Elevation of the Blood Glucose Level is Involved in an Increase in Expression of Sweet Taste Receptors in Taste Buds of Rat Circumvallate Papillae

Sub-chronic and mild social defeat stress exposure to C57BL/6J mice increases visceral fat mass and causes accumulation of cholesterol and bile acids in the liver

Major depressive disorder is accompanied by a high metabolic illness comorbidity and patients with atypical depression are a subgroup with particularly high risk of obesity, dyslipidemia, and metabolic syndrome; however, the underlying mechanisms have not been fully elucidated. In this study, we examined visceral fat deposition, lipid profiles in the liver, and gut microbiota in sub-chronic and mild social defeat stress (sCSDS)-exposed C57BL/6J mice, which exhibit atypical depression-like phenotypes, i.e., increased body weight and food and water intake. We found that visceral fat mass and levels of hepatic cholesterol and bile acids in sCSDS-exposed mice were significantly increased compared to those in controls. The expression of hepatic small heterodimer partner, a negative regulator of cholesterol metabolism, was significantly elevated in sCSDS-exposed mice. We also found that gut microbial diversity and composition including lower relative abundance of Bacteroides spp. and Bifidobacterium spp. in sCSDS-exposed mice were different from those in controls. In addition, relative abundance of Bacteroides spp. and Bifidobacterium spp. was significantly and negatively correlated with body weight, visceral fat mass, and hepatic cholesterol and bile acids levels. These results indicate that sCSDS-exposure induces dysbiosis, and thereby contributes to metabolic disorder development.

Alteration of Sweet and Bitter Taste Sensitivity with Development of Glucose Intolerance in Non-insulin-Dependent Diabetes Mellitus Model OLETF Rats

Patients with diabetes exhibit altered taste sensitivity, but its details have not been clarified yet. Here, we examined alteration of sweet taste sensitivity with development of glucose intolerance in Otsuka Long-Evans Tokushima Fatty (OLETF) rats as a model of non-insulin-dependent diabetes mellitus. Compared to the cases of Long Evans Tokushima Otsuka (LETO) rats as a control, glucose tolerance of OLETF rats decreased with aging, resulting in development of diabetes at 36-weeks-old. In brief-access tests with a mixture of sucrose and quinine hydrochloride, OLETF rats at 25 or more-weeks-old seemed to exhibit lower sweet taste sensitivity than age-matched LETO ones, but the lick ratios of LETO, but not OLETF, rats for the mixture and quinine hydrochloride solutions decreased and increased, respectively, aging-dependently. Expression of sweet taste receptors, T1R2 and T1R3, in circumvallate papillae (CP) was almost the same in LETO and OLETF rats at 10- and 40-weeks-old, while expression levels of a bitter taste receptor, T2R16, were greater in 40-weeks-old rats than in 10-weeks-old ones in both strains. There was no apparent morphological alteration in taste buds in CP between 10- and 40-weeks-old LETO and OLETF rats. Metagenomic analysis of gut microbiota revealed strain- and aging-dependent alteration of mucus layer-regulatory microbiota. Collectively, we concluded that the apparent higher sweet taste sensitivity in 25 or more-weeks-old OLETF rats than in age-matched LETO rats was due to the aging-dependent increase of bitter taste sensitivity in LETO rats with alteration of the gut microbiota.

Dextran sulfate sodium-induced colitis in C57BL/6J mice increases their susceptibility to chronic unpredictable mild stress that induces depressive-like behavior

AIMS

In patients with colitis, the high comorbidity of depressive disorders is well-known, but the detailed mechanisms remain unresolved. In this study, we examined whether colitis induced by dextran sulfate sodium (DSS) increased the susceptibility to chronic unpredictable mild stress (CUMS) in C57BL/6J mice with resilience to CUMS.

MAIN METHODS

To induce experimental colitis and depressive-like behaviors, male 7-weeks old C57BL/6J mice were administered ad libitum 1% DSS solution for 11 days, and subjected to various mild stressors in a chronic, inevitable and unpredictable way according to a random schedule for 21 days, respectively.

