Regulation of Chondrocyte Differentiation by Neural Factors from Sympathetic and Sensory Nerve Fibres

INTRODUCTION Fracture repair constitutes the sequence of cell biological events following bone injury and recapitulates the steps of endochondral ossification observed during embryonic skeletal development and growth. Because of the different phases of fracture healing (inflammation, cartilage formation and remodeling) the fracture callus provides an excellent tool for analysis of cartilage and bone formation in adults (1,4). There is evidence that the peripheral nervous system is involved in fracture healing and bone remodelling (3). Nerve fibres of sympathetic and sensory origin containing neurotransmitters and neuropeptides are known to innervate bone and fracture callus; and the absence of sensory innervation alters callus size and bone formation and may result in non-united fractures (2). In addition, neurotransmitters are known to control vascularization and matrix differentiation during endochondral ossification in embryonic development (5). However, little is known about their role in fracture healing and their influence on callus maturation and bone formation. The current research intends to understand the role of the peripheral nervous system for organization and differentiation of a cartilaginous callus and its impact on endochondral ossification.