A review of experimental methods measuring peripheral nerve regeneration in animals.

We have reviewed the morphologic, electrophysiologic, biochemical, and functional methods of evaluating PN regeneration in animal models. There are a large number of anatomic techniques that can provide clear insights into the processes of peripheral nerve regeneration. Since many of these are costly in terms of labor, careful selection of the technique appropriate for the question asked is important. Two of the more important questions are: 1) What are the neurotrophic factors produced by the distal segment that attract the growing axon tip? and 2) What are the components of the basal lamina that facilitate the directed growth of the axons? To answer these questions, whole mount preparations provide the means to economically evaluate the result of experimental manipulation of the environment. Automated nerve fiber counts will be increasingly used to help interpret electrophysiologic studies. Quantitative as well as descriptive ultrastructural analyses will continue to provide valuable data that will be needed in the interpretation of biochemical and histochemical studies. Immunohistochemical probes are sure to become more important as the range of their specificities broadens. With the diversity of anatomic methods available and their capacity to help us visualize the processes occurring during nerve regeneration they will remain a key tool in these studies. Electrophysiologic methods that integrate the CAP and correlate it with the number of functioning NF are most useful. Functional methods are beginning to become more objective and quantitative. The most precise measurements are muscle weight and the isometric response of muscle to tetanic contraction. Sensory function has now been measured objectively by Horch. Single methods of measuring PN regeneration give only limited data, but by combining methods a better understanding of PN regeneration is possible. While understanding the limitations of each method and technique, multi-parameter animal models may provide data most helpful clinically. However, because of great species variability in the reparative response, caution must be given not to extrapolate too much from animal studies. We urge investigators to use the most objective methods available to measure nerve regeneration. Recognizing these limitations, however, animal studies will continue to provide significant insights into PN regeneration and should point the way to improved clinical practice.