Target cues are not required for the guidance of sympathetic preganglionic axons

The patterns of preganglionic projections in the avian sympathetic system are highly specific. Preganglionic axons arising from the T1 spinal segment, for example, project predominantly in the rostral direction, whereas T4 preganglionic axons project predominantly in the caudal direction. Moreover, each ganglion receives projections from a distinct set of spinal cord segments. These patterns are established during embryonic life and are correct from the outset. In this study, I have examined the patterns of preganglionic projections in embryos deprived of their target ganglia through removal of the neural crest prior to its migration to form the sympathetic ganglia. My results indicate that preganglionic axons of target-deprived embryos still project in the proper directions and terminate in the presumptive target regions. Target cues are thus not required for the guidance of preganglionic axons.