Female-biased anorexia and anxiety in the Syrian hamster.

Anorexia and anxiety cause significant mortality and disability with female biases and frequent comorbidity after puberty, but the scarcity of suitable animal models impedes understanding of their biological underpinnings. It is reported here that in adult or weanling Syrian hamsters, relative to social housing (SH), social separation (SS) induced anorexia characterized as hypophagia, weight loss, reduced adiposity, and hypermetabolism. Following anorexia, SS increased reluctance to feed, and thigmotaxis, in anxiogenic environments. Importantly, anorexia and anxiety were induced post-puberty with female biases. SS also reduced hypothalamic corticotrophin-releasing factor mRNA and serum corticosteroid levels assessed by RT-PCR and RIA, respectively. Consistent with the view that sex differences in adrenal suppression contributed to female biases in anorexia and anxiety by disinhibiting neuroimmune activity, SS elevated hypothalamic interleukin-6 and toll-like receptor 4 mRNA levels. Although corticosteroids were highest during SH, they were within the physiological range and associated with juvenile-like growth of white adipose, bone, and skeletal muscle. These results suggest that hamsters exhibit plasticity in bioenergetic and emotional phenotypes across puberty without an increase in stress responsiveness. Thus, social separation of hamsters provides a model of sex differences in anorexia and anxiety during adulthood and their pathogeneses during adolescence.

A modified anxious behavior test for hamsters.

BACKGROUND: Latency to feed in a novel environment assesses anxious behavior in rodents, but it is unclear whether it distinguishes anxiety from consumption or appetite. NEW METHOD: The anxiety-related feeding/exploration conflict (AFEC) test was used here to assess anxious behavior in Syrian hamsters for which increased cheek-pouching of food, but not overconsumption of it, reflects appetitive drive, and orexigenic stimuli do not increase consumption. The setup of the test prevented cheek-pouching. COMPARISON WITH EXISTING METHODS: Latency to approach test food provided an additional control for non-emotional effects of treatments. Feed and approach latencies in the test cage were normalized to those in the home cage to factor out non-emotional effects. RESULTS: Feed latency and the feed latency ratio (test cage/home cage) were reduced by acute treatment with benzodiazepine, diazepam, or beta-adrenergic receptor antagonist, propranolol, or chronic treatment with norepinephrine reuptake inhibitor, desipramine. Reductions of feed latency and the feed latency ratio were not associated with hyperphagia, and these behaviors were unaltered by acute treatment with opioid receptor antagonist, naltrexone. Latency to approach food in the test cage, with and without normalization, was unaltered by these treatments. Finally, overnight fasting elevated feed latency without hyperphagia, and this effect was attenuated by chronic desipramine treatment. CONCLUSIONS: These results suggest that the AFEC test assesses anxious, but not appetitive or consummatory, behavior, and that its sensitivity increases with food deprivation of hamsters.