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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., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Understanding environmental effects on mouse brain development would allow us to take advantage of powerful genetic tools to determine the interaction between genetic and epigenetic factors governing brain development in C57BL/6 mice. Experiment 1 examined whether time of day for neonatal manipulations affects adult stress-induced hormone secretion. Three rearing groups were examined: early handled (EH; dam removed 10 min/day); maternal separated (MS; dam removed 180 min/day); and an animal facility raised (AFR) control. Separations occurred during either the first or last 3 h of the light phase. Corticosterone (CORT) secretion in response to 100 dB white noise was assessed in adulthood. Both EH and MS males separated during the last 3 h of the light phase exhibited blunted stress-induced CORT compared to all other groups. Experiment 2 varied time of behavior testing. A fourth group was also added: maternal isolated (MI; separated from dam and littermates 180 min/day). Adult male behavior was assessed in three different tests. EH males tested in the elevated zero maze (EZM) during the light phase and MS males tested in the EZM during the dark phase exhibited diminished anxiety-like behavior compared to the other groups. We conclude that the EH protocol is marginally effective in blunting stress-induced CORT secretion and anxiety-like behavior in C57BL/6 mice, and these early handling effects are influenced by time of day. We also conclude that the 3 h MS or MI protocol is not effective in exacerbating future adult stress-induced CORT secretion or anxiety-like behavior in C57BL/6 mice.

Stress decreases sexual activity, but it is uncertain which aspects of stress are detrimental to reproduction. This study used an escapable/inescapable stress paradigm to attempt to dissociate physical from psychological components of stress, and assess each component's impact on reproductive behavior in the male Syrian hamster (Mesocricetus auratus). Two experiments were completed using this protocol where two animals receive the same physical stressor (an electric footshock) but differ in the psychological aspect of control. One group (executive) could terminate the shock for themselves as well as a second group (yoked) by pressing a bar. Experiment 1 demonstrated a significant increase in plasma glucocorticoids at the end of a single 90-min stress session with no difference in glucocorticoid levels between the executive and yoked groups at any time point. Experiment 2 quantified male reproductive behavior prior to and immediately following 12 days of escapable or inescapable stress in executive, yoked, and no-stress control hamsters (n = 12/group). Repeated-measures analysis of variance revealed a number of significant changes in reproductive behavior before and after stress in the three treatment groups. The most striking difference was a decrease in hit rate observed only in the animals that could not control their stress (yoked group). Hit rate in the executive males that received the exact same physical stressor but could terminate the shock by pressing a bar was nearly identical to control animals that never received any foot shock. Therefore, we conclude that coping or control can ameliorate the negative effects of stress on male reproductive behavior.