Developmental iodine deficiency and hypothyroidism impair neural development in rat hippocampus: involvement of doublecortin and NCAM-180

Thyroid function and epilepsy: a two-sample Mendelian randomization study

Background

Thyroid hormones (THs) play a crucial role in regulating various biological processes, particularly the normal development and functioning of the central nervous system (CNS). Epilepsy is a prevalent neurological disorder with multiple etiologies. Further in-depth research on the role of thyroid hormones in epilepsy is warranted.

Methods

Genome-wide association study (GWAS) data for thyroid function and epilepsy were obtained from the ThyroidOmics Consortium and the International League Against Epilepsy (ILAE) Consortium cohort, respectively. A total of five indicators of thyroid function and ten types of epilepsy were included in the analysis. Two-sample Mendelian randomization (MR) analyses were conducted to investigate potential causal relations between thyroid functions and various epilepsies. Multiple testing correction was performed using Bonferroni correction. Heterogeneity was calculated with the Cochran's Q statistic test. Horizontal pleiotropy was evaluated by the MR-Egger regression intercept. The sensitivity was also examined by leave-one-out strategy.

Results

The findings indicated the absence of any causal relationship between abnormalities in thyroid hormone and various types of epilepsy. The study analyzed the odds ratio (OR) between thyroid hormones and various types of epilepsy in five scenarios, including free thyroxine (FT4) on focal epilepsy with hippocampal sclerosis (IVW, OR = 0.9838, p = 0.02223), hyperthyroidism on juvenile absence epilepsy (IVW, OR = 0.9952, p = 0.03777), hypothyroidism on focal epilepsy with hippocampal sclerosis (IVW, OR = 1.0075, p = 0.01951), autoimmune thyroid diseases (AITDs) on generalized epilepsy in all documented cases (weighted mode, OR = 1.0846, p = 0.0346) and on childhood absence epilepsy (IVW, OR = 1.0050, p = 0.04555). After Bonferroni correction, none of the above results showed statistically significant differences.

Conclusion

This study indicates that there is no causal relationship between thyroid-related disorders and various types of epilepsy. Future research should aim to avoid potential confounding factors that might impact the study.

Lissencephaly with Congenital Hypothyroidism: A Case Report

Lissencephaly is a malformation of cortical development associated with deficient neuronal migration and abnormal formation of cerebral convolutions or gyri. The lissencephaly spectrum consists of agyria, pachygyria, and subcortical band heterotopia. At least 19 genes have been identified in the causation of lissencephaly and related syndrome. Lissencephaly is associated with many other congenital disorders but the association of lissencephaly with congenital hypothyroidism is rarely reported. We report a case of a 10-year-old girl having lissencephaly with congenital hypothyroidism. Early diagnosis of lissencephaly and genetic counselling can be made in suspected cases and further possible interventions can be taken. Also, regular follow-up, monitoring, and better conservative management lead to a better prognosis.

Keywords

congenital abnormalities; hypothyroidism; lissencephaly; neuronal migration disorders.

Neuronal Nitric Oxide Inhibitor 7-Nitroindazole Improved Brain-Derived Neurotrophic Factor and Attenuated Brain Tissues Oxidative Damage and Learning and Memory Impairments of Hypothyroid Juvenile Rats

