Identification of a peripheral nerve neurite growth-promoting activity by development and use of an in vitro bioassay.

Abstract

The effective regeneration of severed neuronal axons in the peripheral nerves of adult mammals may be explained by the presence of molecules in situ that promote the effective elongation of neurites. In mammals, severed neuronal axons of peripheral nerves regenerate readily, whereas axons of the central nervous system (CNS) fail to regrow effectively (1). Ramon y Cajal (2) was among the first to postulate that the rapid regeneration of peripheral axons was made possible by the presence of "neurotrophic substances" in the environment of elongating growth cones and that the relative inability of central axons to regenerate was due to the lack of these substances in CNS tissue, rather than an inherent defect of these neurons. This hypothesis was based, at least in part, on two observations: (i) regenerating dorsal root axons will elongate until the spinal cord is reached, where most of the fibers are "detained" or deflected to grow back down the root (ref. 2, p. 543), and (ii) sciatic nerve grafts placed into deeply cut adult rabbit cerebral cortex contained numerous axons originating from the surrounding white matter, "behaving in their growth, ramifications, orientation, energetic progress, etc., exactly like the sprouts of the central stump of a cut [peripheral] nerve" (ref. 2, pp. 738-740). These results have been confirmed by more recent experiments (3)(4)(5)

p75 Is Important for Axon Growth and Schwann Cell Migration during Development

“…Neurite outgrowth assays were performed using cervical DRG from E12.5 p75 ϩ/ϩ, ϩ/Ϫ, and Ϫ/Ϫ embryos. This assay uses neurons that are most likely impaired as visualized from NF staining, and it has been shown to mimic in vivo conditions (Sandrock and Matthew, 1987;Tuttle and Matthew, 1991;Morris et al, 1999). After 72 hr in culture in the presence of 5 ng/ml NGF, neurite outgrowth along sciatic nerve cryosections was measured from the leading edge of the DRG to the farthest neurite visualized with vital dye.…”

Structural requirements for neural cell adhesion molecule-heparin interaction.

“…The heparinbinding domain of fibronectin promotes neurite outgrowth when used to coat culture dishes (Rogers, 1985; aL., 1 988b). A laminin-HSPG complex has been shown to enhance neurite outgrowth in a similar assay (Lander et al, 1985;Davis et aL, 1987;Sandrock and Matthew, 1987), and the heparin-binding region of laminin is involved in neural crest migration (Perris et al, 1989). The role of myelin-associated glycoprotein in neuron-glial interactions may also depend on HSPGs, although the amino acid sequence involved in heparin-HSPG binding has not been identified (Poltorak et aL, 1987).…”

Extensive regeneration in vitro by early embryonic neurons on immature and adult CNS tissue

“…Conversely, in previous in vitro studies, insufficient account has been taken of the age of cultured neurons or of the complex environment encountered in vivo by regenerating neurites. To circumvent these problems, we have adopted the cryoculture assay system (Carbonetto et al, 1987;Covault et al, 1987;Sandrock and Matthew, 1987), which allows the study of neurite regeneration by dissociated neurons in vitro over intact, physiologically relevant substrata. Although the cryoculture method, being based on a two-dimensional assay environment, is only partially representative of the complex environment encountered by developing/regenerating neurons in vivo, it has the advantage of retaining extracellular matrix and cell surface molecules, while the influence of diffusible factors is minimized.…”