Hoping to discover the nature of some of these changes and to gain insight into how spinal motor neurons cope with injury, the scientists experimentally severed the axons of these neurons in animal models. They then used glass needles connected to electronic recording equipment to listen to the injured neurons talking to each other. They also injected dyes into single injured motor neurons and looked for dye passing to other motor neurons. In this way, the researchers were able to assess whether the cells were directly connected by gap junction bridges. They found that the injured cells were connected by gap junction bridges and that they established the bridges only among themselves, failing to connect with nearby healthy cells.
The scientists also examined the proteins used to build these bridges, called connexins. They found that the amount and types of connexin proteins present in the neurons did not change after nerve injury. This suggests that gap junction bridges may be present among normal motor neurons but are perhaps inactive under normal circumstances.
Martin Pinter, PhD, with the Emory University School of Medicine, and Alberto Pereda, PhD, at the Medical College of Pennsylvania/Hahnemann School of Medicine at the time of the experimental work and currently at the Albert Einstein College of Medicine, are additional coauthors on the study. Funding for the research was provided by the National Institutes of Health and the Spinal Cord Research Foundation of the Paralyzed Veterans of America.