The Journal of Neuroscience, June 15, 2001, 21(12):4318-4325
The Role of Nitric Oxide in Development of Topographic Precision
in the Retinotectal Projection of Chick
Hope H.
Wu1,
Daniel J.
Selski1,
Esam E.
El-Fakahany2, and
Steven C.
McLoon1
1 Department of Neuroscience, and
2 Department of Psychiatry, University of Minnesota,
Minneapolis, Minnesota 55455
The axonal projection from the retina to the tectum exhibits a
precise topographic order in the mature chick such that neighboring ganglion cells send axons to neighboring termination zones in the
contralateral tectum. The initial pattern formed during development is
much less organized and is refined to the adult pattern during a
discrete period of development. Refinement includes elimination of
radically aberrant projections, such as those from the temporal side of
the retina to posterior regions of the tectum, as well as a more subtle
improvement in the topographic precision of the projection. The enzyme
that synthesizes nitric oxide is expressed at high levels in the tectum
during the developmental period in which the topography improves.
Pharmacological blockade of nitric oxide synthesis during this period
prevented elimination of topographically inappropriate retinotectal
projections in a dose-dependent manner. This effect could not be
duplicated by treatment of embryos with a vasoconstrictor, indicating
that vascular changes were not a factor. These results show that nitric
oxide is involved in refinement of the topography of the retinotectal
projection as well as in other aspects of refinement of this projection
in developing chick.
Key words:
nitric oxide synthase; retina; tectum; pattern formation; refinement of connections; neuronal development
Copyright © 2001 Society for Neuroscience 0270-6474/01/21124318-08$05.00/0