Journal of Neuroscience, Vol 11, 445-453, Copyright © 1991 by Society for Neuroscience
Elimination of the transient ipsilateral retinotectal projection is not solely achieved by cell death in the developing chick
CV Williams and SC McLoon
Department of Cell Biology and Neuroanatomy, University of Minnesota, Minneapolis 55455.
During development of the projection from the retina to the brain in the
chick, a transient ipsilateral retinotectal projection forms and
disappears. This disappearance is coincident with a wave of ganglion cell
death in the retina. The contribution of cell death to the disappearance of
this projection, as opposed to another mechanism such as axon retraction,
was examined. Retinal ganglion cells with a projection to the ipsilateral
tectum were retrogradely labeled by injection of long-lasting fluorescent
dyes into the tectum prior to the onset of ganglion cell death. Large
injections of fast blue labeled approximately 1800 ganglion cells in the
ipsilateral retina before the period of cell death began. If the injected
embryos were allowed to survive past the peak period of ganglion cell
death, the average number of labeled ganglion cells in the ipsilateral
retina was reduced by somewhat more than half. It is possible that the
remaining labeled ganglion cells projected only to nontectal visual nuclei
and were labeled by fast blue that had diffused out of the tectum. This was
tested by repeating the study using very localized injections of 1,1'-
dioctodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate or
fluorescent microspheres into the tectum. These small injections confirmed
that cells with transient projections to the ipsilateral tectum survived
past the elimination of this projection. Thus, ipsilaterally projecting
ganglion cells have, at most, a slightly greater propensity for death than
the average ganglion cell, and elimination of the transient ipsilateral
retinotectal projection in chick can be explained only, in part, by the
mechanism of cell death.(ABSTRACT TRUNCATED AT 250 WORDS)
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