Abstract
Chronic peripheral elevation of interleukin 6 (IL-6) in humans is associated with cognitive deficits. 4- and 24-month-old IL-6-deficient C57BL/6J (IL-6KO) and reference wild-type (WT) mice were tested in an object recognition test. Discrimination ratios and recognition indexes were significantly lower in 4-month-old IL-6KO and in 24-month-old WT mice vs 4-month-old WT animals. Their discrimination ratios had negative values and recognition indexes were below 50% indicating inability to differentiate the novel from the familiar object after 1-hour delay. In 24-month-old IL-6KO mice recognition index reached 53.17% indicating that their recognition memory was not worsened with age in comparison with younger IL-6-deficient animals. Results of holeboard and elevated plus maze indicated that this effect was memory specific. Inborn IL-6 deficiency attenuated recognition memory in 4-month-old mice and did not altered recognition memory in aged animals. IL-6 signalling may constitute a target for development of the protection against memory disturbances connected with IL-6 overexpression.
Highlights
Interleukin 6 (IL-6) is a multifunctional cytokine, with context-dependent pro- and anti-inflammatory properties (Hunter and Jones 2015; Trapero and Cauli 2014; Yirmiya and Goshen 2011)
Results of the present study supported our previous observation that inborn IL-6 deficiency attenuates recognition memory in young adult mice in comparison with age-matched WT animals (Hryniewicz et al 2007)
The comparison of young adult with aged animals of both genotypes performed in the current study showed attenuation of recognition memory in 24-month-old WT animals as compared to 4-monthold WT ones, and lack of significant differences between 24-month-old IL-6-deficient mice C57BL/6JIL−6−/−TMKopf (IL-6KO) mice and other tested groups
Summary
Interleukin 6 (IL-6) is a multifunctional cytokine, with context-dependent pro- and anti-inflammatory properties (Hunter and Jones 2015; Trapero and Cauli 2014; Yirmiya and Goshen 2011). The detrimental role of IL-6 in age-related memory disturbances was demonstrated in senescence-accelerated mice (Tha et al 2000) implying that IL-6 is involved in the impairment of Handling Editor: Sonoko Ogawa. In our previous study, 12–14-week-old, IL-6-deficient mice showed impaired memory processes in an object recognition test (Hryniewicz et al 2007). This unexpected result concerning recognition memory was described in a novel object recognition test performed on 6-month-old IL-6-deficient mice (Baier et al 2009). Results of our study performed in Morris water maze (Bialuk et al 2018), evaluating spatial memory, showed significant attenuation of learning ability in IL-6-deficient mice that was more pronounced in younger than in aged animals. In the current study we compared cognitive processes in 4- and 24-month-old IL-6-deficient
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