BEHAVIORAL-EFFECTS OF PERIPHERAL INTERLEUKIN-1 ADMINISTRATION IN ADULT CD-1 MICE - SPECIFIC-INHIBITION OF THE OFFENSIVE COMPONENTS OF INTERMALE AGONISTIC BEHAVIOR

Peripheral administration of interleukin-1 beta (IL-1 beta) in rodents reduces exploratory behavior in a novel environment while decreasing social investigation of a juvenile conspecific. In this study we wante d to test the effects of peripherally administered IL-1 beta on anothe r aspect of the mouse social repertoire, namely intraspecific fighting towards an adult male intruder. In the first experiment, sickness beh avior induced by IL-1 beta (1 mu g/mouse) in adult CD-1 mice was asses sed by direct observation of behavioral changes following placement in to a novel environment. Three hours after injection, subjects were ind ividually introduced for 20 min in a cage with clean sawdust and a num ber of behavioral items recorded. Blood samples were collected at the end of the testing session. Body temperature was measured right before , 1 h and 3.5 h following injection. In IL-1 beta treated mice, explor ation (assessed by measuring duration and frequency of Wall Rearing an d Rearing behaviors) was nearly totally suppressed, while duration and frequency of behaviors such as Grooming, Bar Holding, and Digging wer e also markedly reduced. Administration of IL-1 beta significantly ele vated CORT secretion above basal levels and, as previously reported fo r mice, induced hypothermia (about 2 degrees C). In the second experim ent, we assessed mice receiving IL-1 beta (0.25; 0.5 or 1 mu g/mouse o r saline solution) in a social context. Three hours after injection, s ubjects were placed into a neutral cage for 20 min with a non-injected adult male conspecific and aggressive behavior scored. Overall, IL-1 beta administration affected the social repertoire of treated mice in a dose-dependent fashion. Specifically, agonistic components of aggres sive behavior were nearly totally suppressed, while the defensive elem ents, such as Upright Defensive posture, Upright Submissive posture, C rouching, or Flee were not affected by IL-1 beta. Overall these data s upport the notion that sickness behavior induced by IL-1 beta administ ration represents an organized behavioral strategy and is not an aspec ific response to an illness-type of condition. (C) 1998 Elsevier Scien ce B.V.