Guidance of neuronal growth cones in the grasshopper embryo. I. Recognition of a specific axonal pathway by the pCC neuron.

The selective affinities that growth cones display for specific axonal surfaces give rise to stereotyped patterns of selective fasciculation. Previous studies on cell recognition by neuronal growth cones in the grasshopper embryo led to the proposal and initial experimental testing of the labeled-pathways hypothesis. Here we report on a further experimental analysis of this hypothesis, using the first 3 longitudinal axon fascicles, which initially contain only the axons of 7 identified neurons. We describe and experimentally test the selective affinity of the pCC growth cone for the MP1 and dMP2 axons in the MP1/dMP2 fascicle. The pCC growth cone appears to demonstrate an absolute, rather than hierarchical, preference for the MP1/dMP2 fascicle, as compared with other longitudinal axon fascicles, which supports the notion that the surfaces of the MP1 and dMP2 axons have some special distinguishing label that guides the pCC growth cone onto and along them.