The effect of gonadotropin-inhibitory hormone on steroidogenesis and spermatogenesis by acting through the hypothalamic-pituitary-testis axis in mice

Gonadotropin inhibitory hormone (GnIH) is essential for regulating the reproduction of mammals and inhibiting testicular activities in mice. This study aimed to explore the mechanism of GnIH on spermatogenesis and steroidogenesis by acting through the hypothalamus-pituitary-testis axis of mice. Mice were subcutaneously injected with different doses of GnIH (1 μg/150 μL, 3 μg/150 μL, 6 μg/150 μL, 150 μL saline, twice daily) for 11 days. Subsequently, luteinizing hormone (LH), testosterone (T), and inhibin B (INH B) levels of peripheral blood were determined, and the expression of GnRH synthesis-related genes (GnRH-1, Kiss-1, NPY) and gonadotropin synthesis-related genes (FSH β, LH β, GnRH receptor) in the hypothalamus and pituitary gland were respectively detected. Additionally, the expression of steroidogenesis-related genes/proteins (P450scc, StAR and 3β-HSD) and spermatogenesis-related proteins/genes including LH receptor (LHR), androgen receptor (AR), heat shock factor-2 (HSF-2) and INH B were analyzed using western blot and q-PCR. Results showed that GnIH treatment significantly reduced the concentration of LH in the peripheral blood. Further analysis revealed that GnIH treatment markedly reduced the expression of GnRHImRNA and Kiss-1 mRNA in the hypothalamus, and mRNA levels of FSH β, LH β, and GnRHR genes in the pituitary. We also observed that GnIH treatment significantly decreased T levels and expression of the P450scc, StAR, and 3β-HSD proteins in the testis. Furthermore, GnIH treatment down-regulated LHR, AR proteins, and HSF-2 gene in the testis. Importantly, the INH B concentration of and INH βb mRNA levels significantly declined following GnIH treatment. Additionally, GnIH treatment may induce germ cell apoptosis in the testis of mice. In conclusion, GnIH may suppress spermatogenesis and steroidogenesis by acting through the hypothalamus-pituitary-testis axis in mice.

Molecular mechanisms of hypothalamic-pituitary-ovarian/thyroid axis regulating age at first egg in geese

Age at first egg (AFE) has consistently garnered interest as a crucial reproductive indicator within poultry production. Previous studies have elucidated the involvement of the hypothalamic-pituitary-ovarian (HPO) and hypothalamic-pituitary-thyroid (HPT) axes in regulating poultry sexual maturity. Concurrently, there was evidence suggesting a potential co-regulatory relationship between these 2 axes. However, as of now, no comprehensive exploration of the key pathways and genes responsible for the crosstalk between the HPO and HPT axes in the regulation of AFE has been reported. In this study, we conducted a comparative analysis of morphological differences and performed transcriptomic analysis on the hypothalamus, pituitary, thyroid, and ovarian stroma between normal laying group (NG) and abnormal laying group (AG). Morphological results showed that the thyroid index difference (D-) value (thyroid index D-value=right thyroid index-left thyroid index) was significantly (P < 0.05) lower in the NG than in the AG, while the ovarian index was significantly (P < 0.01) higher in the NG than in the AG. Furthermore, between NG and AG, we identified 99, 415, 167, and 1182 differentially expressed genes (DEGs) in the hypothalamus, pituitary, thyroid, and ovarian stroma, respectively. Gene ontology (GO) analysis highlighted that DEGs from 4 tissues were predominantly enriched in the "biological processes" category. Additionally, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that 16, 14, 3, and 26 KEGG pathways were significantly enriched (P < 0.05) in the hypothalamus, pituitary, thyroid, and ovarian stroma. The MAPK signaling pathway emerged as the sole enriched pathway across all 4 tissues. Employing an integrated analysis of the protein-protein interaction (PPI) network and correlation analysis, we found GREB1 emerged as a pivotal component within the HPO axis to regulate estrogen-related signaling in the HPT axis, meanwhile, the HPT axis influenced ovarian development by regulating thyroid hormone-related signaling mainly through OPN5. Then, 10 potential candidate genes were identified, namely IGF1, JUN, ERBB4, KDR, PGF, FGFR1, GREB1, OPN5, DIO3, and THRB. These findings establish a foundation for elucidating the physiological and genetic mechanisms by which the HPO and HPT axes co-regulate goose AFE.

Analyses of mRNA Expression Levels of Pituitary Hormones, Their Hypothalamic Regulating Factors, and Receptors Involved in Metamorphosis with Special Reference to the Summer and Winter Seasons

Bullfrog (Rana catesbeiana) larvae inhabiting the main island of Japan overwinter as preclimax animals, whereas the larvae that reached climax in summer complete metamorphosis. We analyzed the mRNA expression levels of the adenohypophyseal hormones, hypothalamic hormones, and their receptors that are involved in controlling metamorphosis in tadpoles at various developmental stages available in summer and winter in order to understand the hormonal mechanism regulating metamorphosis progression. Corticotropin-releasing factor (CRF) and thyrotropin β-subunit (TSHβ) mRNA expression was enhanced as they reached the climax stage in metamorphosing summer tadpoles, although type 2 CRF receptor (CRFR2) mRNA levels demonstrated a tendency of elevation, indicating the activation of the hypothalamo-hypophyseal axis for stimulating the release of thyroid hormone in summer. Arginine vasotocin (AVT) mRNA levels were elevated as metamorphosis progressed, but mRNA expression levels were not synchronized with those of proopiomelanocortin (POMC) and V1b-type AVT receptor (V1bR). The elevation of mRNA levels of prolactin (PRL) 1A and type 3 thyrotropin-releasing hormone receptor (TRHR3), but not of thyrotropin-releasing hormone (TRH) precursor mRNA levels, was noted in climactic tadpoles, indicating that PRL mRNA levels are not simply dependent on the expression levels of TRH precursor mRNA. In the preclimactic larvae captured in winter, which are in metamorphic stasis, mRNA levels of pituitary hormones, hypothalamic factors, and their receptors remained low or at levels similar to those of the larvae captured in summer. These results indicate the relationship between the mRNA expression of metamorphosis-related factors and the seasonal progression/stasis of metamorphosis.

The association between neuroendocrine/glucose metabolism and clinical outcomes and disease course in different clinical states of bipolar disorders

Objective

The treatment of bipolar disorder (BD) remains challenging. The study evaluated the impact of the hypothalamic-pituitary-adrenal (HPA) axis/hypothalamic-pituitary-thyroid (HPT) axis and glucose metabolism on the clinical outcomes in patients with bipolar depression (BD-D) and manic bipolar (BD-M) disorders.

Methods

The research design involved a longitudinal prospective study. A total of 500 BD patients aged between 18 and 65 years treated in 15 hospitals located in Western China were enrolled in the study. The Young Mania Rating Scale (YMRS) and Montgomery and Asberg Depression Rating Scale (MADRS) were used to assess the BD symptoms. An effective treatment response was defined as a reduction in the symptom score of more than 25% after 12 weeks of treatment. The score of symptoms was correlated with the homeostatic model assessment of insulin resistance (HOMA-IR) index, the HPA axis hormone levels (adrenocorticotropic hormone (ACTH) and cortisol), and the HPT axis hormone levels (thyroid stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), free triiodothyronine (fT3), and free thyroxine (fT4)).

Results

In the BD-M group, the YMRS was positively correlated with baseline T4 (r = 0.349, p = 0.010) and fT4 (r = 0.335, p = 0.013) and negatively correlated with fasting insulin (r = -0.289, p = 0.013). The pre-treatment HOMA-IR was significantly correlated with adverse course (p = 0.045, OR = 0.728). In the BD-D group, the baseline MADRS was significantly positively correlated with baseline fT3 (r = 0.223, p = 0.032) and fT4 (r = 0.315, p = 0.002), while baseline T3 (p = 0.032, OR = 5.071) was significantly positively related to treatment response.

Conclusion

The HPT axis and glucose metabolism were closely associated with clinical outcomes at 12 weeks in both BD-D and BD-M groups. If confirmed in further longitudinal studies, monitoring T3 in BD-D patients and HOMA-IR for BD-M could be used as potential treatment response biomarkers.

Harnessing the power of nutritional antioxidants against adrenal hormone imbalance-associated oxidative stress

Oxidative stress, resulting from dysregulation in the secretion of adrenal hormones, represents a major concern in human health. The present review comprehensively examines various categories of endocrine dysregulation within the adrenal glands, encompassing glucocorticoids, mineralocorticoids, and androgens. Additionally, a comprehensive account of adrenal hormone disorders, including adrenal insufficiency, Cushing's syndrome, and adrenal tumors, is presented, with particular emphasis on their intricate association with oxidative stress. The review also delves into an examination of various nutritional antioxidants, namely vitamin C, vitamin E, carotenoids, selenium, zinc, polyphenols, coenzyme Q10, and probiotics, and elucidates their role in mitigating the adverse effects of oxidative stress arising from imbalances in adrenal hormone levels. In conclusion, harnessing the power of nutritional antioxidants has the potential to help with oxidative stress caused by an imbalance in adrenal hormones. This could lead to new research and therapeutic interventions.

