Embryonic development of the central projection of auditory afferents (Schistocerca gregaria, orthoptera, insecta)

The auditory system of Schistocerca gregaria is a well investigated sensory network in the adult grasshopper. Here we present a first study on the emb ryonic development of this neuronal network. Focussing on the auditory rece ptor cells we show that they differentiate axonal processes at around 45% o f embryonic development. These axons fasciculate with the intersegmental ne rve and enter the central nervous system by 45-50% of development, First co llaterals sprout into the major arborization area, the frontal auditory pro jection area of the metathoracic ganglion by 60%, This projection increases in density until an adult-like morphology is established by 90% of develop ment. Furthermore, by the end of embryogenesis all three types of receptor fiber projections can be distinguished, This development is independent of a hearing ability, which develops much later during postembryonic life. The auditory projection co-develops with the fusion of neuromeres to the metat horacic ganglion, the formation of the target neuropile areas and the expre ssion of the synapse associated molecule synapsin, Fasciclin I and Lachesin , both potential axon-guidance molecules, are expressed strongly on both, p eripheral and central auditory pathways and, although much weaker, within t he synaptic target area. (C) 2001 John Wiley & Sons, Inc.