurophysiological tests, Miami Project investigators hope to use the knowledge gained to devise better therapies and exercise programs to optimize function.

In addition to studying changes in nerve circuitry, investigators are interested in how muscles that have lost some or all of their nerve supply change. Neurophysiological testing is used to help characterize fatigue and spasticity in paralyzed muscles. Understanding how muscles change after injury will also be important in designing effective rehabilitation strategies.

Miami Project research has shown:

• In some research volunteers with complete cervical (neck) injuries, scientists found evidence for a new reflex connection which suggests that new connections can form after injury. [Abstract] In another study, researchers found that new reflexes did not appear until at least 6 months after injury, lending support to the hypothesis that plasticity and perhaps 'regenerative sprouting' may occur in the human spinal cord following traumatic injury.[Abstract]

• A spinal mechanism that helps to turn off a muscle when the muscle responsible for the opposing movement is active can be affected by changes in body position in able-bodied research volunteers but not in volunteers with SCI. These results suggest that after SCI the control of this mechanism is disrupted and may be one reason why muscles contract at the same time and impair movement. [Abstract]
  
• Neural circuitry may be influenced by sensory stimulation. Recent findings suggest that the use of repetitive patterned sensory stimulation may be a component of rehabilitation to improve walking in patients with spinal injury. [Abstract]
  
• Spinal cord injury causes changes in the excitability of neurons in direct contact with muscles [Abstract] and specific types of stimulation may help improve the force produced by weak muscles. [Abstract]

By studying both the pathology and neurophysiology of SCI, researchers are getting a better understanding of the nature of human SCI. This knowledge is important in determining how to enhance or restore spinal cord connections and therefore improve the potential for recovery. It will also help researchers to evaluate current rehabilitations strategies and to design future regeneration strategies.

Miami Project Faculty working in this area of study

W. Dalton Dietrich
Edelle Field-Fote
Allan D.O. Levi
Michael Norenberg
Christine K. Thomas

Other articles related to this topic

Directors' Summaries
Human Neurophysiology Studies Guide Design of Rehabilitation Interventions
Human Pathophysiology
Restoration of Movement

Research Reviews

Winter 2004: Steps toward "Rewiring" Walking

Spring 2000: Do the Locomotion...Training the Spinal Cord to Improve Gait

Summer 1994: Exploring the Intricate Function of the Human Spinal Cord

Spring 1994: Comprehensive Evaluation of Human Spinal Cord Injury