Effects of norethindrone on the growth, behavior, and thyroid endocrine system of adult female western mosquitofish (Gambusia affinis)

Progestins are mainly used in pharmacotherapy and animal husbandry and have received increasing attention as they are widely detected in various aquatic ecosystems. In this study, adult female western mosquitofish (Gambusia affinis) were exposed to different concentrations of norethindrone (NET) (solvent control, 5.0 (L), 50.0 (M), and 500.0 (H) ng/L) for 42 days. Behaviors, morphological parameters, histology of the thyroid, thyroid hormone levels (TSH, T3, and T4), and transcriptional levels of nine genes in the hypothalamic-pituitary-thyroid (HPT) axis were examined. The results showed that NET decreased sociality but increased the anxiety of G. affinis. Sociality makes fish tend to cluster, and anxiety may cause G. affinis to reduce exploration of new environments. Female fish showed hyperplasia, hypertrophy, and glial depletion in their thyroid follicular epithelial cells after NET treatment. The plasma levels of TSH and T4 were significantly reduced, but T3 concentrations were significantly increased in the fish from the H group. In addition, the transcripts of genes (tshb, tshr, tg, dio1, dio2, thrb) in the brains of fish in the M and H treatments were significantly stimulated, while those of trh and pax2a were suppressed. Our results suggest that NET may impact key social behaviors in G. affinis and interfere with the entire thyroid endocrine system, probably via affecting the transcriptional expression of upstream regulators in the HPT axis.

Environmentally relevant concentrations of Mn2+ disrupts the endocrine regulation of growth in juvenile Yunlong groupers (Epinephelus moara♀×Epinephelus lanceolatus♂)

Even though manganese is a bioelement essential for metabolism, excessive manganese levels in water can be detrimental to fish development and growth. Therefore, the aim of this study was to evaluate the effects of Mn2+ (0, 0.5,1, 2, and 4 mg·L-1) exposure for 30 d on the growth performance, growth hormone/insulin-like growth factor (GH/IGF) axis, hypothalamic-pituitary-thyroid (HPT) axis, and monoaminergic neurotransmitters of Epinephelus moara♀×Epinephelus lanceolatus♂(Yunlong grouper). Compared with the control and low Mn2+concentration groups of (0.5 and 1 mg·L-1), the high concentration of Mn2+ (4 mg·L-1) significantly reduced body weight (BW), body length (BL), weight gain rate (WGR), and specific growth rate (SGR), increased the feed coefficient rate (FCR) and mortality of Yunlong groupers (P < 0.05). Further, the levels of GH and IGF, along with the expression of ghra and ghrb were significantly reduced after exposure to 2 and 4 mg·L-1 Mn2+for 30 d, whereas the expression of sst5 was significantly up-regulated after exposure to 2 and 4 mg·L-1 Mn2+for 20 and 30 days. Moreover, Mn2+exposure increased thyroid hormone (T3) and thyroid stimulating hormone (TSH) contents, accompanied by increased mRNA levels of dio1 and dio2, however, the T4 level was decreased. Finally, dopamine (DA) and serotonin (5-HT) levels significantly decreased after long-term exposure to higher concentrations of Mn2+, and the levels their metabolites changed as well, suggesting that the synthesis and metabolism of DA and 5-HT were affected. Accordingly, changes in the GH/IGF and HPT axes-related parameters may be the cause of growth inhibition in juvenile groupers under Mn2+ exposure, indicating that the relationship between endocrine disorder and growth inhibition should not be ignored.

Hypothalamus and Post-Traumatic Stress Disorder: A Review

Humans have lived in a dynamic environment fraught with potential dangers for thousands of years. While fear and stress were crucial for the survival of our ancestors, today, they are mostly considered harmful factors, threatening both our physical and mental health. Trauma is a highly stressful, often life-threatening event or a series of events, such as sexual assault, war, natural disasters, burns, and car accidents. Trauma can cause pathological metaplasticity, leading to long-lasting behavioral changes and impairing an individual's ability to cope with future challenges. If an individual is vulnerable, a tremendously traumatic event may result in post-traumatic stress disorder (PTSD). The hypothalamus is critical in initiating hormonal responses to stressful stimuli via the hypothalamic-pituitary-adrenal (HPA) axis. Linked to the prefrontal cortex and limbic structures, especially the amygdala and hippocampus, the hypothalamus acts as a central hub, integrating physiological aspects of the stress response. Consequently, the hypothalamic functions have been attributed to the pathophysiology of PTSD. However, apart from the well-known role of the HPA axis, the hypothalamus may also play different roles in the development of PTSD through other pathways, including the hypothalamic-pituitary-thyroid (HPT) and hypothalamic-pituitary-gonadal (HPG) axes, as well as by secreting growth hormone, prolactin, dopamine, and oxytocin. This review aims to summarize the current evidence regarding the neuroendocrine functions of the hypothalamus, which are correlated with the development of PTSD. A better understanding of the role of the hypothalamus in PTSD could help develop better treatments for this debilitating condition.

Thyroid and Aging

Older adults are more vulnerable to the negative effects of excess thyroid hormone and may even be protected by lower levels of thyroid hormone. The diagnosis and management of thyroid disease in older adults needs to account for aging-related changes in function and resilliance.

A biologically based computational model for the hypothalamic-pituitary-thyroid (HPT) axis in Xenopus laevis larvae

A biologically based computational model was developed to describe the hypothalamic-pituitary-thyroid (HPT) axis in developing Xenopus laevis larvae. The goal of this effort was to develop a tool that can be used to better understand mechanisms of thyroid hormone-mediated metamorphosis in X. laevis and predict organismal outcomes when those mechanisms are perturbed by chemical toxicants. In this report, we describe efforts to simulate the normal biology of control organisms. The structure of the model borrows from established models of HPT axis function in mammals. Additional features specific to X. laevis account for the effects of organism growth, growth of the thyroid gland, and developmental changes in regulation of thyroid stimulating hormone (TSH) by circulating thyroid hormones (THs). Calibration was achieved by simulating observed changes in stored and circulating levels of THs during a critical developmental window (Nieuwkoop and Faber stages 54-57) that encompasses widely used in vivo chemical testing protocols. The resulting model predicts that multiple homeostatic processes, operating in concert, can act to preserve circulating levels of THs despite profound impairments in TH synthesis. Represented in the model are several biochemical processes for which there are high-throughput in vitro chemical screening assays. By linking the HPT axis model to a toxicokinetic model of chemical uptake and distribution, it may be possible to use this vitro effects information to predict chemical effects in X. laevis larvae resulting from defined chemical exposures.

Discoveries Around the Hypothalamic-Pituitary-Thyroid Axis

Many members of the American Thyroid Association played prominent roles in discovering the various aspects of the hypothalamic-pituitary-thyroid axis. This axis is fundamental for maintaining the normal serum levels of circulating thyroid hormones (THs) and thus the euthyroid state. The pituitary glycoprotein hormone, thyrotropin (TSH), controls the activity of the thyroid gland. Thyrotropin-releasing hormone and the negative feedback mechanism of circulating TH regulate the synthesis and the secretion of TSH. The dynamic interplay of these two dominant mechanisms has essential effects on TSH release. Therefore, the finding of abnormal serum levels of TSH often indicates the presence of a disorder of thyroid gland function. A summary of key historical discoveries in the understanding of the hypothalamic-pituitary axis is presented.

The role of supporting and disruptive mechanisms of FT3 homeostasis in regulating the hypothalamic-pituitary-thyroid axis

BACKGROUND

Thyroid hormones are controlled by the hypothalamic-pituitary-thyroid (HPT) axis through a complex network of regulatory loops, involving the hormones TRH, TSH, FT4, and FT3. The relationship between TSH and FT4 is widely used for diagnosing thyroid diseases. However, mechanisms of FT3 homeostasis are not well understood.

OBJECTIVE

We used mathematical modelling to further examine mechanisms that exist in the HPT axis regulation for protecting circulating FT3 levels.

METHODS

A mathematical model consisting of a system of four coupled first-order parameterized non-linear ordinary differential equations (ODEs) was developed, accounting for the interdependencies between the hormones in the HPT axis regulation. While TRH and TSH feed forward to the pituitary and thyroid, respectively, FT4 and FT3 feed backward to both the pituitary and hypothalamus. Stable equilibrium solutions of the ODE system express homeostasis for a particular variable, such as FT3, if this variable stays in a narrow range while certain other parameter(s) and system variable(s) may vary substantially.

RESULTS

The model predicts that (1) TSH-feedforward protects FT3 levels if the FT4 production rate declines and (2) combined negative feedback by FT4 and FT3 on both TSH and TRH production rates keeps FT3 levels insensitive to moderate changes in FT4 production rates and FT4 levels. The optimum FT4 and FT3 feedback and TRH and TSH-feedforward ranges that preserve FT3 homeostasis were found by numerical continuation analysis. Model predictions were in close agreement with clinical studies and individual patient examples of hypothyroidism and hyperthyroidism.

CONCLUSIONS

These findings further extend the concept of HPT axis regulation beyond TSH and FT4 to integrate the more active sister hormone FT3 and mechanisms of FT3 homeostasis. Disruption of homeostatic mechanisms leads to disease. This provides a perspective for novel testable concepts in clinical studies to therapeutically target the disruptive mechanisms.

