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Cortical target depletion and the developing lateral geniculate nucleus: implications for trophic dependence
T U Woo1, J K Niederer, B L Finlay
1Department of Psychology, Cornell University, Ithaca, NY 14853, USA.
Cerebral Cortex (New York, N.Y. : 1991)
|May 1, 1996
Summary
The developing dorsal lateral geniculate nucleus (LGd) can survive significant loss of its primary visual cortex targets. Cell numbers in the LGd are linearly related to remaining visual cortex neurons after substantial layer IV depletion.
Area of Science:
- Neuroscience
- Developmental Biology
Background:
- The dorsal lateral geniculate nucleus (LGd) relies on visual cortex input for survival during development.
- Complete visual cortex removal causes LGd degeneration.
Purpose of the Study:
- To investigate the trophic relationship between the developing LGd and its primary targets in the visual cortex.
- To determine the quantitative dependence of LGd survival on specific cortical neuron populations.
Main Methods:
- Intraperitoneal injections of methylazoxymethanol acetate (MAM) to pregnant hamsters to deplete specific cortical neuron layers (primarily layer IV).
- Histological analysis and horseradish peroxidase (HRP) tracing to assess LGd cell numbers and geniculocortical axon projections.
Main Results:
- Over 75% depletion of layer IV neurons did not reduce LGd cell numbers.
- Geniculocortical axons showed reduced arborization density and extent in depleted cortical areas.
- LGd neuron survival became linearly dependent on the number of remaining layer II-IV cortical neurons above 75% depletion.
Conclusions:
- The LGd exhibits a remarkable resilience to substantial loss of its primary cortical targets.
- Trophic mechanisms likely match LGd neuron populations to the available cortical neuronal populations during development.