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, recordings were made from afferent axons innervating the tibialis anterior muscle in rats under several different experimental conditions. In two groups 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-anastomosis of the common peroneal nerve. The other rats (group C) were examined 2.5 months after the nerve was cut and ligatured to its stumps to avoid axonal regeneration. No evoked potentials and no activation in response to any test agent were found in group C rats. We found a significant increase in the proportion of group I-II fibers and a significant decrease in group 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 velocity was measured in group IV fibers in group B rats when compared with group A (P < 0.01) and the controls (P < 0.01). The proportion of afferent units 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 KCl (1-20 mM) and lactic acid (0.5-3 mM) concentrations was markedly depressed in group 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 in the direction of enhanced mechanosensitivity to high-frequency tendon vibration and depressed metabosensitivity.