Neural morphological effects of long-term implantation of the self-sizing spiral cuff nerve electrode

The paper reports on the histological effects of chronic implantation of se lf-sizing spiral cuff nerve electrodes on the cat sciatic nerve. The implan tation period is about 4.4 months. Four different experimental conditions a re evaluated: control, sham, bare cuff (cuffs without contacts and leads) a nd full cuff. The total number of axons in the nerves of the control group is compared with the three other groups. The surface occupied by collagen f ibres in the nerve section, perineurium thickness, fibre diameter and myeli n thickness are also measured. The average number of axons in the control n erves is found to be 16416 (+/- 1509) and does not differ significantly fro m the three other groups (p>0.1). Collagen measurements show an extrafascic ular epineurial fibrosis in the two implanted groups that is found to be si gnificantly different (p< 0.05). No differences are encountered in the peri neurium thickness analysis. Fibre diameter distributions show a regular bim odal pattern for all groups. Centrality (mean and P-m) and dispersion stati stics (P-25 and P-75) extracted from fibre diameter distributions do not re veal significant differences. Myelin thickness distributions are also simil ar for all groups, as well as centrality and dispersion statistics. The pre sent morphometrical results suggest that the effects produced by a chronic spiral cuff implant on this animal model are negligible.