Protective effects of curcumin against thyroid hormone imbalance after gas explosion-induced traumatic brain injury via activation of the hypothalamic-pituitary-thyroid axis in male rats

Gas explosion (GE)-induced traumatic brain injury (TBI) can affect thyroid hormone (TH) homeostasis in miners. This study evaluated the effects of hepatic transthyretin and hypothalamic-pituitary-thyroid (HPT) axis on thyroids and explored the protective effect and mechanism of curcumin on GE-induced TBI. Thirty rats were randomly divided into three groups (10 per group): first group (control group)-rats received GE treatment once; second group (GE group)-rats received GE treatment (200 m from the source of the explosion once); third group (GE + Cur group)-rats received curcumin (Cur) by lavage at a dose of 100 mg/kg/day once every other day for 7 days after receiving GE. After GE, the pathological changes were analyzed by hemotoxylin and eosin staining, and the levels of serum reactive oxygen species (ROS), urine iodine (UI), THs, nuclear factor-kappa B (NF-κB), superoxide dismutase (SOD), glutathione peroxidase (Gpx), and malondialdehyde (MDA) were analyzed using ELISA. Expression of proteins in the HPT axis of rats was examined by immunohistochemistry and Western blotting. We found that GE could induce pathologic changes in rat thyroid and liver. Serum levels of THs, NF-κB and serum redox state became unbalanced in rats after GE. GE could inhibit the biosynthesis and biotransformation of THs by affecting key HPT axis proteins. Additionally, GE reduced the level of hepatic transthyretin. Serum THs levels and thyroid sections were almost recovered to normal after curcumin treatment. The aforementioned key HPT axis proteins in the curcumin group showed opposite expression trends. In summary, GE affected THs balance while curcumin can protect against these injury effects by affecting TH biosynthesis, biotransformation, and transport, and inducing oxidative stress and inflammatory responses.

Parental exposure to propiconazole at environmentally relevant concentrations induces thyroid and metabolism disruption in zebrafish (Danio rerio) offspring: An in vivo, in silico and in vitro study

Propiconazole is used against fungal growth in agriculture and is released into the environment, but is a potential health threat to aquatic organisms. Propiconazole induces a generational effect on zebrafish, although the toxic mechanisms involved have not been described. The aim of this study was to investigate the potential mechanisms of abnormal offspring development after propiconazole exposure in zebrafish parents. Zebrafish were exposed to propiconazole at environmentally realistic concentrations (0.1, 5, and 250 μg/L) for 100 days and their offspring were grown in control solution for further study. Heart rate, hatching rate, and body length of hatched offspring were reduced. An increase in triiodothyronine (T₃) content and the T₃/T₄ (tetraiodothyronine) ratio was observed, indicating disruption of thyroid hormones. Increased protein level of transthyretin (TTR) in vivo was consistent with the in silico molecular docking results and T₄ competitive binding in vitro assay, suggests higher binding affinity between propiconazole and TTR, more than with T₄. Increased expression of genes related to the hypothalamus-pituitary-thyroid (HPT) axis and altered metabolite levels may have affected offspring development. These findings emphasizes that propiconazole, even on indirect exposure, represents health and environmental risk that should not be ignored.

Exposure to enrofloxacin and depuration: Endocrine disrupting effect in juvenile grass carp (Ctenopharyngodon idella)

This study aimed to determine the effects of Enrofloxacin (ENR) exposure and depuration on the disruption of thyroid function and growth of juvenile grass carp (Ctenopharyngodon idella) as well as to assess the risk of ENR exposure to human health. Juvenile grass carp were treated with ENR solutions at different concentration gradients for 21 days and then depurated for 14 days. The results indicated ENR accumulation in the juvenile grass carp muscles, which persisted after depuration. In addition, exposure to ENR could alter growth by regulating the expression of genes associated with growth hormone/insulin-like growth factor (GH)/IGF) axis and the hypothalamic-pituitary-thyroid (HPT) axis. During ENR exposure, no significant changes in growth hormone levels were observed; however, a significant increase in the growth hormone level was noted. GH/IGF axis-related genes were upregulated after ENR exposure, and their expression levels remained high after depuration. Notably, a significant increase in the serum triiodothyronine (T3) and thyroxine (T4) levels coincided with the upregulation of HPT axis-related genes in both exposure and depuration treatments, and their expression levels remained high after depuration. Therefore, juvenile grass carp exposure to ENR induces physiological stress through HPT and GH/IGF axes that cannot be recovered after depuration. ENR accumulates in the muscles of juvenile grass carp and may pose a threat to human health. Therefore, exposure of juvenile grass carp to ENR results in impaired thyroid function and impaired growth. In addition, consumption of ENR-exposed fish poses human health risks.

Subacute and low-dose tributyltin exposure disturbs the mammalian hypothalamus-pituitary-thyroid axis in a sex-dependent manner

Tributyltin (TBT) is an endocrine disruptor chemical (EDC) capable of altering the proper function of the hypothalamus-pituitary thyroid (HPT) axis. This study aimed to evaluate the subacute effects of TBT on the HPT axis of male and female rats. A dose of 100 ng/kg/day TBT was used in both sexes over a 15-day period, and the morphophysiology and gene expression of the HPT axis were assessed. TBT exposure increased the body weight in both sexes, while food efficiency increased - only in male rats. It was also possible to note alterations in the thyroid, with the presence of a stratified epithelium, cystic degeneration, and increased interstitial collagen deposition. A reduction in T3 and T4 levels was only observed in TBT male rats. A reduction in TSH levels was observed in TBT female rats. Evaluating mRNA expression, we observed a decrease in hepatic D1 and TRH mRNA levels in TBT female rats. An increase in D2 mRNA expression in the hypothalamus was observed in TBT male rats. Additionally, no significant changes in TRH or hepatic D1 mRNA expression in TBT male rats or in hypothalamic D1 and D2 mRNA expression in TBT female rats were observed. Thus, we can conclude that TBT has different toxicological effects on male and female rats by altering thyroid gland morphophysiology, leading to abnormal HPT axis function, and even at subacute and low doses, it may be involved in complex endocrine and metabolic disorders.

The Hypothalamic Paraventricular Nucleus Is the Center of the Hypothalamic-Pituitary-Thyroid Axis for Regulating Thyroid Hormone Levels

Background: Thyrotropin-releasing hormone (TRH) was the first hypothalamic hormone isolated that stimulates pituitary thyrotropin (TSH) secretion. TRH was also later found to be a stimulator of pituitary prolactin and distributed throughout the brain, gastrointestinal tract, and pancreatic β cells. We previously reported the development of TRH null mice (conventional TRHKO), which exhibit characteristic tertiary hypothyroidism and impaired glucose tolerance due to insufficient insulin secretion. Although in the past five decades many investigators, us included, have attempted to determine the hypothalamic nucleus responsible for the hypothalamic-pituitary-thyroid (HPT) axis, it remained obscure because of the broad expression of TRH. Methods: To determine the hypothalamic region functionally responsible for the HPT axis, we established paraventricular nucleus (PVN)-specific TRH knockout (PVN-TRHKO) mice by mating Trh floxed mice and single-minded homolog 1 (Sim1)-Cre transgenic mice. We originally confirmed that most Sim1 was expressed in the PVN using Sim1-Cre/tdTomato mice. Results: These PVN-TRHKO mice exhibited tertiary hypothyroidism similar to conventional TRHKO mice; however, they did not show the impaired glucose tolerance observed in the latter, suggesting that TRH from non-PVN sources is essential for glucose regulation. In addition, a severe reduction in prolactin expression was observed in the pituitary of PVN-TRHKO mice compared with that in TRHKO mice. Conclusions: These findings are conclusive evidence that the PVN is the center of the HPT axis for regulation of serum levels of thyroid hormones and that the serum TSH levels are not decreased in tertiary hypothyroidism. We also noted that TRH from the PVN regulated prolactin, whereas TRH from non-PVN sources regulated glucose metabolism.

Tanycyte specific ablation of diacylglycerol lipase alpha stimulates the hypothalamic-pituitary-thyroid axis by decreasing the endocannabinoid mediated inhibition of TRH release

In addition to the hypophysiotropic thyrotropin-releasing hormone (TRH)-synthesizing neurons, a glial cell type, the tanycytes, also play a role in the regulation of the hypothalamic-pituitary-thyroid (HPT) axis. Tanycytes modulate the feedback regulation of the axis by regulating the local thyroid hormone availability in the median eminence where the hypophysiotropic axons terminate. Recently, we showed that tanycytes produce diacylglycerol lipase alpha (DAGLα), the synthesizing enzyme of the endocannabinoid 2-arachidonoylglycerol (2-AG) that inhibits the release of TRH from the hypophysiotropic terminals in median eminence explants. To determine the importance of the endocannabinoid production of tanycytes, adult male Rax-CreERT2//DAGLα^fl/fl mice were treated with tamoxifen to induce a tanycyte specific decrease of DAGLα expression (T-DAGLα KO). The effect of this genetic manipulation on the activity of the HPT axis was determined. Tanycyte specific decrease of DAGLα expression resulted in an approximately 2-fold increase of TSHβ mRNA level that was accompanied by increased levels of circulating free T4. The TRH mRNA level was, however, not influenced by the genetic manipulation. In addition to the effects on the HPT axis, the T-DAGLα KO mice showed increased fat mass ratio and decreased blood glucose levels. These data indicate that when endocannabinoid release of tanycytes is decreased, the disinhibition of the TRH release induces increased TSH synthesis and higher circulating T4 levels. Thus it suggests that in wild-type mice, tanycytes exert a tonic inhibitory effect on the TRH release of hypophysiotropic axons. Furthermore, the endocannabinoid release of tanycytes also influences glucose homeostasis and fat deposition.

