PhD: Ronan Chéreau

Investigating morpho-functional plasticity of CA3 axons in living brain slices by a combination of STED microscopy and electrophysiology.

Defended on June 19 2014

Millisecond timing precision in the transfer of information between neurons is essential for the synchrony and plasticity of neural circuits in the brain. Axons are neuronal extensions that ensure the communication via brief electrical impulses called action potentials (AP). Because they are unmyelinated and are extremely thin, hippocampal axons propagate APs slowly and thus generate long delays of conduction (up to 100 ms) that are traditionally considered invariant. However, recent studies have shown that activity changes the morphology of axons and modulate the latency of transmission, thus raising the question whether axons undergo activity-dependent structural changes that could influence the propagation of APs. The diameter of hippocampal axons (ranging between 100-350 nm) are usually too thin to be properly resolved by conventional light microscopy. However, the development of super resolution STED imaging now enables the observation of their detailed morphological dynamics in living tissue.

Using a novel combination of STED microscopy, field recordings, patch-clamp electrophysiology in mouse brain slices and computer simulations we discovered that CA3 axons undergo long-lasting enlargement in their diameter after the induction of long term potentiation (LTP). We provide strong evidence that this diameter enlargement increases AP conduction velocity.

Taken together, our findings indicate that axons can dynamically tune AP propagation delays by changing their diameters, thereby altering the timing of information transfer in neural circuits. This study suggests a novel and powerful structural mechanism for neural plasticity.

Jury

  • Stéphane Oliet
    U. Bordeaux, Président
  • Dominique Debanne
    U. Aix-Marseille, Rapporteur
  • Juan Burrone
    King’s College London, Rapporteur
  • Peter Kind
    University of Edinburgh, Examinateur
  • Andreas Frick
    U. Bordeaux, Examinateur
  • Valentin Nägerl
    Directeur de thèse

Thesis supervisor

Valentin Nägerl
Professor – PhD
Team leader: Synaptic Plasticity and Superresolution Microscopy
IINS / Bordeaux University 

Last update: 19 June 2014