FIBER COMPOSITION OF THE LATERAL PLANTAR AND SUPERFICIAL PERONEAL NERVES IN THE RAT FOOT

This study examines the fiber composition of two nerves projecting to the rat hindpaw: the lateral plantar nerve (LPN), which innervates pla ntar glabrous skin and some plantar muscles, and the foot branch of th e superficial peroneal nerve (fSPN), which projects to dorsal hairy sk in. The LPN contains 872 (33%) myelinated axons with a size range of 1 -7 mu m and a peak at 4 mu m. Some 200 of the myelinated axons are mus cle efferents. There are 1,969 (67%) C-fibers. After neonatal capsaici n treatment, the number of C-fibers in the LPN is 61% below the normal level, but it is not significantly different from control levels afte r chemical sympathectomy with guanethidine. The fSPN is composed of 47 0 (20%) myelinated axons with a size range similar to that in the LPN. Virtually all myelinated fibers are sensory. There are 1,791 (80%) C- fibers. In neonatally capsaicin-treated animals, the occurrence of C-f ibers is 65% below control levels. In chemically sympathectomized anim als, the number of C-fibers in the fSPN is normal. This description of the fiber composition of the LPN and the fSPN in the rat provides a b asis for future experimental studies.