Nerve fiber growth in culture on tissue substrata from central and peripheral nervous systems

In adult mammals, injured neurons regenerate extensively within the PNS but poorly, if at all, within the CNS. We have studied the effect of substrata consisting of tissue sections from various nervous systems on nerve fiber growth in culture and correlated our results with the growth potential of these tissues in vivo. Ganglionic explants from embryonic chicks (9-12 d) fail to extend nerve fibers onto sections of adult rat optic nerve or spinal cord (CNS) but do so on sciatic nerve (PNS). Dissociated DRG neurons behave similarly whether in serum-containing or defined medium. Tissue substrata from nervous systems that support regeneration in vivo--i.e., goldfish optic nerve, embryonic rat spinal cord, degenerating sciatic nerve--also support fiber growth in culture. Within the same culture, neurons will grow onto sciatic nerve rather than neighboring optic nerve sections, suggesting that the responsible agent(s) is not soluble. In addition, neurons adhere more extensively to sciatic nerve substrata than to optic nerve. The occurrence of 3 molecules known to be involved in neuron-substratum adhesion and nerve fiber growth in vitro has been documented immunocytochemically in the tissue sections. One of these, laminin, is demonstrable in all tissues tested that supported nerve fiber growth. Immunoreactivities for fibronectin and heparan sulfate proteoglycan are found in only some of these tissues. None of these 3 molecules can be demonstrated in neural cells of normal adult rat CNS tissue. Our data suggest that these molecules may be important effectors of nerve regeneration in neural tissues.