A quantitative assessment of muscle spindle formation in reinnervated and non-reinnervated grafts of the rat extensor digitorum longus muscle

Free grafting of the rat extensor digitorum longus muscle disrupts the neurovascular supply and results in degeneration and subsequent regeneration of both muscle and nerve. Reinnervation of one group of grafts was prevented by severing and ligating the sciatic nerve. Thirty days after surgery, the number of muscle spindles in each graft was determined by examination of serial sections at the light-microscopic level. Non-operated control muscles contained 37.86 +/- 3.02 () spindles per muscle. Means for the reinnervated and non-reinnervated grafts were 15.63 +/- 3.89 and 18.38 +/- 5.15 respectively. At the time of surgery, all of these grafts had been treated with 0.75% bupivacaine, a local anesthetic which, combined with the grafting technique, ensures degeneration of all muscle fibers. An additional group of grafts was not subjected to this treatment and contained a mean of 27.40 +/- 2.19 spindles.The embryogenesis of muscle spindles is dependent upon interaction between sensory nerves and developing myotubes. The conditions for the formation of these stretch receptors in regenerating muscle have been less clear. Their formation in non-reinnervated grafts demonstrates that this process, unlike spindle development in the embryo, does not require the presence of nerves. When reinnervation of a graft is allowed, large numbers of nerve fibers have been observed in muscle spindles. It is not yet known whether or not the normal pattern of innervation, essential for proper function of the spindle, is restored.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24501/1/0000778.pd