Advanced Mass Spectrometry Imaging in Neuropharmacology

Mass spectrometry imaging (MSI) has emerged as a valuable approach for mapping multiple molecular species in sections of diverse tissues. It enables simultaneous detection of numerous compounds (from neurotransmitters to small proteins) in the brain at relatively high lateral resolution (>5 μm) on a routine basis. Matrix-assisted laser desorption/ionization (MALDI)-MSI and desorption electrospray ionization (DESI)-MSI are the most widely applied MSI techniques in tissue distribution studies. Recent advances in MSI instruments and software allow quantitative analysis of large numbers of compounds with high mass accuracy and high mass resolving power. Thus, in studies this thesis is based upon, MSI technology was used to address several challenging aspects of neuropharmacology. Restricted passage of potentially neuroactive substances into the brain, unpredictable multi-target effects, and the complexity of the central nervous system (CNS) physiology, are major obstacles in the development of efficient drugs. The simultaneous investigation of drugs’ delivery to the brain and potential effects on several CNS pathways in specific brain regions is, therefore, highly important. In addition, localization information is required for more comprehensive insights into CNS responses to both pharmaceutical agents and biological processes such as aging. MSI-based analysis of the transport of two selected drugs into the brain demonstrated effects of efflux membrane proteins on their distributions in the brain. The MDR1 substrate loperamide was found to localize specifically in the choroid plexus, indicating low brain entrance. In addition, MSI uncovered drug-drug interactions at the blood-brain barrier involving MDR1 inhibition. The technology was further used to explore neurochemical alterations induced by aging and acetylcholinesterase inhibition. First, MSI revealed that the cholinergic system’s responsivity in the retrosplenial cortex, a post-cingulate cortical area highly involved in cognition, to acetylcholinesterase inhibition significantly declined with age. Subsequently, simultaneous investigation of multiple brain metabolic pathways in specific brain areas with multivariate data analysis techniques demonstrated age-induced alterations in mitochondrial function, lipid signaling, and acetylcholine metabolism. Finally, MSI unveiled age-induced alterations in levels and distributions of the monoaminergic neurotransmitters and their metabolites in particular brain areas such as the ventral pallidum, caudate putamen, hippocampus, and cortical substructures. Age- and region-specific effects of acetylcholinesterase inhibition on the neurotransmitter systems were also detected. In conclusion, the studies provided novel insights into important brain pharmacokinetic and pharmacodynamic phenomena using advanced MSI techniques, as described and discussed in this thesis