Different effects of peripheral and central ghrelin on regulation of food intake in the Japanese quail

When rat or human ghrelin is administered to chickens or rats it stimulates the release of growth hormone, however, its effects on food intake differ between the two species. To investigate this discrepancy, we measured plasma ghrelin concentrations before and after food intake, and determined the effects of central (intracerebroventricular, icv) and peripheral (intraperitoneal, ip) injections of various ghrelin doses on food intake and body temperature in the Japanese quail. In control quails, plasma ghrelin levels were significantly increased in the fasting state; subsequent feeding produced a reduction, suggesting that ghrelin may act as an orexigenic signal in Japanese quails as well as mammals. Food intake was stimulated by ip, but not icv, injections of small doses of ghrelin, whereas both ip and icv injections of larger doses inhibited feeding. A large dose of ghrelin also increased body temperature. These results suggest that an increase in peripheral ghrelin may act as a hunger signal to induce food intake through stimulation of the afferent vagal nerve in the Japanese quail, as in rats, whereas central ghrelin may inhibit feeding in different ways in the two species.