A LOOSE LIGATURE-INDUCED MONONEUROPATHY PRODUCES HYPERALGESIAS MEDIATED BY BOTH THE INJURED SCIATIC-NERVE AND THE ADJACENT SAPHENOUS NERVE

An experimental mononeuropathy was produced in rats by unilateral loos e ligation of the sciatic nerve, with a contralateral sham surgery. Re peated bilateral sensory testing was performed over time to investigat e any threshold differences between the loose ligature side and the co ntralateral control side. A prolonged reduction in the mean withdrawal threshold to heat was observed on the loose ligature side over the me dial dorsum of the hindpaw (MDH), and over the plantar surface of the hindpaw (PSH). Following loose ligature there was also a significant r eduction in the von Frey fiber withdrawal thresholds over the lateral dorsum of the hindpaw (LDH) and the medial dorsum of the hindpaw (MDH) . In a second experiment the saphenous nerves were transected bilatera lly in rats who had an earlier unilateral loose sciatic ligation. The heat hyperalgesia that had been previously observed over the MDH was a bolished, and no withdrawal response could be elicited with the larges t von Frey fiber over the MDH, indicating that the MDH hyperalgesia in duced by sciatic loose ligature was mediated by the saphenous nerve. T his adjacent neuropathic hyperalgesia (ANH) resembles the saphenous me diated ANH observed over the MDH following sciatic transection, follow s the same temporal course of onset, and may share a similar pathogene sis. The heat threshold over the PSH and the pressure threshold over t he LDH were unaffected by the bilateral saphenous transection, demonst rating that following loose sciatic ligation both of these thresholds are mediated by the sciatic nerve.