Action of thyroid hormone in brain

One Health: Circadian Medicine Benefits Both Non-human Animals and Humans Alike

Circadian biology's impact on human physical health and its role in disease development and progression is widely recognized. The forefront of circadian rhythm research now focuses on translational applications to clinical medicine, aiming to enhance disease diagnosis, prognosis, and treatment responses. However, the field of circadian medicine has predominantly concentrated on human healthcare, neglecting its potential for transformative applications in veterinary medicine, thereby overlooking opportunities to improve non-human animal health and welfare. This review consists of three main sections. The first section focuses on the translational potential of circadian medicine into current industry practices of agricultural animals, with a particular emphasis on horses, broiler chickens, and laying hens. The second section delves into the potential applications of circadian medicine in small animal veterinary care, primarily focusing on our companion animals, namely dogs and cats. The final section explores emerging frontiers in circadian medicine, encompassing aquaculture, veterinary hospital care, and non-human animal welfare and concludes with the integration of One Health principles. In summary, circadian medicine represents a highly promising field of medicine that holds the potential to significantly enhance the clinical care and overall health of all animals, extending its impact beyond human healthcare.

Movement Disorder Perspectives on Monocarboxylate 8 Deficiency: A Case Series of 3 Colombian Patients with Allan-Herndon-Dudley Syndrome

BACKGROUND

Deficiencies in the thyroid hormone transporter monocarboxylate 8 (MCT8) due to pathogenic variants in the SLC16A2 gene (OMIM 300095) result in a complex phenotype with main endocrine and neurologic symptoms. This rare disorder, named Allan-Herndon-Dudley syndrome (AHDS) (OMIM 300523), is inherited in an X-linked trait. One of the prominent features of AHDS is the presence of movement disorders (MD), which are complex and carry a significant burden of the disease.

CASES

Patient 1: male with hypotonia since birth, developmental delay, dystonic posturing at 4 months and at 15 months, and startle reaction developed with sensory stimuli. Patient 2: male, at 2 months, shows hypotonia and developmental delay, paroxysmal episodes triggered by a stimulus with sudden blush, tonic asymmetric posture, and no epileptiform activity. At 10 months, generalized dystonic posturing. Patient 3: typical neurodevelopmental milestones until 6 months; at 24 months, dystonia, startle reaction, and upper motoneuron signs.

CONCLUSIONS

We aim to describe our patients diagnosed with AHDS, focusing on MD phenomenology and strengthening the phenotype-genotype correlations for this rare condition.

The research landscape concerning environmental factors in neurodevelopmental disorders: Endocrine disrupters and pesticides-A review

In recent years, environmental epidemiology and toxicology have seen a growing interest in the environmental factors that contribute to the increased prevalence of neurodevelopmental disorders, with the purpose of establishing appropriate prevention strategies. A literature review was performed, and 192 articles covering the topic of endocrine disruptors and neurodevelopmental disorders were found, focusing on polychlorinated biphenyls, polybrominated diphenyl ethers, bisphenol A, and pesticides. This study contributes to analyzing their effect on the molecular mechanism in maternal and infant thyroid function, essential for infant neurodevelopment, and whose alteration has been associated with various neurodevelopmental disorders. The results provide scientific evidence of the association that exists between the environmental neurotoxins and various neurodevelopmental disorders. In addition, other possible molecular mechanisms by which pesticides and endocrine disruptors may be associated with neurodevelopmental disorders are being discussed.

Developmental programming by prenatal sounds: insights into possible mechanisms

In recent years, the impact of prenatal sound on development, notably for programming individual phenotypes for postnatal conditions, has increasingly been revealed. However, the mechanisms through which sound affects physiology and development remain mostly unexplored. Here, I gather evidence from neurobiology, developmental biology, cellular biology and bioacoustics to identify the most plausible modes of action of sound on developing embryos. First, revealing often-unsuspected plasticity, I discuss how prenatal sound may shape auditory system development and determine individuals' later capacity to receive acoustic information. I also consider the impact of hormones, including thyroid hormones, glucocorticoids and androgen, on auditory plasticity. Second, I review what is known about sound transduction to other - non-auditory - brain regions, and its potential to input on classical developmental programming pathways. Namely, the auditory pathway has direct anatomical and functional connectivity to the hippocampus, amygdala and/or hypothalamus, in mammals, birds and anurans. Sound can thus trigger both immediate and delayed responses in these limbic regions, which are specific to the acoustic stimulus and its biological relevance. Third, beyond the brain, I briefly consider the possibility for sound to directly affect cellular functioning, based on evidence in earless organisms (e.g. plants) and cell cultures. Together, the multi-disciplinary evidence gathered here shows that the brain is wired to allow multiple physiological and developmental effects of sound. Overall, there are many unexplored, but possible, pathways for sound to impact even primitive or immature organisms. Throughout, I identify the most promising research avenues for unravelling the processes of acoustic developmental programming.

Comprehensive Evaluation System for Post-Metabolic Activity of Potential Thyroid-Disrupting Chemicals

Endocrine-disrupting chemicals (EDCs) are compounds that disturb hormonal homeostasis by binding to receptors. EDCs are metabolized through hepatic enzymes, causing altered transcriptional activities of hormone receptors, and thus necessitating the exploration of the potential endocrine-disrupting activities of EDC-derived metabolites. Accordingly, we have developed an integrative workflow for evaluating the post-metabolic activity of potential hazardous compounds. The system facilitates the identification of metabolites that exert hormonal disruption through the integrative application of an MS/MS similarity network and predictive biotransformation based on known hepatic enzymatic reactions. As proof-of-concept, the transcriptional activities of 13 chemicals were evaluated by applying the in vitro metabolic module (S9 fraction). Identified among the tested chemicals were three thyroid hormone receptor (THR) agonistic compounds that showed increased transcriptional activities after phase I+II reactions (T3, 309.1 ± 17.3%; DITPA, 30.7 ± 1.8%; GC-1, 160.6 ± 8.6% to the corresponding parents). The metabolic profiles of these three compounds showed common biotransformation patterns, particularly in the phase II reactions (glucuronide conjugation, sulfation, GSH conjugation, and amino acid conjugation). Data-dependent exploration based on molecular network analysis of T3 profiles revealed that lipids and lipid-like molecules were the most enriched biotransformants. The subsequent subnetwork analysis proposed 14 additional features, including T4 in addition to 9 metabolized compounds that were annotated by prediction system based on possible hepatic enzymatic reaction. The other 10 THR agonistic negative compounds showed unique biotransformation patterns according to structural commonality, which corresponded to previous in vivo studies. Our evaluation system demonstrated highly predictive and accurate performance in determining the potential thyroid-disrupting activity of EDC-derived metabolites and for proposing novel biotransformants.

Potential Role of Anti-Müllerian Hormone in Regulating Seasonal Reproduction in Animals: The Example of Males

Seasonal reproduction is a survival strategy by which animals adapt to environmental changes to improve their fitness. Males are often characterized by a significantly reduced testicular volume, indicating that they are in an immature state. Although many hormones, including gonadotropins, have played a role in testicular development and spermatogenesis, research on other hormones is insufficient. The anti-Müllerian hormone (AMH), which is a hormone responsible for inducing the regression of Müllerian ducts involved in male sex differentiation, was discovered in 1953. Disorders in AMH secretion are the main biomarkers of gonadal dysplasia, indicating that it may play a crucial role in reproduction regulation. A recent study has found that the AMH protein is expressed at a high level during the non-breeding period of seasonal reproduction in animals, implying that it may play a role in restricting breeding activities. In this review, we summarize the research progress on the AMH gene expression, regulatory factors of the gene's expression, and its role in reproductive regulation. Using males as an example, we combined testicular regression and the regulatory pathway of seasonal reproduction and attempted to identify the potential relationship between AMH and seasonal reproduction, to broaden the physiological function of AMH in reproductive suppression, and to provide new ideas for understanding the regulatory pathway of seasonal reproduction.

