Spatial Metabolomics Reveals Microregion-Specific Neurochemical Perturbations in the Brains of PCPA-Induced Insomniac Rats: Integration of MALDI-MSI and Targeted LC-MS/MS

Objectives: Insomnia is a highly prevalent sleep disorder involving complex neurochem-ical dysregulation; however, the spatial distribution of neurotransmitters and small-molecule metabolites across distinct brain microregions in the insomniac state re-mains poorly characterized. This study aimed to map region-specific metabolic perturba-tions in situ in a p-chlorophenylalanine (PCPA)-induced insomnia rat model using opti-mized matrix-assisted laser desorption/ionization mass spectrometry imaging (MAL-DI-MSI) integrated with targeted metabolomics validation. Methods: On-tissue chemical derivatization MALDI-MSI was optimized using α-cyano-4-hydroxycinnamic acid (CHCA) as the matrix on a Bruker tims TOF flex mass spectrometer. The rats received PCPA (400 mg/kg, intraperitoneal) for three days to establish the insomnia model. Metabolite identifi-cation was conducted using MetaboScape® software (2020b) and the Human Metabolome Database. Ultra-performance liquid chromatography–tandem mass spectrometry was em-ployed to quantify nine key neurotransmitters and metabolites across six brain microre-gions. Key synthetic enzyme expression was evaluated by immunofluorescence and West-ern blotting analyses. Results: TMP-TFB-derived brain slices clearly showed the distribu-tion of neurotransmitters in brain microregions. MALDI-MSI demonstrated that the spatial distribution and abundance of eight neurotransmitters were disturbed in brains of PCPA-induced insomniac rats. A total of 346 metabolites were characterized across six brain microregions (cerebellum, cortex, hippocampus, brainstem, hypothalamus, and stri-atum), with principal coordinate analysis revealing clear metabolic separation between control and insomniac rats. PCPA treatment markedly disrupted tryptophan and tyrosine metabolism, evidenced by decreased 5-HT, 5-HTP, and 5-HIAA, alongside region-specific alterations in DA, NE, HVA, and Ach. Additionally, GABA levels decreased in the hippo-campus, striatum, and hypothalamus, whereas glutamate increased throughout the brain. Targeted metabolomics validated the MSI findings, and Bland–Altman analysis confirmed good consistency between the two analytical platforms. PCPA further disturbed the meta-bolic enzymes MAOA, DDC, and TPH2 within the Trp-5-HTP-5-HT-5-HIAA metabolic pathway in the brainstem and TYH and DBA within the tyrosine-DA-NE metabolic pathway in the striatum. Conclusions: This study demonstrates that region-specific altera-tions in tryptophan and tyrosine metabolism pathways provide mechanistic insights into insomnia pathogenesis and potential therapeutic targets.