Secondary ion images of the developing rat brain

Imaging mass spectrometry in neuroscience

Imaging mass spectrometry is an emerging technique of great potential for investigating the chemical architecture in biological matrices. Although the potential for studying neurobiological systems is evident, the relevance of the technique for application in neuroscience is still in its infancy. In the present Review, a principal overview of the different approaches, including matrix assisted laser desorption ionization and secondary ion mass spectrometry, is provided with particular focus on their strengths and limitations for studying different neurochemical species in situ and in vitro. The potential of the various approaches is discussed based on both fundamental and biomedical neuroscience research. This Review aims to serve as a general guide to familiarize the neuroscience community and other biomedical researchers with the technique, highlighting its great potential and suitability for comprehensive and specific chemical imaging.

Tandem mass spectrometric methods for phospholipid analysis from brain tissue

We describe the utility of intermediate-pressure MALDI and tandem mass spectrometry (MS/MS and MS( n )) for the characterization and imaging of phospholipids in brain tissue sections. The use of both MS/MS spectra and MS/MS images allows for identification of isobaric compounds. The structural characterization of phosphatidylcholines, phosphatidylserines, phosphatidylethanolamines, and sphingomyelins directly from tissue sections is described.

Cellular imaging using matrix-enhanced and metal-assisted SIMS

Imaging mass spectrometry (IMS) allows the direct investigation of both the identity and the spatial distribution of the entire molecular content directly in tissue sections, single cells, and many other biological surfaces. We describe here the steps required to retrieve the molecular information from tissue sections using matrix-enhanced (ME) and metal-assisted (MetA) secondary ion mass spectrometry (SIMS). Surface metallization by plasma coating enhances desorption/ionization of membrane components such as lipids and sterols in imaging time-of-flight (ToF) SIMS of tissues and cells. High-resolution images of cholesterol and other membrane components can be obtained for single neuroblastoma cells and reveal subcellular details. Alternatively, in ME-SIMS, 2,5-dihydroxybenzoic acid electrosprayed on neuroblastoma cells allows intact molecular ion imaging of phosphatidylcholine (PC) and sphingomyelin (SM) at the cellular level.

SIMS and MALDI MS imaging of the spinal cord

The application of MS to imaging, or MS imaging (MSI), allows for the direct investigation of tissue sections to identify biological compounds and determine their spatial distribution. We present an approach to MSI that combines secondary ion MS (SIMS) and MALDI MS for the imaging and analysis of rat spinal cord sections, thereby enhancing the chemical coverage obtained from an MSI experiment. The spinal cord is organized into discrete, anatomically defined areas that include motor and sensory networks composed of chemically diverse cells. The MSI data presented here reveal the spatial distribution of multiple phospholipids, proteins, and neuropeptides obtained within single, 20 mum sections of rat spinal cord. Analyte identities are initially determined by primary mass match and confirmed in follow-up experiments using LC MS/MS from extracts of adjacent spinal cord sections. Additionally, a regional analysis of differentially localized signals serves to rapidly screen compounds of varying intensities across multiple spinal regions. These MSI analyses reveal new insights into the chemical architecture of the spinal cord and set the stage for future imaging studies of the chemical changes induced by pain, anesthesia, and drug tolerance.

Imaging mass spectrometry at cellular length scales

Imaging mass spectrometry (IMS) allows the direct investigation of both the identity and the spatial distribution of the molecular content directly in tissue sections, single cells and many other biological surfaces. In this protocol, we present the steps required to retrieve the molecular information from tissue sections using matrix-enhanced (ME) and metal-assisted (MetA) secondary ion mass spectrometry (SIMS) as well as matrix-assisted laser desorption/ionization (MALDI) IMS. These techniques require specific sample preparation steps directed at optimal signal intensity with minimal redistribution or modification of the sample analytes. After careful sample preparation, different IMS methods offer a unique discovery tool in, for example, the investigation of (i) drug transport and uptake, (ii) biological processing steps and (iii) biomarker distributions. To extract the relevant information from the huge datasets produced by IMS, new bioinformatics approaches have been developed. The duration of the protocol is highly dependent on sample size and technique used, but on average takes approximately 5 h.

Profiling and imaging of tissues by imaging ion mobility-mass spectrometry

Molecular profiling and imaging mass spectrometry (IMS) of tissues can often result in complex spectra that are difficult to interpret without additional information about specific signals. This report describes increasing data dimensionality in IMS by combining two-dimensional separations at each spatial location on the basis of imaging ion mobility-mass spectrometry (IM-MS). Analyte ions are separated on the basis of both ion-neutral collision cross section and m/z, which provides rapid separation of isobaric, but structurally distinct ions. The advantages of imaging using ion mobility prior to MS analysis are demonstrated for profiling of human glioma and selective lipid imaging from rat brain.

Static secondary ion mass spectrometry for biological and biomedical research

Static secondary ion mass spectrometry (SSIMS) is a capable of providing detailed atomic and molecular characterization of the surface chemistry of biological and biomedical materials. The technique is particularly suited to the detection and imaging of small molecules such as membrane lipids, metabolites, and drugs. A limit of detection in the ppm range and spatial resolution <1 microm can be obtained. Recent progress in instrumental developments, notably cluster ion beams, and the application of multivariate data analysis protocols, promise further advances. This chapter presents a brief overview of the theory and instrumentation of static secondary ion mass spectrometry followed by examples of a range of biological and biomedical applications. Because of the ultrahigh vacuum requirements and extreme surface sensitivity of the technique, appropriate sample preparation and handling is essential. These protocols, and the analysis methodology required to ensure high-quality, reliable data are described.

Three-dimensional visualization of protein expression in mouse brain structures using imaging mass spectrometry

We have developed a method to visualize matrix-assisted laser desorption ionization imaging mass spectrometry (MALDI IMS) data aligned with optically determinable tissue structures in three dimensions. Details of the methodology are exemplified using the 3-D reconstruction of myelin basic protein (MBP) in the corpus callosum of a mouse brain. In this procedure, optical images obtained from serial coronal sections are first aligned to each other to reconstruct a surface of the corpus callosum from segmented contours of the aligned images. The MALDI IMS data are then coregistered to the optical images and superimposed into the surface to create the final 3-D visualization. Correlating proteomic data with anatomical structures provides a more comprehensive understanding of healthy and pathological brain functions, and holds promise to be utilized in more complex anatomical arrangements.