The laminin component of extracellular matrix is known to promote neuritic extension in vitro. We have previously shown that mature axons of the corpus callosum can regenerate for a limited distance through initially empty metal tubes that eventually became filled with the extracellular fluid provided by the tissue growing into them. We are now asking whether the regeneration of these axons can be enhanced in tubes pre-filled with tissue culture medium, a purified laminin gel, or a crude extract of Schwann cell extracellular matrix. A polyethylene tube (PE-50), shaped in the form of a U, was fitted with a narrow side-arm tube (PE-10), through which the solution of Schwann cell matrix was delivered by an indwelling, osmotic pump over a 1 - 2 week period. Fetal (E-16 days old) association cortex, as target tissues, was placed in one end of the U - shaped tube which was inserted into a lateral ventricle of an adult rat. The opposite end was placed in the contralateral corpus callosum. After 2-20 weeks, the media used had not enhanced axonal regeneration beyond that obtained with empty conduits. Only small fragments of fetal tissue survived within the tubes. However, bundles of remyelinating axons, with thin myelin sheaths and heminodes, and unmyelinated axons entered the tubes for a short distance. Even after 5 months, regeneration continued as indicated by the entry of a few growth cones. Astrocytes entering the tube not only aggregated into gliotic tangles, but were also oriented in the long axis of the tube. While the oriented astocytic processes might serve as a scaffold for elongating axons, some growth cones were in contact with axons and did not appear to use the astroglia for guidance.
