• Methodological convergence on quantifying brain monoamines via colorimetric and fluorimetric assays, enabling distribution and tissue-level estimates for norepinephrine, dopamine, and serotonin across decades [3], [4], [6], [12], [15], [17], [18].

• Systematic mapping of catecholamine distribution and regional/cellular roles in the CNS, highlighting neuromodulatory breadth and tissue-specific patterns (noradrenaline, dopamine, epinephrine) [8], [10], [12], [14], [19].

• Serotonin as a central chemical mediator: its brain distribution, synthesis via decarboxylase, and interplay with MAO, supporting a serotonergic–noradrenergic framework [2], [5], [6], [11].

• Storage and release biology of monoamines: granule-organized catecholamine handling and acetylcholine-containing vesicles reveal early neurophysiological storage mechanisms in brain/adrenal tissues [7], [9], [13].

• Neuropharmacology of mood and behavior through monoaminergic systems, showing pharmacological perturbations (e.g., reserpine effects) and theoretical roles of serotonin and norepinephrine as brain mediators [5], [10], [20].