Quantitative Ultrastructural Analysis of Hippocampal Excitatory Synapses

Quantitative Ultrastructural Analysis of Hippocampal Excitatory Synapses

August 1, 1997, 17(15):5858–5867 | Thomas Schikorski and Charles F. Stevens
The study by Schikorski and Stevens provides a quantitative ultrastructural analysis of excitatory synapses in the CA1 region of the rodent hippocampus, both in vivo and in culture. They estimated the statistical distributions of active zone and postsynaptic density (PSD) sizes, the number of active zones per bouton, the number of docked vesicles per active zone, and the total number of vesicles per bouton. These measurements were related to synaptic physiology, particularly proposing that the distribution of active zone areas can account for the distribution of synaptic release probabilities, with each active zone functioning as a release site. Key findings include: - The average area of active zones and PSDs is ~0.04 μm². - Each bouton typically has one active zone. - Each active zone has approximately 10 docked vesicles. - The total number of vesicles per bouton averages around 200. - These measurements are highly correlated across synapses. The study also compared the synaptic structure in the brain with that in cultured hippocampal neurons, finding similar statistical distributions. The results support the idea that the active zone area is linearly related to the bouton volume and that the number of docked vesicles per active zone is proportional to the release probability. The physiological implications of these findings include: - Active zones and release sites are closely aligned, supporting Katz's theory. - The pool of morphologically docked vesicles corresponds to the readily releasable pool. - The distribution of active zone areas predicts the distribution of release probabilities. Overall, the study provides a detailed understanding of the structural basis of synaptic transmission in the hippocampus, linking morphological features to physiological functions.The study by Schikorski and Stevens provides a quantitative ultrastructural analysis of excitatory synapses in the CA1 region of the rodent hippocampus, both in vivo and in culture. They estimated the statistical distributions of active zone and postsynaptic density (PSD) sizes, the number of active zones per bouton, the number of docked vesicles per active zone, and the total number of vesicles per bouton. These measurements were related to synaptic physiology, particularly proposing that the distribution of active zone areas can account for the distribution of synaptic release probabilities, with each active zone functioning as a release site. Key findings include: - The average area of active zones and PSDs is ~0.04 μm². - Each bouton typically has one active zone. - Each active zone has approximately 10 docked vesicles. - The total number of vesicles per bouton averages around 200. - These measurements are highly correlated across synapses. The study also compared the synaptic structure in the brain with that in cultured hippocampal neurons, finding similar statistical distributions. The results support the idea that the active zone area is linearly related to the bouton volume and that the number of docked vesicles per active zone is proportional to the release probability. The physiological implications of these findings include: - Active zones and release sites are closely aligned, supporting Katz's theory. - The pool of morphologically docked vesicles corresponds to the readily releasable pool. - The distribution of active zone areas predicts the distribution of release probabilities. Overall, the study provides a detailed understanding of the structural basis of synaptic transmission in the hippocampus, linking morphological features to physiological functions.
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Understanding Quantitative Ultrastructural Analysis of Hippocampal Excitatory Synapses