Immunoelectron microscopic localization of laminin in normal and regenerating mouse sciatic nerve.

Laminin, the major non-collagenous protein of basement membranes, has been shown to be a potent stimulator of neurite outgrowth, to potentiate neuronal survival and to stimulate Schwann cell division in vitro. The aim of the present study was to determine the ultrastructural localization of laminin in the mouse sciatic nerve during development and regeneration in order to elucidate whether laminin might also evoke similar effects in vivo. For this purpose polyclonal antibodies against laminin were used for pre-embedding electron microscopic immunocytochemistry of tissue sections from mouse sciatic nerves. In the adult, although laminin immunoreactivity was found to be predominantly associated with basement membranes as expected, the surface membranes of Schwann cells also displayed weak labelling. This distribution pattern was similar in developing sciatic nerves with the exception that laminin immunoreactivity was generally higher and also found to be present on interstitial collagen fibres. One week following sciatic nerve transection, strong laminin immunoreactivity was seen on regenerating axons growing along laminin-positive basement membrane tubes in the distal stump of the transected nerve. Our results demonstrate that laminin immunoreactivity is not restricted to basement membranes of the mouse sciatic nerve, but is also found in direct contact with adult, developing and regenerating axons as well as on the surface of Schwann cells. The finding of laminin immunoreactivity on extracellular matrix components, axons and Schwann cell membranes under conditions of growth and regeneration makes it more likely that axons are able to interact with laminin not only in vitro but also in vivo.