Abstract <p>Phospholipid preparations, including lecithin, are widely used as hepatoprotective and neuroprotective agents, while soy lecithin is intensively used in food industry, with its total dose in the modern human diet potentially reaching high levels. Soy lecithin contains up to 70% of biologically active phospholipids: phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidic acid. These compounds perform a spectrum of key cellular functions, including neuromediation processes, and ensure formation of the cellular membrane structures and vesicles. Previously, in the mouse model of chronic intestinal inflammation, behavioral changes were observed together with the significant increase in the relative content of several phospholipid classes in the intestinal epithelial cells. The animals fed with soy lecithin, which contains a mixture of these phospholipids, showed similar behavioral changes in the absence of inflammation: impaired social recognition and behavior, reduced signs of compulsivity and anxiety, and increased aggression in males. In this study, we found that reducing the dose of soy lecithin in short-term administration restores normal social recognition and behavior in the healthy C57BL/6 animals, while reduction in anxiety is maintained. Comparative electron microscopy analysis of the neurons and synapses in the amygdala, hypothalamus, and frontal motor cortex of the C57BL/6 animals treated with soy lecithin was conducted. Dose-dependent and region-specific changes were observed. High-dose lecithin administration, both long-term and short-term, reduced synapse density in the neuropil, and irregular synaptic vesicles were detected in the amygdala and hypothalamus. Threefold reduction in the lecithin dosage resulted in the increase in the number of vesicles per synapse in the hypothalamus and motor cortex. The obtained results demonstrate dose-dependent effect of soy lecithin on the synaptic ultrastructure in the hypothalamus, amygdala, and motor cortex of the frontal lobe, as well as on the behavioral patterns of the healthy C57BL/6 laboratory mice.</p>