Immunohistochemical characterization of axonal sprouting and reactive tissue changes after long-term implantation of a polyimide sieve electrode to the transected adult rat sciatic nerve

The development of artificial microstructures suited for interfacing of per ipheral nerves is not only relevant for basic neurophysiological research b ut also for future prosthetic approaches. Aim of the present study was to p rovide a detailed analysis of axonal sprouting and reactive tissue changes after implantation of a flexible sieve electrode to the proximal stump of t he adult rat sciatic nerve. We report here that massive neurite growth afte r implantation, steadily increasing over a period of 11 months, was observe d. Parallel to this increase was the expression of myelin markers like Po, whereas non-myelin-forming Schwann cells did not change. Compared to five w eeks post-implantation, where both Schwann-cell phenotypes were intermingle d with each other, non-myelin-forming Schwann cells occupied a peripheral p osition in each microfascicle after 11 months. After an initial increase, h ematogenous macrophages were down-regulated in number but maintained close contact with the implant. However, at no time were signs of its degradation observed. It is concluded that the introduced flexible polyimide electrode is suitable for contacting peripheral nerves since it permits substantial neurite growth and offers excellent long-term stability. (C) 2001 Elsevier Science Ltd. All rights reserved.