Changes in afferent activities from tibialis anterior muscle after nerve repair by self-anastomosis

In order to study sensory nerve plasticity after nerve injury and repair, r ecordings were made from afferent axons innervating the tibialis anterior m uscle in rats under several different experimental conditions. In two group s of rats, reinnervation of the denervated tibialis anterior was examined 2 .5 months (group A) and 7 months (group B) after section, along with self-a nastomosis of the common peroneal nerve. The other rats (group C) were exam ined 2.5 months after the nerve was cut and ligatured to its stumps to avoi d axonal regeneration. No evoked potentials and no activation in response t o any test agent were found in group C rats. We found a significant increas e in the proportion of group I-ii fibers and a significant decrease in grou p IV fibers in the group B rats when compared with group A (P < 0.05 and P < 0.01) and control animals (P < 0.01 and P < 0.01). A higher conduction ve locity was measured in group IV fibers in group B rats when compared with g roup A (P < 0.01) and the controls (P < 0.01). The proportion of afferent u nits showing an optimal discharge in response to tendon Vibration at 70 Hz (range 0-100 Hz) was higher in groups A and B (72.2 and 80%, respectively) than in the controls (36.8%). The response of muscle afferents to KCI (1-20 mM) and lactic acid (0.53 mM) concentrations was markedly depressed in gro up A rats (P < 0.05), whereas it was restored and even accentuated in group B animals when compared with the controls (P < 0.05). Electrically induced fatigue (3 min, 10 Hz) significantly activated (P < 0.05) muscle afferents only in controls. The present study indicates that after self-anastomosis of a cut hindlimb muscle nerve, sensory innervation was markedly modified i n the direction of enhanced mechanosensitivity to high-frequency tendon Vib ration and depressed metabosensitivity. (C) 2001 John Wiley & Sons, Inc.