Thrsp Gene and the ADHD Predominantly Inattentive Presentation

There are three presentations of attention-deficit/hyperactivity disorder (ADHD): the predominantly inattention (ADHD-PI), predominantly hyperactive-impulsive (ADHD-HI), and combined (ADHD-C) presentations of ADHD. These may represent distinct childhood-onset neurobehavioral disorders with separate etiologies. ADHD diagnoses are behaviorally based, so investigations into potential etiologies should be founded on behavior. Animal models of ADHD demonstrate face, predictive, and construct validity when they accurately reproduce elements of the symptoms, etiology, biochemistry, and disorder treatment. Spontaneously hypertensive rats (SHR/NCrl) fulfill many validation criteria and compare well with clinical cases of ADHD-C. Compounding the difficulty of selecting an ideal model to study specific presentations of ADHD is a simple fact that our knowledge regarding ADHD neurobiology is insufficient. Accordingly, the current review has explored a potential animal model for a specific presentation, ADHD-PI, with acceptable face, predictive, and construct validity. The Thrsp gene could be a biomarker for ADHD-PI presentation, and THRSP OE mice could represent an animal model for studying this distinct ADHD presentation.

Finite element analysis to predict temperature distribution in the human neck with abnormal thyroid: A proof of concept

BACKGROUND AND OBJECTIVE

Hyperthyroidism, hypothyroidism, goiter and cancer are some of the dysfunctions that can occur concerning the thyroid, an important body homeostasis regulatory gland located in the cervical region. These disorders are mostly caused by changes in metabolism and can impair quality of life. This study presents a non-invasive approach that can detect changes in thyroid metabolism through the finite element analysis and medical images. The objective of this work was to develop a numerical model to represent the temperature distribution in the human neck with and without the presence of thyroid nodules. The patient-specific computational model for the case with thyroid nodules was calibrated with infrared thermography.

METHODS

A three-dimensional geometrical model of the neck was constructed based on the segmentation of magnetic resonance (MR) images. The Finite Element Method (FEM) was used to simulate heat diffusion and convection in the cervical region. The infrared thermography image was used to calibrate the heat transfer constants to obtain the surface temperature of the human neck model containing the enlarged thyroid with nodules. Subsequently, another case for the entire neck with an abnormally large thyroid without the nodules was simulated using the calibrated physical constants.

RESULTS

Results of the simulations with and without the presence of thyroid nodules were compared, showing the influence of the generation of heat from the nodules, allowing observation of the thermal differences on the cervical surface and at the thyroid itself. The model with nodules presented higher skin temperature distribution in the anterior triangle region when compared to the case without nodules. An average of 0.36^∘C of absolute error and 1% of relative error was obtained for the calibration between the simulated model and the infrared image.

CONCLUSIONS

This research consists of an innovative approach by comparing the results obtained via FEM simulation and the corresponding infrared image of the same neck region under study. Since there are great variability and uncertainties in the determination of the thermal constants, we applied a procedure for calibrating them based on a patient-specific case, which involves a multinodular goiter accompanied by hyperthyroidism. This proof-of-concept study allows the creation of comparative scenarios between the FEM simulations and the corresponding infrared image. Thus, it is expected that, in the future, this approach could be used to include the effect of drugs in the treatment strategies of thyroid diseases and disorders.

Seasonality in tropical birds

The survival of offspring depends on environmental conditions. Many organisms have evolved with seasonality, characterized as initiation-termination-reinitiation of several physiological processes (i.e., body fattening, molt, plumage coloration, reproduction, etc). It is an adaptation for the survival of many species. Predominantly seasonal breeders use photoperiod as the most reliable environmental cue to adapt to seasonal changes but supplementary factors like temperature and food are synergistically involved in seasonal processes. Studies from diverse vertebrate systems have contributed to understanding the mechanism involved in seasonal reproduction at the molecular and endocrine levels. Long-day induced thyrotropin (thyroid-stimulating hormone) released from the pars tuberalis of the pituitary gland triggers local thyroid hormone activation within the mediobasal hypothalamus. This locally produced thyroid hormone, T3, regulates seasonal gonadotropin-releasing hormone secretion. Most of the bird species studied are seasonal in reproduction and linked behavior and, therefore, need to adjust reproductive decisions to environmental fluctuations. Reproductive strategies of the temperate zone breeders are well-documented, but less is known about tropical birds' reproduction and factors stimulating the annual breeding strategies. Here, we address seasonality in tropical birds with reference to seasonal reproduction and the various environmental factors influencing seasonal breeding.

Congenital Hypothyroidism among Infants Undergoing Thyroid Function Test in a Tertiary Care Centre: A Descriptive Cross-sectional Study

Introduction

Congenital hypothyroidism is the most preventable and treatable cause of mental retardation in newborns and infants. Screening for congenital hypothyroidism in newborns and infants is not a routine practice in our part of the world. This study aimed to find out the prevalence of congenital hypothyroidism among infants undergoing thyroid function test in a tertiary care centre.

Methods

A descriptive cross-sectional study was done in the Department of Biochemistry, from laboratory records starting 14th April, 2013 to 13th April, 2020 after obtaining ethical clearance from the Institutional Review Committee (Reference number: 1502/019). Data of infants whose thyroid function tests were performed were obtained using convenience sampling. Thyroid-stimulating hormone was categorised per the European Society of Paediatric Endocrinology guidelines. Data were entered and analysed using Microsoft Excel 2011 and the Statistical Package for the Social Sciences version 11.5. Point estimate at a 95% Confidence Interval was calculated along with frequency and percentages for binary data.

Results

Among 1243 infants, 56 (4.50%) (3.35-5.65 at 95% Confidence Interval) infants were diagnosed with congenital hypothyroidism.

Conclusions

The prevalence of congenital hypothyroidism was higher than other studies done in similar settings. An unexpected finding of treatment-induced hyperthyroidism was observed, indicating a lack of regular and timely follow-up of infants diagnosed with congenital hypothyroidism.

Keywords

congenital hypothyroidism; Nepal; newborn screening; prevalence.

Genetics of Thyroid Disorders

Thyroid diseases in children and adolescents include acquired or congenital conditions, including genetic disorders either isolated or part of a syndrome. Briefly, we will review the physiology and pathophysiology of the thyroid gland and its disorders. The aim of this chapter is to describe genetic abnormalities of the thyroid gland.

Developmental Hypothyroidism Influences the Development of the Entorhinal-Dentate Gyrus Pathway of Rat Offspring

BACKGROUND

Developmental hypothyroidism impairs learning and memory in offspring, which depend on extensive neuronal circuits in the entorhinal cortex, together with the hippocampus and neocortex. The entorhinal-dentate gyrus pathway is the main entrance of memory circuits. We investigated whether developmental hypothyroidism impaired the morphological development of the entorhinal-dentate gyrus pathway.

METHODS

We examined the structure and function of the entorhinal-dentate gyrus pathway in response to developmental hypothyroidism induced using 2-mercapto-1-methylimidazole.

RESULTS

1,1´-Dioctadecyl-3,3,3´,3´-tetramethylindocarbocyanine perchlorate tract tracing indicated that entorhinal axons showed delayed growth in reaching the outer molecular layer of the dentate gyrus at postnatal days 2 and 4 in hypothyroid conditions. The proportion of fibers in the outer molecular layer was significantly smaller in the hypothyroid group than in the euthyroid group at postnatal day 4. At postnatal day 10, the pathway showed a layer-specific distribution in the outer molecular layer, similar to the euthyroid group. However, the projected area of entorhinal axons was smaller in the hypothyroid group than in the euthyroid group. An electrophysiological examination showed that hypothyroidism impaired the long-term potentiation of the perforant and the cornu ammonis 3-cornu ammonis 1 pathways. Many repulsive axon guidance molecules were involved in the formation of the entorhinaldentate gyrus pathway. The hypothyroid group had higher levels of erythropoietin-producing hepatocyte ligand A3 and semaphorin 3A than the euthyroid group.

CONCLUSION

We demonstrated that developmental hypothyroidism might influence the development of the entorhinal-dentate gyrus pathway, contributing to impaired long-term potentiation. These findings improve our understanding of neural mechanisms for memory function.

Cognitive and White Matter Microstructure Development in Congenital Hypothyroidism and Familial Thyroid Disorders

CONTEXT

Children with congenital hypothyroidism (CH) are at risk for suboptimal neurodevelopment.

OBJECTIVES

To evaluate neurocognitive function and white matter microstructure in children with permanent or transient CH and to correlate these findings with disease severity.

DESIGN, PARTICIPANTS AND METHODS

A retrospective and prospective observational study was conducted in 39 children with permanent or transient CH, and in 39 healthy children. Cognitive function was assessed by Wechsler Intelligence Scale, Fourth Edition, and by other tests; the white matter microstructure was investigated by 3 Tesla magnetic resonance imaging.