Maternal Prenatal Stress, Thyroid Function and Neurodevelopment of the Offspring: A Mini Review of the Literature

Fetal brain is extremely plastic and vulnerable to environmental influences that may have long-term impact on health and development of the offspring. Both the Hypothalamic-Pituitary-Adrenal (HPA) and the Hypothalamic-Pituitary-Thyroid (HPT) axes are involved in stress responses, whereas, their final effectors, the Glucocorticoids (GCs) and the Thyroid Hormones (TH s), mediate several fundamental processes involved in neurodevelopment. The effects of these hormones on brain development are found to be time and dose-dependent. Regarding THs, the developing fetus depends on maternal supply of hormones, especially in the first half of pregnancy. It is acknowledged that inadequate or excess concentrations of both GCs and THs can separately cause abnormalities in the neuronal and glial structures and functions, with subsequent detrimental effects on postnatal neurocognitive function. Studies are focused on the direct impact of maternal stress and GC excess on growth and neurodevelopment of the offspring. Of particular interest, as results from recent literature data, is building understanding on how chronic stress and alterations of the HPA axis interacts and influences HPT axis and TH production. Animal studies have shown that increased GC concentrations related to maternal stress, most likely reduce maternal and thus fetal circulating THs, either directly or through modifications in the expression of placental enzymes responsible for regulating hormone levels in fetal microenvironment. The purpose of this review is to provide an update on data regarding maternal stress and its impact on fetal neurodevelopment, giving particular emphasis in the interaction of two axes and the subsequent thyroid dysfunction resulting from such circumstances.

Dietary selenium promotes the growth performance through growth hormone-insulin-like growth factor and hypothalamic-pituitary-thyroid axes in grass carp (Ctenopharyngodon idella)

Selenium (Se), an essential component of deiodinases (DIOs), regulates the contents of thyroid hormones and thus improves animal growth. To explore the influences of selenium supplementation on fish growth metabolism, a total of 270 healthy grass carp (Ctenopharyngodon idella) were divided into three groups and feed three graded dietary selenium (0.141, 0.562, and 1.044 mg Se/kg) levels. The results showed that after 60-day feeding, dietary selenium improved the final body weight and specific growth rate (SGR) of grass carp. The hepatic DIO activities in selenium-supplemented groups were higher than those in control group. A significant increase in triiodothyronine (T3), free triiodothyronine (FT3), and thyroid-stimulating hormone (TSH) levels was accompanied by a decrease in the contents of thyroxine (T4) and free thyroxine (FT4) in selenium-supplemented groups. The histopathological observation of thyroid suggested that selenium deficiency resulted in hypertrophy of follicular epithelial cells. Moreover, the gene relative expression levels of dio1, dio2, and dio3 showed an increasing trend with the rising concentration of dietary selenium. The transcription levels of HPT axis-related genes (crh, tsh-β, ttr, tr-s, tpo, nis) and GH/IGF1-related genes (gh, ghr, igf1, igf1r) were significantly upregulated in selenium-supplemented groups. No significant differences in the above indicators were observed between 0.562 and 1.044 mg Se/kg diet group except T3 content and dio1 relative expression ratio. These results indicate that dietary selenium supplementation improves the hepatic DIO activities and thyroid hormone metabolism and regulates the transcription levels of HPT and GH/IGF axis-related genes, which may be responsible for the growth promotion in grass carp.

The possible hormetic effects of fluorene-9-bisphenol on regulating hypothalamic-pituitary-thyroid axis in zebrafish

Fluorene-9-bisphenol (BHPF) is a bisphenol A substitute, which has been introduced for the production of so-called 'bisphenol A (BPA)-free' plastics. However, it has been reported that BHPF can enter living organisms through using commercial plastic bottles and cause adverse effects. To date, the majority of the toxicologic study of BHPF focused on investigating its doses above the toxicological threshold. Here, we studied the effects of BHPF on development, locomotion, neuron differentiation of the central nervous system (CNS), and the expression of genes in the hypothalamic-pituitary-thyroid (HPT) axis in zebrafish exposed to different doses of BHPF ranging from 1/5 of LD1 to LD50 (300, 500, 750, 1500, 3000, and 4500 nM). As a result, the possible hormetic effects of BHPF on regulating the HPT axis were revealed, in which low-dose BHPF positively affected the HPT axis while this regulation was inhibited as the dose increased. Underlying mechanism investigation suggested that BHPF disrupted myelination through affecting HPT axis including related genes expression and TH levels, thus causing neurotoxic characteristics. Collectively, this study provides the full understanding of the environmental impact of BHPF and its toxicity on living organisms, highlighting a substantial and generalized ongoing dose-response relationship with great implications for the usage and risk assessment of BHPF.

Sub-chronic exposure to ammonia inhibits the growth of juvenile Wuchang bream (Megalobrama amblycephala) mainly by downregulation of growth hormone/insulin-like growth factor axis

In this study, healthy Wuchang bream (Megalobrama amblycephala) juveniles were exposed to 0, 5, 10, 20 and 30 mg/L total ammonia nitrogen for 30 days to elucidate toxic effects and mechanisms of ammonia on growth performance involved with the regulation of growth hormone/insulin-like growth factor (GH/IGF) and hypothalamic-pituitary-thyroid (HPT) axes. Our results showed that the increasing total ammonia nitrogen concentrations caused dose-depend decreases in the weight gain and specific growth rate but increases in the food conversion ratio and mortality in juvenile bream, indicating growth inhibitory effects induced by ammonia. Concurrently, GH, IGF-1 at protein and mRNA levels were significantly decreased in ammonia exposure groups (p < .05), while serum thyroid stimulating hormone, free thyroxine, free triiodothyronine levels were significantly reduced only in fish exposed to higher concentrations of 20 and 30 mg/L ammonia (p < .05), suggesting that ammonia exposure could perturb both GH/IGF-axis and HPT-axis functions. Furthermore, transcriptional levels of extracellular regulated protein kinases 2 (erk2), phosphatidylinositol 3-kinase (pi3k), protein kinase B (akt), target of rapamycin (tom) and ribosomal protein S6 kinase-polypeptide 1(s6k1) in the dorsal muscle were significantly down-regulated in the fish exposed to ammonia (p < .05). This fact indicated that MAPK/ERK pathway and PI3K/AKT pathway should be responsible for the growth inhibition. Combining the results of spearman correlation coefficient, it should be noted that the GH/IGF axis played a more important role in regulating the growth than the HPT axis in Wuchang bream under persistent ammonia stress.

The joint effect of parental exposure to microcystin-LR and polystyrene nanoplastics on the growth of zebrafish offspring

The coexistence of nanoplastics (NPs) and various pollutants in the environment has become a problem that cannot be ignored. In order to identify the microcystin-LR (MCLR) bioaccumulation and the potential impacts on the early growth of F1 zebrafish (Danio rerio) offspring in the presence of polystyrene nanoplastics (PSNPs), PSNPs and MCLR were used to expose adult zebrafish for 21days. The exposure groups divided into MCLR (0, 0.9, 4.5 and 22.5μgL^-1) alone groups and PSNP (100μgL^-1) and MCLR co-exposure groups. F1 embryos were collected and developed to 120 h post-fertilization (hpf) in clear water. Compared with the exposure to MCLR only, the combined exposure increased the parental transfer of MCLR to the offspring and subsequently exacerbated the growth inhibition of F1 larvae. Further research clarified that combined exposure of PSNPs and MCLR could reduce the levels of thyroxine (T4) and 3, 5, 3'-triiodothyronine (T3) by altering the expression of hypothalamus-pituitary-thyroid (HPT) axis-related genes, eventually leading to growth inhibition of F1 larvae. Our results also exhibited combined exposure of PSNPs and MCLR could change the transcription of key genes of the GH/IGF axis compared with MCLR single exposure, suggesting the GH/IGF axis was a potential target for the growth inhibition of F1 larvae in PSNPs and MCLR co-exposure groups. The present study highlights the potential risks of coexistence of MCLR and PSNPs on development of fish offspring, and the environmental risks to aquatic ecosystems.

Transcriptome Analysis During Follicle Development in Turkey Hens With Low and High Egg Production

Low and high egg producing hens exhibit gene expression differences related to ovarian steroidogenesis. High egg producing hens display increased expression of genes involved in progesterone and estradiol production, in the granulosa layer of the largest follicle (F1G) and small white follicles (SWF), respectively, whereas low egg producing hens display increased expression of genes related to progesterone and androgen production in the granulosa (F5G) and theca interna layer (F5I) of the fifth largest follicle, respectively. Transcriptome analysis was performed on F1G, F5G, F5I, and SWF samples from low and high egg producing hens to identify novel regulators of ovarian steroidogenesis. In total, 12,221 differentially expressed genes (DEGs) were identified between low and high egg producing hens across the four cell types examined. Pathway analysis implied differential regulation of the hypothalamo-pituitary-thyroid (HPT) axis, particularly thyroid hormone transporters and thyroid hormone receptors, and of estradiol signaling in low and high egg producing hens. The HPT axis showed up-regulation in high egg producing hens in less mature follicles but up-regulation in low egg producing hens in more mature follicles. Estradiol signaling exclusively exhibited up-regulation in high egg producing hens. Treatment of SWF cells from low and high egg producing hens with thyroid hormone in vitro decreased estradiol production in cells from high egg producing hens to the levels seen in cells from low egg producing hens, whereas thyroid hormone treatment did not impact estradiol production in cells from low egg producing hens. Transcriptome analysis of the major cell types involved in steroidogenesis inferred the involvement of the HPT axis and estradiol signaling in the regulation of differential steroid hormone production seen among hens with different egg production levels.

