The Journal of Neuroscience, May 15, 2000, 20(10):3650-3662
Morphology and Growth Patterns of Developing Thalamocortical
Axons
Irini
Skaliora,
Richard
Adams, and
Colin
Blakemore
University Laboratory of Physiology, University of Oxford, Oxford
OX1 3PT, United Kingdom
It is increasingly evident that the actions of guidance factors
depend critically on the cellular and molecular context in which they
operate. For this reason we examined the growth cone morphology and
behavior of thalamic fibers in the relatively natural environment of a
slice preparation containing the entire pathway from thalamus to
cortex. Axons were labeled with DiI crystals and imaged with a
laser-scanning confocal microscope for up to 8 hr. Their behavior was
analyzed in terms of morphology, extension rates, shape of trajectory,
frequency of branching, and percentage of time spent in advance, pause,
and retraction. Thalamic fibers had distinct and stereotyped growth
patterns that related closely to their position; within the striatum
growth cones were small and elongated, rarely extending filopodia or
side branches. Axons grew quickly, in straight trajectories, with
minimal pauses or retractions. When they reached the ventral
intermediate zone, axons slowed down, often coming to a complete stop
for up to several hours, and their growth cones became larger and more
complex. During pauses there were continuous extensions and retractions of filopodia and/or side branches. When advance resumed, it
was often to a different direction. These results demonstrate
consistent regional variations in growth patterns that identify an
unexpected decision region for thalamic axons. They provide the basis
for examining the roles of guidance cues in an accessible yet intact preparation of the thalamocortical pathway and allow for an evaluation of previously suggested pathfinding mechanisms.
Key words:
growth cones; development; axon guidance; time-lapse confocal imaging; pathfinding; in vitro; thalamocortical
Copyright © 2000 Society for Neuroscience 0270-6474/00/20103650-13$05.00/0
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