Imaging long-range neuronal connections in the mouse brain by light-sheet fluorescence expansion microscopy
1 Functional Neuroconnectomics Group, Institute for Experimental Epileptology and Cognition Research, University Hospital Bonn
2 Biophysical Chemistry, Institute of Physical and Theoretical Chemistry, University of Bonn
Sensory perception is modulated in a top-down fashion by higher brain regions to regulate behavioral responses. In olfaction, the horizontal limb of the diagonal band (HDB) embedded in the basal forebrain modulates olfactory information processing by shaping excitatory olfactory bulb (OB) output. To comprehensively characterize the synaptic targets of HDB projection neurons in “super-resolution” we expressed genetically encoded, Cre-dependent fluorescent indicators in a subset of HDB neurons. Specifically, we utilized 3 different transgenic Cre-lines, namely Parv-Cre, Chat-Cre as well as Vglut1-Cre to target the three main neuronal HDB populations and their projections using rAAVs. Circuit analysis was performed with an optimized light-sheet fluorescence expansion microscopy (LSFEM) protocol (2,3), allowing the preservation of even the smallest auto-fluorescent clusters in presynaptic terminals. This optimized LSFME technique (4) enables zooming from a mesoscopic perspective into super-resolution, but also allows a mesoscopic quantification of the fiber distribution from the different neuronal subtypes. Our results demonstrate a differential innervation of OB interneurons by different HDB subtypes, suggesting a complex top-down modulation of olfactory perception. (1) Bürgers J, Pavlova I, Rodriguez-Gatica JE, et al (2019) Light-sheet fluorescence expansion microscopy: fast mapping of neural circuits at super-resolution. Neurophoton 6:015005 (2) Schwarz MK and Remy S (2019) Rabies virus-mediated connectivity tracing from single neurons. J Neurosci Meth 325:108365 (3) Schwarz MK, Kubitscheck U. Expansion light sheet fluorescence microscopy of extended biological samples: Applications and perspectives. Prog Biophys Mol Biol. 2022 Jan;168:33-36. (4) Rodriguez-Gatica JE, Iefremova V, et al (2022) Imaging three-dimensional brain organoid architecture from meso- to nanoscale across development. Development 149:dev200439