Characterization of hypothalamo-pituitary-thyroid axis gene expression in the hypothalamus, pituitary gland, and ovarian follicles of turkey hens during the preovulatory surge and in hens with low and high egg production

Dysregulation of the preovulatory surge (PS) leads to lowered egg production. The hypothalamo-pituitary-thyroid (HPT) axis has been shown to influence plasma progesterone levels and follicle ovulation. The presence of thyroid hormone receptors (THR) in the reproductive axis suggests possible effects of thyroid hormone. To further understand the potential role of thyroid hormone on the PS, HPT axis plasma hormone concentrations and gene expression were characterized surrounding the PS in average egg producing hens (AEPH), low egg producing hens (LEPH), and high egg producing hens (HEPH) (n = 3 hens/group). Data were analyzed using the mixed models procedure of SAS, with significance indicated at P < 0.05. Average egg producing hens and HEPH displayed lower levels of triiodothyronine (T3) and higher levels of thyroxine (T4) inside of the PS, whereas LEPH showed inverse T3 and T4 levels relative to the PS. Expression of mRNA for hypothalamic thyrotropin-releasing hormone (TRH), pituitary thyrotropin (TSHB), and the main thyroid hormone metabolism enzyme (DIO2) were downregulated during the PS in AEPH and HEPH. Low egg producing hens displayed higher expression of mRNA for hypothalamic TRH as well as pituitary TSHB and DIO2 compared with HEPH. Average egg producing hens expression of THR mRNAs was upregulated during the PS in the hypothalamus but downregulated in the pituitary. High egg producing hens showed decreased expression of THR mRNAs in both the hypothalamus and pituitary when compared with LEPH. In ovarian follicles, THR mRNAs were more prevalent in the thecal layer of the follicle wall compared with the granulosa layer, and expression tended to decrease with follicle maturity. Minimal differences in follicular THR expression were seen between LEPH and HEPH, indicating that THR expression is unlikely to be responsible for steroid hormone production differences occurring between LEPH and HEPH. Generally, downregulation of the HPT axis was seen during the PS in AEPH and HEPH, whereas upregulation of the HPT axis was seen in LEPH. Further studies will be required to clarify the role of the HPT axis in the regulation of ovulation and egg production rates in turkey hens.

PM2.5 disrupts thyroid hormone homeostasis through activation of the hypothalamic-pituitary-thyroid (HPT) axis and induction of hepatic transthyretin in female rats 2.5

Fine particulate matter (PM_2.5), a ubiquitous environmental pollutant, has been indicated to affect thyroid hormone (TH) homeostasis in women, but the detailed mechanism behind this effect remains unclear. The objective of this study was to evaluate the roles of the hypothalamic-pituitary-thyroid (HPT) axis and hepatic transthyretin in the thyroid-disrupting effects of PM_2.5. Sprague Dawley rats were treated with PM_2.5 (0, 15 and 30 mg/kg) by passive pulmonary inhalation for 49 days; and recovery experimental group rats were dosed with PM_2.5 (30 mg/kg) for 35 days, and no treatment was done during the subsequent 14 days. PM_2.5 was handled twice a day by passive pulmonary inhalation throughout the study. After treatment, pathological changes were analyzed by performing haemotoxylin and eosin staining, measuring levels of THs and urine iodine (UI) in serum, plasma, and urine samples using enzyme-linked immunoabsorbent assay, and expression of proteins in the hypothalamus, pituitary, thyroid, and liver tissues of rats were analyzed by immunohistochemistry and Western blotting. The levels of oxidative stress factors, such as reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (Gpx), and nuclear factor-kappa B (NF-κB) in female rats' plasma were also evaluated by ELISA. The results of these analyses revealed that PM_2.5 treatment induced pathologic changes in rat thyroid and liver characterized by increased follicular cavity size and decreased amounts of follicular epithelial cells and fat vacuoles, respectively. Serum levels of triiodothyronine, thyroxine, and thyroid stimulating hormone were significantly decreased, plasma NF-κB level was increased and plasma redox state was unbalanced (enhanced ROS, MDA and Gpx levels; reduced SOD activities) in female rats treated with PM_2.5 (P < 0.05). PM_2.5 treatment suppressed the biosynthesis and biotransformation of THs by increasing sodium iodide symporter, thyroid transcription factor 1, thyroid transcription factor 2, and paired box 8 protein expression levels (P < 0.05). Additionally, thyroid stimulating hormone receptor and thyroid peroxidase levels were significantly decreased (P < 0.05). Both thyrotropin releasing hormone receptor and thyroid stimulating hormone beta levels were enhanced (P < 0.05). Moreover, transport of THs was inhibited due to reduced protein expression of hepatic transthyretin upon treatment with PM_2.5. In summary, PM_2.5 treatment could perturb TH homeostasis by affecting TH biosynthesis, biotransformation, and transport, affecting TH receptor levels, and inducing oxidative stress and inflammatory responses. Activation of the HPT axis and altered hepatic transthyretin levels therefore appear to play a crucial role in PM_2.5-induced thyroid dysfunction.

Thermoregulation in hibernating mammals: The role of the "thyroid hormones system"

Hibernation is a unique evolutionary adaptation to conserve energy. During the pre-hibernation (i.e. fall) season, a progressive decline in core body temperature and further decrease in metabolism underlie a seasonal modulation in thermoregulation. The onset of hibernation requires marked changes in thermoregulatory attributes including adjustment in body temperature and tissue specific increases in thermogenic capacity. The hibernation season is characterized by a regulated suppression in thermogenesis allowing the onset of torpor interrupted by periodic activation of thermogenesis to sustain interbout arousals. Thyroid hormones are known to regulate both body temperature and metabolism, and for this reason, the hypothalamic-pituitary-thyroid axis and thyroid hormones have been investigated as modulators of thermogenesis in the phenomenon of hibernation, but the mechanisms remain poorly understood. In this review, we present an overview of what is known about the thermogenic roles of thyroid hormones in hibernating species across seasons and within the hibernating season (torpor-interbout arousal cycle). Overall, the hypothalamic-pituitary-thyroid axis and thyroid hormones play a role in the pre-hibernation season to enhance thermogenic capacity. During hibernation, thermogenesis is attenuated at the level of sympathetic premotor neurons within the raphe pallidus and by deiodinase expression in the hypothalamus. Further, as recent work highlights the direct effect of thyroid hormones within the central nervous system in activating thermogenesis, we speculate how similar mechanisms may occur in hibernating species to modulate thermogenesis across seasons and to sustain interbout arousals. However, further experiments are needed to elucidate the role of thyroid hormones in hibernation, moving towards the understanding that thyroid hormones metabolism, transport and availability within tissues may be the most telling indicator of thyroid status.

Transcriptome analysis of the hypothalamus and pituitary of turkey hens with low and high egg production

BACKGROUND

High egg producing hens (HEPH) show increased hypothalamic and pituitary gene expression related to hypothalamo-pituitary-gonadal (HPG) axis stimulation as well as increased in vitro responsiveness to gonadotropin releasing hormone (GnRH) stimulation in the pituitary when compared to low egg producing hens (LEPH). Transcriptome analysis was performed on hypothalamus and pituitary samples from LEPH and HEPH to identify novel regulators of HPG axis function.

RESULTS

In the hypothalamus and pituitary, 4644 differentially expressed genes (DEGs) were identified between LEPH and HEPH, with 2021 genes up-regulated in LEPH and 2623 genes up-regulated in HEPH. In LEPH, up-regulated genes showed enrichment of the hypothalamo-pituitary-thyroid (HPT) axis. Beta-estradiol was identified as an upstream regulator regardless of tissue. When LEPH and HEPH samples were compared, beta-estradiol was activated in HEPH in 3 of the 4 comparisons, which correlated to the number of beta-estradiol target genes up-regulated in HEPH. In in vitro pituitary cell cultures from LEPH and HEPH, thyroid hormone pretreatment negatively impacted gonadotropin subunit mRNA levels in cells from both LEPH and HEPH, with the effect being more prominent in HEPH cells. Additionally, the effect of estradiol pretreatment on gonadotropin subunit mRNA levels in HEPH cells was negative, whereas estradiol pretreatment increased gonadotropin subunit mRNA levels in LEPH cells.

CONCLUSIONS

Up-regulation of the HPT axis in LEPH and upstream beta-estradiol activation in HEPH may play a role in regulating HPG axis function, and ultimately ovulation rates. Thyroid hormone and estradiol pretreatment impacted gonadotropin mRNA levels following GnRH stimulation, with the inhibitory effects of thyroid hormone more detrimental in HEPH and estradiol stimulatory effects more prominent in LEPH. Responsiveness to thyroid hormone and estradiol may be due to desensitization to thyroid hormone and estradiol in LEPH and HEPH, respectively, due to up-regulation of the HPT axis in LEPH and of the HPG axis in HEPH. Further studies will be necessary to identify possible target gene desensitization mechanisms and elicit the regulatory role of the HPT axis and beta-estradiol on ovulation rates in turkey hens.

Rare earth elements exposure and the alteration of the hormones in the hypothalamic-pituitary-thyroid (HPT) axis of the residents in an e-waste site: A cross-sectional study

Rare earth elements (REEs) are widely used in electronic products. But the contaminations of REEs in the e-waste sites and the related health effects were barely investigated. In the present study, we analyzed the concentrations of REEs and the hormones of the HPT axis in plasma of subjects recruited from an e-waste area and a reference area in Taizhou, China. The results showed that the concentrations of several REEs like La, Ce were much higher in the exposed group than in the control group (all p < 0.001). The thyroid hormones, FT3 and FT4, and TRH showed no significant difference between the two groups, while the concentration of TSH was significantly higher in the exposed group when compared to the control group (p = 0.002). Separate regression analysis indicated that elevated La and Ce levels were associated with higher TSH concentrations. MDA and 8-iso, the biomarkers of oxidative stress, were also significantly higher in the exposed group than that of the control group (p = 0.002 and p = 0.003, respectively). The increased oxidative stress might be the mechanism underlying the disruptive effects of REEs on TSH. Our results indicated that the quantities of internal exposure of REEs in the subjects in the e-waste area were considerable and the compositional profile of the REEs in the exposed group was different from the control group due to the e-waste dismantling. The expression of TSH were also affected by high La and Ce exposure which showed an endocrine disruption effects of REEs on HPT axis.

