Effects of calorie restriction on reproductive and adrenal systems in Japanese quail: are responses similar to mammals, particularly primates?

The benefits of calorie restriction (CR) have been established across a variety of vertebrate and invertebrate species. Although the effects of CR on lifespan in birds have not been examined, it is clear that CR has beneficial effects on reproductive, metabolic, and physiological function in adult poultry. We examined the effects of CR in Japanese quail, a rapidly maturing avian model, on reproductive endocrine and neuroendocrine systems. Male Japanese quail were pair fed at 0% ad libitum (AL), 20%, or 40% CR of AL, recorded for juveniles (3-7 weeks of age) or adults (12-16 weeks of age). Juvenile males on CR matured more slowly, and both juvenile and adult males had reduced plasma luteinizing hormone (LH) with CR. Adults on 40% CR showed evidence of stress, with increased plasma corticosterone and reduced testes weight and circulating androgens. In a separate study, pituitary gland response was tested in juvenile and adult castrated males that had been on the same CR treatments. All birds responded to gonadotropin releasing hormone (GnRH) challenge, with LH release. However, the 40% CR juvenile and adult birds had quantitatively lower responses, suggesting central inhibition of the reproductive axis. This hypothesis was tested by measurement of sexual behavior and catecholamines known to stimulate GnRH in hypothalamic regions that modulate these responses. Results showed reduced norepinephrine in key hypothalamic regions and reduced dopamine in posterior hypothalamus. These data support the hypothesis that CR affects reproductive function, with evidence for effects in the central nervous system. These data are discussed and compared to data collected in mammals, especially the rhesus monkey, on the effects of timing and degree of CR on reproductive and stress responses.