Sickness behavior in birds caused by peripheral or central injection of endotoxin

Recent evidence indicates that many of the physiologic, metabolic, and behavioral responses that accompany infection in mammals are important for maintaining homeostasis and promoting recovery. In the present report, we have extended this concept to birds by demonstrating that LPS injected IP reduces feed intake, increases somnolence, decreases plasma [Fe] and [Zn], increases plasma [Cu], and elevates plasma corticosterone. To determine if any of these effects could be mediated centrally, LPS was injected intracerebroventricularly (ICV). Whereas peripheral injection of LPS caused a modest increase in body temperature, the hyperthermic effect of LPS injected ICV was intense and long lasting. This hyperthermia following ICV injection of LPS was accompanied by only a transient reduction in food intake and elevation in somnolent activity, with no change in plasma [Fe] or [Zn]. Both peripheral and central injections of LPS increased plasma corticosterone, but the increase caused by peripherally administered LPS was sixfold higher than that caused by LPS injected centrally. Collectively, these data show that chickens respond to both peripheral and central injections of endotoxin by reducing food consumption, increasing somnolence, becoming febrile, and elevating plasma corticosterone. However, the magnitude of these responses depends upon whether LPS acts at central or peripheral sites.