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Comparison of electron microscopy and silver staining for the detection of the first entorhinal synapses to develop
Insights
The developing perforant path shows increasing synapse degeneration in rat dentate gyrus between 7 and 13 days old. This study calibrates the reduced silver method for tracking developing axons and Wallerian degeneration.
Area of Science:
- Neuroscience
- Developmental Biology
- Synaptic Plasticity
Background:
- The perforant path, a projection from the entorhinal cortex to the dentate gyrus, is crucial for memory formation.
- Understanding the developmental timeline of this pathway is essential for comprehending hippocampal circuit maturation.
Purpose of the Study:
- To investigate the developmental trajectory of the perforant path projection to the dentate gyrus.
- To establish a temporal calibration for the reduced silver method in tracing developing axons and Wallerian degeneration.
Main Methods:
- Lesioning of the perforant path in neonatal rats (5-13 days old).
- Electron microscopic examination of the dentate gyrus at various time points (6-72 hours post-lesion).
- Application of the reduced silver method to observe Wallerian degeneration.
Main Results:
- Degenerating synapses were first observed in the dentate neuropile at 7 days of age.
- A sixteen-fold increase in degenerating synapses was noted between 7 and 13 days.
- The reduced silver method detected the first signs of Wallerian degeneration at 9 days post-lesion.
Conclusions:
- Synapse formation and maturation in the perforant path projection are actively occurring during the first two weeks of postnatal life.
- The study provides critical temporal data for utilizing the reduced silver method to study axonal development and degeneration in the central nervous system.
Abstract:
The development of the projection from the entorhinal cortex to the dentate gyrus (perforant path) has been studied with the electron microscope. The projection was lesioned in baby rats 5--13 days old and the dentate gyrus examined after 6--72 hr. Degenerating synapses first appeared in small numbers in the dentate neuropile at 7 days and in greater numbers in progressively older animals. There was a sixteen-fold increase in the number of synapses undergoing degeneration between 7 and 13 days. This investigation provides a calibration for the reduced silver method which has been used to trace developing axons (Singh, 1977). By this method the first signs of Wallerian degeneration, after cutting axons in the perforant path, were seen in the dentate neuropile at 9 days.
