Specificity of synapse formation in the cockroach

The synaptic connection between the filiform hair sensory neurons (FHSNs) and the giant interneurons (GIs) in the terminal abdominal ganglion of the first-instar cockroach Periplaneta americana has been used as a model system for investigating the mechanism of synaptic specificity. Electrophysiological and electron microscopical techniques were used to determine the normal patterns of connectivity between FHSNs and GIs. It was found that, even during synaptogenesis, no incorrect synapses were formed between the sensory axons and the interneuronal dendrites. Studies of a mutant in which there is a supernumerary filiform hair have given an insight into the role of positional information in determining the shape of a sensory neuron, and its connectivity with the GIs. There is electrophysiological evidence for competitive interactions between the supernumerary sensory axon and the original.