Hypothyroidism-associated learning and memory impairment is reported to be connected to oxidative stress and reduced levels of brain-derived neurotrophic factor (BDNF). The effects of neuronal nitric oxide inhibitor 7-nitroindazole (7NI) on brain tissues oxidative damage, nitric oxide (NO), BDNF and memory impairments in hypothyroid juvenile rats were investigated. Male Wistar juvenile rats (20 days old) were divided into five groups, including Martinez et al. (J Neurochem 78 (5):1054-1063, 2001). Control in which vehicle was injected instead of 7NI, (Jackson in Thyroid 8 (10):951-956, 1998) Propylthiouracil (PTU) where 0.05% PTU was added in drinking water and vehicle was injected instead of 7NI, (Gong et al. in BMC Neurosci 11 (1):50, 2010; Alva-Sánchez et al. in Brain Res 1271:27-35, 2009; Anaeigoudari et al. in Pharmacol Rep 68 (2): 243-249, 2016) PTU-7NI 5, PTU-7NI 10 and PTU-7NI 20 in which 5, 10, or 20 mg/kg7NI was injected intraperitoneally (i.p.). Following 6 weeks, Morris water maze (MMW) and passive avoidance learning (PAL) tests were used to evaluate the memory. Finally, the hippocampus and the cortex of the rats were removed after anesthesia by urethane to be used for future analysis. The escape latency and traveled path in MWM test was increased in PTU group (P < 0.001). PTU also reduced the latency to enter the dark box of PAL and the time spent and the distance in the target quadrant in MWM test (P < 0.001 and P < 0.01). Treatment with 7NI attenuated all adverse effects of PTU (P < 0.05 to P < 0.001). PTU lowered BDNF and thiol content and superoxide dismutase (SOD) and catalase (CAT) activities in the brain but increased malondialdehyde (MDA) and nitric oxide (NO) metabolites. In addition, 7NI improved thiol, SOD, CAT, thiol, and BDNF but attenuated MDA and NO metabolites. The results of the current study showed that 7NI improvement in the learning and memory of the hypothyroid juvenile rats, which was accompanied with improving of BDNF and attenuation of NO and brain tissues oxidative damage.

Thymoquinone reverses learning and memory impairments and brain tissue oxidative damage in hypothyroid juvenile rats

In this study, the effect of thymoquinone (TQ) on propylthiouracil (PTU)-induced memory impairment was investigated in juvenile rats. The rats were grouped into control, Hypo, Hypo-TQ5 and Hypo-TQ10. Propylthiouracil increased latency time in the Morris water maze test and decreased delay in entering the dark compartment in the passive avoidance test. Both 5 mg/kg and 10 mg/kg doses of TQ decreased latency time in the Morris water maze test and increased delay in entering the dark compartment in a passive avoidance test. The PTU also increased malondialdehyde and nitric oxide metabolites in the brain while reduced the thiol content and superoxide dismutase and catalase activities and serum T4 level. Both doses of TQ decreased malondialdehyde and nitric oxide metabolites in the brain while enhanced the thiol content and superoxide dismutase and catalase activities and serum T4 level. The results of the present study showed that TQ protected against PTU-induced memory impairments in rats.

Neuroprotective effects of Nigella sativa extract upon the hippocampus in PTU-induced hypothyroidism juvenile rats: A stereological study

This study aimed to examine the neuroprotective effects of Nigella sativa (N. sativa) in the hippocampus of propylthiouracil (PTU)-induced hypothyroid rats during neonatal and juvenile growth. Twenty- five pregnant rats from early gestation (GD 0) were divided into five groups: (1) control (received drinking water), (2) PTU (received 0.005% PTU in drinking water), (3-5) PTU + NS 0.05%, PTU + NS 0.1%, PTU + NS 0.2% (along with PTU, received 0.05%, 0.1% and 0.2% W/V of N. sativa respectively) and treatment continued until postnatal day 60 (PN 60). The brains of male pups were removed for histological and stereological assessments. N. sativa extract significantly reduced the production of dark neurons and apoptotic cells in different areas of the hippocampus compared to the PTU group. Moreover, it significantly attenuated the effect of hypothyroidism on the volume reduction of the hippocampus. The results of the present study suggested that N. sativa extract has a potential ability to prevent the hippocampal neural damage after inducing hypothyroidism during neonatal and juvenile growth in rats.

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).

Implications of the thyroid hormone on neuronal development with special emphasis on the calmodulin-kinase IV pathway

Thyroid hormones influence brain development through regulation of gene expression. This is especially true for Ca²⁺-dependent regulation since a major pathway is controlled by the Ca²⁺/calmodulin-dependent protein kinase IV (CaMKIV) which in turn is induced by the thyroid hormone T₃. In addition, CaMKIV is involved in regulation of alternative splicing of a number of protein isoforms, among them PMCA1a, the neuronal specific isoform of the plasma membrane calcium pump. On the other hand, hypothyroidism or CaMKIV deficiency can have a severe influence on brain development. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

Suggested use of sensitive measures of memory to detect functional effects of maternal iodine supplementation on hippocampal development

