Lifelong enhancement of body mass from adolescent stress in male hamsters

Blunted food conditioned place preference-like behavior in adolescent-stressed male hamsters

Social stress during adolescence results in long lasting weight gain, obesity, and enhanced food hoarding behavior in hamsters. We wanted to determine whether stress also enhanced conditioned place preference-like behavior (CPP-like) for food reward, as would be expected from studies with substances like cocaine. Our experimental animals were exposed daily to aggressive adults for two weeks in early puberty, while also trained to explore a V-shaped maze containing a food reward at one end. They were tested for CPP-like behavior on the last day of social stress. Our results showed that while stress enhanced weight gain, food intake, food efficiency, and body fat, it caused a reduction of Place Preference as compared to controls. In fact, the correlated relationship between Place Preference and body fat was inverted by stress exposure: while it was positively correlated in controls, it was mildly negatively correlated in stressed hamsters. These unexpected data illustrate the extent of adaptive behavior in foraging animals once a resource has become untrustworthy.

Adolescent social stress alters the role of orexin innervation in the hindbrain in male hamsters

Juvenile male hamsters exposed to chronic social stress eat more, gain weight, and have larger fat pads. The purpose of the present study was to address possible changes in food hoarding and orexin/hypocretin innervation in response to social stress. Male hamsters in early adolescence were exposed to a resident-intruder social stress paradigm or control condition daily for 2 weeks. Metabolism-related physiological measures and behaviors were tracked, and brains were immunocytochemically labeled for orexin-A. Our data confirm our previous observations on appetite, weight gain, and obesity, and showed a strong trend toward enhanced food hoarding as in prior studies. In addition, there were no statistically significant differences in orexin innervation in any brain area analyzed. However, unique correlation patterns were observed between orexin innervation and appetite or metabolic outcome. In particular, opposite correlations were observed between groups within the dorsal raphe nucleus, lateral parabrachial nucleus, and nucleus of the solitary tract. These opposite patterns of correlations suggest chronic social stress causes site-specific alterations in synaptic activity in relation with these behaviors.

A hamster model for stress-induced weight gain

This review addresses the translational relevance of animal models of stress and their effects on body weight. In humans, stress, whether chronic or acute, has often been associated with increased food intake and weight gain. In view of the current obesity epidemic, this phenomenon is especially relevant. Such observations contrast with reports with commonly used laboratory animals, especially rats and mice. In these species, it is common to find individuals gaining less weight under stress, even with potent social stressors. However, there are laboratory species that present increased appetite and weight gain under stress, such as golden hamsters. Furthermore, these animals also include metabolic and behavioral similarities with humans, including hoarding behavior which is also enhanced under stress. Consequently, we propose that our comparative perspective provides useful insights for future research on the development of obesity in humans as a consequence of chronic stress exposure.