Androgenic influences on behavior, body weight, and body composition in a model of chronic social stress.

The visible burrow system (VBS) is a model used to study chronic social stress in colony-housed rats. A hierarchy develops among the males resulting in dominant (DOM) and subordinate (SUB) animals. Hierarchy-associated changes in body weight, body composition, behavior, and neuroendocrine measures have been observed. After 14 d of VBS housing, SUB animals have decreased body weight, elevated corticosterone, and decreased testosterone (T), compared with DOM animals and controls, placing SUB animals in an ideal endocrine state to regain lost body weight as adipose tissue. It is hypothesized that maintaining constant androgen concentrations in SUB males during stress will prevent body weight loss by maintaining more lean body mass. To test this, animals were gonadectomized and implanted with SILASTIC implants containing T, 5alpha-dihydrotestosterone (DHT), or cholesterol. Implants maintained constant physiological levels of T. Standard intact, T, and DHT implant colonies formed hierarchies, whereas cholesterol colonies did not. Androgen manipulations significantly altered offensive and defensive behaviors only on the first day of VBS housing. After VBS stress, intact, T, and DHT SUB animals weighed less and lost more adipose and lean tissue than DOM and control males, whereas DOM animals primarily lost adipose tissue. However, on recovery, DHT SUB animals maintained more lean tissue than intact SUB animals. Oral glucose tolerance tests revealed that glucose clears faster in stressed T-implanted males that have increased adipose tissue. Overall, these data suggest that constant androgen concentrations in SUB animals do not prevent weight loss and changes in body composition during stress but do so during recovery.

Social stress and recovery: implications for body weight and body composition.

Social stress resulting from dominant-subordinate relationships is associated with body weight loss and altered body composition in subordinate (SUB) male rats. Here, we extend these findings to determine whether stress-induced changes in energy homeostasis persist when the social stress is removed, and the animal is allowed to recover. We examined body weight (BW), body composition, and relevant endocrine measures after one or two cycles of 14 days of social stress, each followed by 21 days of recovery in each rat's individual home cage. SUB lost significantly more BW during social housing in a visible burrow system (VBS) compared with dominant (DOM) animals. Weight loss during social stress was attributable to a decrease in adipose tissue in DOM and SUB, with an additional loss of lean tissue in SUB. During both 21-day recovery periods, DOM and SUB regained lost BW, but only SUB were hyperphagic. Following recovery, SUB had a relatively larger increase in adipose tissue and plasma leptin compared with DOM, indicating that body composition changes were dependent on social status. Control animals that were weight matched to SUB or male rats exposed to the VBS environment without females, and that did not form a social hierarchy, did not exhibit changes in body composition like SUB in the VBS. Therefore, chronic social stress causes social status-dependent changes in BW, composition and endocrine measures that persist after repeated stress and recovery cycles and that may ultimately lead to metabolic disorders and obesity.

The impact of moderate daily alcohol consumption on aggression and the formation of dominance hierarchies in rats.

RATIONALE AND OBJECTIVE: Group-housed male rats form social hierarchies, and under these conditions, it has been reported that subordinate (SUB) rats consume more alcohol than dominant (DOM) rats. We tested the hypothesis that a history of drinking alcohol would cause SUB rats to consume even greater amounts of alcohol. METHODS: Male Long-Evans rats were trained to drink 10% alcohol or a sucrose/quinine solution equal in calories for 1 h/day using a sucrose-fading procedure. Subsequently, rats were housed in colonies (four males, two females) in a visible burrow system (VBS) for 14 days. Individual control male rats were housed in a tub cage with one female. Rats were removed from the VBS (or control environment) daily and given 1 h to drink alcohol or sucrose/quinine. RESULTS: Colonies given daily access to sucrose/quinine formed clear DOM/SUB relationships in all measured parameters. Alcohol-drinking colonies failed to establish a dominance hierarchy and displayed little aggression, with an average of 14.6 +/- 6.1 offensive attacks compared with 58.5 +/- 12.3 attacks carried out by DOM sucrose/quinine rats. During VBS housing, alcohol and sucrose/quinine intake decreased independent of housing environment or social status. CONCLUSIONS: Contrary to prior reports of the effect of alcohol on aggressive behavior, moderate daily alcohol intake before and during VBS housing reduced aggression and precluded the formation of a dominance hierarchy in rats.