Invited Review
Functional evaluation of peripheral nerve regeneration in the rat: walking track analysis

https://doi.org/10.1016/S0165-0270(01)00378-8Get rights and content

Abstract

The experimental model of choice for many peripheral nerve investigators is the rat. Walking track analysis is a useful tool in the evaluation of functional peripheral nerve recovery in the rat. This quantitative method of analyzing hind limbs performance by examining footprints, known as the sciatic function index (SFI), has been widely used to quantify functional recovery from sciatic nerve injury in a number of different injury models, although some limitations of the SFI has been questioned by several authors. This article is designed to offer the peripheral nerve investigator a noninvasive method to evaluate quantitatively the integrated motor recovery in experimental studies.

Introduction

Despite recent advances in microsurgical techniques and the understanding of nerve regeneration, functional recovery following repair of transected peripheral nerves often remains poor (Millesi, 1990, Fu and Gordon, 1997, Meyer et al., 1997). The clinical results of peripheral nerve repair remain disappointing, with loss of muscle function, impaired sensation and/or painful neuropathies (Evans et al., 1999). The poor functional outcome after peripheral nerve repair has motivated a better understanding of the molecular and cellular events surrounding nerve regeneration (Mackinnon, 1989, Madison et al., 1992, Borkenhagen et al., 1998).

In the biological sciences, a number of animal models have been developed in order to study peripheral nerve regeneration. The experimental model of choice for many neuroscientists remains the rat. It provides an inexpensive source of mammalian nervous tissue of identical genetic stock that is easy to work with and well studied (Mackinnon et al., 1984, Mackinnon et al., 1985b, Bain et al., 1989, Meek et al., 1999). The sciatic nerve shows an equivalent capacity for regeneration in rats and subhuman primates (Mackinnon et al., 1985a).

The rat sciatic nerve model is a widely used model for the evaluation of motor as well as sensory nerve function at the same time (Dellon and Mackinnon, 1989, Shen and Zhu, 1995, Dijkstra et al., 2000). Traditional methods of assessing nerve recovery following peripheral nerve injury and repair, such as electrophysiology and histomorphometry, while universally employed in neural regeneration experiments, do not necessarily correlate with return of motor and sensory functions (Dellon and Mackinnon, 1989). Therefore, extrapolation of the electrophysiological parameters, including the nerve conduction velocity, peak action potential amplitude and the area of the compound action potential may lead to inappropriate interpretation of return of function (Rosen and Jewett, 1980, Kanaya et al., 1996). The withdrawal response after application of a small electric current on the most lateral aspects of the footsole is an easy and simple method, but can only assess return of sensory function after peripheral nerve damage (De Koning et al., 1986). With axon count and degree of myelination studies it is not possible to know if the axon reaches the appropriate target organ or not (Rosen and Jewett, 1980, Mackinnon et al., 1991, Kanaya et al., 1996).

Several investigators have taken the triceps surae muscle from the experimental and control sides and weighed them, obtaining the conservation muscle mass ratio (Kobayashi et al., 1997, Terris et al., 1999). However, adipose tissue and fibrosis seen in denervated muscles can increase their weight (Kanaya et al., 1992, Kanaya et al., 1996). Muscle contractile force measurement is a sensitive and reliable method of assessing the function of individual muscles (Kanaya et al., 1992, Shen and Zhu, 1995, Mackinnon, 1996). On the other hand, it provides no specific information on integrated motor function (Urbanchek et al., 1999).

Using a confining walkway to analyse rat gait, Hruska et al. (1979) developed a novel and relatively simple method to study animal models of neurological diseases, that cause dysfunctions in locomotion. Their analysis of the normal walking pattern in rats indicated that free, spontaneous locomotion in the animals is highly consistent and readily quantifiable. A standard battery of neurobehavioral tests, including gait analysis, providing a sensitive and reliable technique for detecting, quantifying, and differentiating various ataxic syndromes, was proposed by Jolicoeur et al. (1979). Newby-Schmidt and Norton (1981) designed a new method for recording chick footprints to assess motor function in the chicken.

In 1982, De Medinaceli et al. (1982) designed a quantitative method of analysing the sciatic nerve function in rats, known as the sciatic function index (SFI), based on several measurements of the footprints made on X-ray film. Many investigators have used the SFI as an assessment of hind limb function after sciatic nerve lesions and repair, which can be quantified reliably and easily determined by gait analysis through footprints (Carlton and Goldberg, 1986, Bain et al., 1989, Wong and Mattox, 1991, Hare et al., 1992, Hirasé et al., 1992, Hall and Van Way, 1994, Ansselin et al., 1997, Babovic et al., 1998).

Section snippets

Walking tracks

Several strains of Rattus norvegicus have been used to obtain walking tracks. The animal is placed in a walking pathway ending in a darkened cage (De Medinaceli et al., 1982, Brown et al., 1989, Maeda et al., 1993, Maeda et al., 1999, Strasberg et al., 1996, Meek et al., 1999). All rats are first allowed two or three conditioning trials, during which they often stop to explore the corridor, thereafter they walk steadily to the darkened cage (De Medinaceli et al., 1982, Meek et al., 1997) (Fig. 1

Analysis of walking tracks

Several measurements are taken from the footprints (Fig. 4): (i) distance from the heel to the third toe, the print length (PL); (ii) distance from the first to the fifth toe, the toe spread (TS); and (iii) distance from the second to the fourth toe, the intermediary toe spread (ITS). All three measurements are taken from the experimental (E) and normal (N) sides. (Bain et al., 1989, Brown et al., 1989). Several prints of each foot are obtained on each track.