Maternal hypothyroxinemia secondary to iodine deficiency may have neurodevelopmental effects on the specific neurocognitive domain of memory. Associated disruption of thyroid hormone-dependent protein synthesis in the hippocampus has the potential to result in compromised development of the structure with consequential impairments in memory function. Despite links between maternal iodine deficiency during gestation and lactation and abnormal hippocampal development in rat fetuses and pups, there has been little research on the specific function of memory in human infants and young children born to iodine-deficient mothers. Several candidate measures have proven to be sensitive to the effects of gestational iron deficiency on memory function in infants and young children, including habituation and dishabituation, imitation-based tasks, and event-related potentials. Such measures could be used to test the effects of maternal iodine supplementation on the specific neurocognitive domain of memory in infants and young children. Furthermore, progress in understanding the effects of maternal iodine supplementation on neurocognitive development could be accelerated by the development of a nonhuman primate model to complement the rodent model.

Music application alleviates short-term memory impairments through increasing cell proliferation in the hippocampus of valproic acid-induced autistic rat pups

Autism is a neurodevelopmental disorder and this disorder shows impairment in reciprocal social interactions, deficits in communication, and restrictive and repetitive patterns of behaviors and interests. The effect of music on short-term memory in the view of cell proliferation in the hippocampus was evaluated using valproic acid-induced autistic rat pups. Animal model of autism was made by subcutaneous injection of 400-mg/kg valproic acid into the rat pups on the postnatal day 14. The rat pups in the music-applied groups were exposed to the 65-dB comfortable classic music for 1 hr once a day, starting postnatal day 15 and continued until postnatal day 28. In the present results, short-term memory was deteriorated by autism induction. The numbers of 5-bromo-2'-deoxyridine (BrdU)-positive, Ki-67-positive, and doublecortin (DCX)-positive cells in the hippocampal dentate gyrus were decreased by autism induction. Brain-derived neurotrophic factor (BDNF) and tyrosine kinase B (TrkB) expressions in the hippocampus were also suppressed in the autistic rat pups. Music application alleviated short-term memory deficits with enhancing the numbers of BrdU-positive, Ki-67-positive, and DCX-positive cells in the autistic rat pups. Music application also enhanced BDNF and TrkB expressions in the autistic rat pups. The present study show that application of music enhanced hippocampal cell proliferation and alleviated short-term memory impairment through stimulating BDNF-TrkB signaling in the autistic rat pups. Music can be suggested as the therapeutic strategy to overcome the autism-induced memory deficits.

Gestational Hypothyroidism Improves the Ability of the Female Offspring to Clear Streptococcus pneumoniae Infection and to Recover From Pneumococcal Pneumonia

Maternal thyroid hormones are essential for proper fetal development. A deficit of these hormones during gestation has enduring consequences in the central nervous system of the offspring, including detrimental learning and impaired memory. Few studies have shown that thyroid hormone deficiency has a transient effect in the number of T and B cells in the offspring gestated under hypothyroidism; however, there are no studies showing whether maternal hypothyroidism during gestation impacts the response of the offspring to infections. In this study, we have evaluated whether adult mice gestated in hypothyroid mothers have an altered response to pneumococcal pneumonia. We observed that female mice gestated in hypothyroidism have increased survival rate and less bacterial dissemination to blood and brain after an intranasal challenge with Streptococcus pneumoniae. Further, these mice had higher amounts of inflammatory cells in the lungs and reduced production of cytokines characteristic of sepsis in spleen, blood, and brain at 48 hours after infection. Interestingly, mice gestated in hypothyroid mothers had basally increased vascular permeability in the lungs. These observations suggest that gestational hypothyroidism alters the immune response and the physiology of lungs in the offspring, increasing the resistance to respiratory bacterial infections.

The effects of Nigella sativa extract on hypothyroidism-associated learning and memory impairment during neonatal and juvenile growth in rats

OBJECTIVES

It has been shown that hypothyroidism-induced oxidative damage in brain tissue is involved in its adverse effects on learning and memory. Nigella sativa (N. sativa) has been suggested to have antioxidant and neuroprotective effects. The objective of this study was to investigate the effects of hydroalcoholic extract of N. sativa on hypothyroidism-associated learning and memory impairment during neonatal and juvenile growth in rats.

