Spiral cuff electrodes are usually implanted around peripheral nerves to perform either recording or stimulation in the frame of Functional Electrical Stimulation (FES) applications and/or studies. Both electrophysiological parameter instability and morphological changes have been observed during the initial phase after electrode implantation. Variations of the membrane excitability parameters and of the electrode impedance may be related to these morphological changes. To assess this hypothesis, self-sizing cuff electrodes were implanted in rat sciatic nerves to monitor electrophysiological parameters in correlation with the epineurial tissue changes occurring during the first month following implantation. Within a few hours, surgery and cuff electrode implantation induced an epineurial oedema responsible for low electrode impedance and high rheobase. Connective tissue accumulated at the cuff-nerve interface. Infiltration by inflammatory cells and loose connective tissue deposit, observed at day 2 evolved toward denser fibrous layers at day 7 that finally thickened the perineurium (day 30). In the meantime, vascular remodelling, characterised by vasodilation and angiogenesis, occurred. This increase of the vascular supply is required to face the raised metabolic needs resulting from mechanical stress. The rise in electrode impedance observed between day 2 and day 7 appeared to be linked to the epineurial tissue composition. Development of pharmacological strategies to modulate such aspect of the nerve reaction should contribute to improve cuff electrode efficiency.

Supported by the European Community (NEURALPRO project, # HPRN-CT-2000-00030).