The basic goals of this proposal are to show 1) there is a considerable postnatal decline in dorsal root and peripheral axon numbers that is not associated with death of the sensory cells that give rise to these axons, 2) that putting stumps of a transected nerve in a silicone tube protects those sensory cells that would normally die because of the transection. The common thread linking these 2 ideas is that they are both the results of competition for growth factors, and the most likely candidate is nerve growth factor. Experimental surgery will be used to produce the lesions and the data consist of numbers of sensory cells, myelinated and unmyelinated axons and blood vessels and the structure of the perineurium. If these goals can be met, very important health related goals will be achieved. First, our data would show that a loss of axons not caused by death of cells is a relatively general event in mammalian neural development. Second, if placing nerve stumps in silicone tubes keeps dorsal root ganglion cells from dying, this would provide a rational reason for using such tubes in therapy.