METHODS

Thirty pregnant rats were kept in separate cages. After delivery, the mothers and their offspring were randomly divided into six groups including: (1) control, (2) PTU (propylthiouracil), (3) PTU-NS 100, (4) PTU-NS 200, (5) PTU-NS 400, and (6) PTU-Vit C (vitamin C). All dams except the control group received 0.005% PTU in their drinking water during lactation. Besides PTU, dams in groups 3, 4, 5, and 6 received 100, 200, and 400 mg/kg N. sativa extract, or 100 mg/kg Vit C, respectively. After lactation period, pups continued to receive same experimental treatment for the first 8 weeks of their life. Then, 10 male offspring of each group were randomly selected and assessed for the learning and memory abilities by using Morris water maze (MWM) and passive avoidance (PA) tests. Blood samples were collected for thyroxine assessment, animals were euthanized, and the brain tissues were removed and analyzed for total thiol groups and malondialdehyde (MDA) concentrations.

RESULTS

PTU exposure significantly increased the time latency in MWM test, while reduced the time spent in target quadrant, and decreased the latency for entering the dark compartment in PA test. These effects were associated with significant reduction in serum thyroxine levels and brain levels of thiol groups, and significant elevation in hippocampal MDA. Administration of 400 mg/kg N. sativa extract and 100 mg/kg Vit C reduced the time latency, while increased the time spent in target quadrant compared to the PTU group in MWM test. Treatment by 100-400 mg/kg of N. sativa extract and also Vit C significantly increased the time latency for entering the dark compartment in PA test. The serum thyroxine concentrations of the animals treated by all doses of the N. sativa extract as well as by Vit C were higher than that of the PTU group. Two hundred and four hundred milligrams/kilogram of NS extract and 100 mg/kg Vit C decreased the MDA concentration in hippocampal tissues, while increased thiol contents compared to the PTU group.

DISCUSSION

The results of this study demonstrate that the hydroalcoholic extract of N. sativa have protective effects on hypothyroidism-associated learning and memory impairment during neonatal and juvenile growth in rats. The effects were comparable to Vit C and might be due to the protective effects of N. sativa extract against brain tissues' oxidative damage.

The Ever-Changing Morphology of Hippocampal Granule Neurons in Physiology and Pathology

Newborn neurons are continuously added to the hippocampal dentate gyrus throughout adulthood. In this review, we analyze the maturational stages that newborn granule neurons go through, with a focus on their unique morphological features during each stage under both physiological and pathological circumstances. In addition, the influence of deleterious (such as schizophrenia, stress, Alzheimer's disease, seizures, stroke, inflammation, dietary deficiencies, or the consumption of drugs of abuse or toxic substances) and neuroprotective (physical exercise and environmental enrichment) stimuli on the maturation of these cells will be examined. Finally, the regulation of this process by proteins involved in neurodegenerative and neurological disorders such as Glycogen synthase kinase 3β, Disrupted in Schizophrenia 1 (DISC-1), Glucocorticoid receptor, pro-inflammatory mediators, Presenilin-1, Amyloid precursor protein, Cyclin-dependent kinase 5 (CDK5), among others, will be evaluated. Given the recently acquired relevance of the dendritic branch as a functional synaptic unit required for memory storage, a full understanding of the morphological alterations observed in newborn neurons may have important consequences for the prevention and treatment of the cognitive and affective alterations that evolve in conjunction with impaired adult hippocampal neurogenesis.

Thyroid hormone signaling: Contribution to neural function, cognition, and relationship to nicotine

Cigarette smoking is common despite its adverse effects on health, such as cardiovascular disease and stroke. Understanding the mechanisms that contribute to the addictive properties of nicotine makes it possible to target them to prevent the initiation of smoking behavior and/or increase the chance of successful quit attempts. While highly addictive, nicotine is not generally considered to be as reinforcing as other drugs of abuse. There are likely other mechanisms at work that contribute to the addictive liability of nicotine. Nicotine modulates aspects of the endocrine system, including the thyroid, which is critical for normal cognitive functioning. It is possible that nicotine's effects on thyroid function may alter learning and memory, and this may underlie some of its addictive potential. Here, we review the literature on thyroid function and cognition, with a focus on how nicotine alters thyroid hormone signaling and the potential impact on cognition. Changes in cognition are a major symptom of nicotine addiction. Current anti-smoking therapies have modest success at best. If some of the cognitive effects of nicotine are mediated through the thyroid hormone system, then thyroid hormone agonists may be novel treatments for smoking cessation therapies. The content of this review is important because it clarifies the relationship between smoking and thyroid function, which has been ill-defined in the past. This review is timely because the reduction in smoking rates we have seen in recent decades, due to public awareness campaigns and public smoking bans, has leveled off in recent years. Therefore, novel treatment approaches are needed to help reduce smoking rates further.

