Glial response to axonal injury: in vitro manifestation and implication for regeneration

Crushed fish optic axons readily regenerate, while similarly injured rat optic axons do not; the reasons for the differences in regeneration ability may lie in differences in the environment of the axons. We have cultured glial cells from previously crushed optic nerves of fish and rat to determine whether a relationship exists between the ability to regenerate and the nature of the responses of the associated nonneuronal cells to injury. The glial cells were examined using indirect immunofluorescence with antibodies to known glial markers. In the rat cultures, mature GalC oligodendrocytes, which are known to be nonpermissive for axonal growth, were abundant. In contrast, in the fish cultures mature oligodendrocytes were rare, but A2B5 positive cells were abundant. The high number of A2B5 positive cells in the fish may suggest a high number of immature cells. This interpretation, however, should wait until evidence for glial cell lineage of the fish is available. Additional indication is provided also in the present study that the number of mature oligodendrocytes in the fish is regulated by elements external to the nerve. This study thus demonstrates an important difference between rat and fish optic nerves in the response of glial cells to the optic nerve injury.