Competition or inhibition? Developmental strategies in the establishment of peripheral projections by leech neurons

Leech neurons, like those of other invertebrates and those of vertebrates, undergo specific interactions during development which serve to define their adult morphologies and synaptic connections. We review here several observations and experiments that illustrate these interactions. In particular, we consider how they shape and constrain peripheral arborizations and whether the evidence favors competition or inhibition as their mode of action.