Brain Tissues Oxidative Damage as A Possible Mechanism of Deleterious Effects of Propylthiouracil- Induced Hypothyroidism on Learning and Memory in Neonatal and Juvenile Growth in Rats

INTRODUCTION

The role of brain tissues oxidative damage in learning and memory impairments has been well documented. It is also well known that thyroid hormones have a critical role for the brain functions. The purpose of this study was to investigate the role of brain tissues oxidative damage as a possible mechanism of deleterious effects of propylthiouracil (PTU) - induced hypothyroidism on learning and memory in neonatal and juvenile growth in rats.

METHODS

Fourteen pregnant female Wistar rats were kept in separate cages. After delivery, they were randomly divided into two groups including control and PTU. Rats in the control group received normal drinking water, whereas the second group received drinking water supplemented with 0.02% PTU from the first day after delivery through the first two months of the life of offspring (the pups of rats). After 60 days, nine male offspring of each group were randomly selected and tested in the Morris water maze (MWM). Then, samples of blood were collected to measure thyroxine. Finally, the brains were removed and total thiol groups and molondialdehyde (MDA) concentrations were determined.

RESULTS

Compared to the control group's offspring, serum thyroxine levels in the PTU group's off spring were significantly low (P<0.001). In MWM, the escape latency and traveled path in the PTU group were significantly higher than that in the control group (P<0.01- P<0.001). In PTU group, the total thiol concentrations in both cortical and hippocampal tissues were significantly lower and MDA concentrations were higher than control group (P<0.001).

DISCUSSION

It seems that deleterious effect of hypothyroidism during neonatal and juvenile growth on learning and memory is at least in part due to brain tissues oxidative damage.

Developmental iodine deficiency delays the maturation of newborn granule neurons associated with downregulation of p35 in postnatal rat hippocampus

We evaluated the role of p35 in the maturation of hippocampal granule neurons in offspring caused by developmental iodine deficiency. Two developmental rat models were established with either an iodine-deficient diet, or propylthiouracil-adulterated water (5 ppm) to impair thyroid function, in pregnant rats from gestational day 6 until postnatal day 28. The protein levels of p35, cyclin-dependent kinase 5, β-catenin, and N-cadherin were assessed on postnatal day 14, 21, and 28. Dendritic morphogenesis of newborn granule neurons in dentate gyrus was examined. Developmental hypothyroidism induced by iodine deficiency and PTU treatment delayed the maturation of hippocampal granule neurons in the offspring and decreased the percentage of Dcx-positive neurons that expressed β-catenin on postnatal day 21 and 28. In addition, downregulation of p35 was observed in dentate gyrus of hypothyroid groups. Developmental hypothyroidism induced by iodine deficiency and PTU treatment could delay the maturation of newborn granule neurons in dentate gyrus, and this deficit may be attributed to the downregulation of p35.

Growth/differentiation factor 15 promotes EGFR signalling, and regulates proliferation and migration in the hippocampus of neonatal and young adult mice

The activation of epidermal growth factor receptor (EGFR) affects multiple aspects of neural precursor behaviour, including proliferation and migration. Telencephalic precursors acquire EGF responsiveness and upregulate EGFR expression at late stages of development. The events regulating this process and its significance are still unclear. We here show that in the developing and postnatal hippocampus (HP), growth/differentiation factor (GDF) 15 and EGFR are co-expressed in primitive precursors as well as in more differentiated cells. We also provide evidence that GDF15 promotes responsiveness to EGF and EGFR expression in hippocampal precursors through a mechanism that requires active CXC chemokine receptor (CXCR) 4. Besides EGFR expression, GDF15 ablation also leads to decreased proliferation and migration. In particular, lack of GDF15 impairs both processes in the cornu ammonis (CA) 1 and only proliferation in the dentate gyrus (DG). Importantly, migration and proliferation in the mutant HP were altered only perinatally, when EGFR expression was also affected. These data suggest that GDF15 regulates migration and proliferation by promoting EGFR signalling in the perinatal HP and represent a first description of a functional role for GDF15 in the developing telencephalon.