RESULTS

Children with permanent CH have lower cognitive scores at a median age of 9.5 years than those with transient CH and controls. An IQ score between 71 and 84 was found in 28.6% of permanent CH and of <70 (P = 0.06) in 10.7%. The Processing Speed Index (PSI; P = 0.004), sustained visual attention (P = 0.02), reading speed (P = 0.0001), written calculations (P = 0.002), and numerical knowledge (P = 0.0001) were significantly lower than controls. Children born to mothers with Hashimoto's thyroiditis have significantly lower IQ values (P = 0.02), Working Memory Index (P = 0.03), and PSI (P = 0.02). Significantly lower IQ and Verbal Comprehension Index values were found in children with a family history of thyroid disorders (P = 0.004 and P = 0.009, respectively). In children with permanent CH, significant correlations between abnormalities in white matter microstructural, clinical, and cognitive measures were documented.

CONCLUSIONS

These findings indicate that children with CH are at risk of neurocognitive impairment and white matter abnormalities despite timely and adequate treatment. The association between offspring cognitive vulnerability and maternal thyroid disorders requires careful consideration.

Low striatal T3 is implicated in inattention and memory impairment in an ADHD mouse model overexpressing thyroid hormone-responsive protein

Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder, potentially with a biological basis; however, its exact cause remains unknown. Thyroid hormone (TH) abnormalities are more prevalent in patients with ADHD than in the general population, indicating a shared pathogenetic mechanism for these conditions. Previously, we identified that overexpression of thyroid hormone-responsive protein (THRSP), a gene highly responsive to TH status, induced inattention in male mice. Herein, we sought to explore whether TH function in THRSP-overexpressing (THRSP OE) mice influences ADHD-like (inattention) behavior. We now confirm that THRSP overexpression in male mice reproduces behavioral features of ADHD, including sustained inattention and memory impairment, accompanied by excessive theta waves that were found normal in both the THRSP-knockout and hetero groups. Physiological characterization revealed low striatal T3 levels in the THRSP OE mice due to reduced striatal T3-specific monocarboxylate transporter 8 (MCT8), indicating brain-specific hypothyroidism in this transgenic mouse strain. TH replacement for seven days rescued inattention and memory impairment and the normalization of theta waves. This study further supports the involvement of the upregulated THRSP gene in ADHD pathology and indicates that THRSP OE mice can serve as an animal model for the predominantly inattentive subtype of ADHD.

Development of cerebral mitochondrial respiratory function is impaired by thyroid hormone deficiency before birth in a region-specific manner

Thyroid hormones regulate adult metabolism partly through actions on mitochondrial oxidative phosphorylation (OXPHOS). They also affect neurological development of the brain, but their role in cerebral OXPHOS before birth remains largely unknown, despite the increase in cerebral energy demand during the neonatal period. Thus, this study examined prepartum development of cerebral OXPHOS in hypothyroid fetal sheep. Using respirometry, Complex I (CI), Complex II (CII), and combined CI&CII OXPHOS capacity were measured in the fetal cerebellum and cortex at 128 and 142 days of gestational age (dGA) after surgical thyroidectomy or sham operation at 105 dGA (term ~145 dGA). Mitochondrial electron transfer system (ETS) complexes, mRNA transcripts related to mitochondrial biogenesis and ATP production, and mitochondrial density were quantified using molecular techniques. Cerebral morphology was assessed by immunohistochemistry and stereology. In the cortex, hypothyroidism reduced CI-linked respiration and CI abundance at 128 dGA and 142 dGA, respectively, and caused upregulation of PGC1α (regulator of mitochondrial biogenesis) and thyroid hormone receptor β at 128 dGA and 142 dGA, respectively. In contrast, in the cerebellum, hypothyroidism reduced CI&II- and CII-linked respiration at 128 dGA, with no significant effect on the ETS complexes. In addition, cerebellar glucocorticoid hormone receptor and adenine nucleotide translocase (ANT1) were downregulated at 128 dGA and 142 dGA, respectively. These alterations in mitochondrial function were accompanied by reduced myelination. The findings demonstrate the importance of thyroid hormones in the prepartum maturation of cerebral mitochondria and have implications for the etiology and treatment of the neurodevelopmental abnormalities associated with human prematurity and congenital hypothyroidism.

Congenital hypothyroidism impairs spine growth of dentate granule cells by downregulation of CaMKIV

Congenital hypothyroidism (CH), a common neonatal endocrine disorder, can result in cognitive deficits if delay in diagnose and treatment. Dentate gyrus (DG) is the severely affected subregion of the hippocampus by the CH, where the dentate granule cells (DGCs) reside in. However, how CH impairs the cognitive function via affecting DGCs and the underlying mechanisms are not fully elucidated. In the present study, the CH model of rat pups was successfully established, and the aberrant dendrite growth of the DGCs and the impaired cognitive behaviors were observed in the offspring. Transcriptome analysis of hippocampal tissues following rat CH successfully identified that calcium/calmodulin-dependent protein kinase IV (CaMKIV) was the prominent regulator involved in mediating deficient growth of DGC dendrites. CaMKIV was shown to be dynamically regulated in the DG subregion of the rats following drug-induced CH. Interference of CaMKIV expression in the primary DGCs significantly reduced the spine density of dendrites, while addition of T3 to the primary DGCs isolated from CH pups could facilitate the spine growth of dendrites. Insights into relevant mechanisms revealed that CH-mediated CaMKIV deficiency resulted in the significant decrease of phosphorylated CREB in DGCs, in association with the abnormality of dendrites. Our results have provided a distinct cell type in hippocampus that is affected by CH, which would be beneficial for the treatment of CH-induced cognitive deficiency.

Thyroid hormone and thyroid hormone nuclear receptors: History and present state of art

The present review traces the road leading to discovery of L-thyroxine, thyroid hormone (3,5,3´-triiodo-L-thyronine, T₃) and its cognate nuclear receptors. Thyroid hormone is a pleio-tropic regulator of growth, differentiation, and tissue homeostasis in higher organisms. The major site of the thyroid hormone action is predominantly a cell nucleus. T₃ specific binding sites in the cell nuclei have opened a new era in the field of the thyroid hormone receptors (TRs) discovery. T₃ actions are mediated by high affinity nuclear TRs, TRalpha and TRbeta, which function as T₃-activated transcription factors playing an essential role as transcription-modulating proteins affecting the transcriptional responses in target genes. Discovery and characterization of nuclear retinoid X receptors (RXRs), which form with TRs a heterodimer RXR/TR, positioned RXRs at the epicenter of molecular endocrinology. Transcriptional control via nuclear RXR/TR heterodimer represents a direct action of thyroid hormone. T₃ plays a crucial role in the development of brain, it exerts significant effects on the cardiovascular system, skeletal muscle contractile function, bone development and growth, both female and male reproductive systems, and skin. It plays an important role in maintaining the hepatic, kidney and intestine homeostasis and in pancreas, it stimulates the beta-cell proliferation and survival. The TRs cross-talk with other signaling pathways intensifies the T₃ action at cellular level. The role of thyroid hormone in human cancers, acting via its cognate nuclear receptors, has not been fully elucidated yet. This review is aimed to describe the history of T₃ receptors, starting from discovery of T3 binding sites in the cell nuclei to revelation of T₃ receptors as T₃-inducible transcription factors in relation to T₃ action at cellular level. It also focuses on milestones of investigation, comprising RXR/TR dimerization, cross-talk between T₃ receptors, and other regulatory pathways within the cell and mainly on genomic action of T₃. This review also focuses on novel directions of investigation on relationships between T₃ receptors and cancer. Based on the update of available literature and the author's experimental experience, it is devoted to clinicians and medical students.

