Degeneration and Regeneration of Nerves in a Dorsal Skin Flap in the Rat

Abstract

The denervation and the subsequent reinnervation of dorsal skin flaps in the rat was studied histochemically by demonstrating the nonspecific cholinesterase activity and catecholamine fluorescence. The denervation of the skin flap occurred from the apex to near its base. The catecholamine fluorescence induced by treatment with formaldehyde or glyoxylic acid disappeared 32 hours postoperatively from the nerves of the erector pili muscles or from the vascular nerves of the skin flap. The non-specific cholinesterase activity (nsChE) of the degenerating cutaneous nerves disappeared from the nerves of the skin flap up to near its base within two weeks after surgery. Four weeks after the operation, the first regenerating nsChE-positive nerves were observed at the flap margin. Rapid progress in reinnervation of the flap occurred during the first eight to twelve weeks after surgery. These regenerated nsChE-positive nerves were generally distributed in a random way. However, some regenerated nerves were observed in the vicinity of hair follicles from the eighth week following surgery. The hair follicles and erector pili muscles were visible throughout the period of investigation due to an nsChE reaction. In this study only free nerve endings and no encapsulated nerve endings were found in the skin flaps. The role of these free nerve endings in sensation is discussed, in addition to the different factors affecting regenerating cutaneous nerves. Regenerating fluorescent adrenergic nerves were first observed at the flap margin four weeks postoperatively. Some regenerated adrenergic nerves, mainly following blood vessels, were regularly observed from the eighth week. The regeneration made progress but even at 20 weeks postoperatively only some of the blood vessels in the skin flap were partially innervated and the reinnervation of erector pili muscles was observed only occasionally. The regenerating adrenergic nerves were apparently under the control of the target tissue. The biological bases of this phenomenon are discussed.