Exposure to humidifier disinfectants induces developmental effects and disrupts thyroid endocrine systems in zebrafish larvae

Humidifier disinfectants have been widely used in Korea to prevent the growth of microorganisms in humidifier water. However, their use has been banned since 2011 after epidemiological studies reported humidifier disinfectant induced lung injury. In the present study, the developmental effects of exposure to two humidifier disinfectants (Oxy® and Wiselect) and their main component, polyhexamethylene guanidine (PHMG)-phosphate, were investigated in zebrafish embryos/larvae for seven days. The effects on triiodothyronine (T3) and thyroxine (T4) hormones, reactive oxygen species (ROS) generation, antioxidant enzyme activities, and changes in expression of the genes related to the hypothalamus-pituitary-thyroid (HPT) axis and oxidative stress were also investigated. Zebrafish embryos exposed to the highest concentration (amounts recommended for use by the manufacturers) of all tested humidifier disinfectants showed an increase in embryo coagulation, leading to death without hatching. Exposure to Oxy® and Wiselect resulted in significantly decreased body length, increased ROS generation and antioxidant enzyme activities, decreased T4, and up-regulated genes related to the HPT axis (trh, trβ, and tpo) and oxidative damage (sod2 and gpx1b). The humidifier disinfectants and PHMG-phosphate could induce oxidative stress and disrupt thyroid hormone systems in zebrafish, leading to developmental retardation when used at sub-lethal concentrations. Potential effects of long-term exposure to humidifier disinfectants and mixture effects of several major components deserve further investigation.

In early pubertal boys, testosterone and LH are associated with improved anti-oxidation during an aerobic exercise bout

PURPOSE

To investigate the association of the hypothalamic-pituitary-testicular (HPT) axis with pro- and anti- oxidation, in relation to puberty and obesity in boys, before and after an aerobic exercise bout.

METHODS

This is a cross-sectional human observational study of 92 healthy normal-weight, obese pre- and early- pubertal boys that underwent a blood sampling, before, and after an aerobic exercise bout at 70% VO₂max, until exhaustion. LH, FSH, total testosterone (tT) and markers of pro- (TBARS and PCs) and anti- (GSH, GSSG, GPX, catalase, TAC) oxidation were measured.

RESULTS

Baseline LH, FSH, and tT concentrations were greater in early, than in pre- pubertal boys, independently of weight status. Post-exercise, LH concentrations decreased in early pubertal boys while FSH concentrations did not change in any of the studied groups. Baseline and post-exercise tT concentrations were lower in obese than in normal-weight early pubertal boys, while baseline and post-exercise LH and FSH concentrations did not differ between these groups. Post-exercise tT concentrations increased in early pubertal obese boys. Baseline LH, FSH and tT concentrations correlated positively with baseline anti-oxidation markers concentrations in pre-pubertal boys. Baseline tT concentrations correlated positively with the increase of TAC concentrations in early pubertal normal-weight boys. In all boys, baseline LH concentrations were the best positive predictors for the exercise-associated increase of TAC concentrations.

CONCLUSIONS

It appears that the HPT axis maturation during puberty (in particular its LH and testosterone components) is positively associated with the increase of anti-oxidation during a bout of aerobic exercise.

Thyroid endocrine disruption effects of perfluoroalkyl phosphinic acids on zebrafish at early development

Perfluoroalkyl phosphinic acids (PFPiAs, including 6:6, 6:8 and 8:8 PFPiAs) are one kind of emerging perfluoroalkyl substances and usually used as leveling and wetting agents in household cleaning products and pesticide formulations. In this study, zebrafish embryos (6 h post-fertilization [hpf]) were exposed to 6:6, 6:8 and 8:8 PFPiAs individually (0.5, 5 and 50 nM) for 168 hpf. 8:8 PFPiA at 5 and 50 nM reduced the body length, while all treatments of 6:8 and 8:8 PFPiA depressed the heartbeat of the zebrafish larvae. 8:8 PFPiA at 50 nM distinctly enhanced the thyroxine (T4) and triiodothyronine (T3) contents. In a negative feedback mechanism, the three PFPiAs remarkably suppressed the genes responsible for THs regulation (corticotropin-releasing hormone, crh; thyroid stimulating hormone, tshβ), and 8:8 PFPiA displayed the strongest effect. In addition, 8:8 PFPiA significantly promoted the gene expressions corresponding to THs transport, metabolism and action (transthyretin, ttr; uridine diphosphate glucuronosyltransferase, ugt1ab; deiodinases, dio1 and dio2; thyroid hormone receptors, trα and trβ). As a result, 8:8 PFPiA displayed the strongest thyroid endocrine disrupting effect and significantly affected the growth of zebrafish larvae among the three PFPiAs in the present study.

Effects of 25 thyroid hormone disruptors on zebrafish embryos: A literature review of potential biomarkers

It is estimated that many organic compounds found in our environment can interfere with the thyroid system and act as thyroid hormone (TH) disruptor. Despite that, there is a clear lack of assays to identify TH disruptors. Recently zebrafish embryos were suggested as screening tool to identify compounds which impact thyroid synthesis. Effects on hormone level, gene transcript expression, eye development and swim bladder inflation are suggested as potential biomarker for TH disruptors. In order to assess the applicability of these biomarkers we performed a literature review. The effects of 25 known TH disrupting compounds were compared between studies. The studies were limited to exposures with embryos prior 7 days of development. The different study designs and the lack of standardized methods complicated the comparison of the results. The most common responses were morphological alterations and gene transcript expression changes, but no specific biomarker for TH disruption could be identified. In studies addressing TH disruption behavioral effects were more commonly monitored than in studies not mentioning the TH pathway. TH disruption in developing zebrafish embryos might be caused by different modes of action e.g. disruption of follicle development, binding of TH, activation of TH receptors causing different effects. Timing of developmental processes in combination with exposure duration might also play a role. On the other side compound characteristics (uptake, stability, metabolization) could also cause differences between substances. Further studies are necessary to gain better understanding into the mechanisms of TH disruption in early zebrafish development.

Evaluating the Hypothalamic-Pituitary-Thyroid (HPT) Axis in Mice

As the genome of experimental animals has become easier to manipulate, a number of mouse models have been developed to understand in vivo thyroid hormone action. A major site of thyroid hormone action is the HPT axis. While several methods are available that provide a detailed understanding of the HPT axis in mice, many authors choose to include only cursory data about this axis, which can lead to erroneous conclusions about in vivo thyroid hormone action. A standard protocol is proposed to evaluate the HPT axis in mice.

Subclinical Lipopolysaccharide from Salmonella Enteritidis Induces Dysregulation of Bioactive Substances from Selected Brain Sections and Glands of Neuroendocrine Axes

Bacterial lipopolysaccharide (LPS) can contribute to the pathogenesis and the clinical symptoms of many diseases such as cancer, mental disorders, neurodegenerative as well as metabolic diseases. The asymptomatic carrier state of Salmonella spp. is a very important public health problem. A subclinical single dose of LPS obtained from S. Enteritidis (5 μg/kg, i.v.) was administered to discern the consequences of changes of various brain peptides such as corticotropin-releasing hormone (CRH), gonadotropin-releasing hormone (GnRH), thyrotropin-releasing hormone (TRH), galanin (GAL), neuropeptide Y (NPY), somatostatin (SOM), substance P (SP), and vasoactive intestinal polypeptide (VIP) in selected clinically important brain sections and endocrine glands of the hypothalamic-pituitary-adrenal (HPA), -thyroid (HPT), -ovarian (HPO) axes. The study was conducted on ten immature crossbred female pigs. The brain peptides were extracted from the hypothalamus (medial basal hypothalamus, preoptic area, lateral hypothalamic area, mammillary bodies, and the stalk median eminence), and pituitary gland (adenohypophysis and neurohypophysis) sections and from the ovaries and adrenal and thyroid glands. There was no difference in health status between LPS and the control groups during the period of the experiment. Nevertheless, even a low single dose of LPS from S. Enteritidis that did not result in any clinical symptoms of disease induced dysregulation of various brain peptides, such as CRH, GnRH, TRH, GAL, NPY, SOM, SP, and VIP in selected brain sections of hypothalamus, pituitary gland and in the endocrine glands of the HPA, HPO, and HPT axes. In conclusion, the obtained results clearly show that subclinical LPS from S. Enteritidis can affect the brain chemistry structure and dysregulate bioactive substance from selected brain sections and glands of the neuroendocrine axes. The exact mechanisms by which LPS can influence major neuroendocrine axes are not fully understood and require further studies.

Endpoint sensitivity in Amphibian Metamorphosis Assay

The Amphibian Metamorphosis Assay (AMA) is a screening test for detecting chemicals with thyroid activity. There is little experience in data interpretation and in using AMA data for screening, testing and identifying endocrine disruptors. To investigate the sensitivity of different endpoints of the AMA, the publically available data for 57 thyroid active and inactive chemicals were compiled and analyzed. Endpoints body weight and length appeared as sensitive as apical thyroid responsive endpoints hind limb length (HLL) and developmental stage (DS) for 12 thyroid active chemicals. The sensitivity of body weight, length and HLL was comparable, which is higher than that of DS for 45 thyroid inactive chemicals. The decision logic of the AMA suggests that an advanced development alone indicates thyroid activity. The analysis here showed that advanced development at day 7 could indicate thyroid activity of a chemical. However, advanced development at day 21 may be influenced by thyroid inactive chemicals. Among 39 thyroid inactive chemicals, which affected one or more endpoints, 33% and 77% induced changes in HLL and/or DS at day 7 and 21, respectively; only 10% influenced thyroid histology. These results showed that apical thyroid responsive endpoints HLL and DS are influenced by thyroid active chemicals as well as thyroid inactive chemical. Both endpoints should be combined with thyroid histology for the identification of thyroid active chemicals. The use of the AMA in a testing strategy to identify chemicals with thyroid activity is discussed.

