Embryogenesis of peripheral nerve pathways in grasshopper legs. III. Development without pioneer neurons.

We have examined the consequence of deleting the first pathfinding neurons to differentiate in the metathoracic leg, cell pair tibial 1 (Ti1) (C. M. Bate, 1976, Nature (London) 260, 54-56; H. Keshishian, 1980, Dev. Biol. 80, 388-397) on the development of two uniquely identifiable follower sensory neurons, and upon the subsequent development of nerve 5B1 in the leg. Following the equivalent of 10-15% of embryonic development in culture the follower sensory neurons were found to have formed topologically normal axonal trajectories in the leg, and to have established contacts with later differentiating sensory and motor axons in an essentially normal fashion. The results show that followers can navigate the route normally taken by the pioneers, and suggest that the pioneers do not have unusual pathfinding capabilities.