Acute stress increases thyroid hormone levels in rat brain

Background: In experimental animals, exposure to uncontrollable stress induces a number of behavioral and biochemical changes that resemble symptoms seen in human depression and other psychiatric conditions. The present study used a yoked design to examine the effects of uncontrollable footshock stress on brain thyroid hormones in male and female rats. Methods: Animals in one group received 15 trials where footshock could be terminated by pressing a lever (escapable shock). Rats in a second group received the same amount of shock, but had no control over shock termination (inescapable shock). Control rats received no shock. Results: No significant differences were found among the three groups, for either males or females, in whole brain levels of thyroxine (T4) 3 hours after the footshock session. In contrast, significant group differences in brain levels of triiodothyronine (T3) were found for both males and females. In males, brain T3 was elevated by 21% in the inescapable shock group when compared to controls (p< .012). In females, brain T3 increased by 19% in the escapable shock group when compared to controls (p< .026). Plasma levels of both T3 and T4 were at control levels for all groups. Conclusions: These results provide the first demonstration that brain T3 levels change rapidly in response to acute stress. The data further suggest that the effects of stress controllability on brain T3 levels may be different for males and females.