Treadmill exercise ameliorates symptoms of methimazole-induced hypothyroidism through enhancing neurogenesis and suppressing apoptosis in the hippocampus of rat pups

Thyroid hormones play a crucial role in new neuron production and maturation during brain development. Physical exercise is known to promote cell survival and functional recovery after brain injuries. In the present study, we investigated the effects of treadmill exercise on short-term memory, spatial learning ability, neurogenesis, and apoptosis in hypothyroidism rat pups. On the 14th perinatal day, the pregnant rats were divided into two groups: the maternal control group and the maternal methimazole (MMI)-treated group. For the induction of hypothyroidism in rat pups, MMI was added to the drinking water (0.02%, wt/vol), from the 14th prenatal day to the 49th postnatal day. After delivery, the male rat pups born from the maternal control group were assigned into the control group and the control and exercise group. The rat pups born from the maternal MMI-treated group were divided into the hypothyroidism-induction group and the hypothyroidism-induction and treadmill exercise group. The rat pups in the exercise groups were forced to run on a motorized treadmill for 30min once a day, starting on the 22nd postnatal day for 4 weeks. Induction of hypothyroidism during the fetal and early postnatal period showed suppression of neurogenesis and enhancement of apoptosis in the hippocampus. Short-term memory and spatial learning ability were deteriorated in the hypothyroidism rat pups. Treadmill exercise during the postnatal period increased neurogenesis and inhibited apoptosis, and resulted in the improvement of short-term memory and spatial learning ability in the hypothyroidism rat pups.

Effect of maternal excessive iodine intake on neurodevelopment and cognitive function in rat offspring

Background

Iodine deficiency and iodine excess are both associated with adverse health consequences. Iodine deficiency during pregnancy leads to insufficient maternal thyroid hormone, subsequently causing irreversible adverse effects on the neurological and cognitive functions of the offspring. The results of our previous epidemiological study suggested that mild iodine excess might increase the prevalence of subclinical hypothyroidism. In the present study, female Wistar rats maintained on low-iodine grain were randomly assigned to three groups based on iodated water concentration: low iodine (LI, 1.2 μg/d), normal iodine (NI, 5–6 μg/d), and 3-fold high iodine (3HI, 15–16 μg/d). The present study investigated whether higher-than-normal iodine intake (3HI) by rats from before pregnancy until breastfeeding affects the postnatal (PN) neurodevelopment (PN7 and PN45) of their offspring during particularly sensitive periods in brain development.

Results

After 12 weeks of treatment (before pregnancy), iodine concentrations in urine and thyroid tissue and circulating thyroxine of adult females correlated with iodine intake. Brain-derived neurotrophic factor (BDNF) expression in the hippocampi of pups on PN7 and PN45 was decreased in 3HI group compared to the NI controls (P < 0.05, all) On PN7 and PN45, the BDNF levels of the 3HI pups were 83.5% and 88.8%, respectively, that of the NI pups. In addition, the 3HI group had a higher neuroendocrine-specific protein A (NSP-A) level than the NI controls on PN7 (P < 0.05). NSP-A levels of the 3HI pups were 117.0% that of the NI pups. No significant difference was observed in the expressions of c-Fos or c-Jun in the hippocampal CA1 region of the 3HI group compared to the controls (P > 0.05). Results from the Morris water maze test revealed that pups of the 3HI group had mild learning and spatial memory deficits.

Conclusions

The neurodevelopmental and cognitive deficits of the 3HI pups were mild and temporary, likely related to the changes in hippocampal protein expressions of BDNF and NSP-A.

