Journal of Neuroscience, Vol 10, 2476-2484, Copyright © 1990 by Society for Neuroscience
Identification of location and timing of guidance cues in sympathetic preganglionic axons of the chick
JW Yip
Department of Physiology, School of Medicine, University of Pittsburgh, Pennsylvania 15261.
The outgrowth of preganglionic axons into the sympathetic trunk of the
chick occurs at stages 26-27 (5-5 1/2 d), beginning with C16 and T1 and
followed by progressively more caudal spinal cord segments. The direction
of preganglionic projections is segment specific, with T1 preganglionic
neurons projecting predominantly in the rostral direction and T4
preganglionic neurons projecting predominantly in the caudal direction.
These projections are correct from the outset. A previous study (Yip, 1987)
has shown that removal of the neural crest, precursors of target ganglion
cells, did not alter the trajectories of preganglionic axons, indicating
that target cues are not required for the guidance of these axons. The
present work extends that study and examines, through surgical
manipulations of the developing embryo, the location and time of appearance
of preganglionic axonal guidance cues. Spinal cord transplantation
experiments show that segment-specific patterns of preganglionic outgrowth
are determined by the local environment of axonal growth and not by the
identity of preganglionic populations. In addition, spinal cord transplants
of age-mismatched donors and hosts indicate that the timing of
preganglionic outgrowth is also under local environmental control. These
findings suggest that preganglionic axonal outgrowth is guided by local
cues which may appear in a controlled spatiotemporal manner.