GROWTH CONES TURN UP CONCENTRATION GRADIENTS OF DIFFUSIBLE PERIPHERALTARGET-DERIVED FACTORS

Severed peripheral nerve axons grow across a gap in their pathway to r egenerate into the distal nerve stump. At the turn of the century this observation led to the proposal that concentration gradients of facto rs released from the cells of the distal nerve segment orient the grow th of the regenerating axons, Recently, several central nervous system target-derived factors have been shown to direct process outgrowth vi a concentration gradients of the factors during development. The demon stration of target-derived tropic influences in the peripheral nervous system has however remained elusive. We have examined whether concent ration gradients of diffusible factors released by the cells of a leng th of peripheral nerve influence the outgrowth of adult sensory neuron growth cones in vitro. We demonstrate that the growth cones turn and grow up the concentration gradients, providing evidence for the presen ce of diffusible peripheral target-derived neurotropic factors that ca n act in the peripheral nervous system. (C) 1997 Academic Press.