Oligodendrocyte progenitor cell maturation is dependent on dual function of MCT8 in the transport of thyroid hormone across brain barriers and the plasma membrane

Inactivating mutations in the thyroid hormone (TH) transporter monocarboxylate transporter 8 (MCT8) causes a rare and debilitating form of X-linked psychomotor disability known as Allan Herndon Dudley syndrome (AHDS). One of the most prominent pathophysiological symptoms of MCT8-deficiency is hypomyelination. Here, patient-derived induced pluripotent stem cells (iPSCs) were used to study the role of MCT8 and TH on the maturation of oligodendrocytes. Interestingly, neither MCT8 mutations nor reduced TH affected the in vitro differentiation of control or MCT8-deficient iPSCs into oligodendrocytes. To assess whether patient-derived iPSC-derived oligodendrocyte progenitor cells (iOPCs) could provide myelinating oligodendrocytes in vivo, cells were transplanted into the shiverer mouse corpus callosum where they survived, migrated, and matured into myelinating oligodendrocytes, though the myelination efficiency was reduced compared with control cells. When MCT8-deficient and healthy control iOPCs were transplanted into a novel hypothyroid immunodeficient triple knockout mouse (tKO, mct8^-/- ; oatp1c1^-/- ; rag2^-/- ), they failed to provide behavioral recovery and did not mature into oligodendrocytes in the hypothyroid corpus callosum, demonstrating the critical role of TH transport across brain barriers in oligodendrocyte maturation. We conclude that MCT8 plays a cell autonomous role in oligodendrocyte maturation and that functional TH transport into the central nervous system will be required for developing an effective treatment for MCT8-deficient patients.

Changes in the Control of the Hypothalamic-Pituitary Gonadal Axis Across Three Differentially Selected Strains of Laying Hens (Gallus gallus domesticus)

Genetic selection for earlier sexual maturation and extended production cycles in laying hens has significantly improved reproductive efficiency. While limited emphasis has been placed on the underlying physiological changes, we hypothesize that modifications in the control of the hypothalamic-pituitary gonadal (HPG) axis have occurred. Thus, three strains of White leghorn derivatives were followed from hatch to 100 weeks of age (woa), including Lohmann LSL-lite (n = 120) as current commercial hens, heritage Shaver White leghorns (n = 100) as 2000s commercial equivalents, and Smoky Joe hens (n = 68) as 1960s commercial equivalents. Body weight (BW) and egg production were monitored, and blood samples were collected throughout to monitor estradiol (E₂) concentrations. Tissue samples were collected at 12, 17, 20, 25, 45, 60, 75, and 100 woa to capture changes in mRNA levels of key genes involved in the HPG axis and monitor ovarian follicular pools. All hens, regardless of strain, age or photoperiod laid their first egg within a 64-gram BW window and, as E₂ levels increased prior to photostimulation (PS) in Lohmann and Shaver hens, a metabolic trigger likely induced sexual maturation. However, increased levels of Opsin 5 (OPN5) were observed during the maturation period. Although an elevation in gonadotrophin-releasing hormone I (GnRH-I) mRNA levels was associated with early maturation, no changes in gonadotrophin-inhibitory hormone (GnIH) mRNA levels were observed. Nonetheless, a significant shift in pituitary sensitivity to GnRH was associated with maturation. Throughout the trial, Lohmann, Shaver, and Smoky Joe hens laid 515, 417, and 257 eggs, respectively (p < 0.0001). Results show that the extended laying persistency in Lohmann hens was supported by sustained pituitary sensitivity to GnRH-I, recurrent elevations in follicle-stimulating hormone (FSH) mRNA levels, and five cyclical elevations in E₂ levels. This was also associated with a consistently higher pool of small white ovarian follicles. In summary, our results demonstrate first that, regardless of photoperiodic cues, meeting a specific narrow body weight threshold is sufficient to initiate sexual maturation in Leghorn chicken derivatives. Furthermore, recurrent increases in E₂ and FSH may be the key to sustain extended laying period, allowing modern layers to double their reproductive capacity compared to their 1960s-counterparts.

Neuroprotection elicited by resveratrol in a rat model of hypothyroidism: Possible involvement of cholinergic signaling and redox status

Both the cholinergic pathway and oxidative stress are important mechanisms involved in the pathogenesis of hypothyroidism, a condition characterized by low levels of thyroid hormone that predispose the patient to brain dysfunction. Phenolic compounds have numerous health benefits, including antioxidant activity. This study evaluates the preventive effects of resveratrol in the cholinergic system and redox status in rats with methimazole-induced hypothyroidism. Hypothyroidism increases acetylcholinesterase (AChE) activity and density in the cerebral cortex and hippocampus and decreases the α7 and M1 receptor densities in the hippocampus. Hypothyroidism also increases cellular levels of reactive oxygen species (ROS) and thiobarbituric acid reactive substances (TBARS), but reduces total thiol content, and catalase and superoxide dismutase activities in the serum. In the cerebral cortex and hippocampus, hypothyroidism increases the levels of ROS and nitrites. In this study, resveratrol (50 mg/kg) treatment prevents the observed increase in AChE in the cerebral cortex, and increases the protein levels of NeuN, a marker of mature neurons. Resveratrol also prevents changes in serum ROS levels and brain structure, as well as the levels of TBARS, total thiol content, and serum catalase enzyme activity. These collective findings suggest that resveratrol has a high antioxidant capacity and can restore hypothyroidism-triggered alterations related to neurotransmission. Thus, it is a promising agent for the prevention of brain damage resulting from hypothyroidism.

The Laboratory Features of Congenital Hypothyroidism and Approach to Therapy

Congenital hypothyroidism (CH) is one of the most common preventable causes of intellectual disability. Thyroid hormone is required for normal brain development, but neonates with CH typically appear healthy at birth, which leads to delays in diagnosis and treatment. In developed countries, newborn screening programs have led to earlier diagnosis and treatment of CH, resulting in improved neurodevelopmental outcomes. Neonates with an abnormal newborn screen require prompt confirmatory serum thyroid function tests and treatment with thyroid hormone. Further evaluation for the etiology of CH should not delay treatment decisions.

Expression of the sodium iodide symporter (NIS) in reproductive and neural tissues of teleost fish

Iodine, an essential component of thyroid hormones, can only be obtained through the diet. The sodium iodide symporter (NIS) transports iodide across mammalian intestinal and thyroid epithelia to deliver iodide for thyroid hormone production. Using reverse transcription-polymerase chain reaction (RT-PCR) we confirmed that mRNA for a homolog of mammalian NIS is expressed in comparable locations, both sub-pharyngeal thyroid tissue and intestine, in multiple teleost fish species, supporting a conserved mechanism for intestinal-thyroid iodine transport across vertebrates. To determine when in embryogenesis NIS expression is initiated we utilized in situ hybridization (ISH) during development of zebrafish (Danio rerio) embryos. This revealed expression of nis as early as 2 days post fertilization (dpf) along the dorsal surface of the yolk sac, suggesting a function to import iodine from yolk. To evaluate the potential for maternal deposition of iodine in yolk, RT-PCR and further in situ staining of ovarian tissue in gravid female zebrafish confirmed NIS mRNA presence in the ooplasm and granulosa layer of early stage follicles. This further suggests that maternally-deposited NIS mRNA may be available for early embryogenesis. Unexpectedly, ISH in embryos revealed robust nis expression in the central nervous system throughout days 2-5 days post fertilization, with adult whole brain ISH localizing expression in the hypothalamus, cerebellum, and optic tectum. RT-PCR on whole brain tissue from five species of adult fish representing three taxonomic orders likewise revealed robust CNS expression. These unexpected locations of nis expression suggest novel, as yet undescribed reproductive and neural functions of NIS in teleost species.

Mother to Fetus Transfer of Hydroxylated Polychlorinated Biphenyl Congeners (OH-PCBs) in the Japanese Macaque (Macaca fuscata): Extrapolation of Exposure Scenarios to Humans

Prenatal hydroxylated polychlorinated biphenyls (OH-PCBs) exposure may disrupt fetal brain development during the critical period of thyroid hormone (TH) action. However, there are limited studies on the OH-PCB transfer to the fetal brain, particularly in primates. In this study, we selected the Japanese macaque (Macaca fuscata) as a model animal for the fetal transfer of OH-PCBs in humans and revealed OH-PCB concentrations and their relationships in maternal and fetal blood, liver, and brain. l-thyroxine (T4)-like OH-PCBs including 4OH-CB187, a major congener in humans, were found in high proportions in the blood, liver, brain, and placenta of pregnant Japanese macaques. OH-PCBs were detected in the fetal brain and liver in the first trimester, indicating their transfer to the brain in the early pregnancy stage. 4OH-CB187 and 4OH-CB202 were the major congeners found in fetal brain, indicating that these T4-like OH-PCBs are transported from maternal blood to the fetal brain via the placenta. These results indicate that further studies are needed on the effects of OH-PCBs on the developing fetal brain.

