Psychological stress exposure to aged mice causes abnormal feeding patterns with changes in the bout number

Abstract

Stress responses are affected by aging. However, studies on stress-related changes in feeding patterns with aging subject are minimal. We investigated feeding patterns induced by two psychological stress models, revealing characteristics of stress-induced feeding patterns as "meal" and "bout" (defined as the minimum feeding behavior parameters) in aged mice. Feeding behaviors of C57BL/6J mice were monitored for 24 h by an automatic monitoring device. Novelty stress reduced the meal amount over the 24 h in both young and aged mice, but as a result of a time course study it was persistent in aged mice. In addition, the decreased bout number was more pronounced in aged mice than in young mice. The 24-h meal and bout parameters did not change in either the young or aged mice following water avoidance stress (WAS). However, the meal amount and bout number increased in aged mice for 0-6 h after WAS exposure but remained unchanged in young mice. Our findings suggest that changes in bout number may lead to abnormal stress-related feeding patterns and may be one tool for evaluating eating abnormality in aged mice.

Keywords: aged mice; bout; meal microstructure; meal pattern; stress.

Figure 1. Changes in locomotor activity in young and aged mice after fasting or exposure to novelty stress/water avoidance stress

(A) left: average voluntary movements after 24-h fasting in the dark/light phase, right: the 24-h changes after 24-h fasting in young mice, (B) left: average voluntary movements after novelty stress in the dark phase, right: the 24-h changes after novelty stress in young and aged mice, (C) left: average voluntary movements after water avoidance stress (WAS) in the dark phase, right: the 24-h changes after WAS in young and aged mice. *, ***; P < 0.05, 0.001 vs. fed or age-matched basal/control mice, ##, ###; P < 0.01, 0.001 between young and aged mice, n = 8, 14–16, or 7–8.

Figure 2. Microstructure analysis after 24-h fasting in young mice

(A) left: the 24-h meal amount, right: meal amount per 3 h in the dark phase, (B) left: the 24-h meal size, right: meal size per 3 h in the dark phase, (C) left: the 24-h meal number, right: meal number per 3 h in the dark phase, (D) left: the 24-h bout size, right: bout size per 3 h in the dark phase, (E) left: the 24-h bout number, right: bout number per 3 h in the dark phase. *, **; P < 0.05, 0.01 vs. fed, n = 8.

Figure 3. Microstructure analysis of young and aged mice after novelty stress exposure

(A) left: the 24-h meal amount, middle and right: meal amount per 3 h in young and aged mice on dark phase, (B) left: the 24-h meal size, middle and right: meal size per 3 h in young and aged mice on dark phase, (C) left: the 24-h meal number, middle and right: meal number per 3 h in young and aged mice on dark phase, (D) left: the 24-h bout size, middle and right: bout size per 3 h in young and aged mice on dark phase, (E) left: the 24-h bout number, middle and right: bout number per 3 h in young and aged mice on dark phase. *, **, ***; P < 0.05, 0.01, 0.001 vs. age-matched basal mice, #, ###; P < 0.05, 0.001 between young and aged mice, n = 14–16.

Figure 4. Microstructure analysis of young and aged mice after water avoidance stress exposure

(A) left: the 24-h meal amount, middle and right: meal amount per 3 h in young and aged mice on dark phase, (B) left: the 24-h meal size, middle and right: meal size per 3 h in young and aged mice on dark phase, (C) left: the 24-h meal number, middle and right: meal number per 3 h in young and aged mice on dark phase, (D) left: the 24-h bout size, middle and right: bout size per 3 h in young and aged mice on dark phase, (E) left: the 24-h bout number, middle and right: bout number per 3 h in young and aged mice on dark phase. *, ***; P < 0.05, 0.001 vs. age-matched control mice, ###; P < 0.001 between young and aged mice, n = 7–8.

Figure 5. Experimental schedule and schematic feeding bout

(A and B) It is shown experimental schedule. (C) Green indicates “Meal” parameters, and red indicates “Bout” parameters. It is shown a chart when meal number is 3 and bout number is 9 as an example. Each value indicates the number of times per analysis time. Feeding bout was defined as a new bout when the time without feeding was longer than 5 sec from the previous response and was equal to or greater than 0.01 g. Food consumption was considered to be a “Meal” when the feeding bouts occurred within 5 min of the previous response and the sum of the food consumed during the bout was equal to or greater than 0.02 g; when the feeding bouts were longer than 5 min apart, these were considered to be a new meal.