Voluntary Exercise-Induced Activation of Thyroid Axis and Reduction of White Fat Depots Is Attenuated by Chronic Stress in a Sex Dimorphic Pattern in Adult Rats

The activity of the hypothalamus-pituitary-thyroid (HPT) axis is inhibited by energy deficit, by acute or chronic stress, but activated by cold exposure or exercise. Because stress curtails acute cold induced activation of HPT, we evaluated the effect of chronic stress on HPT axis response to voluntary exercise, a persistent energy-demanding situation. Adult male and female Wistar rats were exposed to restraint stress, 30 min/day for 2 weeks, or to isolation (Iso) [post-natal day [PND] 30-63]. Exercise was performed (7 p.m.-7 a.m.) in a running wheel, sedentary controls stayed in individual cages (Sed); at 7 a.m. they were housed with their cage mate or individually (Iso); food intake by the exercised group was measured day and night to pair-fed Sed. At sacrifice, hormones, mRNA levels and tissue weights were quantified. Control or restrained adult rats had access to running wheel daily for 2 weeks. Compared to C, exercise decreased white adipose tissue (WAT) mass in females and males, increased hypothalamic paraventricular nucleus (PVN)-Trh expression in males proportionally to exercise performed, and increased TSH and T4 serum concentration in females. These changes were not detected in restrained groups. Starting at PND 63 control (2/cage) and isolated (1/cage) rats either exercised on 10 alternated nights or were sedentary. In control male animals, compared to Sed rats, exercise did not decrease WAT mass, nor changed HPT axis activity, but increased Pomc and deiodinase 2 (Dio2) expression in mediobasal hypothalamus (MBH), adrenergic receptor β3 and uncoupling protein-1 in brown adipose tissue. In control female animals, exercise decreased WAT mass, increased Pomc, Dio2, and Trhde expression in MBH, and TSH serum concentration. Iso females had lower TSH and T4 serum concentration, Dio2 and Trhde expression in MBH than controls. The stress response was higher in isolated males than females, but in males it did not alter the effects of exercise, in contrast to isolated females that had a blunted response to exercise compared to controls. In conclusion, chronic stress interferes with metabolic effects produced by exercise, such as loss of WAT mass, coincident with dampening of HPT activity.

NEUROENDOCRINE INSIGHTS INTO BURNOUT SYNDROME

Debates flow in the medical and psychological field about burnout symptoms: from considering it as a distinct illness, a separate entity or correlated with physiological changes and/or job-related reaction. Seen as a form of depression, the researches are investigating the correlations between various changes in the normal human body functioning, environmental and job lever / implications. The following pages refer to the recent studies of neuroendocrine indicators involved in burnout. It is known that the endocrine system is highly interrelated with the immune and neural systems, the neuro-immuno-endocrine axis is subject to clear biphasic changes in the acute and chronic phases of a critical illness, most likely reflecting a beneficial adaptation.

Gene transcription ontogeny of hypothalamic-pituitary-thyroid axis development in early-life stage fathead minnow and zebrafish

The hypothalamic-pituitary-thyroid (HPT) axis is known to play a crucial role in the development of teleost fish. However, knowledge of endogenous transcription profiles of thyroid-related genes in developing teleosts remains fragmented. We selected two model teleost species, the fathead minnow (Pimephales promelas) and the zebrafish (Danio rerio), to compare the gene transcription ontogeny of the HPT axis. Control organisms were sampled at several time points during embryonic and larval development until 33 days post-fertilization. Total RNA was extracted from pooled, whole fish, and thyroid-related mRNA expression was evaluated using quantitative polymerase chain reaction. Gene transcripts examined included: thyrotropin-releasing hormone receptor (trhr), thyroid-stimulating hormone receptor (tshr), sodium-iodide symporter (nis), thyroid peroxidase (tpo), thyroglobulin (tg), transthyretin (ttr), deiodinases 1, 2, 3a, and 3b (dio1, dio2, dio3a and 3b), and thyroid hormone receptors alpha and beta (thrα and β). A loess regression method was successful in identifying maxima and minima of transcriptional expression during early development of both species. Overall, we observed great similarities between the species, including maternal transfer, at least to some extent, of almost all transcripts (confirmed in unfertilized eggs), increasing expression of most transcripts during hatching and embryo-larval transition, and indications of a fully functional HPT axis in larvae. These data will aid in the development of hypotheses on the role of certain genes and pathways during development. Furthermore, this provides a background reference dataset for designing and interpreting targeted transcriptional expression studies both for fundamental research and for applications such as toxicology.

Expression of two glycoprotein hormone receptors in larval, parasitic phase, and adult sea lampreys

All jawed vertebrates have three canonical glycoprotein hormones (GpHs: luteinizing hormone, LH; follicle stimulating hormone, FSH; and thyroid stimulating hormone, TSH) with three corresponding GpH receptors (GpH-Rs: LH-R, FSH-R, and TSH-R). In contrast, we propose that the jawless vertebrate, the sea lamprey (Petromyzon marinus), only has two pituitary glycoprotein hormones, lamprey (l)GpH and l-thyrostimulin, and two functional glycoprotein receptors, lGpH-R I and II. It is not known at this time whether there is a specific receptor for lGpH and l-thyrostimulin, or if both GpHs can differentially activate the lGpH-Rs. In this report, we determined the RNA expression of lGpH-R I and II in the gonads and thyroids of larval, parasitic phase, and adult lampreys. A highly sensitive dual-label fluorescent in situ hybridization technique (RNAScope™) showed lGpH-R I expression in the ovaries of larval lamprey, and co-localization and co-expression of lGpH-R I and II in the ovaries of parasitic phase and adult lampreys. Both receptors were also highly co-localized and co-expressed in the endostyle of larval lamprey and thyroid follicles of parasitic and adult lampreys. In addition, we performed in vivo studies to determine the actions of lamprey gonadotropin releasing hormones (lGnRHs) on lGpH-R I and II expression by real time PCR, and determined plasma concentrations of estradiol and thyroxine. Administration of lGnRH-III significantly (p ≤ 0.01) increased lGpHR II expression in the thyroid follicles of adult female lampreys but did not cause a significant increase in RNA expression of lGpH-R I and II in ovaries. Concomitantly, there was a significant increase (p ≤ 0.01) of plasma estradiol without any significant changes of plasma thyroxine concentrations in response to treatment to lGnRH-I, -II, or -III. In summary, our results provide supporting evidence that the lamprey pituitary glycoprotein hormones may differentially activate the lamprey GpH-Rs in regulating both thyroid and gonadal activities during each of the three life stages of the sea lamprey.

Impaired hypothalamic cocaine- and amphetamine-regulated transcript expression in lateral hypothalamic area and paraventricular nuclei of dehydration-induced anorexic rats

Negative energy balance promotes physiological adaptations that ensure the survival of animals. The hypothalamic-pituitary-thyroid axis regulates basal energy expenditure and its down-regulating adaptation to negative energy balance is well described: in fasting, the serum content of thyrotrophin (TSH) and thyroid hormones (TH) decreases, enhancing the survival odds of individuals. By contrast, dehydration-induced anorexic (DIA) rats present an impaired hypothalamic-pituitary-thyroid (HPT) axis adaptation despite their negative energy balance: increased circulating TSH levels. The implication of cocaine- and amphetamine-regulated transcript (CART), an anorexic peptide, in HPT axis function impairment and food-avoidance behaviour displayed by DIA animals is unknown. Because CART is co-expressed with the peptide that regulates the HPT axis in hypophysiotrophic paraventricular nucleus (PVN) neurones (TSH-releasing hormone), we analysed CART expression and possible implications with respect to high TSH levels of DIA animals. We examined whether changes in CART expression from the lateral hypothalamic area (LHA) and arcuate nucleus (ARC) could participate in food-avoidance of DIA rats. DIA and forced-food restricted (FFR) animals reduced their body weight and food intake. FFR rats had a down-regulation of their HPT axis (reduced serum TH and TSH content), whereas DIA animals had reduced TH but increased TSH levels. CART mRNA expression in the ARC decreased similarly between experimental groups and diminished in anterior, medial PVN and in LHA of FFR animals, whereas DIA animals showed unchanged levels. This impaired CART mRNA expression in the anterior PVN and LHA could be related to the aberrant feeding behaviour of DIA rats but not to their deregulated HPT axis function.

Repetitive Transcranial Magnetic Stimulation (rTMS) Modulates Lipid Metabolism in Aging Adults

Hyperlipidemia, one of the cardiovascular (CV) risk factors, is associated with an increase in the risk for dementia. Repetitive transcranial magnetic stimulation (rTMS) was applied over the right dorsolateral prefrontal cortex (DLPFC) to modulate serum lipid levels in older adults. Participants received 10 sessions of rTMS or sham stimulation intervention within 2 weeks. The serum lipid and thyroid hormone-related endocrine levels were assessed before and after the treatment. We found that rTMS significantly decreased serum lipid levels, including the total cholesterol (CHO) and triglyceride (TG); meanwhile, it also increased the thyroid-stimulating hormone (TSH) as well as thyroxine (T4) levels. This suggests that rTMS modulated the serum lipid metabolism by altering activity in the hypothalamo-pituitary-thyroid (HPT) axis. The trial was registered on the website of Chinese Clinical Trial Registry (http://www.chictr.org.cn).

