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| * all images with kind permission of the authors |
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Activation of a synapse in the hippocampus
The left panel is a projection image of 50 optical sections through a distal apical dendrite of a hippocampal CA3 pyramidal neuron, injected intracellularly with fluorescent Ca2+ indicator (Oregon Green 488 BAPTA-1, 0.5mM in micropipette).
Brief paired electrical stimuli (70 ms apart) were applied via an extracellular electrode ~1 mm away in stratum radiatum; these were observed to evoke Ca2+ transients in the spine indicated by the arrow, as demonstrated in the line scan at right (scan trajectory shown by the stippled vertical line in the left panel). The scan was oriented to pass through both the responsive spine (a) and the adjacent dendritic shaft (b). Fluorescence intensity in these 2 regions during the line scan is depicted quantitatively in the lower traces; the rapid synaptically-evoked Ca2+ signals are restricted to the spine, and a slower, smaller increase in Ca2+ in the shaft is presumably due to diffusion of the elevated Ca2+ from the spine.
Alan Fine and D. Dixon, National Institute for Medical Research, London UK
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