DEVELOPMENT OF SENSORY INNERVATION IN CHICK SKIN - COMPARISON OF NERVE-FIBER AND CHONDROITIN SULFATE DISTRIBUTIONS IN-VIVO AND IN-VITRO

In bird skin, nerve fibres develop in the dermis but do not enter the epidermis. In co-cultures of 7-day-old chick embryo dorsal root gangli a and epidermis, the neurites also avoid the epidermis. Previous studi es have shown that chondroitin sulphate proteoglycans may be involved. Chondroitin sulphate has therefore been visualized by immunocytochemi stry, using the monoclonal antibody CS-56, both in vivo and in vitro u sing light and electron microscopy. Its distribution was compared to t hose of 2 other chondroitin sulphate epitopes and to that of the growi ng nerve fibres. In cultures of epidermis from 7-day-old embryonic chi cks, immunoreactivity is found uniformly around the epidermal cells wh ile at 7.5 days the distribution in dermis is heterogeneous, and parti cularly marked in feather buds. In vivo, chondroitin sulphate immunore activity is detected in the epidermis, on the basal lamina, on the sur faces of fibroblasts and along collagen fibrils. This localization is complementary to the distribution of cutaneous nerves. Chondroitin sul phate in the basal lamina could prevent innervation of the epidermis a nd the dermal heterogeneities could partly explain the nerve fibres su rrounding the base of the feathers. Chondroitin sulphate could therefo re be important for neural guidance in developing chick skin.