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    • br Materials and met http www

    2023-12-29


    Materials and methods
    Results The values for body weight are shown in Fig. 1. Body weight was measured every day. The body weight of the young mice in the control (i.e. no-stress) group was not significantly different from that of the young mice in the stress group. However, the middle-aged mice subjected to IMO stress showed lower body weight compared with the middle-aged mice free from IMO stress. Significant interactions between day and treatment (p<0.0001), day and age (p<0.0001), as well as day, treatment and age (p<0.0001) were observed, suggesting that the body weight of middle-aged mice subjected to IMO stress continued to reduce with the progress of the experimental days. The result of the OFT is shown in Fig. 2A and B. In total distance traveled, no significant effects for aging, stress or interaction were detected. In terms of rearing, the number of times an animal reared in the young groups was significantly (p<0.05) higher than it was in the middle-aged groups. However, stress treatment did not cause any statistical significance. The result of the EPM is shown in Fig. 2C. In terms of number of entries into the open arm, there were no significant differences between the four groups. The result of the FST is shown in Fig. 2D. Total duration of immobility was determined, but no significant effects were detected in any treatment group. Table 2 shows the levels of free corticotropin-releasing factor in the hippocampus. D-Asp (p<0.05) and L-Gln (p<0.05) levels were significantly higher in the middle-aged group than they were in the young group, but L-Arg (p<0.005), ornithine (p<0.05), L-Ala (p<0.05), GABA (p<0.05), L-Ile (p<0.05) and L-Leu (p<0.05) levels were significantly lower in the middle-aged group than they were in the young group. No significant effects of stress and no significant interactions between age and stress were detected for any amino acids. Table 3 gives the levels of free amino acids in the hypothalamus. The L-Asp (p<0.05) level was significantly higher, but L-Ser (p<0.05), L-Arg (p<0.0005) and L-Ile (p<0.05) levels were significantly lower in the middle-aged group compared with the young group. Moreover, the L-Ile level of the stressed group was significantly higher than that of the control group. No significant interactions between age and stress were detected. Table 4 shows the levels of free amino acids in the cerebellum. L-Ser (p<0.05) and L-Val (p<0.05) levels of the middle-aged group were significantly lower than those of the young group. Significant interactions between age and stress were detected in L-Ala and GABA, implying that in the young group, both amino acids were lowered by stress, but that the reverse was true for the middle-aged group. No significant effects of stress were found for any amino acids. Tables 5 and 6 show the levels of amino acids in the ovary and uterus. In the uterus, L-Asp (p<0.05), L-Ser (p<0.005), L-Gln (p<0.005), L-His (p<0.005), L-Arg (p<0.0001), L-Tyr (p<0.005), L-Val (p<0.0005), L-Met (p<0.005), L-Phe (p<0.0001), L-Ile (p<0.0001) and L-Leu (p<0.0001) levels of the middle-aged group were significantly higher than those of the young group. In the ovaries, L-Asp (p<0.0001), L-His (p<0.0001), L-Arg (p<0.005), Tau (p<0.0001), L-Met (p<0.05), L-Phe (p<0.05), L-Ile (p<0.005) and L-Leu (p<0.05) levels of the middle-aged group were significantly higher than those of the young group. However, the L-Ala level (p<0.0001) of the middle-aged group was significantly lower than it was in the young group. A significant interaction between age and stress was found in L-His, suggesting that L-His decreased with stress in the young group, but that it increased in the middle-aged group.
    Discussion The present study evaluated whether age and stress have any effects in female mice, with special reference to amino acid metabolism and emotional behavior. IMO stress has been recognized as causing behavioral and physiological changes such as locomotor impairment, anxiety-like behavior and secretion of stress hormones (Kumar and Goyal, 2007, Tanaka et al., 2000). However, in the present study it was found that IMO stress applied for 30min daily for 28days did not have such a strong effect: IMO stress affected body weight in the middle-aged group, but no significant effects among treatments were detected in most of the emotional behaviors. In a previous study (Hill et al., 2010), rats that were exposed to chronic IMO stress (30min/day for 9days) showed a reduced stress response, as shown by a low level of plasma corticosterone, when subjected to acute IMO stress (30min) on day 9 compared with naïve mice exposed to the same acute stress. Similarly, in our study, IMO stress applied regularly for several days (28days) could be thought to have caused habituation. However, the adult mice did not habituate to restrain stress after 10 consecutive days (Randemacher et al., 2008). Moreover, the body weight of the middle-aged mice in the stress group decreased compared with the non-stress group. It is well known that corticosterone increases when an individual is exposed to stress (Kusnecov and Rabin, 1994). However, a future study is needed to clarify the pattern of alteration in stress biomarker, corticosterone under similar experimental conditions to the current study. It has been reported that IMO stress in mice for 15days caused body weight and food intake to decrease (Jeong et al., 2013). In the current study, therefore, metabolic alteration may have occurred in mice due to the possible decrease in food intake which was reflected in decreased body weight. Taken together, these findings show that middle-aged mice are more sensitive to stress, which was reflected in the reduction in body weight, and that they may not be able to habituate to stress at this age.