Prior intraperitoneal injection of rat recombinant IL-6 increases hypothalamic IL-6 contents in subsequent forced swim stressor in rats.
BACKGROUND
Cytokines do not only mediate responses to infection, but are also involved in behavioral and physiological responses to psychological stressors. IL-6 has received special attention in relation to the development of posttraumatic stress disorders and depression.


OBJECTIVE
We tested effects of prior injection of rat recombinant IL-6 (rrIL-6) on behaviors induced by the forced swim (FS) stressor, and central and peripheral responses of IL-6 to FS.


METHODS
Rats were injected intraperitoneally with either rrIL-6 (250 ng/0.5 ml) or equal-volume sterile saline twice within an interval of 24 h. One hour after each injection, the rats were exposed to FS or remained at the home cage (control).


RESULTS
Injection of rrIL-6 did not affect immobility, swimming or climbing behaviors during FS compared with the saline control. Although FS was not a significant factor for hypothalamic and midbrain IL-6 mRNA and plasma IL-6 responses, FS with prior administration of rrIL-6 significantly increased hypothalamic IL-6 contents in response to FS compared with the saline injection-FS condition.


CONCLUSIONS
Our results suggested that stressor alone had no influence on plasma IL-6 levels and IL-6 mRNA expression levels in midbrain and hypothalamus, but administration of rrIL-6 followed by FS significantly increased hypothalamic IL-6. Our results support the notion that the interaction between IL-6 and stressor might have implications for the pathophysiology of IL-6-induced depressive symptoms.
Matsumoto
Takuya
T
Department of Psychiatry, Division of Neuroscience, Institute of Medical Science, Mie University Graduate School of Medicine, Tsu, Japan. matutaku@clin.medic.mie-u.ac.jp
Komori
Teruhisa
T
Yamamoto
Masato
M
Shimada
Yasuhito
Y
Nakagawa
Masanori
M
Shiroyama
Takashi
T
Inui
Koji
K
Okazaki
Yuji
Y
D000818:Animals; D007031:Hypothalamus / Q000276:immunology / Q000378:metabolism*; D007274:Injections, Intraperitoneal; D015850:Interleukin-6 / Q000008:administration & dosage / Q000235:genetics / Q000378:metabolism*; D008297:Male; D008636:Mesencephalon / Q000276:immunology / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins; D013315:Stress, Psychological / Q000276:immunology / Q000378:metabolism*; D013550:Swimming / Q000502:physiology / Q000523:psychology
D015850:Interleukin-6; D012333:RNA, Messenger; D011994:Recombinant Proteins