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

Perinatal bisphenol A exposure has an age- and dose-dependent association with thyroid allostasis adaptive response, as well as anxiogenic-depressive-like and asocial behaviors in juvenile and adult male rats

Thyroid hormones are essential for brain development, and a shortage throughout the fetal and postnatal periods can result in mood disorders. Perinatal exposure to bisphenol A (BPA) affects thyroid activity and dependent processes indirectly during pregnancy or early postnatal life. This is particularly important because it may cause changes in tissue ontogeny, increasing the risk of developing disorders later in life. The study aimed to investigate the consequences of thyroid hormone deficiency on anxiety, social, and depressive behaviors, as well as disruption in thyroid peroxidase (TPO) gene expression, which influences the NF-κB/Nrf-2/HO-1/iNOS signaling pathway, leading to oxidative stress, inflammation, and DNA fragmentation in perinatal BPA exposure (PND18), and whether these effects can be observed in juvenile (PND60) and adult (PND95) male offspring rats. BPA increased anxiety-like behavior while decreasing sucrose preference and sociability on a choice task between novel conspecific male rats and enhanced immobility on the forced swim test. Perinatal exposure to BPA causes thyroid insult by overproducing ROS, increasing iNOS, and NF-κB levels-these effects, in turn, down-regulate Nrf-2/HO-1 signaling, resulting in DNA fragmentation within thyroid tissues. Furthermore, perinatal BPA exposure for 60 and 95 days resulted in a significant fold decrease in TPO mRNA levels in the thyroid tissues, with an insignificant fold rise in TPO expression levels in BPA 50-60. In conclusion, the present study found that perinatal BPA exposure induced thyroid allostasis-adaptive response by inhibiting the NF-κB/Nrf-2/HO-1/iNOS signaling pathway and altering the transcriptional expression of TPO, where TSH reinforced a possible association with TPO activity, disrupting thyroid hormone synthesis in juvenile rats and gradual deterioration reaching the adult stage.

Arcuate dopaminergic/GABAergic neurons project within the hypothalamus and to the median eminence

Cotransmission, meaning the release of multiple neurotransmitters from one synapse, allows for increased diversity of signaling in the brain. Dopamine (DA) and γ-aminobutyric acid (GABA) are known to coexpress in many regions such as the olfactory bulb and the ventral tegmental area. Tuberoinfundibular dopaminergic neurons (TIDA) in the arcuate nucleus of the hypothalamus (Arc) project to the median eminence (ME) and regulate prolactin release from the pituitary, and prior work suggests dopaminergic Arc neurons also cotransmit GABA. However, the extent of cotransmission, and the projection patterns of these neurons have not been fully revealed. Here, we used a genetic intersectional reporter expression approach to selectively label cells that express both tyrosine hydroxylase (TH) and vesicular GABA transporter (VGAT). Through this approach, we identified cells capable of both DA and GABA cotransmission in the Arc, periventricular (Pe), paraventricular (Pa), ventromedial, and the dorsolateral hypothalamic nuclei, in addition to a novel population in the caudate putamen. The highest density of labeled cells was in the Arc, 6.68% of DAPI-labeled cells at Bregma -2.06 mm, and in the Pe, 2.83% of DAPI-labeled cells at Bregma -1.94 mm. Next, we evaluated the projections of these DA/GABA cells by injecting an mCherry virus that fluoresces in DA/GABA cells. We observed a cotransmitting DA/GABA population, with projections within the Arc, and to the Pa and ME. These data suggest DA/GABA Arc neurons are involved in prolactin release as a subset of TIDA neurons. Further investigation will elucidate the interactions of dopamine and GABA in the hypothalamus.NEW & NOTEWORTHY Cotransmitting dopaminergic (DA) and γ-aminobutyric acid (GABA)ergic (DA/GABA) neurons contribute to the complexity of neural circuits. Using a new genetic technique, we characterized the locations, density, and projections of hypothalamic DA/GABA neurons. DA/GABA cells are mostly in the arcuate nucleus (Arc), from which they project locally within the arcuate, to the median eminence (ME), and to the paraventricular (Pa) nucleus. There is also a small and previously unreported group of DA/GABA cells in the caudate putamen.

Thyroid hormone deficiency affects anxiety-related behaviors and expression of hippocampal glutamate transporters in male congenital hypothyroid rat offspring

