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Morphological correlates of long-term potentiation imply the modification of existing synapses, not synaptogenesis, in the hippocampal dentate gyrus

✍ Scribed by Dr. Nancy L. Desmond; William B. Levy

Publisher: John Wiley and Sons
Year: 1990
Tongue: English
Weight: 638 KB
Volume: 5
Category: Article
ISSN: 0887-4476
DOI: 10.1002/syn.890050208

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✦ Synopsis

This report evaluates two morphological markers of synaptogenesis following the induction of long-term potentiation (LTP) in the dentate gyrus of the anesthetized rat. These two morphological features, polyribosomes and multiple synaptic contacts, are known to increase in number with synaptogenesis in the mature hippocampus.

The analysis focused on the middle third of the dentate molecular layer. As shown previously, this is the region of primary synaptic activation in our electrophysiological protocol and the region of localized morphological changes with LTP. Here the incidence of a polyribosome at the base of a dendritic spine declined 57% with LTP. In addition, the number of multiple synaptic contacts decreased 18% there with LTP. Both decreases were more pronounced immediately following conditioning stimulation than at later intervals. Because both morphological features decrease with LTP but increase with synaptogenesis, the data do not support the hypothesis that new synapses form with LTP. Instead, the data add further support to the view that the strengthening of existing excitatory synapses underlies LTP

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