Monosodium l-glutamate-obesity onset is associated with disruption of central control of the hypothalamic-pituitary-adrenal axis and autonomic nervous system.

The hypothalamic-pituitary-adrenal axis (HPA) exerts important catabolic peripheral effects and influences autonomic nervous system (ANS)-mediated processes. Impaired negative-feedback control or reduced HPA axis sensitivity and altered ANS activity appear to be associated with the development and maintenance of obesity. In the present study, we examined the hypothesis that the central HPA axis is dysregulated favouring ANS disbalance in monosodium l-glutamate (MSG)-induced rat obesity. Glucose homeostasis, corticosterone, leptin and ANS electrical activity were evaluated. Adult MSG-induced obese rats exhibited fasting hyperinsulinaemia, insulin resistance, glucose intolerance, hypercorticosteronaemia, hyperleptinaemia and altered ANS activity. A decrease in food intake was observed during corticotrophin-releasing hormone (CRH) treatment in both control and MSG-treated rats. By contrast, food intake was significantly elevated in control rats treated with dexamethasone (DEXA), whereas no alterations were observed following DEXA treatment in MSG-induced obese rats. After DEXA injection, an increase in fasting insulin and glucose levels, associated with insulin resistance, was seen in both groups. As expected, there was a decrease of parasympathetic activity and an increase of sympathetic nervous activity in CRH-treated control animals and the opposite effect was seen after DEXA treatment. By contrast, there was no effect on ANS activity in MSG-rats treated with CRH or DEXA. In conclusion, impairment of the HPA axis can lead to disbalance of ANS activity in MSG-treated rats, contributing to the establishment and maintenance of obesity.

Analyzing the sensory characteristics and taste-sensor ions of MSG substitutes.

This study analyzed the sensory attributes of MSG substitutes to determine whether they exerted synergistic or inhibition effects on taste, and the correlation between sensory attributes (which are subjective measures) and the results of electronic-tongue analysis (which are objective measures). Descriptive and electronic-tongue analyses were conducted with 10 MSG substitutes comprising combinations of 3 commercial products, and with MSG. In the descriptive analysis, the sensory characteristics of MSG substitutes were evaluated using 16 attributes; and in the electronic-tongue analysis, the taste-sensor ions of MSG substitutes were evaluated using 10 taste-sensor types. Principal components analysis was applied separately to the sensory evaluation data and the electronic-tongue data to summarize the structure of each data set. Partial least-squares regression was used to assess the relationship between the sensory evaluation data and the electronic-tongue data. The MSG substitutes show different sensory attributes when they are used alone or in mixtures, suggesting the presence of synergistic or inhibitory effects between them. Therefore, when replacing MSG, the characteristics of each possible substitute should be determined in relation to the particular food system.