Intrafascicular electrodes for stimulation and recording from mudpuppy spinal roots

This paper presents a technique for stimulating and recording from multiple intact spinal roots in the in vitro mudpuppy (Necturus maculatus) spinal c ord-forearm preparation using fine wire electrodes, a modified intrafascicu lar electrode. We found that multiple spinal roots of the preparation could be implanted with these modified electrodes for independent stimulation or recording of the roots without inducing mechanical vibrations, disrupting conduction, or obscuring the view of or access to the spinal cord. Recordin g and stimulation performance using these electrodes was compared with resu lts obtained using conventional hook electrodes. We found that intrafascicu lar electrodes were more efficient than hook electrodes for stimulating ner ve fibers, being able to produce equivalent levels of activation using stim ulation levels that were an order of magnitude smaller. Compound action pot ential signals recorded from electrodes implanted in the spinal roots were found to be larger than those from hook electrodes placed around the corres ponding spinal nerve, showing that intrafascicular electrodes are more effi cient at recording activity in the nerve. Moreover, it was possible to reco rd evoked activity from cutaneous mechanoreceptors, even though the signal to noise ratio was low. Rough estimates of the conduction velocities for th e fastest components in the compound action potentials were calculated and found to be around 17.5 m/s for both dorsal and ventral roots. (C) 2000 Els evier Science B.V. All rights reserved.