NOTES AND NEW DEVELOPMENTS REINNERVATION OF RAT EXTENSOR DlGlTORUM LONGUS MUSCLES AFTER FREE GRAFTING

Free grafts of the extensor digitorum longus (EDL) muscle of the rat are invaded by regenerating nerve fibers during the second postoperative week. Neuromuscular junctions are established during the third week. Levels of choline acetyltransferase (CAT) activity parallel the invasion of the graft by nerve fibers, but this activity never returns to control levels. We conclude that incomplete reinnervation of free muscle grafts may be a factor in the failure of such grafts to reattain the mass of control muscles. MUSCLE & NERVE 2:304-307 1979 Autogenous free muscle grafts have proved useful in several respects in the study of skeletal muscle regenerat i~n.~ The procedure is such that the grafted muscle is cut off from the beginning from both a neural and a vascular supply. Blood vessels must enter the graft before muscle regeneration can begin, and reinnervation must occur if the regenerative process is to be completed. Results of a recent study, which examined the role of enzymes associated with glucose metabolism in regenerating free grafts of the extensor digitorum longus (EDL) muscle, were consistent with the interpretation that the grafts did not attain complete maturity, at least not in the biochemical sense.I3 It is possible that the lack of biochemical maturation, as well as the failure of free muscle grafts to attain the mass of a normal muscle, might reflect deficient innervation of the grafts. Indeed, Hall-Craggs and Brand7 showed that facilitation of reinnervation at the time of grafting markedly enhances the extent of regeneration. We conducted a correlative morphologic and biochemical study to determine ( 1 ) the relationship between early reinnervation of the graft and choline acetyltransferase (CAT) activity; and (2) the extent to which the innervation of a mature free muscle graft approaches that of the normal ungrafted muscle. These data have appeared elsewhere in preliminary form.I4 MATERIALS AND METHODS All operations were conducted on male SpragueDawley rats (Charles River) weighing 175-200 g. During surgical procedures, the rats were anesthetized with ether. Upon removal, the right EDL muscle was injected with 100-200 pl of bupivacaine (Marcaine) solution (0.75% bupivacaine in 0.9% NaCl, Winthrop Laboratories, New York, NY). The muscle was then soaked in bupivacaine solution for 10 min to expose the peripheral fibers to the effects of the local anesthetic. The muscle was immediately grafted back into its own bed and sutured to its proximal and distal tendons. No attempt was made to reestablish nervous or vascular continuity between graft and host. The left EDL remained untouched and served as a normal conFrom the Department of Anatomy, University of Michigan School of Medicine, Ann Arbor MI (Dr Carlson), and the Departments of Neurology and Pediatrics, University of Maryland School of Medicine, Baltimore. MD (Drs Max and Wagner) Acknowledgments This work was supported by grants from the Muscular Dystrophy Association of America, the National Amyotrophic Lateral Sclerosis Foundation, and NIH (NS-13116) Address reprint requests to Dr Carlson at the Department of Anatomy, 4622 Medical Sciences 1 1 , University of Michigan, Ann Arbor, MI 48109 Received for publication September 13, 1978, revised manuscript accepted for publication December 28, 1978 01 48-639W0204/0304 $00 OO/O @ 1979 Houghton Mifflin Professional Publishers 304 Reinnervation of Muscle Grafts MUSCLE 8, NERVE Jul/Aug 1979 C holine Acetyltransferase