Animals and tissue preparation

The images used in this study were provided by Eduardo Romero, from the Neural Rehabilitation Engineering Laboratory of the UCL. The sciatic nerves were obtained from one female cat (3250 gr). The cat was anaesthetized with Sodium pentobarbital (30 mg/kg I.M), the abdominal aorta was canalized with a catheter 14 G, between the renal branches and iliac bifurcation and perfused with a solution of phosphate-buffered paraformaldehyde. The sciatic nerve was dissected from 2 cm distal from the spinal cord to the popliteal fossa, after the tibial and peroneal bifurcation. A 3 cm segment was excised where the sural branche was coming out from the nerve (i.e. 4 cm proximal to the sciatic nerve bifurcation in a tibial and a peroneal branches). Nerves were stored in Karnovsky fixative ($2.0 \%$ paraformaldehyde and $2.5 \%$ glutaraldehyde in 0.1 M Sodium cacodylate buffer solution) for 24 hours, postfixed in $1 \%$ Osmium tetroxide during 4 hours and embedded in epon Ladd LX - 112. Semi-thin nerve cross sections ($1 \mu m$) were cut on a Reichter Ultracut microtome (Reichter, Wien, Austria) and stained with toluidine blue.