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We have previously provided evidence that the rat optic nerve contains three types of macroglial cells that develop as two distinct lineages: one lineage comprises type 1 astrocytes, which develop before birth, while the other comprises oligodendrocytes and type 2 astrocytes, which develop after birth from a common, bipotential glial progenitor cell. In the present study we have examined the influence of axons on the development of these two glial cell lineages by cutting the optic nerve at birth so that the retinal ganglion cell axons in the nerve degenerate. Using antibodies to distinguish the different types of glial cells in suspensions and semithin frozen sections of cut and uncut optic nerves, we show that neonatal transection results in a striking decrease in the total number of oligodendrocytes, type 2 astrocytes and their progenitor cells but has much less effect on the number of type 1 astrocytes. Since the [3H]thymidine labelling indices of oligodendrocytes and their progenitor cells were not significantly decreased in cut nerves, our results suggest that the progenitor cells and/or their progeny die in large numbers following neonatal nerve transection. We conclude that axons are required for the survival of cells of the oligodendrocyte-type 2 astrocyte lineage, at least during postnatal development.

A regeneration chamber was created in vivo by suturing a synthetic tube sealed at its distal end onto the proximal stump of a severed rat sciatic nerve. Nerves regenerated into tubes coated with laminin at a rate of 0.33 mm/day after a lag of about 2 days. At 25 days, regenerating nerves had extended 23% farther into laminin-coated tubes as compared with uncoated ones. Monoclonal antibody 3A3, which functionally interferes with a dual lanminin/collagen receptor, inhibited nerve regeneration into laminin-coated tubes by 32%. In contrast, monoclonal antibody JG22, which inhibits chicken matrix receptors, had no significant effect on regeneration. Immunohistochemical studies of teased adult rat sciatic nerves indicate that 3A3 bound to Schwann cells and possibly to axons. In other studies, the heterodimeric, laminin/collagen receptor recognized by 3A3 has been shown to be a member of the integrin superfamily of adhesive receptors. These data provide evidence that an integrin receptor functions in nerve regeneration in vivo.In adult mammals, damaged axons can regenerate for many centimeters within the peripheral nervous system. These regenerating axons are typically found within conduits of basement membranes, often in contact with Schwann cells (1, 2). Like many other basement membranes, those in the peripheral nervous system are comprised of laminin, collagen, fibronectin, and other extracellular matrix (ECM) components (3-7). In culture, purified fibronectin, collagen, and especially laminin stimulate outgrowth as well as guide nerve processes (8)(9)(10)(11)(12). This growth requires binding of cell-surface receptors to ECM adhesive proteins. Several ECM receptors and binding proteins have been identified, most notably a superfamily of heterodimeric proteins called integrins. Integrins are found in a wide variety of cell types where they mediate both cell-cell and cell-matrix adhesion (13-15). Of particular note are observations that integrins mediate neurite outgrowth in culture (16)(17)(18)(19).Prompted by recent studies implicating laminin in nerve regeneration in vivo (20, 21), we have sought to identify ECM receptors responsible for matrix-mediated nerve regeneration. To accomplish this, we have employed a method for isolating in vivo regenerating peripheral nerves within synthetic tubes (21-24). Peripheral nerves are severed, and their proximal stumps are capped with a tube sealed at its distal end (24) to form a chamber. The tubes are then filled with a solution containing monoclonal antibody (mAb) 3A3 (IgGl), which inhibits neurite outgrowth by PC12 cells (a rat pheochromocytoma cell line) on laminin and collagen culture substrata (25). It has been shown elsewhere (25) that mAb 3A3 binds to a heterodimeric receptor complex (185 kDa, 125 kDa) of the integrin superfamily. mAb 3A3 appears to recognize the a subunit of this laminin/collagen receptor, which can be immunoprecipitated from detergent extracts not only of PC12 cells but also of embryonic rat neural tissues (26). We show here that (i) lamin...