Figure 1.

Elevations of interleukin-6 (IL-6) in rat cortex are a key feature of depressive-like behavior induced by stress. (a) Sprague–Dawley rats exposed to inescapable footshock (n=18) demonstrated helpless behavior indicated by an increase in the % of response failures in an active-avoidance paradigm relative to sham controls (n=12). A subset of rats subjected to inescapable footshock were resilient to the effects of inescapable footshock (n=5). (b) Protein levels of IL-6 were increased in the cortex of helpless rats relative to sham controls in the absence of elevations in IL-1β, while a trend for reduced IL-6 was observed in the resilient cohort (n=3–4 per treatment group). (c) Dominant–submissive relationships observed over a 6-week period in rats competing for a food reward (n=6 per group). (d) No significant increases in IL-6 or IL-1β in the cortex of submissive subjects relative to dominant subjects (n=6 per treatment group). (e) In competing pairs in which the hierarchy was unstable and rats continued to fight for dominance, both subjects of the pair demonstrated significant elevations of IL-6 in the absence of IL-1β in the cortex relative to pairs in which dominance level was stable (*P<0.05; n=6 per treatment group).