Structural and functional alterations in the hippocampus due to hypothyroidism

Thyroid function variations within the reference range and cognitive function: A two-sample Mendelian randomization study

BACKGROUND

The causal relationship between thyroid function variations within the reference range and cognitive function remains unknown. We aimed to explore this causal relationship using a Mendelian randomization (MR) approach.

METHODS

Summary statistics of a thyroid function genome-wide association study (GWAS) were obtained from the ThyroidOmics consortium, including reference range thyroid stimulating hormone (TSH) (N = 54,288) and reference range free thyroxine (FT4) (N = 49,269). GWAS summary statistics on cognitive function were obtained from the Social Science Genetic Association Consortium (SSGAC) and the UK Biobank, including cognitive performance (N = 257,841), prospective memory (N = 152,605), reaction time (N = 459,523), and fluid intelligence (N = 149,051). The primary method used was inverse-variance weighted (IVW), supplemented with weighted median, Mr-Egger regression, and MR-Pleiotropy Residual Sum and Outlier. Several sensitivity analyses were conducted to identify heterogeneity and pleiotropy.

RESULTS

An increase in genetically associated TSH within the reference range was suggestively associated with a decline in cognitive performance (β = -0.019; 95%CI: -0.034 to -0.003; P = 0.017) and significantly associated with longer reaction time (β = 0.016; 95 % CI: 0.005 to 0.027; P = 0.004). Genetically associated FT4 levels within the reference range had a significant negative relationship with reaction time (β = -0.030; 95%CI:-0.044 to -0.015; P = 4.85 × 10-5). These findings remained robust in the sensitivity analyses.

CONCLUSIONS

Low thyroid function within the reference range may have a negative effect on cognitive function, but further research is needed to fully understand the nature of this relationship.

LIMITATIONS

This study only used GWAS data from individuals of European descent, so the findings may not apply to other ethnic groups.

Two thyroperoxidase-inhibiting chemicals induce shared transcriptional changes in hippocampus of developing rats

Thyroid hormone (TH) system disrupting compounds can impair brain development by perturbing TH action during critical life stages. Human exposure to TH system disrupting chemicals is therefore of great concern. To better protect humans against such chemicals, sensitive test methods that can detect effects on the developing brain are critical. Worryingly, however, current test methods are not sensitive and specific towards TH-mediated effects. To address this shortcoming, we performed RNA-sequencing of rat brains developmentally exposed to two different thyroperoxidase (TPO) inhibiting compounds, the medical drug methimazole (MMI) or the pesticide amitrole. Pregnant and lactating rats were exposed to 8 and 16 mg/kg/day(d) MMI or 25 and 50 mg/kg/d amitrole from gestational day 7 until postnatal day 16. Bulk-RNA-seq was performed on hippocampus from the 16-day old male pups. MMI and amitrole caused pronounced changes to the transcriptomes; 816 genes were differentially expressed, and 425 gene transcripts were similarly affected by both chemicals. Functional terms indicate effects from key cellular functions to changes in cell development, migration and differentiation of several cell populations. Of the total number of DEGs, 106 appeared to form a consistent transcriptional fingerprint of developmental hypothyroidism as they were similarly and dose-dependently expressed across all treatment groups. Using a filtering system, we identified 20 genes that appeared to represent the most sensitive, robust and dose-dependent markers of altered TH-mediated brain development. These markers provide inputs to the adverse outcome pathway (AOP) framework where they, in the context of linking TPO inhibiting compounds to adverse cognitive function, can be used to assess altered gene expression in the hippocampus in rat toxicity studies.

Synaptic Plasticity and Cognitive Ability in Experimental Adult-Onset Hypothyroidism

Adult-onset hypothyroidism impairs normal brain function. Research on animal models of hypothyroidism has revealed critical information on how deficiency of thyroid hormones impacts the electrophysiological and molecular functions of the brain, which leads to the well known cognitive impairment in untreated hypothyroid patients. Currently, such information can only be obtained from experiments on animal models of hypothyroidism. This review summarizes important research findings that pertain to understanding the clinical cognitive consequences of hypothyroidism, which will provide a better guiding path for therapy of hypothyroidism. SIGNIFICANCE STATEMENT: Cognitive impairment occurs during adult-onset hypothyroidism in both humans and animal models. Findings from animal studies validate clinical findings showing impaired long-term potentiation, decreased CaMKII, and increased calcineurin. Such findings can only be gleaned from animal experiments to show how hypothyroidism produces clinical symptoms.

Dynamic risk factors of psychiatric readmission for major depressive disorder: A longitudinal study on patients treated with mono-antidepressant

In this comprehensive study, we sought to unravel the risk factors for recurrence in Major Depressive Disorder (MDD), uniquely focusing on patients undergoing mono-antidepressant treatment. By considering psychiatric readmission as a direct indicator of MDD recurrence, we meticulously analyzed the records of 1,456 inpatients from a Chinese mental health center from 2012 to 2020. Our follow-up periods, spanning 90, 180, and 365 days post-discharge, allowed for a nuanced understanding of the recurrence dynamics. We identified four critical risk factors: thyroid function (FT3 and TSH), high-density lipoprotein (HDL) levels, and region of residence. Notably, the study revealed an increasing risk of readmission associated with decreased FT3 and HDL over time, while elevated TSH and residing in another province 's impact diminished. The antidepressant type did not significantly alter readmission risks, providing a unique perspective on MDD management. This research contributes to the field by offering a deeper understanding of how demographic and biochemical factors influence the likelihood of MDD recurrence, guiding more effective treatment approaches.

Relationship between thyroid-stimulating hormone, BDNF levels, and hippocampal volume in antipsychotic-naïve first-episode psychosis patients

Introduction

Thyroid hormones play an essential role in hippocampal development, a key structure in psychosis. However, the role of these hormones in first-episode psychosis (FEP) has received limited attention. It has been hypothesized that thyroid hormones could cause morphological modifications in the hippocampal structure through the upregulation of brain-derived neurotrophic factor (BDNF). In this study, we primarily aimed to determine the relationship between thyroid-stimulating hormone (TSH) levels, peripheral BDNF levels, and hippocampal volume in antipsychotic-naïve FEP patients. We also aimed to determine whether TSH levels were associated with clinical symptomatology.

Materials and methods

A total of 50 antipsychotic-naïve FEP patients were included in the study. At baseline, we collected fasting blood samples and registered sociodemographic and clinical variables (substance use, DUP, PANSS, GAF, and CDSS). Structural T1 MRI was performed at baseline to quantify brain volumes. No control group was used for this study.

Results

Of the 50 patients, more than one-third (36%) presented alterations in TSH levels, mainly elevated levels (32% of patients). The TSH levels were inversely correlated with both peripheral BDNF and hippocampal volume. On the multivariate analysis, the model that best predicted the relative hippocampal volume was a single variable model (TSH levels). No significant association was observed between TSH levels and clinical symptomatology.

Discussion

These results suggest that thyroid hormones could have a neuroprotective effect on the hippocampus in FEP patients, possibly through their effect by increasing BDNF concentrations, which could attenuate brain injury and neuroinflammation. Nevertheless, thyroid hormones could also affect hippocampal volume through other pathways.

