Of the twelve cranial nerves that pass through the skull, the facial nerve is most susceptible to traumatic injury and paralysis. One technique for repairing such damage is polyethylene glycol-mediated cell fusion – or PEG-fusion – but this hasn’t been tested on facial nerves. Moreover, when looking at other nerve types, it’s only been applied immediately after injury. This doesn’t reflect real-world clinical practice, where nerve damage may not be addressed for days as life-saving interventions are prioritized. Now, researchers have applied PEG-fusion to facial nerves using a more clinically relevant timeline, and the results suggest that nerve regeneration is possible even when treatment is delayed.
PEG-fusion helps restore the protective boundary of a nerve cell’s plasma membrane by plugging the holes caused by traumatic injury, which can seal the cell off from potentially toxic substances. But it hasn’t been clear whether delayed treatment can still help cells heal. To answer this question, the researchers created a rat model of peripheral facial nerve paralysis by severing the right mandibular branch of the facial nerve. Then, they microsutured the nerves back together either 24 or 72 hours after injury and bathed them in solutions either with or without added PEG.
To examine how the nerves fared under these conditions, the researchers compared pre- and post-operative assessments of nerve function and morphology. They tested nerve function by using electromyography to monitor the compound muscle action potential, or CMAP, which gives insights into the strength and speed of nerve impulses.
The results showed a decrease in the latency of nerve conduction 6 weeks after the PEG treatment – in other words, electrical impulses travelled faster through the damaged nerves in the treated animals than the untreated groups. A closer look at nerve morphology also showed that the treated animals had thicker axons, indicating that PEG may have helped keep the nerves’ myelin sheath intact.
Although PEG-fusion still seems to work better when applied immediately after injury, these findings suggest that even delayed treatment can help regenerate damaged nerves. By understanding how timing impacts recovery, researchers are better equipped to develop new methods for nerve repair, which may just help reverse the effects of injury-induced paralysis.