Light and Hormones in Seasonal Regulation of Reproduction and Mood

Organisms that inhabit the temperate zone exhibit various seasonal adaptive behaviors, including reproduction, hibernation, molting, and migration. Day length, known as photoperiod, is the most noise-free and widely used environmental cue that enables animals to anticipate the oncoming seasons and adapt their physiologies accordingly. Although less clear, some human traits also exhibit seasonality, such as birthrate, mood, cognitive brain responses, and various diseases. However, the molecular basis for human seasonality is poorly understood. Herein, we first review the underlying mechanisms of seasonal adaptive strategies of animals, including seasonal reproduction and stress responses during the breeding season. We then briefly summarize our recent discovery of signaling pathways involved in the winter depression-like phenotype in medaka fish. We believe that exploring the regulation of seasonal traits in animal models will provide insight into human seasonality and aid in the understanding of human diseases such as seasonal affective disorder (SAD).

Experimental hypothyroidism raises brain kynurenic acid - Novel aspect of thyroid dysfunction

Hypothyroidism frequently manifests with altered mood and disturbed cognition. Kynurenic acid may influence cognition through antagonism of N-methyl-d-aspartate receptors (NMDA) and α7 nicotinic receptors. In here, thyroid hormones effects on kynurenic acid synthesis in rat cortical slices and on kynurenine aminotransferases (KATs) activity in semi-purified cortical homogenates were studied. Furthermore, brain kynurenic acid levels and KATs activities were evaluated in experimental model of hypothyroidism, induced by chronic administration of 0.05% propylthiouracil in drinking water. In vitro, L-thyroxine (T₄) and 3,3,5-triiodothyronine (T₃), reduced kynurenic acid synthesis and KATs activities (IC₅₀ ~ 50-150 μM). In vivo, propylthiouracil increased cortical, hippocampal and striatal, but not cerebellar kynurenic acid content (192%, 142% and 124% of control, respectively), despite uniformly decreased KAT II activity and lower cortical and striatal KAT I activity. T₄ application to hypothyroid animals restored kynurenic acid levels to control values and reversed enzymatic changes. T₄ alone did not change brain kynurenic acid levels, despite increased activities of brain KATs. Hence, thyroid hormones modulate kynurenic acid levels by two opposing mechanisms, stimulation of KATs activity, most probably transcriptional, and direct, post-translational inhibition of KATs. Lack of correlation between KATs activity and kynurenic acid level may reflect the influence of T₄ on organic anion transporter and result from impaired removal of kynurenic acid from the brain during hypothyroidism. Our data reveal novel mechanism linked with thyroid hormones deficiency and imply the potential involvement of increased brain kynurenic acid in the hypothyroidism-related cognitive disturbance.

Should I Lay or Should I Grow: Photoperiodic Versus Metabolic Cues in Chickens

While photoperiod has been generally accepted as the primary if not the exclusive cue to stimulate reproduction in photoperiodic breeders such as the laying hen, current knowledge suggests that metabolism, and/or body composition can also play an influential role to control the hypothalamic-pituitary gonadal (HPG)-axis. This review thus intends to first describe how photoperiodic and metabolic cues can impact the HPG axis, then explore and propose potential common pathways and mechanisms through which both cues could be integrated. Photostimulation refers to a perceived increase in day-length resulting in the stimulation of the HPG. While photoreceptors are present in the retina of the eye and the pineal gland, it is the deep brain photoreceptors (DBPs) located in the hypothalamus that have been identified as the potential mediators of photostimulation, including melanopsin (OPN4), neuropsin (OPN5), and vertebrate-ancient opsin (VA-Opsin). Here, we present the current state of knowledge surrounding these DBPs, along with their individual and relative importance and, their possible downstream mechanisms of action to initiate the activation of the HPG axis. On the metabolic side, specific attention is placed on the hypothalamic integration of appetite control with the stimulatory (Gonadotropin Releasing Hormone; GnRH) and inhibitory (Gonadotropin Inhibitory Hormone; GnIH) neuropeptides involved in the control of the HPG axis. Specifically, the impact of orexigenic peptides agouti-related peptide (AgRP), and neuropeptide Y (NPY), as well as the anorexigenic peptides pro-opiomelanocortin (POMC), and cocaine-and amphetamine regulated transcript (CART) is reviewed. Furthermore, beyond hypothalamic control, several metabolic factors involved in the control of body weight and composition are also presented as possible modulators of reproduction at all three levels of the HPG axis. These include peroxisome proliferator-activated receptor gamma (PPAR-γ) for its impact in liver metabolism during the switch from growth to reproduction, adiponectin as a potential modulator of ovarian development and follicular maturation, as well as growth hormone (GH), and leptin (LEP).

Interactive Effects of Apolipoprotein E ε4 and Triiodothyronine on Memory Performance in Patients With Subjective Cognitive Decline

Background: The aim of the present study was to investigate the associations between thyroid hormones, cognitive performance, and apolipoprotein E (APOE) genotype in euthyroid patients with subjective cognitive decline (SCD). Methods: We recruited 197 euthyroid patients that fulfilled the criteria for SCD. All participants were classified into APOE ε4 carriers and non-carriers based on the presence of the APOE ε4 allele. Patients with SCD who had the APOE ε2/ε4 genotype were excluded from the study. We then performed correlation and regression analyses to evaluate the associations between cognitive performance and thyroid hormones in APOE ε4 carriers and non-carriers. Results: We found no significant differences in cognitive function between APOE ε4 carriers and non-carriers. However, higher levels of triiodothyronine (T3) were associated with better verbal memory performance (immediate and delayed recall tasks) in APOE ε4 carriers, whereas a negative association was found in APOE ε4 non-carriers. Furthermore, there was a significant interactive effect of APOE ε4 status and T3 levels on verbal memory performance (immediate and delayed recall tasks). Conclusions: These findings suggest that in patients with SCD, T3 might have a protective effect on memory in those who are APOE ε4 carriers. The differential susceptibility hypothesis would thus support a gene-by-hormone crossover interaction between APOE ε4 allele and T3 in this study. Early identification and intervention of high-risk individuals for cognitive decline is important to establish new strategies for preventing dementia.

A Pivotal Genetic Program Controlled by Thyroid Hormone during the Maturation of GABAergic Neurons

Mammalian brain development critically depends on proper thyroid hormone signaling, via the TRα1 nuclear receptor. The downstream mechanisms by which TRα1 impacts brain development are currently unknown. In order to investigate these mechanisms, we used mouse genetics to induce the expression of a dominant-negative mutation of TRα1 specifically in GABAergic neurons, the main inhibitory neurons in the brain. This triggered post-natal epileptic seizures and a profound impairment of GABAergic neuron maturation in several brain regions. Analysis of the transcriptome and TRα1 cistrome in the striatum allowed us to identify a small set of genes, the transcription of which is upregulated by TRα1 in GABAergic neurons and which probably plays an important role during post-natal maturation of the brain. Thus, our results point to GABAergic neurons as direct targets of thyroid hormone during brain development and suggest that many defects seen in hypothyroid brains may be secondary to GABAergic neuron malfunction.

A Review of Medical Conditions and Behavioral Problems in Dogs and Cats

Not all animals behave identically when faced with the same situation. These individual differences in the expression of their behavior could be due to many factors, including medical conditions. These medical problems can change behavior directly or indirectly. The aims of this review are to describe the state of the art of the relationship among some medical and behavioral problems, and to propose new lines of investigation. The revision is focused on the relation between behavioral problems and pain, endocrine diseases, neurological problems, vomeronasal organ alterations, and cardiac disorders. These problems represent a diagnostic challenge from a practical point of view. The most common sign of pain in animals is a change in behavior. Although the relation of pain to behavioral problems has been widely studied, it is not absolutely clear. As an example, the relation between sleep disorders and pain is poorly known in veterinary medicine. New studies in humans and laboratory animals show that a reciprocal relationship does, in fact, exist. More specifically, the literature suggests that the temporal effect of sleep deprivation on pain may be stronger than that of pain on sleep. Some behavioral problems could modify the sleep-awake cycle (e.g., cognitive dysfunction). The impact of these behavioral problems on pain perception is completely unknown in dogs and cats. Thyroid hormones play an important role, regarding behavioral control. Both hypothyroidism and hyperthyroidism have been related to behavioral changes. Concerning hypothyroidism, this relationship remains controversial. Nonetheless, new neuro-imaging studies provide objective evidence that brain structure and function are altered in hypothyroid patients, both in laboratory animals and in humans. There are many neurological problems that could potentially change behavior. This paper reviews those neurological problems that could lead to behavioral changes without modifying neurological examination. The most common problems are tumors that affect central nervous system silent zones, mild traumatic brain injury, ischemic attacks, and epilepsy. Most of these diseases and their relationship to behavior are poorly studied in dogs and cats. To better understand the pathophysiology of all of these problems, and their relation to behavioral problems, may change the diagnostic protocol of behavioral problems.

