Influence of chronic interleukin-2 infusion and stressors on sickness behaviors and neurochemical change in mice.
OBJECTIVE
Major depression is associated with increased circulating interleukin-2 (IL-2) levels, and IL-2 immunotherapy may provoke depressive symptoms, leading to the suggestion that this cytokine may contribute to the evolution of affective disorders. Although depression is a relatively chronic condition, and immunotherapy involves repeated cytokine administration, animal studies have typically assessed the consequences of acute cytokine treatment. The present investigation assessed several behavioral and neurochemical effects of chronic IL-2 infusion.


METHODS
Behaviors reflecting anhedonia and/or anorexia, sickness behavior, plasma corticosterone and norepinephrine (NE) activity in the paraventricular nucleus (PVN) of the hypothalamus were assessed following continuous infusion of IL-2 over 7 days in CD-1 mice.


RESULTS
The cytokine treatment reduced the consumption of a highly favored palatable substance (chocolate milk) and reduced locomotor activity monitored over the course of the 7-day period. Although sickness behaviors were also increased significantly by the treatment, the degree of sickness behavior was actually modest. While a chronic, variable stressor also affected consumption of the palatable food, this treatment did not enhance the effects of IL-2. Furthermore, in contrast to acute and chronic stressors that increased plasma corticosterone levels and the utilization of NE within the PVN of the hypothalamus, IL-2 did not promote such effects and did not modify the impact of the stressors.


CONCLUSIONS
While IL-2 may induce anorexia or anhedonia, the effects of this treatment are distinguishable from those elicited by stressors and those typically elicited by proinflammatory cytokines. The data are related to findings suggesting a link between IL-2 and depressive illness.
Institute of Neuroscience, Carleton University, Ottawa, Ont. K 1S 5B6, Canada.
Kerry
K
Sudom
Nicolas P
NP
Turrin
Shawn
S
Hayley
Hymie
H
Anisman
D000208:Acute Disease; D000818:Animals; D000855:Anorexia / Q000276:immunology* / Q000503:physiopathology*; D001522:Behavior, Animal; D015306:Biogenic Monoamines / Q000378:metabolism; D001921:Brain / Q000276:immunology / Q000378:metabolism; D002099:Cacao; D002908:Chronic Disease; D003345:Corticosterone / Q000097:blood; D003863:Depression / Q000276:immunology; D007376:Interleukin-2 / Q000097:blood / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008892:Milk; D009043:Motor Activity / Q000187:drug effects; D015213:Neuroimmunomodulation / Q000187:drug effects / Q000276:immunology*; D013312:Stress, Physiological / Q000276:immunology
D015306:Biogenic Monoamines; D007376:Interleukin-2; D003345:Corticosterone