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.