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Séminaire - Kristen HarrisSilent synaptic growth and the augmentation of hippocampal plasticity

Abstract :

I will discuss our recent work suggesting that synapses form or enlarge with no additional change in physiological strength by 2 hours following the induction of long-term potentiation in the hippocampus. This "silent" synaptic growth appears to produce a latent capacity for subsequent strengthening of synapses. The silent growth takes time to prepare synapses for augmentation of prior plasticity.
The data in support of these hypotheses are generated using 3D reconstructions from serial section electron microscopy in adult and P15 rat hippocampus.  I will discuss changes in postsynaptic areas that have distinct regions of active zones with presynaptic vesicles as well as vesicle-free nascent zones. I will present new data showing a sustained mobilization of presynaptic vesicles - especially in boutons that contain a mitochondrion.
We will explore other crucial subcellular changes that support the redistribution of synaptic weights especially along mature dendrites, which can support many small dendritic spines or a few large one.

We will discuss how synapses on mature neurons differe from immature neurons in their response to test pulses and theta-burst stimulation that induces LTP. We speculate that silent growth and augmentation could underlie latent learning and may serve enhanced learning known to occur with spaced versus massed episodes. 

Selected publications

Watson DJ, Ostroff L, Cao G, Parker PH, Smith H, Harris KM (2015) LTP enhances synaptogenesis in the developing hippocampus. Hippocampus. (PDF)

Harris KM, Spacek J, Bell ME, Parker PH, Lindsey LF, Baden AD, Vogelstein JT, Burns R (2015) A resource from 3D electron microscopy of hippocampal neuropil for user training and tool development. Sci Data Sep 1;2:150046. PMCID: PMC4555877. (PDF; Tables)

Bell ME, Bourne JN, Chirillo MA, Mendenhall JM, Kuwajima M, Harris KM (2014) Dynamics of nascent and active zone ultrastructure as synapses enlarge during long-term potentiation in mature hippocampus. J Comp Neurol, 522(17):3861-84. PMCID: PMC4167938. (2MB PDF)

Cao G, Harris KM (2014) Augmenting saturated LTP by broadly spaced episodes of theta-burst stimulation in hippocampal area CA1 of adult rats and mice. J Neurophysiol, 112(8):1916-24. PMCID: PMC4200006. (2MB PDF)

Bourne JN, Chirillo MA, Harris KM (2013) Presynaptic ultrastructural plasticity along CA3->CA1 axons during LTP in mature hippocampus. J Comp Neurol, 521(17):3898-912. PMCID: PMC3838200. (1MB PDF)