Theanine modulation of monoamine metabolism visualized by derivatized imaging mass spectrometry.

L-Theanine (LT), a derivative of glutamic acid, is abundant in tea leaves and contributes to tea's umami and sweetness. In recent years, its neurological effects, notably its role in promoting relaxation, have attracted intense research interest. The purpose of this study was to elucidate the detailed mechanisms underlying the relaxation effects of LT by thoroughly investigating the dynamics of neurotransmitters in the brain using mice after LT administration. Imaging mass spectrometry (IMS) was employed to visualize changes in the catecholamine system within the brain after LT administration. Simultaneous imaging of catecholamines, such as L-dihydroxyphenylalanine, dopamine, and norepinephrine, as well as representative amino acids such as γ-aminobutyric acid, revealed dynamic variations across time. Our findings revealed links between LT administration and the modulation of both inhibitory and excitatory neurotransmission, through its influence on the GABAergic and catecholaminergic systems, following the entry of exogenous LT into the brain. This approach enhanced our understanding of the mechanisms underlying LT's effects on the brain by visualizing neurotransmitter and amino acid distribution, as well as accompanying metabolic processes, at specific time points using IMS.