Effects of melatonin injections on plasma corticosterone rhythms in Fischer 344 rats.

<p>Rats maintained under long-day condition (LD, 16 h of light, 8 h of darkness) were daily injected either vehicle (<i>white bars</i>) or melatonin (<i>shaded bars</i>) at late afternoon for 3 weeks. The other group of rats was maintained under short-day condition (SD, 8 h of light, 16 h of darkness, <i>black bars</i>). Plasma concentrations of corticosterone at Zeitgeber time (ZT: ZT0 corresponds to the light onset) 2 and 10 are shown. Values are means + SEM (n=4–5). **, <i>P</i><0.01, <i>t</i>-test. Different characters indicate significant differences among the levels at ZT10 (one-way ANOVA followed by Bonferroni's multiple comparison test, <i>P</i><0.05).