Retrograde labeling of regenerating motor and sensory neurons using silicone caps

- Description of two detailed approaches to the retrograde labeling of peripheral nerves.
- The novel approach is validated using both neuron counts and labeling intensity.
- The novel approach to retrograde labeling significantly reduces the time required for the procedure.

BackgroundRetrograde labeling permits the investigation of the number, distribution and axonal projections of neurons in the peripheral nervous system. The well technique for labeling peripheral nerves consists of incubating the exposed peripheral nerve in a well for one hour, a time intensive technique. However, other techniques that inject tracers directly into the nerve or muscle may result in variable labeling depending on nerve preparation and location of injection.New methodWe describe a method of retrograde labeling peripheral nerves that increases tracer uptake and improves labeling efficiency. This technique utilizes a silicone cap over the nerve that is kept in place with fibrin glue, permitting closure of the incision with the cap in place, mitigating the need to wait one hour for back-labeling as with the standard well technique.ResultsIn the rat common peroneal nerve, the new silicone cap technique, compared to the standard well technique, labeled 405 ± 11 (SEM) vs. 378 ± 21 motoneurons and 953 ± 40 vs. 948 ± 57 sensory neurons. These counts were not statistically different. Labeling intensity was greater in DRG neurons with the silicone cap technique, but this difference was not evident in motoneurons.Comparison with existing methodRetrograde-labeling with silicone caps labels an equal number of motor and sensory neurons in comparison with the standard well technique and labels sensory neurons with greater intensity.ConclusionsRetrograde-labeling with silicone caps reliably labels neurons and significantly decreases the time required for labeling, reducing anesthetic exposure and improving the efficiency of the technique.