Long-term feeding on powdered food causes hyperglycemia and signs of systemic illness in mice

Aims

Dietary habits are crucial factors affecting metabolic homeostasis. However, few animal experiments have addressed the effects of long-term feeding with soft food on parameters reflecting systemic health.

Main methods

Using mice, we compared the effects of short (3 days) and long (17 weeks from weaning) feeding periods between powdered food and normal pellet food on the levels of blood glucose, serum levels of insulin, catecholamines, and corticosterone, blood pressure, and/or social interaction behaviors. In addition, the effects of a human glucagon-like peptide-1 analog, liraglutide (a new drug with protective effects against neuronal and cardiovascular diseases), were compared between the powder and pellet groups.

Key finding

(i) Powdered food, even for such a short period, resulted in a greater glycemic response than pellet food, consistent with powdered food being more easily digested and absorbed. (ii) Long-term feeding on powdered food induced hyperglycemia and related systemic signs of illness, including increases in serum adrenaline, noradrenaline, and corticosterone, higher blood pressures (especially diastolic), and increased social interaction behaviors. (iii) Liraglutide, when administered subcutaneously for the last 2 weeks of the 17-week period of feeding, improved these changes (including those in social interaction behaviors).

Significance

The hyperglycemia associated with long-term powdered-food feeding may lead to certain systemic illness signs, such as elevations of blood glucose, hypertension, and abnormal behaviors in mice. Mastication of food of adequate hardness may be very important for the maintenance of systemic (physical and mental) health, possibly via reduction in the levels of blood glucose and/or adrenal stress hormones (catecholamines and glucocorticoids).     

Subchronic stress-induced depressive behavior in ovariectomized mice

AimsMood disorders including depression are more common in women than men, particularly in times of lower estradiol levels. In this study, we investigated the effect of estrogen on emotional behavior in mice in a stress environment.Main methodsFemale mice were divided into four groups: two groups were ovariectomized (OVX) and two were sham-operated. One group each of OVX and sham mice was kept in a normal environment and the other groups were assigned to a daily stress (1 h/day) for 7 days from 5 days after operation. On the 14th day after operation, subjects were measured to assess behavioral specificity, locomotor activity, elevated plus-maze (EPM) behavior, passive avoidance (PA) behavior and forced swimming behavior.Key findingsThe OVX plus stress (OVX + S) group showed a significant prolongation of immobility compared with the other groups. In all the groups there were no changes in locomotor activity, EPM behavior or PA behavior. We further examined the effect of estrogen against depressive behavior in the OVX + S group. The vehicle or 17β-estradiol (E2) was administered s.c. to OVX + S mice for 4 days beginning on post-operative day 11. Subchronic E2 treatment decreased the stress response and improved depressive behavior relative to the vehicle group.SignificanceThese data have important implications regarding the prevention of depression in postmenopausal women undergoing estrogen therapy.     

Influence of a long-term powdered diet on the social interaction test and dopaminergic systems in mice

It is well known that the characteristics of mastication are important for the maintenance of our physical well-being. In this study, to assess the importance of the effects of food hardness during mastication, we investigated whether a long-term powdered diet might cause changes in emotional behavior tests, including spontaneous locomotor activity and social interaction (SI) tests, and the dopaminergic system of the frontal cortex and hippocampus in mice. Mice fed a powdered diet for 17 weeks from weaning were compared with mice fed a standard diet (control). The dopamine turnover and expression of dopamine receptors mRNA in the frontal cortex were also evaluated. Spontaneous locomotor activity, SI time and dopamine turnover of the frontal cortex were increased in powdered diet-fed mice. On the other hand, the expression of dopamine-4 (D4) receptors mRNA in the frontal cortex was decreased in powdered diet-fed mice. Moreover, we examined the effect of PD168077, a selective D4 agonist, on the increased SI time in powdered diet-fed mice. Treatment with PD168077 decreased the SI time. These results suggest that the masticatory dysfunction induced by long-term powdered diet feeding may cause the increased SI time and the changes in the dopaminergic system, especially dopamine D4 receptor subtype in the frontal cortex.