Thyroid Hormones in the Brain and Their Impact in Recovery Mechanisms After Stroke

Thyroid hormones are of fundamental importance for brain development and essential factors to warrant brain functions throughout life. Their actions are mediated by binding to specific intracellular and membranous receptors regulating genomic and non-genomic mechanisms in neurons and populations of glial cells, respectively. Among others, mechanisms include the regulation of neuronal plasticity processes, stimulation of angiogenesis and neurogenesis as well modulating the dynamics of cytoskeletal elements and intracellular transport processes. These mechanisms overlap with those that have been identified to enhance recovery of lost neurological functions during the first weeks and months after ischemic stroke. Stimulation of thyroid hormone signaling in the postischemic brain might be a promising therapeutic strategy to foster endogenous mechanisms of repair. Several studies have pointed to a significant association between thyroid hormones and outcome after stroke. With this review, we will provide an overview on functions of thyroid hormones in the healthy brain and summarize their mechanisms of action in the developing and adult brain. Also, we compile the major thyroid-modulated molecular pathways in the pathophysiology of ischemic stroke that can enhance recovery, highlighting thyroid hormones as a potential target for therapeutic intervention.

White matter microstructural abnormalities in children with severe congenital hypothyroidism

This study assessed white matter microstructural integrity and behavioral correlates for children with severe congenital hypothyroidism (CH) who were identified and treated early following newborn screening. Eighteen children with severe CH and 21 healthy controls underwent a battery of behavioral measures of hearing, language and communication, along with diffusion MR imaging. Tract-based spatial statistics were performed on standard diffusion parameters of fractional anisotropy and diffusivity metrics. Microscopic diffusion anisotropy mapping based on the Spherical Mean Technique was also used to evaluate biologically specific metrics. Compared with age-matched controls, children with severe CH had poorer hearing and communication skills, albeit generally within normal limits. Children with severe CH had fractional anisotropy that was significantly lower in the cerebellum, bilateral thalami and right temporal lobe, and radial diffusivity that was significantly higher in the cerebellum and bilateral thalami. Microscopic fractional anisotropy and intra-neurite volume fraction were also significantly decreased, and transverse microscopic diffusivity was significantly increased, in the CH group in areas including the cerebellum, thalamus, occipital lobe, and corpus callosum, and in the white matter adjacent to sensorimotor cortex, particularly in the left hemisphere. Significant and widespread correlations were observed between behavioral measures and measures of white matter microstructural integrity in children with CH. The results indicate that children with severe CH who are identified through newborn screening may have significant brain white matter microstructural abnormalities despite early treatment.

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Children with severe CH show reductions in white matter microstructural integrity.

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Hearing and communication abilities are impaired for some children with severe CH.

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White matter abnormalities are associated with communication abilities in CH.

Arctic charr brain transcriptome strongly affected by summer seasonal growth but only subtly by feed deprivation

Background

The Arctic charr (Salvelinus alpinus) has a highly seasonal feeding cycle that comprises long periods of voluntary fasting and a short but intense feeding period during summer. Therefore, the charr represents an interesting species for studying appetite-regulating mechanisms in fish.

Results

In this study, we compared the brain transcriptomes of fed and feed deprived charr over a 4 weeks trial during their summer feeding season. Despite prominent differences in body condition between fed and feed deprived charr at the end of the trial, feed deprivation affected the brain transcriptome only slightly. In contrast, the transcriptome differed markedly over time in both fed and feed deprived charr, indicating strong shifts in basic cell metabolic processes possibly due to season, growth, temperature, or combinations thereof. The GO enrichment analysis revealed that many biological processes appeared to change in the same direction in both fed and feed deprived fish. In the feed deprived charr processes linked to oxygen transport and apoptosis were down- and up-regulated, respectively. Known genes encoding for appetite regulators did not respond to feed deprivation. Gene expression of Deiodinase 2 (DIO2), an enzyme implicated in the regulation of seasonal processes in mammals, was lower in response to season and feed deprivation. We further found a higher expression of VGF (non-acronymic) in the feed deprived than in the fed fish. This gene encodes for a neuropeptide associated with the control of energy metabolism in mammals, and has not been studied in relation to regulation of appetite and energy homeostasis in fish.

Conclusions

In the Arctic charr, external and endogenous seasonal factors for example the increase in temperature and their circannual growth cycle, respectively, evoke much stronger responses in the brain than 4 weeks feed deprivation. The absence of a central hunger response in feed deprived charr give support for a strong resilience to the lack of food in this high Arctic species. DIO2 and VGF may play a role in the regulation of energy homeostasis and need to be further studied in seasonal fish.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5874-z) contains supplementary material, which is available to authorized users.

Interactive Effects of Exercise, Sex Hormones, and Transient Congenital Hypothyroidism on Long-Term Potentiation in Hippocampal Slices of Rat Offspring

Introduction:

The long-term adverse effects of transient thyroid function abnormalities at birth on intellectual development are proven. The effect of exercise increases in the presence of sex hormones. The current study aimed at investigating the possibility that a combination of sex hormones and exercise has synergistic effects on neural plasticity in Transient Congenital Hypothyroidism (TCH) rats.

Methods:

To induce hypothyroidism in the mothers, Propylthiouracil (PTU) was added to drinking water (100 mg/L) on the 6th day of gestation and continued until the 21^st Postnatal Day. From Postnatal Day (PND) 28 to 47, the female and male pups received 17β-estradiol and testosterone, respectively. The mild treadmill exercise began 30 minutes after the sex hormones or vehicle administration. On PND 48, electrophysiological experiments were performed on brain slices.

Results:

Increase of Long-Term Potentiation (LTP) was observed in sedentary-non-hormone female rats of TCH group, compared with that of the control. The exercise enhanced LTP in control rats, but the hormones showed no significant effect. The effect of exercise and sex hormone was not significant in the TCH group. The combination of exercise and testosterone enhanced LTP in TCH male rats, while the combination of exercise and estradiol or each of them individually did not produce such an effect on LTP in TCH female rats.

Conclusion:

The study findings showed an increase in excitatory transmission despite the returning of thyroid hormone levels to normal range in TCH female rats. Also a combination treatment including exercise and testosterone enhanced LTP in male rats of TCH group, which was a gender-specific event.

Molecular mechanism of endocrine-disruptive effects induced by Bisphenol A: The role of transmembrane G-protein estrogen receptor 1 and integrin αvβ3

Bisphenol A (BPA) is one of the highest volume industrial products worldwide and has been widely used to make various products as the intermediates of polycarbonate plastics and epoxy resins. Inevitably, general population has been widely exposed to BPA due to extensive use of BPA-containing products. BPA has similar chemical structure with the natural estrogen and has been shown to induce a variety of estrogen-like endocrine effects on organism in vivo or in vitro. High doses of BPA tend to act as antagonist of estrogen receptors (ERs) by directly regulating the genomic transcription. However, BPA at environmentally relevant low-dose always disrupt the biological function via a non-genomic manner mediated by membrane receptors, rather than ERs. Although some studies had investigated the non-genomic effects of low-dose BPA, the exact molecular mechanism still remains unclear. Recently, we found that membrane G protein-coupled estrogen receptor 1 and integrin αvβ3 and its relative signal pathways participate in the induction of male germ cell proliferation and thyroid transcription disruption by the low-dose BPA. A profound understanding for the mechanism of action of the environmentally relevant BPA exposure not only contributes to objectively evaluate and predict the potential influence to human health, but also provides theoretical basis and methodological support for assessing health effects trigged by other estrogen-like environmental endocrine disruptors. Based mainly on our recent findings, this review outlines the research progress of molecular mechanism on endocrine disrupting effects of environmental low-dose BPA, existing problems and some consideration for future studies.

