Remodelling of synaptic morphology but unchanged synaptic density during late phase long-term potentiation(ltp): A serial section electron micrograph study in the dentate gyrus in the anaesthetised rat

doi:10.1016/j.neuroscience.2004.06.029

Neuroscience

Volume 128, Issue 2, 2004, Pages 251-262

https://doi.org/10.1016/j.neuroscience.2004.06.029 Get rights and content

Abstract

In anaesthetised rats, long-term potentiation (LTP) was induced unilaterally in the dentate gyrus by tetanic stimulation of the perforant path. Animals were killed 6 h after LTP induction and dendritic spines and synapses in tetanised and untetanised (contralateral) hippocampal tissue from the middle molecular layer (MML) were examined in the electron microscope using stereological analysis. Three-dimensional reconstructions were also used for the first time in LTP studies in vivo, with up to 130 ultrathin serial sections analysed per MML dendritic segment. A volume sampling procedure revealed no significant changes in hippocampal volume after LTP and an unbiased counting method demonstrated no significant changes in synapse density in potentiated compared with control tissue.

In the potentiated hemisphere, there were changes in the proportion of different spine types and their synaptic contacts. We found an increase in the percentage of synapses on thin dendritic spines, a decrease in synapses on both stubby spines and dendritic shafts, but no change in the proportion of synapses on mushroom spines. Analysis of three-dimensional reconstructions of thin and mushroom spines following LTP induction revealed a significant increase in their volume and area. We also found an increase in volume and area of unperforated (macular) and perforated (segmented) postsynaptic densities.

Our data demonstrate that whilst there is no change in synapse density 6 h after the induction of LTP in vivo, there is a considerable restructuring of pre-existing synapses, with shaft and stubby spines transforming to thin dendritic spines, and mushroom spines changing only in shape and volume.

Section snippets

Induction of LTP in vivo

Male Sprague–Dawley rats weighing 300–400 g were anaesthetised with urethane (1.8 g/kg i.p.), and held in a semi-stereotaxic apparatus. A glass recording pipette, filled with artificial cerebrospinal fluid containing Pontamine Sky Blue was placed 4.1 mm posterior and 2.5 mm lateral to bregma and advanced into the dentate gyrus (DG). A bipolar stimulating electrode (Rhodes SNE 100) was inserted on the same side 4.4 mm lateral to lambda and lowered into the angular bundle to activate fibres of

Volume measurements

In order to interpret changes in synaptic density, derived from stereological analysis of EM sections, in terms of changes in synaptic number, we first determined whether the induction of LTP causes any change in volume of the DG.

All rats stimulated exhibited potentiation of the synaptic response that was more than 20% above the pre-tetanus level. The slope of the field excitatory postsynaptic potential (fEPSP) was normalised to the mean value before the tetanus for each animal, and group means

Discussion

This is the first detailed 3D reconstruction study of changes in synaptic and dendritic spine morphology associated with late LTP in vivo. In order to ensure that our morphometric estimations were not influenced by volume changes of hippocampal tissue we have compared the volumes of both hippocampus and DG in each hemisphere and have confirmed that there are no significant differences in tissue volume following the unilateral induction of LTP. This lends strong support to the conclusion that

Acknowledgments

This work was supported in part by grants BBSRC 108/S08513 and BBSRC 108/NEU15416 (to M.G.S) and The Leverhulme Trust (grant F00269G) and Russian Foundation for Basic Research (grant 48890a to V.I.P.). We thank Dr. John C. Fiala (Boston University, Boston, MA, USA) for consultations on use of the IGL Trace programme, and for helpful comments on the manuscript

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Remodelling of synaptic morphology but unchanged synaptic density during late phase long-term potentiation(ltp): A serial section electron micrograph study in the dentate gyrus in the anaesthetised rat

Abstract

Section snippets

Induction of LTP in vivo

Volume measurements

Discussion

Acknowledgments

Brain Res

Brain Res

Brain Res

Trends Neurosci

Neuron

Brain Res

Neuron

Brain Res

Curr Opin Neurobiol

Brain Res Rev

Neuron

Neuroscience

Neuroscience

Neuroscience

Prog Neurobiol

Neuroscience

J Neurosci Methods

Induction and experience dependent consolidation of stable long-term potentiation lasting months in the hippocampus

J Neurosci

A synaptic model of memory: long-term potentiation in the hippocampus

Nature

Long-lasting potentiation of synaptic transmission in the dentate area of the anaesthetized rabbit following stimulation of the perforant path

J Physiol (Lond)

Methods for determining numbers of cells and synapses: a case for more uniform standards of review

J Comp Neurol

Changes in the numerical density of synaptic contacts with long-term potentiation in the hippocampal dentate gyrus

J Comp Neurol

Changes in the postsynaptic density with long-term potentiation in the dentate gyrus

J Comp Neurol

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

Synapse

Dendritic spine changes associated with hippocampal long-term synaptic plasticity

Nature

Extending unbiased stereology of brain ultrastructure to three-dimensional volumes

J Am Med Inform Assoc

Cylindrical diameters method for calibrating section thickness in serial electron microscopy

J Microsc

Synaptogenesis via dendritic filopodia in developing hippocampal area CA1

J Neurosci

Synaptic tagging and long-term potentiation

Nature

Structural synaptic plasticity associated with the induction of long-term potentiation is preserved in the dentate gyrus of aged rats

Hippocampus