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Early retrograde effects of blocking axoplasmic transport in the axons of developing neurons
1Institute of Cell Biology and Morphology, University of Lausanne, Switzerland.
Insights
Blocking axoplasmic transport in developing neurons disrupted their development and survival. Early neuronal death decreased, suggesting retrograde signals have both life-promoting and death-promoting components.
Area of Science:
- Neuroscience
- Developmental Biology
- Cell Biology
Background:
- Developing neurons require retrograde trophic support for survival and proper development.
- Disruption of axoplasmic transport can lead to neuronal death.
Purpose of the Study:
- To investigate the effects of eliminating retrograde trophic support on developing neurons in the chick embryo isthmo-optic projection.
- To determine the temporal effects of blocking axoplasmic transport on neuronal survival and development.
Main Methods:
- Chick embryos were used to study the isthmo-optic projection.
- Axoplasmic transport was blocked in the terminal axons of isthmo-optic neurons.
- Neuronal survival and developmental changes were assessed at various time points (3, 6, and 9 hours post-injection).
Main Results:
- Blocking axoplasmic transport perturbed cellular reorganization within 9 hours, affecting the laminated structure of the isthmo-optic nucleus.
- An early, transient decrease in neuronal death (observed at 3-9 hours) preceded the expected increase in dying neurons at later time points.
- The number of dying neurons initially decreased below control levels before significantly increasing.
Conclusions:
- Retrograde trophic signals appear to contain both life-promoting and death-promoting components.
- The death-promoting components of retrograde signals may act more rapidly than life-promoting components in this system.
- This suggests a complex regulatory mechanism for neuronal survival during development.
Abstract:
Depriving developing neurons of retrograde trophic support may disrupt their development and often causes them to die. We here report the effects, in chick embryos, of eliminating retrograde support in the isthmo-optic projection by blocking axoplasmic transport in the terminal parts of the axons, which is known ultimately to kill the isthmo-optic neurons. Within only 9 h, this had perturbed the process of cellular reorganisation that eventually leads to the laminated appearance of the mature isthmo-optic nucleus. Neuron survival in the isthmo-optic nucleus was affected even more quickly, but the earliest change, occurring in as little as 3 h, was not an increase in the number of dying neurons, but a decrease below control values. This novel effect was still present at 6 and 9 h after the injection, but at longer survival times the number of dying neurons increased well above control values as expected. Our interpretation of the transient decrease in neuronal death is that retrograde trophic signals include both death-promoting and life-promoting components, and that the former act faster in this system.