Experimentally-induced maternal hypothyroidism alters enzyme activities and the sensorimotor cortex of the offspring rats

In this study, we used an experimental model of congenital hypothyroidism to show that deficient thyroid hormones (TH) disrupt different neurochemical, morphological and functional aspects in the cerebral cortex of 15-day-old offspring. Our results showing decreased glutamine synthetase (GS) activity and Ca²⁺ overload in the cerebral cortex of hypothyroid pups suggest misregulated glutamate metabolism associated with developmentally induced TH deficiency. The ¹⁴C-MeAIB accumulation indicates upregulated System A activity and glutamine uptake by neurons. Energy metabolism in hypothyroid cortical slices was preserved, as demonstrated by unaltered glucose metabolism. We also found upregulated acetylcholinesterase activity, depleting acetylcholine from the synaptic cleft, pointing to disrupted cholinergic system. Increased reactive oxygen species (ROS) generation, lipid peroxidation, glutathione (GSH) depletion, which were associated with glutathione peroxidase, superoxide dismutase and gamma-glutamyltransferase downregulation suggest redox imbalance. Disrupted astrocyte cytoskeleton was evidenced by downregulated and hyperphosphorylated glial fibrillary acidic protein (GFAP). Morphological and structural characterization of the sensorimotor cerebral cortex (SCC) showed unaltered thickness of the SCC. However, decreased size of neurons on the layers II & III and IV in the right SCC and increased NeuN positive neurons in specific SCC layers, suggest that they are differently affected by the low TH levels during neurodevelopment. Hypothyroid pups presented increased number of foot-faults in the gridwalk test indicating affected motor functions. Taken together, our results show that congenital hypothyroidism disrupts glutamatergic and cholinergic neurotransmission, Ca²⁺ equilibrium, redox balance, cytoskeleton integrity, morphological and functional aspects in the cerebral cortex of young rats.

Hypothyroidism and Cognitive Disorders during Development and Adulthood: Implications in the Central Nervous System

Thyroid hormones (THs) play a critical function in fundamental signaling of the body regulating process such as metabolism of glucose and lipids, cell maturation and proliferation, and neurogenesis, to name just a few. THs trigger biological effects both by directly affecting gene expression through the interaction with nuclear receptors (genomic effects) and by activating protein kinases and/or ion channels (short-term effects). For years, a close relationship between the THs hormones and the central nervous system (CNS) has been described, not only for neuronal cells but also for glial development and differentiation. A deficit in thyroid hormones triiodothyronine (T₃) and thyroxine (T₄) is observed in the hypothyroid condition, generated by a iodine deficiency or an autoimmune response of the body. In the hypothyroid condition, several cellular deregulation and alterations have been described in dendrite spine morphology, cell migration and proliferation, and impaired synaptic transmission in the hippocampus, among others. The aim of this review is to describe the role of the thyroid hormones with focus in brain function and neurodegenerative disorders.

Iodoacetic Acid Disrupting the Thyroid Endocrine System in Vitro and in Vivo

Exposure to drinking water disinfection byproducts (DBPs) is potentially associated with adverse developmental effects. Iodoacetic acid (IAA), an unregulated DBP, has been shown to be cytotoxic, mutagenic, genotoxic, and tumorigenic. However, its endocrine-disrupting effects remain unknown. This study evaluated the IAA-induced disruption of the thyroid endocrine system using in vitro and in vivo assays. Rat pituitary tumor GH3 cells were treated with IAA in the presence and absence of triiodothyronine (T3). IAA exposure significantly reduced T3-activated GH3 cell proliferation, indicating the antagonistic activity of IAA in vitro. Sprague-Dawley rats were also subjected to IAA treatment through oral gavage for 28 consecutive days. IAA exposure significantly down-regulated the mRNA expression levels of the thyrotropin receptor (TSHR), the sodium/iodide symporter (NIS), and type I deiodinase and simultaneously reduced the protein expression levels of TSHR and NIS. IAA exposure decreased T3 levels but increased the weights of hypothalamus and the levels of thyrotropin releasing hormone and thyrotropin. In addition, IAA induced the formation of smaller and more depleted follicles or even vacuolization in the thyroid. These results suggested that IAA potentially disrupts the thyroid endocrine system both in vitro and in vivo.

The Thyroid Hormone-target Gene Rhes a Novel Crossroad for Neurological and Psychiatric Disorders: New Insights from Animal Models

Ras homolog enriched in striatum (Rhes) is predominantly expressed in the corpus striatum. Rhes mRNA is localized in virtually all dopamine D1 and D2 receptor-bearing medium-sized spiny neurons (MSNs), and cholinergic interneurons of striatum. Early studies in rodents showed that Rhes is developmentally regulated by thyroid hormone, as well as by dopamine innervation in adult rat, monkey and human brains. At cellular level, Rhes interferes with adenosine A2A- and dopamine D1 receptor-dependent cAMP/PKA pathway, upstream of the activation of the heterotrimeric G protein complex. Besides its involvement in GPCR-mediated signaling, Rhes modulates Akt pathway activation, acts as E3-ligase of mutant huntingtin, whose sumoylation accounts for neurotoxicity in Huntington's disease, and physically interacts with Beclin-1, suggesting its potential involvement in autophagy-related cellular events. In addition, this protein can also bind to and activate striatal mTORC1, one of the key players in l-DOPA-induced dyskinesia in rodent models of Parkinson's disease. Accordingly, lack of Rhes attenuated such motor disturbances in 6-OHDA-lesioned Rhes knockout mice. In support of its role in MSN-dependent functions, several studies documented that mutant animals displayed alterations in striatum-related phenotypes reminiscent of psychiatric illness in humans, including deficits in prepulse inhibition of startle reflex and, most interestingly, a striking enhancement of behavioral responses elicited by caffeine, phencyclidine or amphetamine. Overall, these data suggest that Rhes modulates molecular and biochemical events underlying striatal functioning, both in physiological and pathological conditions.

Cloning and expression characterization in hypothalamic Dio2/3 under a natural photoperiod in the domesticated Brandt's vole (Lasiopodomys brandtii)

The Dio2/3 gene is related to the photoperiodic response in mammals and plays an important role in the development of gonadal organs and seasonal breeding. Our previous studies have reported synchronous variations in the gonadal mass and photoperiodical transition around the summer solstice in a wild Brandt's vole population, a species with striking seasonal breeding. To investigate the role of the Dio2/3 gene in the control of seasonal breeding in this species, we cloned and characterized its expression levels by high-throughput Real-Time PCR during the period around the summer solstice. We selected a domesticated strain to ensure similar development of samples. The synchronous variation pattern between the Dio2/3 expression levels and gonadal mass around the summer solstice supports the prediction that the Dio2/3 gene plays an important role in the seasonal transition in this species. We suggest that the observed photoperiod response may be triggered by differences in the day length rather than the absolute daylength in this species. However, the similar Dio2/3 gene expression patterns but inconsistent gonadal mass patterns between the domesticated strain and the wild strain in the samples collected on Sep 8th, an absolute nonbreeding stage in the wild, lead us to speculate that the core function of the Dio2/3 gene should be restricted in response to the photoperiod rather than factors directly regulating gonadal development, and this laboratory strain could be used as an animal model to test the mechanism of environmental adaptation.

Seasonal Rhythms: The Role of Thyrotropin and Thyroid Hormones

BACKGROUND

Seasonal changes in various physiological events have been reported in humans, including metabolism, immune function, and mood. However, the molecular and endocrine basis of these seasonal changes remains unclear.

SUMMARY

Animals that breed seasonally, such as Japanese quail and the Siberian hamster, have sophisticated seasonal mechanisms, and hence they provide excellent opportunities to understand the underlying processes. Functional genomic analysis in quail uncovered the photoperiodic signal transduction pathway, which regulates avian seasonal reproduction: a long-day stimulus induces secretion of thyrotropin (TSH) from the pars tuberalis (PT) of the anterior pituitary gland. This PT-derived TSH locally activates thyroid hormone within the hypothalamus, which in turn induces gonadotropin-releasing hormone and then gonadotropin secretion, leading to gonadal growth.

CONCLUSIONS

Studies using TSH receptor-null mice confirmed the involvement of PT-derived TSH in mammalian seasonal reproduction. The pars distalis of the anterior pituitary gland is the major source of circulating TSH. Although the pars distalis and PT are in close proximity, tissue-specific glycosylation of circulating TSH alters its function to avoid cross talk.