Perinatal iodine deficiency and hypothyroidism increase cell apoptosis and alter doublecortin and reelin protein expressions in rat cerebellum

BACKGROUND AND AIMS

Adequate thyroid hormone is critical for cerebellar development. Developmental hypothyroidism induced by iodine deficiency during the perinatal period results in permanent impairments of cerebellar development with an unclear mechanism. In the present study we investigated effects of perinatal iodine deficiency and hypothyroidism on cerebellar cell apoptosis, doublecortin (Dcx) and reelin. Apoptosis is an essential part of neural development. Dcx and reelin are two important molecules involved in neuronal migration, structure, and development in cerebellum.

METHODS

Two developmental rat models were created by administering dam rats with either iodine-deficient diet or propylthiouracil (PTU, 5 ppm or 15 ppm)-added drinking water from gestational day (GD) 6 until postnatal day (PND) 28. TUNEL assay and protein levels of Dcx and reelin in cerebella were assessed on PND14, 21 and 28.

RESULTS

Apoptotic cells were increased in the iodine-deficient and PTU-treated rats. Dcx protein levels in the cerebella of iodine-deficient and PTU-treated rats were significantly downregulated on PND14. Interestingly, iodine deficiency and PTU treatment upregulated the levels of Dcx protein on PND21 and 28. Reelin expressions in iodine-deficient and PTU-treated rats were significantly decreased on PND14 and 21. On PND28, reelin expressions of three treated groups were still lower than control group, although without significant difference.

CONCLUSIONS

These findings may implicate alterations in cell apoptosis and levels of Dcx and reelin in the impairments of cerebellar development induced by developmental iodine deficiency and hypothyroidism.

Cocaine decreases expression of neurogranin via alterations in thyroid receptor/retinoid X receptor signaling

Mounting evidence suggests a potential link between cocaine abuse, disruptions in hypothalamic-pituitary-thyroid axis signaling, and neuroplasticity, but molecular mechanisms remain unknown. Neurogranin (Ng) is a gene containing a thyroid hormone-responsive element within its first intron that is involved in synaptic plasticity. Transcriptional activation requires heterodimerization of thyroid hormone receptor (TR) and retinoid X receptor (RXR) bound by their respective ligands, tri-iodothryonine and 9-cis-retinoic acid (9-cis-RA), and subsequent binding of this complex to the thyroid hormone-responsive element of the Ng gene. In this study, the effects of chronic cocaine abuse on Ng expression in euthyroid and hypothyroid mice were assessed. In cocaine-treated mice, decreased Ng expression was observed in the absence of changes in levels of thyroid hormones or other hypothalamic-pituitary-thyroid signaling factors. Therefore, we hypothesized that cocaine decreases Ng expression via alterations in 9-cis-RA availability and TR/RXR signaling. In support of this hypothesis, RXR-γ was significantly decreased in brains of cocaine-treated mice while CYP26A1, the main enzyme responsible for neuronal RA degradation, was significantly increased. Results from this study provide the first evidence for a direct effect of cocaine abuse on TR/RXR signaling, RA metabolism, and transcriptional regulation of Ng, a gene essential for adult neuroplasticity.

Developmental iodine deficiency and hypothyroidism impair neural development, upregulate caveolin-1, and downregulate synaptotagmin-1 in the rat cerebellum

Adequate thyroid hormone is critical for cerebellar development. Developmental hypothyroidism induced by iodine deficiency during gestation and postnatal period results in permanent impairments of cerebellar development with an unclear mechanism. In the present study, we implicate cerebellar caveolin-1 and synaptotagmin-1, the two important molecules involved in neuronal development, in developmental iodine deficiency, and in developmental hypothyroidism. Two developmental rat models were created by administrating dam rats with either iodine-deficient diet or propylthiouracil (PTU, 5 or 15 ppm)-added drinking water from gestational day 6 till postnatal day (PN) 28. Nissl staining and the levels of caveolin-1 and synaptotagmin-1 in cerebella were assessed on PN28 and PN42. The results show that the numbers of Purkinje cells were reduced in the iodine-deficient and PTU-treated rats. The upregulation of caveolin-1 and the downregulation of synaptotagmin-1 were observed in both iodine-deficient and PTU-treated rats. These findings may implicate decreases in the number of Purkinje cells and the alterations in the levels of caveolin-1 and synaptotagmin-1 in the impairments of cerebellar development induced by developmental iodine deficiency and hypothyroidism.