Unveiling the nongenomic actions of thyroid hormones in adult mammalian brain: The legacy of Mary B. Dratman

A comprehensive review was conducted to compile the contributions of Mary B. Dratman and studies by other researchers in the field of nongenomic actions of thyroid hormones in adult mammalian brain. Dratman and her collaborators authored roughly half of the papers in this area. It has been almost fifty years since Dratman introduced the novel concept of thyroid hormones as neurotransmitters for the first time. The characterization of unique brain-region specific accumulation of thyroid hormones within the nerve terminals in adult mammals was a remarkable contribution by Dratman. It suggested a neurotransmitter- or neuromodulator-like role of thyroid hormone and/or its derivative, 3-iodothyronamine within adrenergic systems in adult mammalian brain. Several studies by other researchers using synaptosomes as a model system, have contributed to the concept of direct nongenomic actions of thyroid hormones at synaptic regions by establishing that thyroid hormones or their derivatives can bind to synaptosomal membranes, alter membrane functions including enzymatic activities and ion transport, elicit Ca2+/NO-dependent signaling pathways and induce substrate-protein phosphorylation. Such findings can help to explain the physiological and pathophysiological roles of thyroid hormone in psychobehavioral control in adult mammalian brain. However, the exact mode of nongenomic actions of thyroid hormones at nerve terminals in adult mammalian brain awaits further study.

Impaired Sensitivity to Thyroid Hormones is Associated with Mild Cognitive Impairment in Euthyroid Patients with Type 2 Diabetes

Purpose

The prevalence of mild cognitive impairment (MCI) in patients with type 2 diabetes (T2D) is rapidly increasing. Thyroid hormones are key regulators of cognitive function in adults. The purpose of this study was to investigate the relationship between thyroid hormone sensitivity and MCI in euthyroid T2D patients.

Patients and Methods

A total of 400 euthyroid T2D patients were enrolled in this cross-sectional study, including 218 patients with normal cognition and 182 MCI patients. The Montreal Cognitive Assessment (MoCA) was used to evaluate cognitive function. The free triiodothyronine to free thyroxine (FT3/FT4) ratio was calculated as a measure of peripheral sensitivity to thyroid hormones; the thyroid-stimulating hormone index (TSHI), thyrotrophic thyroxine resistance index (TT4RI) and thyroid feedback quantile-based index (TFQI) were calculated as measures of central sensitivity to thyroid hormones. Linear regression analysis and logistic regression analysis were performed to explore the relationships between these indices of thyroid hormone sensitivity and the MoCA score and MCI, respectively.

Results

Compared with the normal cognitive function group, patients in the MCI group had higher TSHI, TT4RI and TFQI but a lower FT3/FT4 ratio (P<0.05). The MoCA score was positively correlated with the FT3/FT4 ratio but negatively correlated with TSHI, TT4RI and TFQI (P< 0.05). Multivariate logistic regression analysis showed that a low FT3/FT4 ratio and high TSHI, TT4RI and TFQI were independently associated with MCI (P<0.05). After adjustment for confounding factors, the odds ratio (OR) for the association between MCI and the highest tertile of the FT3/FT4 was 0.455 (95% CI: 0.264-0.785), for the highest tertile of TSHI, the OR was 2.380 (95% CI: 1.376-4.119), for the highest tertile of TT4RI, the OR was 2.342 (95% CI:1.353-4.054), and for the highest tertile of TFQI, the OR was 2.536 (95% CI: 1.466-4.387) (P< 0.05).

Conclusion

Impaired sensitivity to thyroid hormones is associated with MCI in euthyroid T2D patients.

Memory impairments in rodent depression models: A link with depression theories

More than 80% of depressed patients struggle with learning new tasks, remembering positive events, or concentrating on a single topic. These neurocognitive deficits accompanying depression may be linked to functional and structural changes in the prefrontal cortex and hippocampus. However, their mechanisms are not yet completely understood. We conducted a narrative review of articles regarding animal studies to assess the state of knowledge. First, we argue the contribution of changes in neurotransmitters and hormone levels in the pathomechanism of cognitive dysfunction in animal depression models. Then, we used numerous neuroinflammation studies to explore its possible implication in cognitive decline. Encouragingly, we also observed a positive correlation between increased oxidative stress and a depressive-like state with concomitant memory deficits. Finally, we discuss the undeniable role of neurotrophin deficits in developing cognitive decline in animal models of depression. This review reveals the complexity of depression-related memory impairments and highlights the potential clinical importance of gathered findings for developing more reliable animal models and designing novel antidepressants with procognitive properties.

Attenuation of Hypothyroidism-Induced Cognitive Impairment by Modulating Serotonin Mediation

Thyroid hormones play an important role in the modeling of neural networks in the brain. Besides its metabolic effects, thyroid dysfunction, and hypothyroidism in particular, is frequently associated with cognitive decline and depressive-like behavior. The current study aimed to examine the changes in behavior, cognition, and memory in rats with propylthiouracil-induced overt hypothyroidism. The behavior and cognition were assessed using the open field test, T-maze, and novel object recognition test. We found significant differences in the behavioral patterns of the hypothyroid animals showing a reduction in locomotor activity, frequency of rearing, and impaired memory function compared to the euthyroid controls. As serotonin is an essential biomarker regulating cognition and mood, we tried to modulate the serotonin mediation in hypothyroid animals through tryptophan administration. Treatment with 5-hydroxy-tryptophan (5-OH-TRP) intraperitoneally for 10 days or directly into the hippocampus as a single injection led to attenuation of the hypothyroidism-induced cognitive and memory decline. A staggering amount of research is suggesting that the common denominators in the pathophysiology of depression and the behavior changes in hypothyroidism are the hippocampal complex and the distorted serotonin metabolism. In our study, it was observed a significant alleviation of cognitive impairment and an improvement of memory performance in hypothyroid rats after 5-OH-TRP administration. Current results are promising and may serve as groundwork for further investigation of functional and structural changes in the hippocampus during a hypothyroid state, and in particular, the effects of serotonin mediation in hypothyroid-associated depressive-like behavior.

Neuropsychological Alterations in Patients with Congenital Hypothyroidism Treated with Levothyroxine: Linked Factors and Thyroid Hormone Hyposensitivity

Eighty-five percent of the studies of patients with congenital hypothyroidism (CH) treated with Levothyroxine (L-T₄) report neuropsychological sequelae throughout life. In neonates and infants, there is a deficit in sensorimotor skills (impaired balance). In preschool and elementary school children and adolescents, there are alterations in intellectual quotient (low scores), language (delayed phonological acquisition), memory (visual, verbal, visuospatial, visuoconstructive, autobiographical, and semantic), sensorimotor skills (impaired fine and gross motor control), and visuoconstructive–visuospatial domain (low scores in spatial location, block design, and object assembly). These neuropsychological domains are also affected in young adults, except for language (adequate verbal fluency) and visuoconstructive–visuospatial domain (no data). The onset and severity of neuropsychological sequelae in patients with treated CH depend on several factors: extrinsic, related to L-T₄ treatment and social aspects, and intrinsic, such as severity and etiology of CH, as well as structural and physiological changes in the brain. In this review, we hypothesized that thyroid hormone hyposensitivity (THH) could also contribute to neuropsychological alterations by reducing the effectiveness of L-T₄ treatment in the brain. Thus, further research could approach the THH hypothesis at basic and clinical levels to implement new endocrinological and neuropsychological therapies for CH patients.

Histological, functional and transcriptomic alterations in the juvenile hippocampus in a mouse model of thyroid hormone resistance

BACKGROUND

Proper thyroid hormone signaling via the TRα1 nuclear receptor is required for normal neurodevelopmental processes. The specific downstream mechanisms mediated by TRα1 that impact brain development remain to be investigated.