Stimulating effect of thyroid hormones in peripheral nerve regeneration: research history and future direction toward clinical therapy

Injury to peripheral nerves is often observed in the clinic and severe injuries may cause loss of motor and sensory functions. Despite extensive investigation, testing various surgical repair techniques and neurotrophic molecules, at present, a satisfactory method to ensuring successful recovery does not exist. For successful molecular therapy in nerve regeneration, it is essential to improve the intrinsic ability of neurons to survive and to increase the speed of axonal outgrowth. Also to induce Schwann cell phenotypical changes to prepare the local environment favorable for axonal regeneration and myelination. Therefore, any molecule that regulates gene expression of both neurons and Schwann cells could play a crucial role in peripheral nerve regeneration. Clinical and experimental studies have reported that thyroid hormones are essential for the normal development and function of the nervous system, so they could be candidates for nervous system regeneration. This review provides an overview of studies devoted to testing the effect of thyroid hormones on peripheral nerve regeneration. Also it emphasizes the importance of combining biodegradable tubes with local administration of triiodothyronine for future clinical therapy of human severe injured nerves. We highlight that the local and single administration of triiodothyronine within biodegradable nerve guide improves significantly the regeneration of severed peripheral nerves, and accelerates functional recovering. This technique provides a serious step towards future clinical application of triiodothyronine in human severe injured nerves. The possible regulatory mechanism by which triiodothyronine stimulates peripheral nerve regeneration is a rapid action on both axotomized neurons and Schwann cells.

Lamprey metamorphosis: Thyroid hormone signaling in a basal vertebrate

As one of the most basal living vertebrates, lampreys represent an excellent model system to study the evolution of thyroid hormone (TH) signaling. The lamprey hypothalamic-pituitary-thyroid and reproductive axes overlap functionally. Lampreys have 3 gonadotropin-releasing hormones and a single glycoprotein hormone from the hypothalamus and pituitary, respectively, that regulate both the reproductive and thyroid axes. TH synthesis in larval lampreys takes place in an endostyle that transforms into typical vertebrate thyroid tissue during metamorphosis; both the endostyle and follicular tissue have all the typical TH synthetic components found in other vertebrates. Furthermore, lampreys also have the vertebrate suite of peripheral regulators including TH distributor proteins (THDPs), deiodinases and TH receptors (TRs). Although at the molecular level the components of the lamprey thyroid system are ancestral to other vertebrates, their functions have been largely conserved. TH signaling as it relates to lamprey metamorphosis represents a particularly interesting phenomenon. Unlike other metamorphosing vertebrates, lamprey THs increase throughout the larval period, peak prior to metamorphosis and decline rapidly at the onset of metamorphosis; patterns of deiodinase activity are consistent with these increases and declines. Moreover, goitrogens (which suppress TH levels) initiate precocious metamorphosis, and exogenous TH treatment blocks goitrogen-induced metamorphosis and disrupts natural metamorphosis. Despite this clear physiological difference, TH action via TRs is consistent with higher vertebrates. Based on observations that TRs are upregulated in a tissue-specific fashion during morphogenesis and the finding that lamprey TRs upregulate genes via THs in a fashion similar to higher vertebrates, we propose the following hypothesis for further testing. THs have a dual role in lampreys where high TH levels promote larval feeding and growth and then at the onset of metamorphosis TH levels decrease rapidly; at this time the relatively low TH levels function via TRs in a fashion similar to that of other metamorphosing vertebrates.

Exploring the Validity of Proposed Transgenic Animal Models of Attention-Deficit Hyperactivity Disorder (ADHD)

Attention-deficit/hyperactivity disorder (ADHD) is a common, behavioral, and heterogeneous neurodevelopmental condition characterized by hyperactivity, impulsivity, and inattention. Symptoms of this disorder are managed by treatment with methylphenidate, amphetamine, and/or atomoxetine. The cause of ADHD is unknown, but substantial evidence indicates that this disorder has a significant genetic component. Transgenic animals have become an essential tool in uncovering the genetic factors underlying ADHD. Although they cannot accurately reflect the human condition, they can provide insights into the disorder that cannot be obtained from human studies due to various limitations. An ideal animal model of ADHD must have face (similarity in symptoms), predictive (similarity in response to treatment or medications), and construct (similarity in etiology or underlying pathophysiological mechanism) validity. As the exact etiology of ADHD remains unclear, the construct validity of animal models of ADHD would always be limited. The proposed transgenic animal models of ADHD have substantially increased and diversified over the years. In this paper, we compiled and explored the validity of proposed transgenic animal models of ADHD. Each of the reviewed transgenic animal models has strengths and limitations. Some fulfill most of the validity criteria of an animal model of ADHD and have been extensively used, while there are others that require further validation. Nevertheless, these transgenic animal models of ADHD have provided and will continue to provide valuable insights into the genetic underpinnings of this complex disorder.

Chronic anemia and thyroid function

Anaemia is a global public health problem affecting both developing and developed countries with major consequences for human health as well as social and economic development. It occurs at all stages of the life cycle, but is more prevalent in pregnant women and young children. Iron deficiency anaemia (IDA) impairs thyroid metabolism in animals and human and may negatively affect growth and develpment of children. On the other hand both overt and subclinical hypothyroidism are associated with anemia and adding iron to thyroxine therapy improves both conditions compared to thyroxine therapy alone. In addition patients with chronic hemolytic anemia requiring repeated blood transfusion have high prevalence of hypothalamic-pituitary thyroid axis. Both primary hypothyroidism and central hypothyroidism occur in these patients with increasing prevalence with age, severity of the anemia and higher ferritin concentration denoting poor chelation.  Proper blood transfusion and intensive chelation appears to prevent deterioration of thyroid function and in many cases can reverse thyroid pathology. Physicians treating these forms of anemia should be aware of thyroid disorders in these patients for early screening, prevention and proper management of any thyroid dysfunction.

Molecular and Neuroendocrine Mechanisms of Avian Seasonal Reproduction

Animals living outside tropical zones experience seasonal changes in the environment and accordingly, adapt their physiology and behavior in reproduction, molting, and migration. Subtropical birds are excellent models for the study of seasonal reproduction because of their rapid and dramatic response to changes in photoperiod. For example, testicular weight typically changes by more than a 100-fold. In birds, the eyes are not necessary for seasonal reproduction, and light is instead perceived by deep brain photoreceptors. Functional genomic analysis has revealed that long day (LD)-induced thyrotropin from the pars tuberalis of the pituitary gland causes local thyroid hormone (TH) activation within the mediobasal hypothalamus. This local bioactive TH, triiodothyronine (T₃), appears to regulate seasonal gonadotropin-releasing hormone (GnRH) secretion through morphological changes in neuro-glial interactions. GnRH, in turn, stimulates gonadotropin secretion and hence, gonadal development under LD conditions. In marked contrast, low temperatures accelerate short day (SD)-induced testicular regression in winter. Interestingly, low temperatures increase circulating levels of T₃ to support adaptive thermogenesis, but this induction of T₃ also triggers the apoptosis of germ cells by activating genes involved in metamorphosis. This apparent contradiction in the role of TH has recently been clarified. Central activation of TH during spring results in testicular growth, while peripheral activation of TH during winter regulates adaptive thermogenesis and testicular regression.

Developmental and Thyroid Hormone Regulation of the DNA Methyltransferase 3a Gene in Xenopus Tadpoles

Thyroid hormone is essential for normal development in vertebrates. In amphibians, T3 controls metamorphosis by inducing tissue-specific gene regulation programs. A hallmark of T3 action is the modification of chromatin structure, which underlies changes in gene transcription. We found that mRNA for the de novo DNA methyltransferase (DNMT) dnmt3a, but not dnmt1, increased in the brain of Xenopus tadpoles during metamorphosis in parallel with plasma [T3]. Addition of T3 to the rearing water caused a time-dependent increase in dnmt3a mRNA in tadpole brain, tail, and hind limb. By analyzing data from a genome-wide analysis of T3 receptor (TR) binding in tadpole tail, we identified several putative T3 response elements (TREs) within the dnmt3a locus. Using in vitro DNA binding, transient transfection-reporter, and chromatin immunoprecipitation assays for TRs, we identified two functional TREs at -7.1 kb and +5.1 kb relative to the dnmt3a transcription start site. Sequence alignment showed that these TREs are conserved between two related frog species, X. laevis and X. tropicalis, but not with amniotes. Our previous findings showed that this gene is directly regulated by liganded TRs in mouse brain, and whereas the two mouse TREs are conserved among Eutherian mammals, they are not conserved in Xenopus species. Thus, although T3 regulation of dnmt3a may be an ancient pathway in vertebrates, the genomic sites responsible for hormone regulation may have diverged or arisen by convergent evolution. We hypothesize that direct T3 regulation of dnmt3a may be an important mechanism for modulating global changes in DNA methylation.