Développements endoscopiques pour l’imagerie par fluorescence à deux photons in vivo des neurones de la souris


Team “A developmental scaffolding of adult hippocampal circuits”


Abstract: Neuroscientists have been increasingly using optical techniques for probing neuronal networks due to the excellent spatial resolution, the ability to measure simultaneously at multiple spatial locations, and cellular and subcellular specificity with the use of targetable probes. As such research and development of head-mounted devices such as mini-microscopes and endoscopes, that allow for the imaging of neurons in freely moving animals (such as mice) have seen a significant increase in recent years. This thesis presents the progress of work at Institut Fresnel, the Mediterranean Institute of Neurobiology (INMED) and collaborators regarding the development and application of two different endoscope technologies that allow for in-vivo imaging of neurons in mice.

The first endoscope technology presented in this thesis is a “Lensless” endoscope where the waveguide is a multi-core single-mode fibre bundle. Here by wavefront shaping of the in-coupled field and the knowledge of the transmission matrix of optical fibre, a focal spot is formed and scanned across the field of view and further the back-scattered fluorescence signal is collected and propagated back to a detector. The key advantage of this technique is the absence of any optical or mechanical components at the distal end, meaning the endoscope head is as thin as the optical fiber itself (few 100 microns). This allows the endoscope to be inserted directly into the tissue and image planes previously inaccessible using optical techniques.

The second technology presented in this thesis is a fully integrated micro-endoscope system based on hollow-core fiber. The system consists of a micro-endoscope and a helmet assembly for securing the endoscope to the head of the mice for freely moving imaging experiments. The waveguide used here is a double-clad, tubular, antiresonant, hollow core fiber. These fibers have a large transmission band, low group velocity dispersion and introduce very little temporal or spectral distortion to the femtosecond pulses needed for 2-photon fluorescence imaging. Scanning is implemented using a miniature doubly resonant piezoelectric tube, which allows for an electrically tunable field of view of up to 300 microns at frame rates of up to 10Hz. Finally, some of the first results from in-vivo imaging of mice cortex and hippocampus done with this endoscope are presented.


Dr. Laurent Bourdieu,  Président du jury – Ibens, Paris
Dr. Cathie Ventalon, Rapporteure – Ibens, Paris
Pr. Frédéric Louradour, Rapporteur – Xlim, Limoges
Dr. Esben Ravn Andresen, Examinateur – PhLAM, Lille
Dr. Hervé Rigneault, Co-directeur de thèse – Insitut Fresnel, Marseille
Dr. Rosa Cossart Co-directrice de thèse – Inmed, Marseille

Tuesday 28 March 2023 at 1pm, Inmed conference room

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