Elsevier

Hormones and Behavior

Volume 60, Issue 3, August 2011, Pages 284-291
Hormones and Behavior

Thyroid hormone regulation by stress and behavioral differences in adult male rats

https://doi.org/10.1016/j.yhbeh.2011.06.003Get rights and content

Abstract

Thyroid hormones are essential regulators of growth, development and normal bodily function and their release is coordinated by the hypothalamic–pituitary–thyroid (HPT) axis. While the HPT axis has been established as an acutely stress-responsive neuroendocrine system, relatively little is known about the mechanisms of its stress regulation. The present study examined acute stress-induced changes in peripheral hormone levels [triiodothyronine (T3); thyroxine (T4), thyroid-stimulating hormone (TSH), reverse triiodothyronine (rT3)] and central mRNA levels of regulators of the HPT axis [thyrotropin-releasing hormone (TRH), somatostatin (SST), type II deiodinase (D2)] in response to an inescapable tail-shock, a rodent model of stress. Additionally, we examined whether individual differences in spontaneous exploratory behavior in an open field test predicted basal levels of TH or differential susceptibility to the effects of stress. The stress condition was associated with decreases in peripheral T3, T4 and TSH, but not rT3, when compared with controls. No changes were observed in TRH or SST mRNA levels, but there was a trend suggesting stress-related increases in D2 mRNA. We also found that an animal's exploratory behavior in an unfamiliar open field arena was positively related to peripheral thyroid hormone levels and predicted the magnitude of stress-induced changes.

In conclusion, we found suggestive evidence for stress-induced decrease in central drive HPT axis, but the central mechanisms of its stress regulation remain to be elucidated. Additionally, we found that individual differences in animals' exploratory behavior were correlated with peripheral TH levels.

Research highlights

► In male rats, acute stress causes a decrease in thyroid hormones within 120 min. ► Hormone changes were not associated with alterations in PVN TRH mRNA levels. ► Thyroid hormone levels are correlated with an animal's exploratory drive.

Section snippets

Animals

Seventy-five adult male Sprague–Dawley rats (Charles River Laboratories), body weight 250–310 g at the beginning of the stress sessions were used for this study. All animals were housed two per tub in 40 × 18 × 20 cm tubs. Lights were on 0730 to 1930 h and food and water were available ad libitum. All animals were acclimated to the housing facility for at least 5 days before testing. Within each tub, each animal was randomly assigned to either the inescapable tail-shock stress group or control group.

Stress paradigm

A

Experiment 1

As shown in Fig. 1, we found that 80 trials of inescapable tail-shock stress caused a decrease in peripheral TH levels. Specifically for T3, a two-way ANOVA revealed a significant main effect for stress (F(1, 66) = 8.75, p < .01). Bonferroni-corrected post-hoc tests indicated that this decrease was significant at 120 min post-stress initiation (Fig. 1A). Stress also caused a significant decrease in circulating levels of T4, indicated by a significant stress x time interaction (F(4, 66) = 3.32, p < .01;

Discussion

In the current series of experiments, we sought to further characterize acute stress-induced changes in HPT axis function and to also determine if TH levels are correlated with an animals' spontaneous behavior. In Experiment 1 we replicated our previous results, showing that acute stress can cause a decrease in circulating T3 levels within 120 min post-stress initiation (Helmreich et al., 2006). We extended these findings by demonstrating that acute stress also causes a decrease in circulating T4

Acknowledgments

We would like to thank the vivarium staff at the University of Rochester for their excellent animal care and James Walton for his excellent technical assistance. Daniel Tylee earned course credit and received an undergraduate research grant from SUNY Geneseo to support his work on these experiments. This work was supported by the Department of Psychiatry at the University of Rochester, and grant MH1R03MH080789 to DLH. The authors appreciate the thoughtful comments from Drs. R. Ader, J. Fudge,

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