Laminin-immunoreactive sites are induced by growth-associated triggering factors in injured rabbit optic nerve.

We have previously demonstrated that application of soluble growth-associated triggering factors (GATFs) from regenerating fish optic nerve or neonatal rabbit optic nerve to a non-regenerative crushed adult rabbit optic nerve provokes regeneration-like changes in the adult rabbit. In this study we show that the responses initiated by GATFs also include a change in pattern of appearance of an extracellular matrix component, laminin, known to play a role in neurite outgrowth and elongation. These findings suggest a mechanism whereby GATFs activate the adult rabbit glial cells to produce or to accumulate laminin and thereby allow partial compensation for the low inherent regenerative ability of the adult rabbit optic nerve.

Environmental changes induced by growth-associated triggering factors in injured optic nerve of adult rabbit.

Central nervous system (CNS) neurons of mammals regenerate poorly after axonal injury. However, if an injured CNS neuron (rabbit optic nerve) is supplied with appropriate soluble substances ("growth-associated triggering factors") derived from medium conditioned by regenerating fish optic nerve or newborn rabbit optic nerve, it can express regeneration-associated characteristics. Such characteristics include a general increase in protein synthesis, changes in synthesis of specific polypeptides, and sprouting of nerve fibers in culture. The present study of rabbit optic nerves demonstrates that such active substances affect the neuronal environment (i.e., the non-neuronal cells), thereby perhaps causing a shift in the environment from an inhibitory to a regenerative supportive one. Apparently, such an environment is spontaneously achieved in injured CNS nerves of lower vertebrates (e.g., fish optic nerves), which are regenerable. Treatment of injured rabbit optic nerve with soluble factors from medium conditioned by regenerating carp optic nerve resulted in a selective increase in proliferation ([3H]thymidine incorporation) of perineural cells and the appearance of a 12-kDa polypeptide in a homogenate derived from the nerve and its associated cells. This polypeptide may be related to growth, since it comigrates in NaDodSO4/polyacrylamide gel electrophoresis with a 12-kDa polypeptide that is continuously present in a regenerative system. In addition, there were injury-induced changes in the polypeptides of the nerve that were independent of treatment with conditioned medium and were correlated with nerve maturation. The most prominent changes of this type were in 18-kDa and 25-kDa polypeptides whose levels were reduced after injury and were found to be correlated with the nerve maturation (myelination) state.

Molecular and cellular aspects of axon-glia interaction in CNS regeneration.

The relationships of neurons and non-neuronal cells are vital for the maintenance and function of neurons. Trauma alters these relationships causing proliferation of non-neuronal cells and, in adult mammalian CNS, presumably disturbs the environmental support needed for regeneration. A supportive environment can be restored by introducing a regenerating nerve to injured mammalian CNS. This response is probably due, at least in part, to diffusible substances secreted by the non-neuronal cells. We have obtained diffusible substances from either regenerating fish optic nerves or neonatal rabbit optic nerves and applied them around crushed adult rabbit optic nerves. This manipulation caused the adult nerve to show regenerative changes: a general increase of protein synthesis in the retinas; selective increase in synthesis of a few polypeptides in the retinas; sprouting from the retinas in vitro; increased viability of nerve fibers as shown by HRP staining; and the appearance of growth cones adjacent to glial limitans in the injured nerves. We termed these diffusible, active substances "Growth Associated Triggering Factors" (GATFs). In addition to the phenomena described above, the active substances (obtained in the form of media conditioned by regenerating fish optic nerve or neonatal rabbit optic nerve) caused various other changes in the injured nerve itself: acceleration of non-neuronal cell proliferation; changes in the protein pattern, e.g. an increase in a 12 kDa polypeptide which might be a second mediator in the cascade of events leading to regeneration; increased laminin immunoreactive sites in the nerve; and the acquisition of growth supportive activity in media conditioned by the implanted injured nerves.(ABSTRACT TRUNCATED AT 250 WORDS)