DEGENERATION AND REGENERATION IN RABBIT PERIPHERAL-NERVE WITH LONG-TERM NERVE CUFF ELECTRODE IMPLANT - A STEREOLOGICAL STUDY OF MYELINATED AND UNMYELINATED AXONS

Selective and dynamically co-ordinated functional electrical stimulati on (FES) of paralysed/paretic limbs in upper motor neuron lesioned peo ple depends on optimal contact at the neural interface. Implanted nerv e cuff electrodes may form a stable electrical neural interface, but m ay also inflict nerve damage. In this study the immediate and long-ter m effects of cuff implantation on the number and sizes of myelinated a nd unmyelinated axons have been evaluated with unbiased stereological techniques. Cuff electrodes were implanted in rabbit tibial nerves jus t below the knee joint, and the stereological analyses were carried ou t 2 weeks and 16 months after implantation. Myelinated axons were anal ysed at standardised levels proximal to, underneath, and distal to the cuff; unmyelinated axons underneath the cuff. A 27% loss of myelinate d axons was found underneath and distal to the nerve cuff 2 weeks post surgery. All axonal sizes were equally lost except for the very small est. At 16 months post surgery the number of myelinated axons was rest ored to control values at both levels. Except for the presence of rege nerative sprouts at 2 weeks post surgery, no changes in the number or sizes of unmyelinated axons were revealed at either 2 weeks or 16 mont hs post surgery. Our study demonstrates that implanted cuff electrodes may cause an initial loss of myelinated axons but with subsequent reg eneration.