METHODS

In this study, the structure, function and transcriptome of hippocampal tissue in a mouse model expressing the first RTHα mutation discovered in a patient, THRA E403X, were analyzed. RNAscope was used to visualize the spatial and temporal expression of Thra1 mRNA in the hippocampus of WT mice, which is corresponding to THRA1 mRNA in humans. The morphological structure was analyzed by Nissl staining, and the synaptic transmission was analyzed on the basis of long-term potentiation. The Morris water maze test and the zero maze test were used to evaluate the behavior. RNA-seq and quantitative real-time PCR were used to analyze the differentially expressed genes (DEGs) of the hippocampal tissues in the mouse model expressing the Thra E403X mutation.

RESULTS

The juvenile mutant Thra E403X mice presented with delayed neuronal migration, disordered neuronal distribution, and decreased synaptic plasticity. A total of 754 DEGs, including 361 upregulated genes and 393 downregulated genes, were identified by RNA-seq. DEG-enriched Gene Ontology (GO) and KEGG pathways were associated with PI3K-Akt signaling, ECM-receptor interaction, neuroactive ligand-receptor interaction, and a range of immune-related pathways. 25 DEGs were validated by qPCR.

CONCLUSIONS

The ThraE403X mutation results in histological and functional abnormalities, as well as transcriptomic alterations in the juvenile mouse hippocampus. This study of the ThraE403X mutant offers new insights into the biological cause of RTHα-associated neurological diseases.

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.

Brain-Derived Neurotrophic Factor-Mediated Cognitive Impairment in Hypothyroidism

Brain-derived neurotrophic factor (BDNF), which is expressed at high levels in the limbic system, has been shown to regulate learning, memory and cognition. Thyroid hormone is crucial for brain development. Hypothyroidism is a clinical condition in which thyroid hormones are reduced and it affects the growth and development of the brain in neonates and progresses to cognitive impairment in adults. The exact mechanism of how reduced thyroid hormones impairs cognition and memory is not well understood. This review explores the possible role of BDNF-mediated cognitive impairment in hypothyroid patients.

Hypothyroidism and Diabetes-Related Dementia: Focused on Neuronal Dysfunction, Insulin Resistance, and Dyslipidemia

The incidence of dementia is steadily increasing worldwide. The risk factors for dementia are diverse, and include genetic background, environmental factors, sex differences, and vascular abnormalities. Among the subtypes of dementia, diabetes-related dementia is emerging as a complex type of dementia related to metabolic imbalance, due to the increase in the number of patients with metabolic syndrome and dementia worldwide. Thyroid hormones are considered metabolic regulatory hormones and affect various diseases, such as liver failure, obesity, and dementia. Thyroid dysregulation affects various cellular mechanisms and is linked to multiple disease pathologies. In particular, hypothyroidism is considered a critical cause for various neurological problems-such as metabolic disease, depressive symptoms, and dementia-in the central nervous system. Recent studies have demonstrated the relationship between hypothyroidism and brain insulin resistance and dyslipidemia, leading to diabetes-related dementia. Therefore, we reviewed the relationship between hypothyroidism and diabetes-related dementia, with a focus on major features of diabetes-related dementia such as insulin resistance, neuronal dysfunction, and dyslipidemia.

Thyroid Disorders and Development of Cognitive Impairment: A Review Study

Dementia is a neurological disorder that is spreading with increasing human lifespan. In this neurological disorder, memory and cognition are declined and eventually impaired. Various factors can be considered as the background of this disorder, one of which is endocrine disorders. Thyroid hormones are involved in various physiological processes in the body; one of the most important of them is neuromodulation. Thyroid disorders, including hyperthyroidism or hypothyroidism, can affect the nervous system and play a role in the development of dementia. Despite decades of investigation, the nature of the association between thyroid disorders and cognition remains a mystery. Given the enhancing global burden of dementia, the principal purpose of this study was to elucidate the association between thyroid disturbances as a potentially modifiable risk factor of cognitive dysfunction. In this review study, we have tried to collect almost all of the reported mechanisms demonstrating the role of hypothyroidism and hyperthyroidism in the pathogenesis of dementia.

The Neuroprotective Effect of α-Lipoic Acid and/or Metformin against the Behavioral and Neurochemical Changes Induced by Hypothyroidism in Rat

OBJECTIVE

The present study evaluates the neuroprotective effect of α-lipoic acid (ALA) and/or metformin (MET) on the behavioral and neurochemical changes induced by hypothyroidism.

METHODS

Rats were divided into control, rat model of hypothyroidism induced by propylthiouracil, and rat model of hypothyroidism treated with ALA, MET, or their combination.

RESULTS

Behaviorally, hypothyroid rats revealed impaired memory and reduced motor activity as indicated from the novel object recognition test and open-field test, respectively. Hypothyroidism induced a significant increase in lipid peroxidation (malondialdehyde [MDA]) and a significant decrease in reduced glutathione (GSH) and nitric oxide (NO) in the cortex and hippocampus. These were associated with a significant increase in tumor necrosis factor-α (TNF-α) and a significant decrease in brain-derived neurotrophic factor (BDNF). Hypothyroidism decreased significantly the levels of serotonin (5-HT), norepinephrine (NE), and dopamine (DA) and reduced the activities of acetylcholinesterase (AchE) and Na+, K+-ATPase in the cortex and hippocampus. Treatment of hypothyroid rats with ALA and/or MET showed an improvement in memory function and motor activity. Moreover, ALA and/or MET prevented the increase in MDA and TNF-α, and the decline in GSH, NO, BDNF, 5-HT, NE, and DA. It also restored AchE and Na+, K+-ATPase activities in the studied brain regions.

CONCLUSION

ALA and/or MET has a potential neuroprotective effect against the adverse behavioral and neurochemical changes induced by hypothyroidism in rats.

Thyroid hormone regulation of adult hippocampal neurogenesis: Putative molecular and cellular mechanisms

Adult hippocampal neurogenesis is sensitive to perturbations in thyroid hormone signaling, with evidence supporting a key role for thyroid hormone and thyroid hormone receptors (TRs) in the regulation of postmitotic progenitor survival and neuronal differentiation. In this book chapter we summarize the current understanding of the effects of thyroid hormone signaling on adult hippocampal progenitor development, and also critically address the role of TRs in regulation of distinct aspects of stage-specific hippocampal progenitor progression. We highlight actions of thyroid hormone on thyroid hormone responsive target genes, and the implications for hippocampal progenitor regulation. Given the influence of thyroid hormone on both mitochondrial and lipid metabolism, we discuss a putative role for regulation of metabolism in the effects of thyroid hormone on adult hippocampal neurogenesis. Finally, we highlight specific ideas that require detailed experimental investigation, and the need for future studies to obtain a deeper mechanistic insight into the influence of thyroid hormone and TRs in the developmental progression of adult hippocampal progenitors.

