Sleep, but not febrile responses of Fisher 344 rats to immune challenge are affected by aging

Sleep is altered in response to infection and immune challenge in humans and non-human animals. Although there are changes in sleep and facets of immune function with aging, sleep responses of aged subjects to immune challenge have received little, if any attention. To test the hypothesis that aging affects sleep responses to immune challenge, intracerebroventricular injections of interleukin 1 (IL-1) were given to young and aged rats and subsequent sleep-wake behavior was determined. Under basal conditions and in the absence of an immune challenge, sleep patterns of young (3 months) and aged (25–27 months) Fisher 344 rats did not differ. In young animals, IL-1 (2.5 ng) enhanced non-rapid eye movement (NREM) sleep, inhibited rapid eye movement (REM) sleep, and induced fever. In aged animals, IL-1 administration did not alter NREM sleep, but REM sleep was inhibited and brain temperature increased to the same extent observed in young animals. These results show that alterations in sleep following immune challenge are impacted by aging, whereas febrile responses are not. Since it has been postulated that enhanced NREM sleep may facilitate recovery from microbial infection, the present results also suggest that the lack of NREM sleep responses of aged rats to immune challenge may contribute to the increased infection-induced morbidity and mortality of aged organisms.