Introduction

The objective of this review is to consider evidence that Schwann cells, the glial cells of the peripheral nervous system, play a crucial role in guiding and supporting the regeneration of peripheral axons. The presentation is biased by the author's own research perspective. It is certainly not encyclopedic and, for the inevitable slighting of important contributions, apologies are offered. The interest in peripheral nerve regeneration comes from its history, the substantial body of knowledge already obtained, and from its clinical import (see Volume II, Chapter 40). This interest is shown by the large number of reviews of the topic that have appeared, many in the last few years (cf. Hall, 1989; Fawcett and Keynes, 1990; Welcher et al., 1991; Bunge, 1993; 1994; Reynolds and Woolf, 1993; Brecknell and Fawcett, 1996; Ide, 1996; Scherer and Salzer, 1996; Fu and Gordon, 1997; Scherer, 1997; Taylor and Suter, 1997; Anderson et al., 1998; Frostick et al., 1998; Stoll and Muller, 1999; Terenghi, 1999; Hall, 2001; Jones et al., 2001; Fenrich and Gordon, 2004).

Schwann cells are derived embryologically from the neural crest (cf. Lobsiger et al., 2002). These cells associate with developing peripheral axons, migrate along these axons as they extend to their peripheral targets, and ultimately separate and wrap these axons (Peters and Muir, 1959; Lubinska, 1961; Speidel, 1964). Schwann cells provide two distinct types of axonal wrappings, one for larger axons that contains myelin and one for smaller axons that does not.