Gallic Acid Prevents the Oxidative and Endoplasmic Reticulum Stresses in the Hippocampus of Adult-Onset Hypothyroid Rats

Thyroid hormone is essential for hippocampal redox environment and neuronal viability in adulthood, where its deficiency causes hypothyroidism related to oxidative and endoplasmic reticulum stresses in the hippocampus, resulting in neuronal death. One option of treatment is antioxidants; however, they must be transported across the blood-brain barrier. Gallic acid is a polyphenol that meets these criteria. Thus, this study aimed to prove that the neuroprotective mechanism of GA is associated with the prevention of oxidative and endoplasmic reticulum stresses in the hippocampus of adult-onset hypothyroid rats. Male Wistar rats were divided into euthyroid (n = 20) and hypothyroid groups (n = 20). Thyroidectomy with parathyroid gland reimplementation caused hypothyroidism. Each group was subdivided into two: vehicle and 50 mg/kg/d of gallic acid. 3 weeks after thyroidectomy, six animals of each group were euthanized, and the hippocampus was dissected to evaluate oxidative and endoplasmic reticulum stress markers. The rest of the animals were euthanized after 4 weeks of treatment for histological analysis of the hippocampus. The results showed that hypothyroidism increased lipid peroxidation, reactive oxygen species, and nitrites; it also increased endoplasmic reticulum stress by activating the inositol-requiring enzyme-1α (IRE1α) pathway, the protein kinase RNA-like endoplasmic reticulum kinase (PERK) and activated transcription factor 6α (ATF6α) pathways associated with a proapoptotic state that culminates in hippocampal neuronal damage. Meanwhile, the hypothyroid rat treated with gallic acid reduced oxidative stress and increased endoplasmic reticulum-associated degradation (ERAD) through IRE1α and ATF6. Also, the gallic acid treatment prevented the Bax/BCl2 ratio from increasing and the overexpression of p53 and caspase 12. This treatment in hypothyroid animals was associated with the neuronal protection observed in the hippocampus. In conclusion, gallic acid prevents hypothyroidism-induced hippocampal damage associated with oxidative and endoplasmic reticulum stresses.

The relation between thyroid dysregulation and impaired cognition/behaviour: An integrative review

Despite decades of research on the relation between thyroid diseases and cognition, the nature of this relationship remains elusive. An increasing prevalence of cognitive impairment and thyroid dysfunction has been consistently observed with ageing. Also, there appears to be an association between thyroid disorders and cognitive decline. Given the increasing global burden of dementia, elucidating the relationship between thyroid disorders as a potentially modifiable risk factor of cognitive impairment was the main goal of this review. We summarise the current literature examining the relationship between thyroid hormonal dysregulation and cognition or behaviour. We present the available imaging and pathological findings related to structural and functional brain changes related to thyroid hormonal dysregulation. We also propose potential mechanisms of interaction between thyroid hormones, autoantibodies and cognition/behaviour. Effects of gender, ethnicity and environmental factors are also briefly discussed. This review highlights the need for long-term prospective studies to capture the course of brain functional changes associated with the incidence and progression of thyroid dysregulations along with the confounding effects of non-modifiable risk factors such as gender and ethnicity. Moreover, double-blind controlled clinical trials are necessary to devise appropriate treatment plans to prevent cognitive consequences of over or undertreatment of thyroid disorders.

Brain GABA+ changes in primary hypothyroidism patients before and after levothyroxine treatment: A longitudinal magnetic resonance spectroscopy study

OBJECTIVE

Increasing evidence indicates the involvement of the GABAergic system in the pathophysiology of hypothyroidism. We aimed to investigate longitudinal changes of brain GABA in primary hypothyroidism before and after levothyroxine (L-T4) treatment.

MATERIAL AND METHODS

In 18 patients with hypothyroidism, we used the MEGA-PRESS (Mescher-Garwood point-resolved spectroscopy) editing sequence to measure brain GABA levels from medial prefrontal cortex (mPFC) and posterior cingulate cortex (PCC) at baseline and after 6-months of L-T4 treatment. Sex- and age-matched healthy controls (n = 18) were scanned at baseline. Thyroid function and neuropsychological tests were also performed.

RESULTS

GABA signals were successfully quantified from all participants with fitting errors lower than 15%. GABA signal was labeled as GABA+ due to contamination from co-edited macromoleculars and homocarnosine. In hypothyroid patients, mean GABA+ was significantly lower in the mPFC region compared with controls (p = 0.031), and the mPFC GABA+ measurements were significantly correlated with depressive symptoms and memory function (r = -0.558, p = 0.016; r = 0.522, p = 0.026, respectively). After adequate L-T4 treatment, the mPFC GABA+ in hypothyroid patients increased to normal level, along with relieved neuropsychological impairments.

CONCLUSION

The study suggested the decrease of GABA+ may be an important neurobiological factor in the pathophysiology of hypothyroidism. Treatment of L-T4 may reverse the abnormal GABA+ and hypothyroidism-induced neuropsychiatric impairments, indicating the action mode of L-T4 in adjunctive treatment of affective disorders.

Neuropsychological Impairments in Young Patients With Subclinical Hypothyroidism: A Case Control Study

Background:

There is a lack of clarity about the cognitive dysfunction in young patients with subclinical hypothyroidism (SCH). This study was done to explore the neuropsychological impairments in young patients with SCH and compare them with euthyroid controls.

Methods:

Patients between 18 and 45 years of age and diagnosed with SCH were recruited. Controls were euthyroid age, gender, and education matched. All the cases and controls underwent a detailed neuropsychological assessment with a battery of tests validated for use in the age groups of 18 to 65 years.

Results:

Thirty-nine patients with a mean age of 30.3 ± 7.7 years (female:male ratio 12:1) and 23 controls (female:male ratio 21:2) with a mean age of 33.4 ± 7.1 years (P = .24) were included in the study. The mean TSH value was 6.36 ± 1.3 mIU/L and 2.49 ± 1.03 mIU/L in cases and controls, respectively (P < .001). The visual memory delayed recall was impaired, in 48.71% (n = 19) and 21.7% (n = 5) cases and controls, respectively (P = .03). The category fluency test showed impairment in a greater number of cases (35.9%, n = 14) as compared to controls (13%, n = 3; P = .04).

Conclusion:

This study shows that younger patients with SCH have delayed visual memory recall and category fluency deficits, which are suggestive of dysfunction of the prefrontal cortex and temporal lobe in young SCH patients. These impairments may justify the treatment of young SCH patients with replacement therapy.

Neuroprotective Effect of Ashwagandha Extract against the Neurochemical Changes Induced in Rat Model of Hypothyroidism

The current aim is to evaluate the effect of ashwagandha root extract (AE) on the neurochemical changes induced in the cortex and hippocampus as a consequence of thyroid dysfunction induced by propylthiouracil (PTU). Male Wistar rats were divided into; control, AE treated rats, rat model of hypothyroidism and rat model of hypothyroidism treated with either AE or L-thyroxine (T4) for 1 month. Rat model of hypothyroidism showed a significant decrease in serum levels of tri-iodothyronine (T3) and T4 and a significant increase in cortical and hippocampal lipid peroxidation (MDA), nitric oxide (NO), superoxide dismutase (SOD) and catalase (CAT). However, reduced glutathione (GSH) decreased significantly. This was associated with a significant increase in hippocampal tumor necrosis factor-α (TNF-α) and cortical dopamine levels. Both L-thyroxine and AE restored T3 and T4 levels. In the hippocampus L-Thyroxine prevented the increase in MDA and restored GSH but failed to restore the increased NO and TNF-α. In the cortex L-thyroxine didn't change the increased MDA and NO and the decreased GSH induced by PTU. L-thyroxine increased cortical and hippocampal SOD and CAT. AE prevented the increased hippocampal MDA, NO and TNF-α and the decreased GSH level induced by PTU. In the cortex AE failed to restore MDA and NO but prevented the decrease in GSH. The increase in cortical dopamine level induced by PTU was ameliorated by L-thyroxine and improved by AE. The present data indicate that AE could prevent thyroid dysfunction and reduce its complications on the nervous system including oxidative stress and neuroinflammation.

