REGENERATION OF CERCAL FILIFORM HAIR SENSORY NEURONS IN THE FIRST-INSTAR COCKROACH RESTORES ESCAPE BEHAVIOR

Neural regeneration in the escape circuit of the first-instar cockroac h is described using behavioral analysis, electrophysiology, intracell ular staining, and electron microscopy, Each of the two filiform hairs on each of the animal's cerci is innervated by a single sensory neuro n, which specifically synapses with a set of giant interneurons (GIs) in the terminal ganglion, These trigger a directed escape run. Severin g the sensory axons causes them to degenerate and perturbs escape beha vior, which is restored to near normal after 4-6 days, Within this tim e, afferents regenerate and reestablish arborizations in the terminal ganglion. In most cases, regenerating afferents enter the cereal glome rulus and re-form most of the specific monosynaptic connections they a cquired during embryogenesis, although their morphology deviates marke dly from normal; these animals reestablish near normal escape behavior , In a few cases, regenerating afferents remain within the cercus or b ypass the cereal glomerulus, and thereby fail to re-form synapses with GIs; these animals continue to exhibit perturbed escape behavior. We conclude that in most cases, specific synapses are reestablished and a ppropriate escape behavior is restored. This regeneration system there fore provides a tractable model for the establishment of synaptic spec ificity in a simple neuronal circuit. (C) 1997 John Wiley & Sons, Inc.