Termino-lateral neurorrhaphy: the functional axonal anatomy.

The goal of this study was to determine the functional axonal anatomy of a termino-lateral neurorrhaphy (TLN). We hypothesize that axons populating a TLN must relinquish functional connections with their original targets prior to establishing new connections via the TLN. Two-month-old F344 rats underwent a TLN between the left peroneal nerve and a nerve graft tunneled to the contralateral hindlimb. Three months postoperatively, an end-to-end neurorrhaphy was performed between the nerve graft and the right peroneal nerve. Four months after the second operation, contractile properties and electromyographic (EMG) signals were measured in the bilateral hindlimbs. Left peroneal nerve stimulation proximal to the TLN site resulted in bilateral extensor digitorum longus (EDL) and tibialis anterior (TA) muscle contractions, with significantly lower forces on the side reinnervated by TLN. Evoked EMGs demonstrated that the right and left hindlimb musculature were electrically discontinuous following TLN. These data support our hypothesis that axons can form functional connections via a TLN, but they must first relinquish functional connections with their original targets.

Rat walking tracks do not reflect maximal muscle force capacity.

The relationship between walking-track measurements and maximum force generation in reinnervated rat hindlimb muscles was assessed. A rat model was designed to result in a broad range of recoveries of both muscle force and walking-track measurements after unilateral sciatic nerve injury and reconstruction. Three months following sciatic nerve injury, maximal force in the extensor digitorum longus (EDL) muscle ranged from 1325 to 3666 mN, and maximal specific forces ranged from 137.5 to 359.4 kNm(-2). In the same animals, functional intermediate toe spread factor (FIS) ranged from -0.03 to -0.78. Neither the correlation coefficient between EDL muscle maximal force and FIS (r = 0.4) nor that between EDL maximal specific force and FIS (r = -0.2) were statistically significant. The lack of correlation between muscle maximal force values and walking-track measurements suggests that these neuromuscular tests are assessing different factors.

Deletion of individual muscles alters rat walking-track parameters.

Rat walking-track analysis has been employed extensively to quantify motor recovery in studies of hindlimb nerve injury and repair. In order to clarify the relationship between individual print measurements and the function of specific hindlimb muscles, 40 young adult rats were assigned to one of five groups (n = 8/group) in which specific deletions of motors were created as follows: Group 1--division of the tendon of insertion of the gastrocnemius, soleus, and plantaris muscles (GSP); Group 2--division of the extensor digitorum longus muscles tendons of insertion (EDL); Group 3--division of the extensor hallicus longus muscle tendon of insertion (EHL); Group 4--division of the tibialis anterior muscle tendon of insertion (TA); or Group 5--division of the tibial nerve at the ankle (TNA). Parameters for print length (PL), intermediate toe spread (IS), and total toe spread (TS) were calculated from walking tracks recorded before and again five days after deletion of the motors. Specific, predictable patterns of change in footprint parameters were observed for each group. It was concluded that triceps surae and tibialis anterior muscle function directly affects print length; EHL function directly influences total toe spread; and EDL function is directly related to intermediary toe spread. These data demonstrate a direct relationship between individual print measurements and the function of individual rat hindlimb muscles.