Functional Reinnervation of the Distal Hindlimb Muscles in Rats after Compression of the Sciatic Nerve

Abstract

Chronic experiments (12 weeks long) were carried out on two groups of pubertate-age Wistar rats. The sciatic nerve in one hindlimb was compressed, and complex analysis of the dynamics of functional reinnervation of the distal hindlimb muscles was performed. We used videorecording of images of the feet in the course of locomotion for estimation of the level of functional reinnervation of the toe extensors (the technique was modified in our laboratory) and a tensometric technique (measuring of the contraction force of the toe flexors and ankle extensors in the course of realization of the burrowing instinct by the animals). In the first group of animals (n = 21), we studied the dynamics of recovery of the force developed by the toe flexors and ankle extensors and of the functional sciatic index after sciatic nerve traumatization with no additional pharmacological influences. In the second group (n = 29), the same indices were analyzed, but after single injections of gamma-hydroxybutyrate (GHB) into animals before compression of the sciatic nerve and within early and late (3–4 and 14 weeks, respectively) terms after such intervention. Within the first week after compression, the smallest loss of activity was observed in the toe flexors, as compared with that in the toe and ankle extensors. Significant functional reinnervation of the ankle and toe extensors (to 52 and 87%, respectively) was observed on the 3rd to 7th weeks after the nerve injury. Functional reinnervation of the toe flexors was characterized by a relatively greater initial force of concentrations and more rapid recovery than those of the ankle and toe extensors. Practically complete recovery of the functions of the toe flexors was observed on the 10th week, while that of the ankle extensors was found on the 12th week. To make clearer possible reasons for differences between the processes of recovery of functions of the flexor and extensor muscles, we analyzed the effects of GHB on the contractile activity of these muscle groups within different time intervals after traumatization. In the second animal group, injection of GHB before operation resulted in drops of the muscle contraction force. After injury of the right sciatic nerve and injection of GHB on the 3rd posttraumatic week, recovery of the contraction force of all the examined muscles on the side of operation was more considerable. The functional loss of the muscle force in the left (intact) hindlimb in this case was 10 and 7% for the ankle extensors and toe flexors, respectively. Single injections of GHB within a late posttraumatic period resulted in a relative decrease in the contraction force of both flexors and extensors, and the functional loss was the greatest (35%) in the toe flexors.