Meeting Abstract

P1.151  Wednesday, Jan. 4  Leptin and seasonal variation in sickness responses in Siberian hamsters (Phodopus sungorus) CARLTON, E.D.*; DEMAS, G.E.; Indiana University, Bloomington; Indiana University, Bloomington

Sickness behaviors (e.g. fever, anorexia) characterize an adaptive response generated by an organism to aid in clearance of pathogens. However, these behaviors are energetically costly, and the magnitude to which organisms display these behaviors varies seasonally. One hypothesis regarding this seasonal variation is that the intensity of the sickness response may track the energetic state of an organism, such that the response is attenuated in the season in which an animal has the lowest fat stores. Energetic state may be signaled via leptin, a peptide hormone that is produced by body fat in direct proportion with tissue mass. Siberian hamsters respond to short, winter-like days by reducing food intake and thus, decreasing fat stores and circulating leptin levels. Previous work in this species has demonstrated that sickness behavior is attenuated in animals exposed to short photoperiods compared with long, summer-like photoperiods. We hypothesized that circulating leptin provides a physiological signal by which animals modulate sickness responses. To test this, we housed male Siberian hamsters in long-day (LD) or short-day (SD) photoperiods for 10 weeks and collected baseline food intake and body mass measurements for 10 days. Next, we provided LD and SD hamsters with daily injections of leptin (or saline control), to provide SD animals with a LD-like leptin signal. After 6 days of injections, animals were inoculated with lipopolysaccharide (LPS), to induce a sickness response, or a saline control. Data (i.e. body temperature, food intake, body mass, and blood serum levels of cortisol and cytokines) will be presented and discussed in regards to the effects of photoperiod manipulation and leptin supplementation on the modulation of the sickness response.