The SFI was originally developed by

Toe spread

Hasegawa (1978) reported that the use of the distances between the first and the fifth digits and between the second and fourth digits of the rat's hind paw provide a useful method to evaluate the functional recovery after sciatic nerve crushing. As noted by De Medinaceli et al. (1982), when there is a serious lesion, such as sciatic nerve transection, determining the toe spread from the walking track alone can be very difficult. In this case, they employed an arbitrary value of 6 mm for the

Limitations of the SFI

Since its development by De Medinaceli's group in 1982, the validity of the SFI has been questioned by several investigators. Sometimes several trials are required to obtain the most representative prints for analysis (Bain et al., 1989, Shenaq et al., 1989, Hare et al., 1992). It is also crucial to observe the rat's progress along the walking pathway: when the animal is placed for the first time in the corridor, they often stop, pressing the entire footpad and heeldown, creating a false,

Conclusions and future perspectives

Selection of appropriate evaluation methods is crucial when measuring experimental nerve recovery. In 1982, De Medinaceli first reported that the SFI could be used to evaluate total lower limb function, including nerve, muscle and joint function in rats. Since then, many investigators have used walking track analysis as an assessment of global function recovery after sciatic nerve injuries or repair methods.

The use of walking track analysis provides a non-invasive method of assessing the

Acknowledgements

This research was supported by a grant from the Ministry of Education-PRODEP III (Educational Development Program for Portugal) and co-financed by the European Social Fund. We gratefully acknowledge the efforts of Professor P.H. Robinson, MD, PhD, FRCS for his careful reading of the manuscript.

References (71)

  • T. Kauppila

    Correlation between autotomy-behavior and current theories of neuropathic pain

    Neurosci. Biobehav. Rev

    (1998)
  • I.M.R. Lowdon et al.

    An improved method of recording rat tracks for measurement of the sciatic functional index of de Medinaceli

    J. Neurosci. Methods

    (1988)
  • T. Maeda et al.

    Regeneration across ‘stepping-stone’ nerve grafts

    Brain Res

    (1993)
  • R.E. Sporel-Ozakat et al.

    A simple method for reducing autotomy in rats after peripheral nerve lesions

    J. Neurosci. Methods

    (1991)
  • D.J. Terris et al.

    Functional recovery following nerve injury and repair by silicon tubulization: comparision of laminin-fibronectin, dialyzed plasm, collagen gel, and a phosphate buffered solution

    Auris Nasus Larynx

    (1999)
  • N.L.U. Van Meeteren et al.

    Exercise training improves functional recovery and motor nerve conduction velocity after sciatic nerve crush lesion in the rat

    Arch. Phys. Med. Rehabil

    (1997)
  • J.L. Walker et al.

    Gait-stance duration as measure of injury and recovery in the rat sciatic nerve model

    J. Neurosci. Methods

    (1994)
  • J. Westerga et al.

    Development of locomotion in the rat

    Dev. Brain Res

    (1990)
  • B.J. Wong et al.

    Experimental nerve regeneration. A review

    Otolaryngol. Clin. North Am

    (1991)
  • A.D. Ansselin et al.

    Peripheral nerve regeneration through nerve guides seeded with adult Schwann cells

    Neuropathol. Appl. Neurobiol

    (1997)
  • S. Babovic et al.

    Nerve regeneration in diabetic rats

    Microsurgery

    (1998)
  • J.R. Bain et al.

    Functional evaluation of complete sciatic, peroneal, and posterior tibial nerve lesions in the rat

    Plast. Reconstr. Surg

    (1989)
  • M. Borkenhagen et al.

    Three dimensional extracellular matrix engineering in the nervous system

    J. Biomed. Mater. Res

    (1998)
  • C.J. Brown et al.

    Self-evaluation of walking-track measurement using a sciatic function index

    Microsurgery

    (1989)
  • J.M. Carlton et al.

    Quantitating integrated muscle function following reinnervation

    Surg. Forum

    (1986)
  • M.M. Carr et al.

    Strain differences in autotomy in rats undergoing sciatic nerve transection or repair

    Ann. Plast. Surg

    (1992)
  • L.J. Chamberlain et al.

    Near-terminus axonal structure and function following rat sciatic nerve regeneration through a Collagen-GAG matrix in a ten-millimeter gap

    J. Neurosci. Res

    (2000)
  • E.S. Dellon et al.

    Functional assessment of neurologic impairment: track analysis in diabetic and compression neuropathies

    Plast. Reconstr. Surg

    (1991)
  • A.L. Dellon et al.

    Selection of the appropriate parameter to measure neural regeneration

    Ann. Plast. Surg

    (1989)
  • S.Y. Fu et al.

    The cellular and molecular basis of peripheral nerve regeneration

    Mol. Neurobiol

    (1997)
  • T. Hadlock et al.

    A novel, biodegradable polymer conduit delivers neurotrophins and promotes nerve regeneration

    The Laryngoscope

    (1999)
  • G.D. Hall et al.

    A comparision of nerve grafting and tissue expansion techniques in the rat

    Microsurgery

    (1994)
  • G.M.T. Hare et al.

    Walking track analysis: a long-term assessment of peripheral nerve recovery

    Plast. Reconstr. Surg

    (1992)
  • K. Hasegawa

    A new method of measuring functional recovery after crushing the peripheral nerves in unanesthetized and unrestrained rats

    Experientia

    (1978)
  • Y. Hirasé et al.

    Cryopreserved allogeneic vessel and nerve grafts: hind limb replantation model in the rat

    J. Reconstr. Microsurg

    (1992)
  • Cited by (256)

    View all citing articles on Scopus
    View full text