Thyroid hormones are crucial for brain development and their deficiency during fetal and postnatal periods can lead to mood and cognitive disorders. We aimed to examine the consequences of thyroid hormone deficiency on anxiety-related behaviors and protein expression of hippocampal glutamate transporters in congenital hypothyroid male offspring rats. Possible beneficial effects of treadmill exercise have also been examined. Congenital hypothyroidism was induced by adding propylthiouracil (PTU) to drinking water of pregnant Wistar rats from gestational day 6 until the end of the weaning period (postnatal day 28). Next, following 4 weeks of treadmill exercise (5 days per week), anxiety-related behaviors were examined using elevated plus maze (EPM) and light/dark box tests. Thereafter, protein expression of astrocytic (GLAST and GLT-1) and neuronal (EAAC1) glutamate transporters were measured in the hippocampus by immunoblotting. Hypothyroid rats showed decreased anxiety-like behavior, as measured by longer time spent in the open arms of the EPM and in the light area of the light/dark box, compared to control rats. Hypothyroid rats had significantly higher GLAST and GLT-1 and lower EAAC1 protein levels in the hippocampus than did the euthyroid rats. Following exercise, anxiety levels decreased in the euthyroid group while protein expression of EAAC1 increased and returned to normal levels in the hypothyroid group. Our findings indicate that thyroid hormone deficiency was associated with alterations in protein expression of glutamate transporters in the hippocampus. Up-regulation of hippocampal GLAST and GLT-1 could be at least one of the mechanisms associated with the anxiolytic effects of congenital hypothyroidism.

Structural Malformations in the Neonatal Rat Brain Accompany Developmental Exposure to Ammonium Perchlorate

Environmental contaminants are often flagged as thyroid system disruptors due to their actions to reduce serum thyroxine (T4) in rodent models. The presence of a periventricular heterotopia (PVH), a brain malformation resulting from T4 insufficiency, has been described in response to T4 decrements induced by pharmaceuticals that reduce the hormone synthesis enzyme thyroperoxidase. In this report, we extend these observations to the environmental contaminant perchlorate, an agent that interferes with thyroid status by inhibiting iodine uptake into the thyroid gland. Pregnant rat dams were administered perchlorate in their drinking water (0, 30, 100, 300, 1000 ppm) from gestational day (GD) 6 until the weaning of pups on postnatal day (PN) 21. Serum T4 was reduced in dams and fetuses in late gestation and remained lower in lactating dams. Pup serum and brain T4, however, were not reduced beyond PN0, and small PVHs were evident in the brains of offspring when assessed on PN14. To emulate the developmental time window of the brain in humans, a second study was conducted in which pups from perchlorate-exposed dams were administered perchlorate orally from PN0 to PN6. This treatment reduced serum and brain T4 in the pup and resulted in large PVH. A third study extended the period of serum and brain TH suppression in pups by coupling maternal perchlorate exposure with maternal dietary iodine deficiency (ID). No PVHs were evident in the pups from ID dams, small PVHs were observed in the offspring of dams exposed to 300 ppm of perchlorate, and very large PVHs were present in the brains of pups born to dams receiving ID and perchlorate. These findings underscore the importance of the inclusion of serum hormone profiles in pregnant dams and fetuses in in vivo screens for thyroid-system-disrupting chemicals and indicate that chemical-induced decreases in fetal rat serum that resolve in the immediate postnatal period may still harbor considerable concern for neurodevelopment in humans.

Thyroid hormone action during GABAergic neuron maturation: The quest for mechanisms

Thyroid hormone (TH) signaling plays a major role in mammalian brain development. Data obtained in the past years in animal models have pinpointed GABAergic neurons as a major target of TH signaling during development, which opens up new perspectives to further investigate the mechanisms by which TH affects brain development. The aim of the present review is to gather the available information about the involvement of TH in the maturation of GABAergic neurons. After giving an overview of the kinds of neurological disorders that may arise from disruption of TH signaling during brain development in humans, we will take a historical perspective to show how rodent models of hypothyroidism have gradually pointed to GABAergic neurons as a main target of TH signaling during brain development. The third part of this review underscores the challenges that are encountered when conducting gene expression studies to investigate the molecular mechanisms that are at play downstream of TH receptors during brain development. Unravelling the mechanisms of action of TH in the developing brain should help make progress in the prevention and treatment of several neurological disorders, including autism and epilepsy.

Pre- and postsynaptic alterations in the visual cortex of the P23H-1 retinal degeneration rat model

P23H rats express a variant of rhodopsin with a mutation that leads to loss of visual function with similar properties as human autosomal dominant retinitis pigmentosa (RP). The advances made in different therapeutic strategies to recover visual system functionality reveal the need to know whether progressive retina degeneration affects the visual cortex structure. Here we are interested in detecting cortical alterations in young rats with moderate retinal degeneration, and in adulthood when degeneration is severer. For this purpose, we studied the synaptic architecture of the primary visual cortex (V1) by analyzing a series of pre- and postsynaptic elements related to excitatory glutamatergic transmission. Visual cortices from control Sprague Dawley (SD) and P23H rats at postnatal days 30 (P30) and P230 were used to evaluate the distribution of vesicular glutamate transporters VGLUT1 and VGLUT2 by immunofluorescence, and to analyze the expression of postsynaptic density protein-95 (PSD-95) by Western blot. The amount and dendritic spine distribution along the apical shafts of the layer V pyramidal neurons, stained by the Golgi-Cox method, were also studied. We observed that at P30, RP does not significantly affect any of the studied markers and structures, which suggests in young P23H rats that visual cortex connectivity seems preserved. However, in adult rats, although VGLUT1 immunoreactivity and PSD-95 expression were similar between both groups, a narrower and stronger VGLUT2-immunoreactive band in layer IV was observed in the P23H rats. Furthermore, RP significantly decreased the density of dendritic spines and altered their distribution along the apical shafts of pyramidal neurons, which remained in a more immature state compared to the P230 SD rats. Our results indicate that the most notable changes in the visual cortex structure take place after a prolonged retinal degeneration period that affected the presynaptic thalamocortical VGLUT2-immunoreactive terminals and postsynaptic dendritic spines from layer V pyramidal cells. Although plasticity is more limited at these ages, future studies will determine how reversible these changes are and to what extent they can affect the visual system's functionality.

