Figure 3
Effects of central administration of recombinant mouse interleukin-6 (IL-6) to Swiss Webster mice. (a) IL-6 produced dose-dependent increases in immobility time in the tail suspension and (b) forced swim tests indicative of a depressive-like effect (*P<0.05 vs vehicle-treated control; n=9–15 per treatment group). (c) IL-6 did not produce increases in sickness behavioral score at doses that produce depressive-like behaviors. (d) Central administration of recombinant mouse IL-6 produced significant increases in IL-6 protein levels in the cortex of mice as measured via multiplex enzyme-linked immunosorbent assay (ELISA) (*P<0.05; n=4–6 per treatment group). (e) IL-1β protein levels were not significantly elevated in the cortex following central administration of recombinant mouse IL-6 as measured via multiplex ELISA (*P>0.05; n=4–6 per treatment group). (f) A single dose of 1 μg recombinant mouse IL-6 (intracerebroventricularly (i.c.v.)) produces significant increases in immobility time in the tail suspension test up to 48 h post administration, indicative of a sustained depressive-like effect (*P<0.05 vs vehicle-treated control at each timepoint; n=6–12 per treatment group per timepoint). Twenty-four hour pretreatment of recombinant mouse IL-6 into the left lateral ventricle (1 μg, i.c.v.) produces significant increases in IL-6 protein levels across brain regions relative to vehicle-infused controls as demonstrated in (g) the hippocampus, (h) the hypothalamus, (i) the frontal cortex and (j) nonsignificant increases in the striatum (*P<0.05 vs vehicle; n=4 per treatment group per brain region). (k) Central administration of IL-6 (24 h pretreatment) produced reductions in social interaction behavior as measured by investigation time of an intact female stimulus mouse relative to vehicle-treated controls (*P<0.05 vs vehicle-treated control within trial analysis; n=16–17 per treatment group), with no significant differences in initial reaction to a female stimulus mouse (latency) indicating no impairment in general exploratory behavior in IL-6-treated mice relative to vehicle-treated controls.
