Chronic Administration of Monosodium Glutamate under Chronic Variable Stress Impaired Hypothalamic-Pituitary-Adrenal Axis Function in Rats

Abstract

The hypothalamic-pituitary-adrenal (HPA) axis is the primary endocrine system to respond to stress. The HPA axis may be affected by increased level of corticotrophin-releasing factors under chronic stress and by chronic administration of monosodium glutamate (MSG). The purpose of this study was to investigate whether chronic MSG administration aggravates chronic variable stress (CVS)-induced behavioral and hormonal changes. Twenty-four adult male Sprague-Dawley rats, weighing 200∼ 220 g, were divided into 4 groups as follows: water administration (CON), MSG (3 g/kg) administration (MSG), CVS, and CVS with MSG (3 g/kg) administration (CVS＋ MSG). In addition, for the purpose of comparing the effect on plasma corticosterone levels between chronic stress and daily care or acute stress, 2 groups were added at the end of the experiment; the 2 new groups were as follows: naïve mice (n=7) and mice exposed to restraint stress for 2 h just before decapitation (A-Str, n=7). In an open field test performed after the experiment, the CVS＋ MSG group significant decrease in activity. The increase in relative adrenal weights in the CVS and CVS＋ MSG group was significantly greater than those in the CON and/or MSG groups. In spite of the increase in the relative adrenal weight, there was a significant decrease in the plasma corticosterone levels in the CVS＋ MSG group as compared to all other groups, except the naïve group. These results suggest that impaired HPA axis function as well as the decrease in the behavioral activity in adult rats can be induced by chronic MSG administration under CVS rather than CVS alone.

The Effects of Monosodium Glutamate on Thymic and Splenic Immune Functions and Role of Recovery (Biochemical and Histological study)

“…The median lethal dose (LD 50 ) is between 15 and 18 g/kg body weight in rats and mice [37]. The selected dose was based on the toxicity levels reported by previous studies [35,36]. The duration of the study (8 weeks) may provide the potential for long-term effects associated with MSG intake.…”

“…For the exposures, rats were randomly allocated into three groups (N=10/group): Group I (control group) rats received 1 ml distilled water daily (MSG vehicle) for 8 weeks by oral gavages; Group II (MSG group) rats received 3 g/kg body weight of MSG (1/5 LD 50 ) daily for 8 weeks by oral gavages [35,36] and Group III (recovery group) rats received the same dose of MSG for the same period as Group II rats and then nothing for a subsequent 4 weeks after the final MSG dosing. Rats were weighed daily to allow for adjustment of the daily dose volume; in no case did the volume of MSG used for treatment ever exceed 3 g/kg.…”

Stress and visceral pain: From animal models to clinical therapies

“…Male Wistar rats exposed intermittently to a combination of cold restraint stress, WAS or forced swimming (one stressor per day for 9 consecutive days) were found to develop visceral hypersensitivity at 8h but not at 24h or 7 days after the end of the last stressor (Winston et al, 2010). The use of more complex and long lasting heterotypic stressors including 2–3 stressors per day for up to 35–40 days (Seo et al, 2010; Tagliari et al, 2010) causes behavioral changes in rodents that parallel symptoms of depression (Gamaro et al 2008; Ni et al 2008; Wilner 2005; Katz and Hersh 1981). This later CMS model may display strong construct validity in the context of subset of IBS patients presenting depression symptoms (Folks, 2004) when sustained alterations in visceral sensitivity will be established in these models.…”

The Knockout of Secretin in Cerebellar Purkinje Cells Impairs Mouse Motor Coordination and Motor Learning

“…An open field test was employed to observe spontaneous movements as an indicator of the motor function and stress level (Seo et al, 2010) The wire hanging test was employed to measure the neuromuscular strength of transgenic mice. Both WT and Sct fl/fl animals had significantly higher holding latencies (144.9±8.1 and 122.9±5.3 s, respectively) than Sct À / À , Sctr À / À , and Pur-Sct À / À mice (34.1 ± 9.4, 52.0 ± 15.8, and 38.0 ± 4.7 s, respectively) by one-way ANOVA followed by post-hoc analysis (post-hoc Tukey's test, po0.001 in all three cases).…”