KEY FINDINGS

In naïve mice exposed to CUMS, their immobility times in a forced swim (FS) test were almost equal to those in control mice. The DSS administration to naïve mice induced colitis without depressive-like behavior, and at 18 days after termination of the DSS administration, the colitis had recovered to control levels, while altered diversity and composition of bacterial genera such as Bacteroides spp., Alistipes spp., etc., were found in the gut microbiota. Exposure of mice with DSS-induced colitis to CUMS (DSS + CUMS) significantly increased the immobility times in the FS test. In the gut microbiota of DSS + CUMS mice, the alteration profile of the relative abundance of bacterial genera differed from in the DSS ones.

SIGNIFICANCE

These findings indicate that mice with colitis exhibit increased susceptibility to psychological stress, resulting in induction of depressive-like behavior, and this might be due, at least in part, to altered characteristics of the gut microbiota.

Reproducible induction of depressive-like behavior in C57BL/6J mice exposed to chronic social defeat stress with a modified sensory contact protocol

AIMS

C57BL/6J mice are well-known to exhibit resilience to chronic social defeat stress (CSDS) for induction of depressive-like behavior. Establishment of protocols for reproducible induction of depressive-like behavior in C57BL/6J mice would be useful to elucidate the underlying molecular mechanisms using target gene-knock-in and -out mice whose background is generally C57BL/6J. Here, we developed a modified CSDS protocol for reproducible induction of depressive-like behavior in C57BL/6J mice, and compared the profile of their gut microbiota with that with the standard CSDS protocol.

MAIN METHODS

To prevent acclimation of defeated C57BL/6J mice to aggressive ICR mice, the sensory contact following a daily 10 min-defeat episode was performed by housing an individual defeated mouse in a cage set next to a cage for the aggressor one.

KEY FINDINGS

The number of attacks by ICR mice on C57BL/6J ones was significantly increased with the modified CSDS protocol, and the susceptible mice exhibited greater hippocampal inflammation and an increased immobility time in the forced swim test, compared in the case of the standard CSDS protocol, and the reproducibility was confirmed in another set of experiments. Both the standard and modified CSDS protocols changed the diversity and relative composition of gut microbiota in the susceptible mice, but there was no apparent difference in them between the standard and modified CSDS-susceptible mice.

SIGNIFICANCE

We established a CSDS protocol for reproducible induction of depressive-like behavior in C57BL/6J mice, and the features of the gut microbiota were similar in the susceptible mice with and without the depressive-like behavior.

Liposomalization of Oxaliplatin Exacerbates the Non-Liposomal Formulation-Induced Decrease of Sweet Taste Sensitivity in Rats

Here, we investigated whether or not the characteristics of the oxaliplatin-induced sweet taste sensitivity were altered by PEGylated liposomalization of oxaliplatin (liposomal oxaliplatin), which enhances its anticancer efficacy. Liposomal oxaliplatin and oxaliplatin were intravenously and intraperitoneally, respectively, administered to male Sprague-Dawley rats at the total dose of 8 mg/kg. A brief-access test for evaluation of sweet taste sensitivity on day 7 revealed that both liposomal oxaliplatin and oxaliplatin decreased the sensitivity of rats, the degree with the former being greater than in the case of the latter. Liposomalization of oxaliplatin increased the accumulation of platinum in lingual non-epithelial tissues, through which taste nerves passed. The lingual platinum accumulation induced by not only liposomal oxaliplatin but also oxaliplatin was decreased on cooling of the tongue during the administration. In the current study, we revealed that liposomalization of oxaliplatin exacerbated the oxaliplatin-induced decrease of sweet taste sensitivity by increasing the accumulation of platinum/oxaliplatin in lingual non-epithelial tissues. These findings may suggest that reduction of liposomal oxaliplatin distribution to the tongue on cooling during the administration prevents exacerbation of the decrease of sweet taste sensitivity, maintaining the quality of life and chemotherapeutic outcome in patients.