Hypothyroidism stimulates D2 receptor-mediated breathing in response to acute hypoxia and alters D2 receptors levels in carotid bodies and brain

Hypothyroidism can depress breathing and alter dopamine D2 receptor expression and function. We hypothesized that relative to euthyroid hamsters (EH), hypothyroid hamsters (HH) contain increased D2 receptors in brain regions associated with breathing and carotid bodies (CB), and that stimulation of D2 receptors would decease ventilation more in the HH compared to the EH. Hamsters were treated with vehicle, carmoxirile (peripherally acting D2 receptor agonist), or bromocriptine (central and peripherally acting D2 receptor agonist) and breathing was evaluated during exposure to air, hypoxia, and then air. HH exhibited increased D2 receptor protein levels in the striatum and CB, but decreased levels in the paraventricular hypothalamic nucleus. Relative to vehicle, carmoxirole and bromocriptine stimulated ventilation in the HH during and following exposure to hypoxia. Only bromocriptine depressed ventilation in the EH during and after exposure to hypoxia. Thus, hypothyroidism impacts the expression of D2 receptors in the carotid body, PVN and striatum, and D2 stimulation affects ventilation remarkably differently than in EH.

The effect of folic acid as an antioxidant on the hypothalamic monoamines in experimentally induced hypothyroid rat

Thyroid hormones are recognized as key metabolic hormones that play a critical role in the central nervous system development throughout life. In the present study, we studied the biochemical changes of hypothalamus of hypothyroid rats at post-pubertal stage, and the possible ameliorating effect of folic acid. A total of 50 male albino rats were equally divided into five groups; the first and second groups were the control and folic acid groups, respectively, while the third group was the hypothyroid group in which rats received daily 6-n-propyl-2-thiouracil (PTU) in drinking water for 6 weeks to induce hypothyroidism. The fourth and fifth groups were hypothyroid rats treated with folic acid for 4 weeks during and after receiving PTU, respectively, and were dissected after 6 and 10 weeks, respectively. There was a significant increase in plasma total homocysteine, malondialdehyde (MDA), oxidized glutathione\reduced glutathione and total nitric oxide and hypothalamic MDA, serotonin and norepinephrine in the hypothyroid rats group as compared to the control group. This reflects hyperhomocysteinaemia and oxidative stress associated with hypothyroid state. On the other hand, hypothalamic total nitric oxide and dopamine in the hypothyroid rats group were significantly decreased when compared to the control group. Treatment of hypothyroid rats with folic acid improves the oxidative stress and hypothalamic monoamines. Our results revealed that, folic acid treatment was better if it is administered as an adjuvant after returning to the euthyroid state.

Hypothyroidism attenuates SCH 23390-mediated depression of breathing and decreases D1 receptor expression in carotid bodies, PVN and striatum of hamsters

Hypothyroidism can lead to depressed breathing. We determined if propylthiouracil (PTU)-induced hypothyroidismin hamsters (HH) altered dopamine D1 receptor expression, D1 receptor-modulated ventilation, and ventilatory chemoreflex activation by hypoxia or hypercapnia. Hypothyroidism was induced by administering 0.04% PTU in drinking water for 3 months. Ventilation was evaluated following saline or 0.25mg/kg SCH 23390,a D1 receptor antagonist, while awake hamsters breathed normoxic (21% O(2) in N(2)), hypoxic (10% O(2)in N(2)) and hypercapnic (5% CO(2) in O(2))air. Relative to euthyroid hamsters (EH), HH exhibited decreased D1 receptor protein levels in carotid bodies, striatum, and hypothalamic paraventricular nucleus, but not in the nucleus tractus solitarius. Relative to EH, HH exhibited lower ventilation during exposure to normoxia, hypoxia, or hypercapnia, but comparable ventilatory responsiveness to chemoreflex activation. SCH23390 decreased ventilation of EH hamsters exposed to normoxia, hypoxia, and hypercapnia. In HH SCH23390 increased ventilation during baseline normoxia and did not affect ventilation during exposure to hypoxia and hypercapnia, resulting in reduced ventilatory responsivess to chemoreflex activation by hypoxia and hypercapnia. Furthermore, in HH D1 receptor protein levels are decreased in several brain regions and within the carotid bodies. Moreover, D1 receptor-modulation of breathing at rest and during gas exposures were depressed in EH but not HH.