Thesis defense – Thomas Pfeiffer

Supervisor: Valentin Nägerl / IINS

Activity-dependent changes in neuronal connectivity are thought to underlie learning and memory. I developed and applied novel high-resolution imaging-based approaches to study (i) microglia-spine interactions and (ii) the turnover of dendritic spines in the mouse hippocampus, which are both thought to contribute to the remodeling of synaptic circuits underlying memory formation.

(i) Microglia have been implicated in a variety of novel tasks beyond their classic immune defensive roles. I examined the effect of synaptic plasticity on microglial morphological dynamics and interactions with spines, using a combination of electrophysiology and two-photon microscopy in acute brain slices. I demonstrated that microglia intensify their physical interactions with spines after the induction of hippocampal synaptic plasticity. To study these interactions and their functional impact in greater detail, I optimized and applied time-lapse STED imaging in acute brain slices.

(ii) Spine structural plasticity is thought to underpin memory formation. Yet, we know very little about it in the hippocampus in vivo, which is the archetypical memory center of the mammalian brain. I established chronic in vivo STED imaging of hippocampal spines in the living mouse using a modified cranial window technique. The super-resolution approach revealed a spine density that was two times higher than reported in the two-photon literature, and a spine turnover of 40% over 5 days, indicating a high level of structural remodeling of hippocampal synaptic circuits.

The developed super-resolution imaging approaches enable the examination of microglia-synapse interactions and dendritic spines with unprecedented resolution in the living brain (tissue).

Keywords: super-resolution STED microscopy, two-photon microscopy, microglia, synaptic plasticity, dendritic spine, structural plasticity, in vivo imaging;

Publications

In vivo STED imaging reveals high spine turnover in the hippocampus over days Pfeiffer T*, Stefanie Poll*, Stéphane Bancelin*, Kevin Keppler, Martin Fuhrmann# and Nägerl UV#; in preparation.

Two-photon STED microscopy for nanoscale imaging of neural morphology in vivo ter Veer MTV*, Pfeiffer T* and Nägerl UV; Methods in Molecular Biology 2017 1663:45-64.

Induction of hippocampal long-term potentiation increases the morphological dynamics of microglial processes and prolongs their contacts with dendritic spines Pfeiffer T, Avignone E# and Nägerl UV#; Scientific Reports 2016 6:32422.