NREM sleep is increased in high-aggressive, but not in non-aggressive rats by an immune challenge

Abstract

Sleep is altered in response to an immune challenge: NREM sleep is increased and fragmented, REM sleep is inhibited. Different levels of trait aggressiveness are associated with specific patterns of neuroendocrine and autonomic stress responsiveness. Sleep and immune response are affected by stress. Aim of the present study was to test the hypothesis that sleep patterns are differentially affected by an immune challenge in animals that differ widely for aggression. High-aggressive (HA, n = 7) and non-aggressive (NA, n = 8) rats were selected on the basis of their latency time to attack a male intruder in the resident-intruder test. Afterwards, they were instrumented for chronic polygraphic recording of sleep-wake patterns and kept on a 12:12 h light:dark cycle. At dark onset, on different days, each rat was intraperitoneally injected with pyrogen free saline (vehicle, VEH) and 250 microgram/kg lipopolysaccharide. In HA rats, lipopolysaccharide administration induced a significant and long lasting (from hour 3 to hour 8 post-injection) increase (in comparison to VEH administration) in NREM sleep, and a biphasic fever. No changes in NREM sleep, and only a short lasting fever were induced by lipopolysaccharide administration in NA rats. REM sleep was inhibited in both HA and NA rats, but with a different time course. Results show that sleep and febrile responses to an immune challenge are different in HA and NA rats.