Dynamic body weight and body composition changes in response to subordination stress

Abstract

Social stress is prevalent in many facets of modern society. Epidemiological data suggest that stress is linked to the development of overweight, obesity and metabolic disease. Although there are strong associations between the incidence of obesity with stress and elevated levels of hormones such as cortisol, there are limited animal models to allow investigation of the etiology of increased adiposity resulting from exposure to stress. Perhaps more importantly, an animal model that mirrors the consequences of stress in humans will provide a vehicle to develop rational clinical therapy to treat or prevent adverse outcomes from exposure to chronic social stress. In the visible burrow system (VBS) model of chronic social stress mixed gender colonies are housed for 2 week periods during which male rats of the colony quickly develop a dominance hierarchy. We found that social stress has significant effects on body weight and body composition such that subordinate rats progressively develop characteristics of obesity that occurs, in part, through neuroendocrine alterations and changes in food intake amount. Although subordinate rats are hyperphagic following social stress they do not increase their intake of sucrose solution as control and dominants do suggesting that they are anhedonic. Consumption of a high fat diet does not appear to affect development of a social hierarchy and appears to enhance the effect that chronic stress has on body composition. The visible burrow system (VBS) model of social stress may be a potential laboratory model for studying stress-associated metabolic disease, including the metabolic syndrome.

Figure 1

Body weight during VBS. SUB in colonies lost a significant amount of body weight over 14-days in the VBS compared to DOM. * P < 0.05 vs. CON; ** P < 0.05 vs. CON and DOM.

Figure 2

Body composition prior to (Day 0) and on Day 13 of VBS housing measured by NMR. Following 14 days in the VBS, both DOM and SUB had significantly decreased % body fat. SUB did not gain lean body mass as CON and DOM did. DOM did not lose body weight and appears to have shifted fat to lean body mass. * P < 0.05 vs. DAY 0; # P < 0.05 vs. CON on DAY 13.

Figure 3

Adipose tissue distribution of VBS rats sacrificed following 14 days in VBS (n = 4 colonies). * P < 0.05 vs. CON.

Figure 4

Percentage of original body weight over two cycles of chronic social stress in the VBS (14 days each) and recovery (21 days each) in individual cages. SUB rats lost a significant amount of body weight during both VBS 1 and VBS 2, while DOM lost little or maintained their weight and CON continued to gain weight. During the recovery periods, SUB regained lost weight but did not attain the same body weight level as CON. [Adapted from Sakai and Tamashiro, 2005]

Figure 5

Intake of 1% sucrose solution. CON and DOM significantly increase their intake of sucrose solution with each trial. In contrast SUB consistently have lower sucrose intake than CON and DOM and do not increase their intakes across trials. *P < 0.05 vs. CON; ** P < 0.05 vs. CON and DOM.