Thursday, March 20, 2003
New research into what makes some mice hop like a bunny reveals a bit more about how the spinal cord controls normal movements.
A better understanding of the spinal cord's role in controlling movement, researchers say, could eventually lead to new treatments for people whose legs are paralyzed.
Scientists have known that mice that are genetically engineered to lack one of two related spinal-cord molecules do not move as other mice do. Instead of moving one hind leg and then the other, these altered mice move both legs at once, making them hop rather than scurry.
But how these missing molecules cause mice to hop has been uncertain.
Now researchers in Europe have identified the neurons in the spinal cord that seem to make mice hop. These neurons are located within spinal-cord networks called central pattern generators.
A report on the research appears in the March 21st issue of the journal Science. Dr. Klas Kullander of Gothenburg University and AstraZeneca Transgenics and Comparative Genomics in Sweden led the study.
Normally, the activity of neurons on each side of the spinal cord is balanced. Neurons that encourage movement are balanced out by neurons that inhibit it. This balance leads to smooth movements in normal mice, with the muscles in the right hind leg contracting as the muscles in the left leg relax.
But in the mutant mice, the neurons Kullander's team identified upset the balance in the spinal cord's central pattern generators. The signal to move overwhelms the signal to rest, which causes both legs to move at once rather than to alternate.
The researchers were able to use chemicals to restore the balance in the spinal cord, which resulted in normal movements.
The neurons identified in the study make up just a part of the system that controls movement, but learning more about this system could lead to new treatments for people whose legs are paralyzed, according to Kullander and his colleagues.
Eventually, they speculate, it may be possible to improve their movements by stimulating the spinal cord circuits that are involved in walking.
SOURCE: Science 2003;299:1889-1892.
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