Growth cones respond in diverse ways upon encountering neurites in cultures of chick dorsal root ganglia.

To help in understanding the role that interactions with other axons may have in helping to guide sensory neuron growth cones along the appropriate pathways in the chick hindlimb, we have examined how sensory growth cones respond when they contact the processes of other sensory neurons. Videotaping of neurons in dissociated cell cultures, as they participated in such encounters, showed that sensory growth cones can demonstrate any one of a number of responses: crossing, fasciculation, parallel growth, or retraction. We observed a variety of responses even among neurons from a single segment, suggesting the possibility that this is due to a heterogeneity of cell-surface labels among the neurons present within an individual dorsal root ganglion. If sensory neurons behave in vivo as we found they do in culture, the diverse behaviors of sensory growth cones may contribute to the process by which different subsets of axons sort out into separate, discrete bundles as they extend into the periphery during development. The diversity of responses we observed stands in contrast to the results of Kapfhammer, J.P., and Raper, J.A., [(1987) J. Neurosci. 7, 1595-1600] who found that sensory growth cones always cross sensory neurites. Possible explanations for the differences in the results were explored and are discussed.