Rat amnion membrane matrix as a substratum for regenerating axons from peripheral and central neurons: effects in a...

An extracellular matrix preparation, the human amnion membrane matrix (hAMM) can serve as a neurite-promoting substratum for cultured peripheral and central neurons, and also as a support for axonal growth in experimentally injured adult brain in vivo. In the present study, we tested similar materials as bridges in a silicone chamber model for the regeneration of sciatic nerve in the adult rat. Since hAMM elicited an inflammatory response, we developed a rat amnion membrane matrix (rAMM), which proved to be an excellent neurite-promoting substratum for cultured ganglionic and spinal cord neurons. The rAMM was coiled and inserted in the 10 mm gap between the two nerve stumps from the silicone chambers. At 16 days after implantation, temporal progress of regeneration was grossly similar as in saline-prefilled control chambers. However, rAMM-prefilled chambers displayed significantly higher number of vessels and a markedly different geometry of the regenerate: an endoneurium, surrounded by a perineurial-like cell layer, was formed outside the largely preserved central portion of the rAMM coil. After longer regeneration times (28 days), a rAMM core was no longer detected, but some rAMM-like materials remained interspersed in the endoneurium. The overall organization of the regenerate and the number of myelinated axons at this time were similar to those of control chambers, although the endoneurial cross-sectional area was larger in the rAMM chambers. One specimen, however, displayed the very patterns for which the experiments were designed, namely an array of numerous, myelinated axons tracing the spiraling spaces between consecutive lamellae of the rAMM coil.