Association of LHPP genetic variation (rs35936514) with structural and functional connectivity of hippocampal-corticolimbic neural circuitry

A single nucleotide polymorphism at the LHPP gene (rs35936514) has been reported to be associated with major depressive disorder (MDD) in genome-wide association studies. We conducted a neuroimaging analysis to explore whether and which brain neural systems are affected by LHPP variation. Since LHPP variants seem to be associated with the hippocampus, we assessed the relationship between rs35936514 variation and structural-functional connectivity within a hippocampal-corticolimbic neural system implicated in MDD. A total of 122 Chinese subjects were divided into a CC homozygous group (CC genotype, n = 60) and a T allele-carrier group (CT/TT genotypes, n = 62). All subjects participated in resting-state functional magnetic resonance imaging (rs-fMRI) and diffusion tensor imaging (DTI) scans. Structural and functional connectivity data analyses were then performed. Compared to the CC group, the T allele-carrier group showed significantly higher fractional anisotropy (FA) values in the fornix as well as increased functional connectivity from the hippocampus to the rostral part of the anterior cingulate cortex (rACC). Moreover, a significant negative correlation between fornix FA value and hippocampus-rACC functional connectivity was identified (P < 0.05). These findings suggest that there is a relationship between rs35936514 variation and both structural and functional hippocampal-corticolimbic neural system involvement in MDD. LHPP may play an important role in the neuropathophysiology of MDD.

Thyroid hormone treatment alleviates the impairments of neurogenesis, mitochondrial biogenesis and memory performance induced by methamphetamine

Chronic use of methamphetamine (MA), a neurotoxic psychostimulant, leads to long-lasting cognitive dysfunctions in humans and animal models. Thyroid hormones (THs) have several physiological actions and are crucial for normal behavioral, intellectual and neurological development. Considering the importance of THs in the cognitive processes, the present study was designed to evaluate the therapeutic effects of THs on cognitive and neurological impairments induced by MA. Escalating doses of MA (1-10 mg/kg, IP) were injected twice daily for 10 consecutive days in rats and cognitive functions were evaluated using behavioral tests. The expression of factors involved in neurogenesis (NES and DCX), mitochondrial biogenesis (PGC-1α, NRF-1, and TFAM), neuroinflammation (GFAP, Iba-1, and COX-2) as well as Reelin and NT-3 (synaptic plasticity and neurotrophic factor, respectively) was measured in the hippocampus of MA-treated animals. The effects of three different doses of T4 (20, 40 or 80 μg/kg; intraperitoneally) or T3 (20, 40 or 80 μg/rat; 2.5 μl/nostril; intranasal) treatment, once a day for one week after MA cessation, were assessed in MA-treated rats. After the last behavioral test, serum T4 and T3 levels were measured using radioimmunoassay. The results revealed that repeated escalating regimen of MA impaired cognitive functions concomitant with neurogenesis and synaptic plasticity impairments, mitochondrial dysfunction, and neuroinflammation. T4 or T3 treatment partially decreased the alterations induced by MA. These findings suggest that THs can be considered as potential candidates for the reduction of MA abuse related neurocognitive disturbances.

Neurogranin Expression Is Regulated by Synaptic Activity and Promotes Synaptogenesis in Cultured Hippocampal Neurons

Neurogranin (Ng) is a calmodulin (CaM)-binding protein that is phosphorylated by protein kinase C (PKC) and is highly enriched in the dendrites and spines of telencephalic neurons. It is proposed to be involved in regulating CaM availability in the post-synaptic environment to modulate the efficiency of excitatory synaptic transmission. There is a close relationship between Ng and cognitive performance; its expression peaks in the forebrain coinciding with maximum synaptogenic activity, and it is reduced in several conditions of impaired cognition. We studied the expression of Ng in cultured hippocampal neurons and found that both protein and mRNA levels were about 10% of that found in the adult hippocampus. Long-term blockade of NMDA receptors substantially decreased Ng expression. On the other hand, treatments that enhanced synaptic activity such as long-term bicuculline treatment or co-culture with glial cells or cholesterol increased Ng expression. Chemical long-term potentiation (cLTP) induced an initial drop of Ng, with a minimum after 15 min followed by a slow recovery during the next 2-4 h. This effect was most evident in the synaptosome-enriched fraction, thus suggesting local synthesis in dendrites. Lentiviral expression of Ng led to increased density of both excitatory and inhibitory synapses in the second and third weeks of culture. These results indicate that Ng expression is regulated by synaptic activity and that Ng promotes the synaptogenesis process. Given its relationship with cognitive function, we propose targeting of Ng expression as a promising strategy to prevent or alleviate the cognitive deficits associated with aging and neuropathological conditions.

High Thyrotropin Is Associated with Reduced Hippocampal Volume in a Population-Based Study from Germany

BACKGROUND

Previous patient studies suggest that thyroid dysfunction affects volumes of particular regions of the brain. So far, population-based data related to this topic are lacking. The aim of this study was to investigate associations of serum levels of thyrotropin (TSH), free triiodothyronine, and free thyroxine (fT4) with total brain volume, gray matter volume, white matter volume (WMV), and hippocampal volume (HV) in a population-based study.

METHODS

Data on 2557 individuals were pooled from two independent population-based surveys of the Study of Health in Pomerania conducted in Northeast Germany. Brain volumes were determined from images derived from 1.5 T magnetic resonance imaging. Low and high TSH were defined using the cutoffs 0.40 and 3.29 mIU/L, respectively. Associations between thyroid hormone levels and segmented brain volumes were analyzed by linear regression models. Further, voxel-based morphometry was conducted to search for associations with thyroid hormone levels in a hypothesis-free way throughout the whole brain. All models were adjusted for confounders.

RESULTS

Only 9/70 individuals with high TSH had low free triiodothyronine or fT4 levels. Individuals with high TSH had significantly lower total brain volume (β = -26.9 [confidence interval (CI) -49.0 to -4.8]; p = 0.017), WMV (β = -16.1 [CI -29.4 to -2.7]; p = 0.018), and HV (β = -223 [CI -395 to -50]; p = 0.011) than individuals with TSH within the reference range, while low TSH was not significantly associated with any of the brain volumes. Voxel-based morphometry analyses revealed a significant positive association with serum fT4 levels in the left middle frontal gyrus.

CONCLUSIONS

In conclusion, the results of this study indicate that the subclinical hypothyroid state may lead to a reduced brain volume affecting particularly HV in younger subjects and WMV, which might correspond to subtle microstructural changes in white matter fiber tracts or myelination of the axones. Gray matter seems not to be affected by subclinical hypothyroid states.

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.

Hypothyroidism increases cyclooxygenase-2 levels and pro-inflammatory response and decreases cell proliferation and neuroblast differentiation in the hippocampus

The present study investigated the effects of hypothyroidism on cyclooxygenase-2 (COX-2) and pro‑inflammatory cytokines in the dentate gyrus to elucidate the roles of COX‑2 in the hypothyroid hippocampus. Hypothyroidism was induced in rats by treating with 0.03% 2‑mercapto‑1‑methyl‑imidazole dissolved in drinking water for 5 weeks. The animals were sacrificed at 12 weeks of age. Hypothyroidism rats exhibited decreased triiodothyronine and thyroxine levels in the serum, while the levels of thyroid‑stimulating hormone and the weight of thyroid glands were significantly higher in the hypothyroid rats compared with those in the vehicle‑treated group. COX‑2 immunoreactivity was significantly increased in the hippocampal CA2/3 region and the dentate gyrus compared with the vehicle‑treated group. Levels of pro‑inflammatory cytokines including interleukin (IL)‑1β, IL‑6 and tumor necrosis factor‑α were significantly higher in the hippocampal homogenates of hypothyroid rats. Cell proliferation and neuroblast differentiation based on Ki67 and doublecortin immunohistochemistry were decreased in the dentate gyrus of hypothyroid rats compared with those in the vehicle‑treated group. These results suggested that hypothyroidism‑mediated COX‑2 expression affected hippocampal plasticity by upregulating the levels of pro‑inflammatory cytokines in the hippocampus. Therefore, COX‑2 may be suggested as a candidate molecule for preventing hypothyroidism‑induced neurological side effects.

