Recovery of function using nerve bridges

I wrote earlier on biomaterials. This fits nicely with a poster I saw today from the Silver lab (Case Western University, Ohio) who have been using peripheral nerve (PN) bridges to circumvent a complete hemisection injury of the cervical cord. Such an injury interrupts signals from respiratory control system in the brain to motor neurons in the spinal cord that drive breathing. The result in this injury is paralysis of the diaphragm on one side. It is an excellent system to investigate both regeneration (through the grafted nerve bridge) and plasticity, which is to say, the reorganisation of the connections in the respiratory system after injury. The group published earlier in the year on their findings demonstrating successful long-distance regeneration through the bridge and out again into the cord tissue below the injury where they connect with respiratory circuits. This new circuitry could be “trained” to restore breathing.

Obviously the loss of the peripheral nerve in patients with high cervical injuries with poor respiratory function is an insignificant concern when compared with the possibility of restored breathing but the clinical potential may be tempered if peripheral nerve bridges are to be used for those with lower injuries.

Unfortunately, sourcing from donor tissue would be associated with immune response issues. Recently, a group led by Schmidt (an author on the poster) have developed a technique that can take peripheral nerves and strip them of all the cells leaving only the structural proteins and extracellular matrix (ECM) as a lattice-like scaffold. The ECM is important as it acts as a permissive surface over which cells and axons can grow. The value of this technique is that donor tissue can be used as it will not illicit an immune response now that the cells have been removed. In their poster (#441.01), the group compared the acellular bridging grafts with standard nerve grafts for their ability to support axonal growth after a cervical C3/C4 hemisection injury. This type of injury allowed them to assess forelimb function which they did in a variety of ways. Immediately after injury they found animals in all groups lost the ability to use the affected limb during vertical exploration. Recovery in both the acellular and conventional nerve graft groups was seen and similar. In one test This is an important new finding as it suggests there is clinical potential in this donor-sourced material in SCI repair strategies.