SPATIAL MAPPING OF LIPIDS AND NEUROTRANSMITTER IN RAT BRAIN SECTIONS USING DESI ION MOBILITY MASS SPECTROMETRY

Importance of the Topic

Mapping the spatial distribution of lipids and neurotransmitters in brain tissue is critical for understanding molecular mechanisms underlying neurological function and disease. Techniques that enable label-free, high-resolution imaging of small molecules directly from tissue sections can provide unique insights into neurochemical pathways and regional metabolism.

Objectives and Study Overview

This study demonstrates the use of desorption electrospray ionization mass spectrometry imaging (DESI-MSI) combined with ion mobility separation to visualize and identify lipids and neurotransmitters in rat brain sections. The goals were to:

• Simultaneously detect a range of endogenous small molecules (amino acids, neurotransmitters) and lipids.
• Avoid extensive sample preparation by employing ambient DESI ionization.
• Leverage ion mobility for enhanced signal discrimination and collisional cross-section (CCS) measurement.

Methodology and Instrumentation

Tissue Preparation and Imaging

• Coronal rat brain slices were thaw-mounted on glass slides and analyzed without additional chemical treatment.
• DESI spray parameters were optimized for negative ion mode detection of polar metabolites and lipids.

Mass Spectrometry and Data Acquisition

• Analysis was performed on a SYNAPT G2-Si QToF instrument equipped with ion mobility separation (HDMS) to resolve analyte ions from background and isobaric species.
• In-line lock mass or endogenous ions were used to correct systematic mass drift, achieving high mass accuracy (low ppm error).
• Data were acquired using MassLynx 4.1 and processed in High Definition Imaging (HDI) version 1.4.

Data Processing and Identification

• High-accuracy mass and isotopic pattern matching were complemented by CCS measurements obtained via ion mobility experiments.
• Database searches against METLIN and other curated libraries provided putative identifications with increased confidence.

Main Results and Discussion

Simultaneous visualization of small molecules and lipids showed distinct anatomical localization, including amino acids (taurine, glutamine) and neurotransmitters (GABA, serotonin), alongside lipids such as phosphatidylcholine and lysophosphatidylcholine. Ion mobility separation significantly improved signal-to-noise by excluding solvent clusters and chemical background. CCS values further distinguished lipid classes and supported confident annotation.

Spatial correlation analysis using Pearson coefficients highlighted co-localization patterns, for example, different cholesterol ion forms showing varying association strength with specific brain regions. Overlay images on histological references confirmed anatomical relevance of molecular distributions.

Benefits and Practical Applications

• No-label, minimal preparation workflow reduces analysis time and preserves tissue integrity.
• Broad molecular coverage enables concurrent mapping of polar metabolites and nonpolar lipids.
• Ion mobility and CCS data enhance selectivity and confidence in compound identification.
• Applicable to neurochemical research, biomarker discovery, and pathological studies of brain disorders.

Future Trends and Potential Applications

Advancements may include higher spatial resolution DESI probes, integration with quantitative MSI approaches, and expansion of CCS libraries for automated annotation. Combining DESI-IMS-MSI with complementary imaging modalities (e.g., MALDI, optical microscopy) will enrich multi-omics tissue profiling. Translation toward clinical neurodiagnostics and drug distribution studies is anticipated as throughput and robustness improve.

Conclusion

This work demonstrates that DESI-MSI coupled with ion mobility on a high-definition mass spectrometer provides a powerful platform for spatially resolved lipid and neurotransmitter analysis in brain sections. The integrated approach delivers rapid, preparation-free imaging with enhanced molecular identification, offering a valuable tool for neurochemical mapping and related biomedical applications.