Molecular composition of the human primary visual cortex profiled by multimodal mass spectrometry imaging

Estibaliz González De San Román,Katrin Amunts,Iuliana Susnea,Pitter F Huesgen,Milena Malisic,Andreas Wree,Rene Hübbers,Volker Nischwitz,Hans-Jürgen Bidmon,Astrid Küppers

doi:10.1007/s00429-018-1660-y

Abstract

The primary visual cortex (area V1) is an extensively studied part of the cerebral cortex with well-characterized connectivity, cellular and molecular architecture and functions (for recent reviews see Amunts and Zilles, Neuron 88:1086–1107, 2015; Casagrande and Xu, Parallel visual pathways: a comparative perspective. The visual neurosciences, MIT Press, Cambridge, pp 494–506, 2004). In humans, V1 is defined by heavily myelinated fibers arriving from the radiatio optica that form the Gennari stripe in cortical layer IV, which is further subdivided into laminae IVa, IVb, IVcα and IVcβ. Due to this unique laminar pattern, V1 represents an excellent region to test whether multimodal mass spectrometric imaging could reveal novel biomolecular markers for a functionally relevant parcellation of the human cerebral cortex. Here we analyzed histological sections of three post-mortem brains with matrix-assisted laser desorption/ionization mass spectrometry imaging and laser ablation inductively coupled plasma mass spectrometry imaging to investigate the distribution of lipids, proteins and metals in human V1. We identified 71 peptides of 13 different proteins by in situ tandem mass spectrometry, of which 5 proteins show a differential laminar distribution pattern revealing the border between V1 and V2. High-accuracy mass measurements identified 123 lipid species, including glycerolipids, glycerophospholipids and sphingolipids, of which at least 20 showed differential distribution within V1 and V2. Specific lipids labeled not only myelinated layer IVb, but also IVa and especially IVc in a layer-specific manner, but also and clearly separated V1 from V2. Elemental imaging further showed a specific accumulation of copper in layer IV. In conclusion, multimodal mass spectrometry imaging identified novel biomolecular and elemental markers with specific laminar and inter-areal differences. We conclude that mass spectrometry imaging provides a promising new approach toward multimodal, molecule-based cortical parcellation.

Highlights

Delineation of distinct functional regions of the brain is a prerequisite for a deeper understanding of brain function under both normal and pathological conditions
In MALDI-mass spectrometry imaging (MSI) studies, measurement time and data size dramatically increase with higher spatial resolution, which further negatively correlates with sensitivity (Gessel et al 2014)
The remaining adjacent tissue blocks were cut in 30 μm thick serial sections and used for element analysis by LA-ICP-MSI or histological staining

Summary

Introduction

Delineation of distinct functional regions of the brain is a prerequisite for a deeper understanding of brain function under both normal and pathological conditions. More recent approaches have introduced observer-independent mapping techniques which significantly increased the number of cortical areas compared to Brodmann’s map and provided maps of areas in 3D-space (Zilles and Amunts 2010; Amunts and Zilles 2015). Such maps allowed the interpretation of in vivo studies employing, for example, functional magnetic resonance imaging (fMRI) with respect to the topography of activated networks and provide the basis for analyzing structure–function correlations (e.g. Rosenke et al 2017; Eickhoff et al 2005). All commonly used cytochemical approaches to cortical parcellation require the selection of specific, previously known and often wellcharacterized molecules such as (radio-) labeled neurotransmitter receptor ligands, or antibodies towards peptides and proteins

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