Treated hypothyroidism is associated with cerebrovascular disease but not Alzheimer's disease pathology in older adults

Thyroid hormone disease is common among older adults and is associated with cognitive impairment. However, pathologic correlates are not well understood. We studied pathologic and clinical factors associated with hypothyroidism, the most common manifestation of thyroid disease, in research subjects seen annually for clinical evaluations at U.S. Alzheimer's Disease Centers. Thyroid disease and treatment status were assessed during clinician interviews. Among autopsied subjects, there were 555 participants with treated hypothyroidism and 2146 without known thyroid disease; hypothyroidism was associated with severe atherosclerosis (odds ratio: 1.35; 95% confidence interval: 1.02, 1.79) but not Alzheimer's disease pathologies (amyloid plaques or neurofibrillary tangles). Among participants who did not undergo autopsy (4598 with treated hypothyroidism and 20,945 without known thyroid hormone disease), hypercholesterolemia and cerebrovascular disease (stroke and/or transient ischemic attack) were associated with hypothyroidism, complementing findings in the smaller autopsy sample. This is the first large-scale evaluation of neuropathologic concomitants of hypothyroidism in aged individuals. Clinical hypothyroidism was prevalent (>20% of individuals studied) and was associated with cerebrovascular disease but not Alzheimer's disease-type neuropathology.

Iodine Deficiency and the Brain: Effects and Mechanisms

Iodine is an essential micronutrient needed in human diets. As iodine is an integral component of thyroid hormone, it mediates the effects of thyroid hormone on brain development. Iodine deficiency is the most prevalent and preventable cause of mental impairment in the world. The exact mechanism through which iodine influences the brain is unclear, but is generally thought to begin with genetic expression. Many brain structures and systems appear to be affected with iodine deficiency, including areas such as the hippocampus, microstructures such as myelin, and neurotransmitters. The clearest evidence comes from the studies examining cognition in the cases of iodine deprivation or interventions involving iodine supplementation. Nevertheless, there are many inconsistencies and gaps in the literature of iodine deficiency, especially over the lifespan. This paper summarizes the literature on this topic, suggests a causal mechanism for iodine's effect on the brain, and indicates areas for the future research (e.g., using magnetic resonance imaging (MRI) and functional MRI to examine how iodine supplementation facilitates cognitive functioning).

Induction of hypothyroidism during early postnatal stages triggers a decrease in cognitive performance by decreasing hippocampal synaptic plasticity

Thyroid hormones are vital in the control of multiple body functions, including the correct performance of the brain. Multiple diseases are associated with thyroid gland functioning, including hypothyroidism. To date, little is known regarding the effects of the establishment of this condition at a young age on brain function. Here, we evaluated the effect of hypothyroidism in an early postnatal stage in cognitive abilities with focus on the hippocampus. In our model, hypothyroidism was induced in young rats at 21days of age using 0.05% 6-propyl-2-thiouracil (PTU) for 4weeks reaching significantly lower levels of fT₄ (control: 1.337ng/dL±0.115, PTU: 0.050ng/dL±0.001). Following the induction of hypothyroidism, several cognitive tasks were assessed to investigate the effects of hypothyroidism on cognition performance. We determined that hypothyroidism triggers a significant dysfunction in learning and memory processes observed in the Morris Water Maze were the latency times were higher in PTU rats (controls: 37s; PTU: 57s). The cognitive impairment was correlated with a reduction in hippocampal plasticity with respect to both long-term potentiation (LTP) (control: 1.45, PTU: 1.00) and depression (LTD) (control: 0.71, PTU: 1.01). Furthermore, a decrease in the rate of glucose utilization (control: 223nmol∗mg of protein, PTU:148nmol∗mg of protein) was observed, along with an increase in oxidative stress and a decrease in MAP2 marker in the hippocampus. Our findings suggest that the induction of hypothyroidism in a young rat model alters numerous functions at the level of the hippocampus.

Effects of Dendropanax morbifera Léveille extract on hypothyroidism-induced oxidative stress in the rat hippocampus

In this experiment, we verified the effects of Dendropanax morbifera Léveille stem extract (DMS) on hypothyroidism-induced oxidative stress in the hippocampus of rats. Hypothyroidism was induced in rats by treating them with 0.03% 2-mercapto-1-methyl-imidazole dissolved in drinking water for 5 weeks. DMS (100 mg/kg) was also orally administered to the rats during the same period and the animals were sacrificed at 12 weeks of age. DMS administration tended to ameliorate these hypothyroidism-induced changes in serum triiodothyronine (T₃), thyroxine (T₄), and thyroid-stimulating hormone levels. DMS administration significantly reduced the hypothyroidism-induced increases in reactive oxygen species production as well as in lipid peroxidation in the hippocampus. In addition, DMS administration increased hippocampal Cu, Zn-superoxide dismutase (SOD1), catalase (CAT), and glutathione peroxidase (GPx) levels. These results suggest that DMS potentially ameliorates hypothyroidism-induced neuroendocrine phenotypes and oxidative stress in the hippocampus via the induction of antioxidant enzymes.

Induction of the UDP-Glucuronosyltransferase 1A1 during the Perinatal Period Can Cause Neurodevelopmental Toxicity

Anticonvulsants can increase the risk of developing neurotoxicity in infants; however, the underlying mechanism has not been elucidated to date. Thyroxine [3,5,3',5'-l-tetraiodothyronine (T4)] plays crucial roles in the development of the central nervous system. In this study, we hypothesized that induction of UDP-glucuronosyltransferase 1A1 (UGT1A1)-an enzyme involved in the metabolism of T4-by anticonvulsants would reduce serum T4 levels and cause neurodevelopmental toxicity. Exposure of mice to phenytoin during both the prenatal and postnatal periods significantly induced UGT1A1 and decreased serum T4 levels on postnatal day 14. In the phenytoin-treated mice, the mRNA levels of synaptophysin and synapsin I in the hippocampus were lower than those in the control mice. The thickness of the external granule cell layer was greater in phenytoin-treated mice, indicating that induction of UGT1A1 during the perinatal period caused neurodevelopmental disorders. Exposure to phenytoin during only the postnatal period also caused these neurodevelopmental disorders. A T4 replacement attenuated the increase in thickness of the external granule cell layer, indicating that the reduced T4 was specifically associated with the phenytoin-induced neurodevelopmental disorder. In addition, these neurodevelopmental disorders were also found in the carbamazepine- and pregnenolone-16-α-carbonitrile-treated mice. Our study is the first to indicate that UGT1A1 can control neurodevelopment by regulating serum T4 levels.

Antidepressant behavior in thyroidectomized Wistar rats is induced by hippocampal hypothyroidism

Thyroidectomy is a surgical procedure indicated in cases of several maligned or benign thyroid diseases, thus, the aim of our study was to verify how the hypothyroidism induced by thyroidectomy influences behavioral parameters and its relation to thyroid hormones metabolism and neurogenesis at hippocampus. For this purpose, Adult male Wistar rats underwent to thyroidectomy to induce hypothyroidism. Behavioral tests, the thyroid profile and hippocampal gene expression were evaluated in control and in thyroidectomized animals. It was observed that thyroidectomized group had a significant increasing in serum thyroid-stimulating hormone (TSH) and a decreasing in thyroxine (T4) levels as well as in triiodothyronine (T3) serum level. It was also observed reduction of the monocarboxylate transporter 8 (Mct8), thyroid hormone receptor alfa (Trα1), deiodinase type 2 (Dio2), ectonucleotide pyrophosphatase/phosphodiesterase 2 (Enpp2) and brain-derived neurotrophic factor (Bdnf) mRNA expression in hippocampus of thyroidectomized animals. In the forced swimming test, it was verified that thyroidectomy promotes a decrease in time of immobility and climbing when compared with the control group. In summary, we demonstrated that antidepressant behavior in thyroidectomized Wistar rats is induced by hippocampal hypothyroidism. This effect could be associated to an impaired neuronal activity in acute stress response as it is observed in forced swimming paradigm.

