Social behavior disorders in Alzheimer's disease in social isolation

Aim. To investigate the effect of social isolation on social behavior and levels of psychoemotional markers (oxytocin and vasopressin) in mice with an injection-induced model of Alzheimer’s disease (AD). Materials and Methods. The study was conducted on CD1 male mice aged 3–4 months, which received intrahippocampal injection of either β-amyloid (in order to induce AD) or control phosphate-buffered saline (sham-operated mice). Subsets of experimental and control animals were subjected to social isolation for 21 days. To assess social behavior, a battery of neurobehavioral tests was applied, including the five-trial social memory/recognition test, the three-chamber social interaction test, and the extended open field test. Levels of oxytocin and vasopressin in specific brain regions were measured using enzyme-linked immunosorbent assay. Results. Neurobehavioral testing showed impaired socialization and reduced ability to memorize and recognize novel conspecifics in AD mice. Social isolation induced increased locomotor activity, diminished exploratory interest toward inanimate objects, and altered the character and frequency of social interactions. These transformations of emotional and social behavior were associated with dysregulation of the oxytocinergic and vasopressinergic systems in the amygdala. A reduction in oxytocin levels was observed in the olfactory bulbs of AD mice compared with controls. Isolated AD mice had elevated vasopressin levels and a trend toward decreased oxytocin levels in the amygdala as compared with the isolated control mice. Conclusion. Our results highlight the critical need to prevent social isolation in patients diagnosed with AD. The link between oxytocinergic and vasopressinergic systems and the progression of behavioral disorders underscores the importance of further studies on oxytocin and vasopressin as potential therapeutic molecules in Alzheimer’s disease.

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