Meeting Abstract

131.4  Tuesday, Jan. 7 14:15  Energetic regulation of seasonal sickness responses in Siberian hamsters (Phodopus sungorus) CARLTON, E.D.*; DEMAS, G.E.; Indiana Univ., Bloomington; Indiana Univ., Bloomington elcarlto@indiana.edu

The acute phase response is one of the first responses to infection and is accompanied by behavioral and physiological manifestations of sickness. Sickness is an adaptive response generated to clear pathogens but carries great energetic costs. Seasonally breeding species exhibit variation in sickness responses. Sickness intensity tracks an animal’s energetic state and is attenuated in the season in which an animal has the lowest fat stores. Energetic state may be signaled via leptin, a hormone that provides a signal of fat stores. Siberian hamsters are seasonal breeders that respond to short, winter-like days (SDs) by reducing food intake, fat stores, and leptin levels, relative to those in long, summer-like days (LDs). Sickness is also attenuated in hamsters exposed to SDs as compared to LDs. We hypothesized that leptin provides a physiological signal by which animals modulate sickness responses, such that animals with higher leptin levels show increased sickness intensity. To test this, we provided SD hamsters with a LD-like leptin signal and assessed their responses to lipopolysaccharide (LPS), a sickness-inducing antigen. We compared this response to SD-control, LD-control, and LD-leptin treated hamsters. Surprisingly, hamsters in all groups exhibited a hypothermic response to LPS rather than fever. However, the SD-controls exhibited the greatest hypothermia, and leptin attenuated this response in SD hamsters, making hypothermia more LD-like. Alternatively, SD-leptin treated animals showed the least pronounced LPS-induced anorexia among all groups. These results suggest that leptin signals may mediate some, but not all, aspects of seasonal sickness variation and have prompted research into how other energetic signals may influence seasonal modulation of sickness.