Serum thyroid-stimulating hormone level and relation with size of hippocampus in patients with mild cognitive disorders

Background:

Cognitive disorders and dementia are common problems, and Alzheimer's disease is one of the major leading causes of death worldwide. Thyroid hormone disorders as a common problem effect on hippocampus size which as a prognostic factor in dementia. The aim of the present study was to investigate the relationship between serum thyroid-stimulating hormone (TSH) level and the size of hippocampus in patients with mild cognitive disorders.

Materials and Methods:

In a descriptive-analytical study, 41 patients with symptoms of mild cognitive disorders whom referred to take the brain magnetic resonance image (MRI) in a radiology center under the direction of Tabriz University of Medical Sciences (Tabriz, Iran) were evaluated. The right and left hippocampal and brain volume was calculated by MRI at coronal T1-weighted. Serum TSH level was also measured in these patients. Correlation between serum TSH level and hippocampal volume size was evaluated.

Results:

Male to female ratio was 1.05:1 with mean age of 54.09 ± 3.11 years. Mean serum TSH level of patients was 1.55 ± 1.45 uU/ml. The right and left hippocampal volumes were 1.61 ± 0.42 and 1.62 ± 0.39 ml, respectively. There were slight negative correlations between the right and left hippocampal volumes with TSH level (r = −0.133 and r = −0.092, respectively). Correlations between the right and left hippocampal volumes with TSH level were not statistically significant (P = 0.406, P = 0.566, respectively).

Conclusion:

Based on findings of the present study, there was a weak negative correlation between serum level of TSH with the right and left hippocampal and brain volume ratio, but the correlation was not statistically significant. It seems that controlling of clinical or subclinical hypothyroidism may have a role in slowing of dementia progression and also have a preventive role.

Hypothyroxinemia induced by maternal mild iodine deficiency impairs hippocampal myelinated growth in lactational rats

Hypothyroxinemia induced by maternal mild iodine deficiency causes neurological deficits and impairments of brain function in offspring. Hypothyroxinemia is prevalent in developing and developed countries alike. However, the mechanism underlying these deficits remains less well known. Given that the myelin plays an important role in learning and memory function, we hypothesize that hippocampal myelinated growth may be impaired in rat offspring exposed to hypothyroxinemia induced by maternal mild iodine deficiency. To test this hypothesis, the female Wistar rats were used and four experimental groups were prepared: (1) control; (2) maternal mild iodine deficiency diet inducing hypothyroxinemia; (3) hypothyroidism induced by maternal severe iodine deficiency diet; (4) hypothyroidism induced by maternal methimazole water. The rats were fed the diet from 3 months before pregnancy to the end of lactation. Our results showed that the physiological changes occuring in the hippocampal myelin were altered in the mild iodine deficiency group as indicated by the results of immunofluorescence of myelin basic proteins on postnatal day 14 and postnatal day 21. Moreover, hypothyroxinemia reduced the expressions of oligodendrocyte lineage transcription factor 2 and myelin-related proteins in the treatments on postnatal day 14 and postnatal day 21. Our data suggested that hypothyroxinemia induced by maternal mild iodine deficiency may impair myelinated growth of the offspring.

Thyroid hormones are associated with longitudinal cognitive change in an urban adult population

Recent evidence indicates that thyroid hormones may be closely linked to cognition among adults. We investigated associations between thyroid hormones and longitudinal cognitive change, within and outside of reference ranges, stratifying by sex and race. This longitudinal study used data from the Healthy Aging in Neighborhoods of Diversity Across the Lifespan study, set in Baltimore City, MD, 2004-2013, on adults aged 30-64 years at baseline visit, with a length of follow-up between visits 1 and 2 ranging from <1 to 8 years; mean ± standard deviation: 4.64 ± 0.93. The final analytic sample sizes ranged from 1486 to 1602 participants with 1.6-1.7 visits per participant (total visits: 2496-2757), depending on the cognitive test. Eleven cognitive test scores spanning domains of learning or memory, language or verbal, attention, visuospatial and/or visuoconstruction, psychomotor speed, executive function, and mental status were used. Mixed-effects regression models were conducted, interacting time of follow-up with several thyroid exposures. Whites performed better than African Americans, with only 4 cognitive test scores of 11 declining significantly over time. Importantly, above reference range thyroid stimulating hormone (vs. reference range, thyroid stimulating hormone, above reference range [TSHarr]) was linked to faster rates of decline on the digits span backwards test, reflecting working memory (TSHarr × time γ ± standard error: -0.14 ± 0.05, p = 0.006) and clock-command, at test of visuospatial and/or visuoconstruction abilities (TSHarr × Time γ ± standard error: -0.10 ± 0.04, p = 0.004). The latter finding was replicated when comparing normal thyroid function to "subclinical hypothyroidism". Within-reference ranges, a higher thyroid stimulating hormone was related to faster decline on the clock-command test scores in women. In sum, higher baseline thyroid stimulating hormone was associated with faster cognitive decline over-time among urban US adults, specifically in domains of working memory and visuospatial and/or visuoconstruction abilities.

Gestational and early postnatal hypothyroidism alters VGluT1 and VGAT bouton distribution in the neocortex and hippocampus, and behavior in rats

Thyroid hormones are fundamental for the expression of genes involved in the development of the CNS and their deficiency is associated with a wide spectrum of neurological diseases including mental retardation, attention deficit-hyperactivity disorder and autism spectrum disorders. We examined in rat whether developmental and early postnatal hypothyroidism affects the distribution of vesicular glutamate transporter-1 (VGluT1; glutamatergic) and vesicular inhibitory amino acid transporter (VGAT; GABAergic) immunoreactive (ir) boutons in the hippocampus and somatosensory cortex, and the behavior of the pups. Hypothyroidism was induced by adding 0.02% methimazole (MMI) and 1% KClO4 to the drinking water starting at embryonic day 10 (E10; developmental hypothyroidism) and E21 (early postnatal hypothyroidism) until day of sacrifice at postnatal day 50. Behavior was studied using the acoustic prepulse inhibition (somatosensory attention) and the elevated plus-maze (anxiety-like assessment) tests. The distribution, density and size of VGluT1-ir and VGAT-ir boutons in the hippocampus and somatosensory cortex was abnormal in MMI pups and these changes correlate with behavioral changes, as prepulse inhibition of the startle response amplitude was reduced, and the percentage of time spent in open arms increased. In conclusion, both developmental and early postnatal hypothyroidism significantly decreases the ratio of GABAergic to glutamatergic boutons in dentate gyrus leading to an abnormal flow of information to the hippocampus and infragranular layers of the somatosensory cortex, and alter behavior in rats. Our data show cytoarchitectonic alterations in the basic excitatory hippocampal loop, and in local inhibitory circuits of the somatosensory cortex and hippocampus that might contribute to the delayed neurocognitive outcome observed in thyroid hormone deficient children born in iodine deficient areas, or suffering from congenital hypothyroidism.

