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Introduction
Aging is a complex process characterized by a progressive loss of functions; in particular, learning and memory impairments (1). In women, decrease in estrogen levels is an important component of the aging following menopause, and brain and endocrine aging occur simultaneously and are closely associated with cognitive impairment and pathological states (2-6).
Inflammation was discovered to be a biomarker of both normal and accelerated aging (7). The cells and tissues of older organisms tend to have higher levels of inflammatory markers, which can lead to low, aseptic, and chronic inflammatory conditions (8,9). This phenomenon has been defined as immune aging and is associated with numerous types of age-related diseases, such as cancer, cardiovascular disease, and neurodegenerative diseases (10-15). Neuroinflammation is a common feature of the majority of central nervous system (CNS) diseases, and has been discovered to cause cognitive impairments (16,17). Aging was reported to influence neuroinflammatory responses by promoting the release of a large number of neuroinflammatory cytokine levels, such as IL-1, IL-6, IL-8, transforming growth factor-β (TGFβ), TNF-α, and activating immune system cells involved in the regulation of neurogenesis, synaptic plasticity, neuronal survival and other critical processes. These changes, in turn, were demonstrated to affect cognitive functions (18-20).
The effect of estrogen replacement therapy on aging-related changes in cognition remains controversial (2). Therefore, a variety of natural polysaccharides from functional and medicinal foods have attracted considerable attention due to their significant pharmacological activities (21). For example, the polysaccharides of Pleurotus bisporus were reported to have antioxidant and anti-aging effects (22), Sargassum polysaccharide exerted numerous pharmacological activities, including antioxidative proinflammatory, anti-aging and anti-fatigue effects (23) and Cordyceps sinensis polysaccharides were demonstrated to exert significant antioxidant and anti-aging activities (24). As an edible Chinese herbal medicine, Lycium barbarum polysaccharides (LBPs) have been reported to exert antioxidant and neuroimmune regulatory functions (25,26), in addition to anti-inflammatory and anti-aging effects (26-28). However, although the benefits of LBPs have been reported, their effects on learning and memory during the aging process induced by estrogen deficiency are poorly understood, at least to the best of our knowledge.
Ovariectomized (OVX) rodents are useful models for neurocognitive impairments caused by decreased estrogen levels in women (29-31). Hence, the present study aimed to investigate the therapeutic effects of LBP on neuroinflammation...