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Updated: Aug 8, 2026
Evaluation of Synapse Density in Hippocampal Rodent Brain Slices
Published on: October 6, 2017
Confocal imaging of mossy fiber growth in live hippocampal slices
1Department of Molecular and Cellular Physiology, Stanford University School of Medicine, CA 94305-5426.
Abstract:
Acutely isolated slices of developing rat hippocampus have been used to study axon growth and synapse formation. Mossy fibers, which are the axons of dentate granule cells, were labeled in living brain slices by injection of a fluorescent membrane dye (DiI or DiO) into the dentate gyrus. Time-lapse observations were made in area CA3 at a time when mossy fibers are normally growing in and forming en passant synapses with pyramidal neurons. Single scan images were collected at 1-2 min intervals over a period of several hours using a scanning laser confocal microscope. At the tips of growing mossy fibers were highly motile growth cones with several filopodia and small lamellae. Labeled fibers typically extended at rates up to 15 microns/h, but occasionally individual axons abruptly stopped elongating and the leading growth cone became quiescent. In addition, dynamic filopodia-like structures were found to be associated with axonal varicosities proximal to the leading growth cone. We are currently pursuing methods to determine whether these motile activities correlate with synapse formation.
Insights
Researchers observed developing rat hippocampus axons using fluorescent dyes and time-lapse microscopy. They documented axon growth dynamics and identified motile structures potentially involved in synapse formation.
Area of Science:
- Neuroscience
- Developmental Biology
Background:
- The developing hippocampus is crucial for learning and memory.
- Understanding axon growth and synapse formation is key to neural development.
Purpose of the Study:
- To investigate the dynamic behavior of growing mossy fibers in the developing rat hippocampus.
- To observe axon elongation rates and growth cone motility in real-time.
Main Methods:
- Acutely isolated slices of developing rat hippocampus.
- Fluorescent membrane dye labeling (DiI or DiO) of mossy fibers.
- Time-lapse confocal laser scanning microscopy over several hours.
Main Results:
- Mossy fiber axons extended at rates up to 15 microns/h.
- Growth cones exhibited high motility with filopodia and lamellae.
- Axonal varicosities displayed dynamic filopodia-like structures.
- Observed instances of axon elongation cessation and growth cone quiescence.
Conclusions:
- Growing mossy fibers display complex dynamic behaviors, including periods of rapid extension and quiescence.
- Motile filopodia-like structures near varicosities suggest potential roles in synapse formation.
- Further research is needed to correlate these dynamic activities with actual synapse formation.