Experimentally-induced maternal hypothyroidism alters crucial enzyme activities in the frontal cortex and hippocampus of the offspring rat

Thyroid hormone insufficiency during neurodevelopment can result into significant structural and functional changes within the developing central nervous system (CNS), and is associated with the establishment of serious cognitive impairment and neuropsychiatric symptomatology. The aim of the present study was to shed more light on the effects of gestational and/or lactational maternal exposure to propylthiouracil (PTU)-induced hypothyroidism as a multilevel experimental approach to the study of hypothyroidism-induced changes on crucial brain enzyme activities of 21-day-old Wistar rat offspring in a brain region-specific manner. This experimental approach has been recently developed and characterized by the authors based on neurochemical analyses performed on newborn and 21-day-old rat offspring whole brain homogenates; as a continuum to this effort, the current study focused on two CNS regions of major significance for cognitive development: the frontal cortex and the hippocampus. Maternal exposure to PTU in the drinking water during gestation and/or lactation resulted into changes in the activities of acetylcholinesterase and two important adenosinetriphosphatases (Na(+),K(+)- and Mg(2+)-ATPase), that seemed to take place in a CNS-region-specific manner and that were dependent upon the PTU-exposure timeframe followed. As these findings are analyzed and compared to the available literature, they: (i) highlight the variability involved in the changes of the aforementioned enzymatic parameters in the studied CNS regions (attributed to both the different neuroanatomical composition and the thyroid-hormone-dependent neurodevelopmental growth/differentiation patterns of the latter), (ii) reveal important information with regards to the neurochemical mechanisms that could be involved in the way clinical hypothyroidism could affect optimal neurodevelopment and, ultimately, cognitive function, as well as (iii) underline the need for the adoption of more consistent approaches towards the experimental simulation of congenital and early-age-occurring hypothyroidism.

Effects of thyroxine and donepezil on hippocampal acetylcholine content, acetylcholinesterase activity, synaptotagmin-1 and SNAP-25 expression in hypothyroid adult rats

A growing number of studies have revealed that neurocognitive impairment, induced by adult-onset hypothyroidism, may not be fully restored by traditional hormone substitution therapies, including thyroxine (T4). The present study has investigated the effect of T4 and donepezil (DON; an acetylcholinesterase (AChE) inhibitor) treatment on the hypothyroidism-induced alterations of acetylcholine (ACh) content and AChE activity. Furthermore, we examined synaptotagmin-1 (syt-1) and SNAP-25 expression in the hippocampus of adult rats. Adding 0.05% propylthiouracil to their drinking water for five weeks induced hypothyroidism in the rat models. From the fourth week, the rats were treated with T4, DON or a combination of both. Concentration of ACh and the activity of AChE was determined colorimetrically. The results demonstrated that hypothyroidism induced a significant decrease of Ach content and AChE activity (by 17 and 34%, respectively), which were restored to control values by T4 administration. DON treatment also restored Ach to the normal level. Protein levels of syt-1 and SNAP-25 were determined by immunohistochemistry. The results demonstrated that syt-1 was expressed at significantly lower levels in hypothyroid rats, while SNAP-25 levels were notably higher compared with the controls. Two-week treatment with T4 alone failed to normalize the expression levels of these two proteins, while co-administration of T4 and DON was able to induce this effect. These data suggested that the thyroid hormone, T4, may have a direct effect on the metabolism of hippocampal ACh in adult rats, and that the DON treatment may facilitate the recovery of synaptic protein impairments induced by hypothyroidism.

Inhibition of Na(+),K(+)-ATPase in the hypothalamus, pons and cerebellum of the offspring rat due to experimentally-induced maternal hypothyroidism

Neurodevelopment is known to be particularly susceptible to thyroid hormone insufficiency and can result in extensive structural and functional deficits within the central nervous system (CNS), subsequently leading to the establishment of cognitive impairment and neuropsychiatric symptomatology. The current study evaluated the effects of gestational and/or lactational maternal exposure to propylthiouracil (PTU)-induced hypothyroidism (as a suggestive multilevel experimental approach to the study of hypothyroidism-induced changes that has been developed and characterized by the authors) on crucial brain enzyme activities of 21-day-old Wistar rat offspring in a CNS region-specific manner. The activities of acetylcholinesterase (AChE), Na(+),K(+)-ATPase and Mg(2+)-ATPase in the offspring hypothalamus, cerebellum and pons were assessed. The study demonstrated that maternal exposure to PTU (0.05% w/v in the drinking water) during the critical periods of neurodevelopment can result in an inhibition of hypothalamic, pontine and cerebellar Na(+),K(+)-ATPase; a major marker of neuronal excitability and metabolic energy production as well as an important regulator of important systems of neurotransmission. On the other hand, no significant changes in the activities of the herein offspring CNS regions' AChE and Mg(2+)-ATPase were recorded. The observed Na(+),K(+)-ATPase inhibition: (i) is region-specific (and non-detectable in whole brain homogenetes), (ii) could constitute a central event in the pathophysiology of clinically-relevant hypothyroidism-associated developmental neurotoxicity, (iii) occurs under all examined experimental schemes, and (iv) certainly deserves further clarification at a molecular and histopathological level. As these findings are analyzed and compared to the available literature, they also underline the need for the adoption and further study of Na(+),K(+)-ATPase activity as a consistent neurochemical marker within the context of a systematic comparative study of existing (and novel) simulation approaches to congenital and early age hypothyroidism.

Psychiatric disease in late adolescence and young adulthood. Foetal programming by maternal hypothyroidism?

OBJECTIVE

Lack of maternal thyroid hormones during foetal brain development may lead to structural abnormalities in the brain. We hypothesized that maternal hypothyroidism during the pregnancy could programme the foetus to development of psychiatric disease later in life.

DESIGN

Danish nationwide register study.

PARTICIPANTS

Singletons live-born 1980-1990.

MEASUREMENTS

Cox proportional hazards model was used to estimate adjusted hazard ratio (aHR) with 95% confidence interval for offspring redemption of ≥2 prescriptions of a psychiatric drug from age 15 to 31 years.

RESULTS

Among 542 100 adolescents and young adults included, altogether 3979 (0·7%) were born to mothers with hypothyroidism registered before 1996. In crude analyses, the use of a psychiatric drug was more frequent in late adolescence and young adulthood when the mother had hypothyroidism (P < 0·001); however, several possible confounders had to be taken into account. For example, mothers with hypothyroidism often also had a psychiatric registration (38·5% vs 27·7%, P < 0·001) and the use of psychiatric drugs changed over time. After adjustment for confounders including birth year, maternal age and maternal psychiatric history, maternal hypothyroidism was associated with an increased risk of having redeemed prescriptions of anxiolytics [aHR 1·23 (1·03-1·48)] and antipsychotics [aHR 1·22 (1·03-1·44)] in late adolescence and young adulthood. For antidepressants, aHR was 1·07 (0·98-1·17).

CONCLUSIONS

The association between maternal hypothyroidism and the use of a psychiatric drug in late adolescence and young adulthood was partly confounded by maternal psychiatric history, but foetal programming by maternal hypothyroidism may be part of the mechanisms leading to the use of anxiolytics and antipsychotics.

Thyroid disease and cognition

Overt hypothyroidism and thyrotoxicosis are associated with significant decrements in mood and cognitive function, and therapy usually leads to improvement in these symptoms. In contrast, major affective or cognitive dysfunction is not typical of subclinical thyroid disease. Subtle deficits in specific cognitive domains (primarily working memory and executive function) likely exist in subclinical hypothyroidism and thyrotoxicosis, but these are unlikely to cause major problems in most patients. Patients with mild thyroid disease and significant distress related to mood or cognition most likely have independent diagnoses that should be evaluated and treated separately.