Hypophysectomy abolishes rhythms in rat thyroid hormones but not in the thyroid clock

The endocrine body rhythms including the hypothalamic-pituitary-thyroid axis seem to be regulated by the circadian timing system, and daily rhythmicity of circulating thyroid-stimulating hormone (TSH) is well established. The circadian rhythms are generated by endogenous clocks in the central brain oscillator located in the hypothalamic suprachiasmatic nucleus (SCN) as well as multiple peripheral clocks, but information on the existence and function of a thyroid clock is limited. The molecular machinery in all clock cells is composed of a number of clock genes and their gene products are connected by autoregulatory feedback loops. Here, we provide evidence for a thyroid clock in the rat by demonstrating 24-h antiphase oscillations for the mRNA of the canonical clock genes Per1 and Bmal1, which was unaffected by hypophysectomy. By immunostaining, we supported the existence of a core oscillator in the individual thyroid cells by demonstrating a daily cytoplasmatic-nuclear shuttling of PER1 protein. In normal rats, we found a significant daily rhythmicity in the circulating thyroid hormones preceded by a peak in TSH. In hypophysectomised rats, although the thyroid clock was not affected, the oscillations in circulating thyroid hormones were abolished and the levels were markedly lowered. No daily oscillations in the expression of TSH receptor mRNA were observed in neither control rats nor hypophysectomised rats. Our findings indicate that the daily rhythm of thyroid hormone secretion is governed by SCN signalling via the rhythmic TSH secretion rather than by the local thyroid clock, which was still ticking after hypophysectomy.

Adverse effects of BDE-47 on in vivo developmental parameters, thyroid hormones, and expression of hypothalamus-pituitary-thyroid (HPT) axis genes in larvae of the self-fertilizing fish Kryptolebias marmoratus

2,2',4,4'-tetrabromodiphenylether (BDE-47) is known to have the potential to disrupt the thyroid endocrine system in fishes due to its structural similarity to the thyroid hormones triiodothyronine (T3) and thyroxine (T4). However, the effects of BDE-47 on thyroid function in fishes remain unclear. In this study, abnormal development (e.g. deformity, hemorrhaging) and an imbalance in thyroid hormone (TH) homeostasis was shown in the early developmental stages of the mangrove killifish Kryptolebias marmoratus in response to BDE-47 exposure. To examine the thyroid endocrinal effect of BDE-47 exposure in mangrove killifish K. marmoratus larvae, transcript levels of genes involved in TH homeostasis and hypothalamus-pituitary-thyroid (HPT) axis-related genes were measured. The expression of thyroid hormone metabolism-related genes (e.g. deiodinases, UGT1ab) and HPT axis-related genes was up-regulated and there were significant changes in TH levels (P < 0.05) in response to BDE-47 exposure. This study provides insights into the regulation of TH homeostasis at the transcriptional level and provides a better understanding on the potential impacts of BDE-47 on the thyroid endocrine system of fishes.

Genetics of thyroid function

Recent studies show that subtle variations in thyroid function, including subclinical thyroid dysfunction, and even variation in thyroid function within the normal range, are associated with morbidity and mortality. It is estimated that 40-65% of the inter-individual variation in serum TSH and FT4 levels is determined by genetic factors. To identify these factors, various linkage and candidate gene studies have been performed in the past, which have identified only a few genes. In the last decade, genome-wide association studies identified many new genes, while recent whole-genome sequencing efforts have also been proven to be effective. In the current review, we provide a systematic overview of these studies, including strengths and limitations. We discuss new techniques which will further clarify the genetic basis of thyroid function in the near future, as well as the potential use of these genetic markers in personalizing the management of thyroid disease patients.

Influence of maternal thyroid hormones during gestation on fetal brain development

Thyroid hormones (THs) play an obligatory role in many fundamental processes underlying brain development and maturation. The developing embryo/fetus is dependent on maternal supply of TH. The fetal thyroid gland does not commence TH synthesis until mid gestation, and the adverse consequences of severe maternal TH deficiency on offspring neurodevelopment are well established. Recent evidence suggests that even more moderate forms of maternal thyroid dysfunction, particularly during early gestation, may have a long-lasting influence on child cognitive development and risk of neurodevelopmental disorders. Moreover, these observed alterations appear to be largely irreversible after birth. It is, therefore, important to gain a better understanding of the role of maternal thyroid dysfunction on offspring neurodevelopment in terms of the nature, magnitude, time-specificity, and context-specificity of its effects. With respect to the issue of context specificity, it is possible that maternal stress and stress-related biological processes during pregnancy may modulate maternal thyroid function. The possibility of an interaction between the thyroid and stress systems in the context of fetal brain development has, however, not been addressed to date. We begin this review with a brief overview of TH biology during pregnancy and a summary of the literature on its effect on the developing brain. Next, we consider and discuss whether and how processes related to maternal stress and stress biology may interact with and modify the effects of maternal thyroid function on offspring brain development. We synthesize several research areas and identify important knowledge gaps that may warrant further study. The scientific and public health relevance of this review relates to achieving a better understanding of the timing, mechanisms and contexts of thyroid programing of brain development, with implications for early identification of risk, primary prevention and intervention.

High levels of Nesfatin-1 in relation to the dysfunction of the hypothalamic-pituitary-adrenal and hypothalamus-pituitary-thyroid axes in depressed patients with subclinical hypothyroidism

Despite the increasing amount of evidence suggesting a relationship between depression and subclinical hypothyroidism (SCH), the exact mechanism underlying this relationship remains unclear. The main purpose of this study was to investigate the roles of plasma Nesfatin-1 levels and dysfunction of the hypothalamic-pituitary-adrenal (HPA) and hypothalamus-pituitary-thyroid (HPT) axes in the comorbidity of depression and SCH. Dysfunctions of the HPA and HPT axes were detected by measuring plasma corticosterone and thyroid-stimulating hormone (TSH) concentrations, respectively. Subjects in the patient group were selected from patients hospitalized at the Anhui Mental Health Center, and subjects in the control group were recruited from healthy volunteers. Healthy control subjects were matched to the patients in terms of weight and body mass index. The Hamilton Depression Rating Scale was administered to both the groups. The enzyme-linked immunosorbent assay method was used to measure plasma Nesfatin-1, corticosterone, and TSH levels. A radioimmunoassay kit was used for the measurement of the plasma-free triiodothyronine and plasma-free thyroxine. The results showed that the Hamilton Depression Rating Scale scores and average Nesfatin-1, corticosterone, and TSH levels were significantly higher in depressed patients with SCH than in the control group. Moreover, positive relationships were observed between Nesfatin-1 levels and the concentrations of corticosterone (r=0.626, P<0.001) and TSH (r=0.229, P=0.036) in depressed patients with SCH. These findings indicate that Nesfatin-1 is involved in the comorbidity of depression and SCH, and the mechanism underlying this involvement might be related to the dysfunction of the HPA and HPT axes.

Effects of ZnO nanoparticles on perfluorooctane sulfonate induced thyroid-disrupting on zebrafish larvae

Perfluorooctane sulfonate (PFOS) and ZnO nanoparticles (nano-ZnO) are widely distributed in the environment. However, the potential toxicity of co-exposure to PFOS and nano-ZnO remains to be fully elucidated. The test investigated the effects of co-exposure to PFOS and nano-ZnO on the hypothalamic-pituitary-thyroid (HPT) axis in zebrafish. Zebrafish embryos were exposed to a combination of PFOS (0.2, 0.4, 0.8mg/L) and nano-ZnO (50mg/L) from their early stages of life (0-14days). The whole-body content of TH and the expression of genes and proteins related to the HPT axis were analyzed. The co-exposure decreased the body length and increased the malformation rates compared with exposure to PFOS alone. Co-exposure also increased the triiodothyronine (T3) levels, whereas the thyroxine (T4) content remained unchanged. Compared with the exposure to PFOS alone, exposure to both PFOS (0.8mg/L) and nano-ZnO (50mg/L) significantly up-regulated the expression of corticotropin-releasing factor, sodium/iodidesymporter, iodothyronine deiodinases and thyroid receptors and significantly down-regulated the expression of thyroid-stimulating hormone, thyroglobulin (TG), transthyretin (TTR) and thyroid receptors. The protein expression levels of TG and TTR were also significantly down-regulated in the co-exposure groups. In addition, the expression of the thyroid peroxidase gene was unchanged in all groups. The results demonstrated that PFOS and nano-ZnO co-exposure could cause more serious thyroid-disrupting effects in zebrafish than exposure to PFOS alone. Our results also provide insight into the mechanism of disruption of the thyroid status by PFOS and nano-ZnO.

Role of the Orexin System on the Hypothalamus-Pituitary-Thyroid Axis

Hypocretin/orexin (ORX) are two hypothalamic neuropeptides discovered in 1998. Since their discovery, they have been one of the most studied neuropeptide systems because of their projecting fields innervating various brain areas. The orexinergic system is tied to sleep-wakefulness cycle, and narcolepsy is a consequence of their system hypofunction. Orexinergic system is also involved in many other autonomic functions such as feeding, thermoregulation, cardiovascular and neuroendocrine regulation. The main aim of this mini review article is to investigate the relationship between ORX and thyroid system regulation. Although knowledge about the ORX system is evolving, its putative effects on hypothalamic-pituitary-thyroid (HPT) axis still appear unclear. We analyzed some studies about ORX control of HPT axis to know better the relationship between them. The studies that were analyzed suggest Hypocretin/ORX to modulate the thyroid regulation, but the nature (excitatory or inhibitory) of this possible interaction remains actually unclear and needs to be confirmed.