Abnormal thalamocortical connectivity of preterm infants with elevated thyroid stimulating hormone identified with diffusion tensor imaging

While thyroid disturbances during perinatal and postnatal periods in preterm infants with congenital hypothyroidism reportedly disrupt neuronal development, no study has considered the effect of thyroid disturbances in premature infants with subclinical hypothyroidism with elevations of thyroid stimulating hormone. We aimed to identify altered fiber integrity from the thalamus to cortices in preterm infants with subclinical hypothyroidism. All preterm infants born were categorized according to thyroid stimulating hormone levels through serial thyroid function tests (36 preterm controls and 29 preterm infants with subclinical hypothyroidism). Diffusion tensor images were acquired to determine differences in thalamocortical fiber lengths between the groups, and cerebral asymmetries were investigated to observe neurodevelopmental changes. Thalamocortical fiber lengths in the subclinical hypothyroidism group were significantly reduced in the bilateral superior temporal gyrus, heschl's gyrus, lingual gyrus, and calcarine cortex (all p < 0.05). According to the asymmetric value in the orbitofrontal regions, there is a left dominance in the subclinical hypothyroidism group contrary to the controls (p = 0.012), and that of the cuneus areas showed significant decreases in the subclinical hypothyroidism group (p = 0.035). These findings could reflect altered neurodevelopment, which could help treatment plans using biomarkers for subclinical hypothyroidism.

Synergistic gene regulation by thyroid hormone and glucocorticoid in the hippocampus

The hippocampus is considered the center for learning and memory in the brain, and its development and function is greatly affected by the thyroid and stress axes. Thyroid hormone (TH) and glucocorticoids (GC) are known to have a synergistic effect on developmental programs across several vertebrate species, and their effects on hippocampal structure and function are well-documented. However, there are few studies that focus on the processes and genes that are cooperatively regulated by the two hormone axes. Cross-regulation of the thyroid and stress axes in the hippocampus occurs on multiple levels such that TH can regulate the expression of the GC receptor (GR) while GC can modulate tissue sensitivity to TH by controlling the expression of TH receptor (TR) and enzymes involved in TH biosynthesis. Thyroid hormone and GC are also known to synergistically regulate the transcription of genes associated with neuronal function and development. Synergistic gene regulation by TH and GC may occur through the direct, cooperative action of TR and GR on common target genes, or by indirect mechanisms involving gene regulatory cascades activated by TR and GR. In this chapter, we describe the known physiological effects and underlying molecular mechanisms of TH and GC synergistic gene regulation in the hippocampus.

Hexachlorobenzene, a pollutant in hypothyroidism and reproductive aberrations: a perceptive transgenerational study

Hexachlorobenzene (HCB), a widespread environmental pollutant, contributes to endocrine disruption resulting in hypothyroidism. We investigated the effect of chronic exposure of HCB to explore the functional interconnection between hypothyroidism and infertility. All observations were made through the F1 and F2 generations. Thyroidectomy was also performed to evaluate the contribution of the thyroid gland in affecting ovarian dysfunction and reproductive aberrations. We confirmed that the preconception exposure of HCB leads to hypothyroidism which was reflected by an increase in the body weight, alteration in the thyroid hormones, and alteration of the lipid profile. Hypothyroid female rats exhibited a poor reproductive profile with altered steroidogenic pathways, altered estrus cyclicity, reduced litter size, and stunted growth. The external supplementation of thyroxine in thyroidectomized animals rescues the reproductive aberrations confirming the protective role of the thyroid gland in reproductive biology. All results highlight the jeopardizing functional connection of the thyroid and ovary due to HCB, leading to serious consequences on upcoming generations.

Thyroid disrupting chemicals and developmental neurotoxicity - New tools and approaches to evaluate hormone action

It is well documented that thyroid hormone (TH) action is critical for normal brain development and is mediated by both nuclear and extranuclear pathways. Given this dependence, the impact of environmental endocrine disrupting chemicals that interfere with thyroid signaling is a major concern with direct implications for children's health. However, identifying thyroid disrupting chemicals in vivo is primarily reliant on serum thyroxine (T4) measurements within greater developmental and reproductive toxicity assessments. These studies do not examine known TH-dependent phenotypes in parallel, which complicates chemical evaluation. Additionally, there exist no recommendations regarding what degree of serum T4 dysfunction is adverse, and little consideration is given to quantifying TH action within the developing brain. This review summarizes current testing strategies in rodent models and discusses new approaches for evaluating the developmental neurotoxicity of thyroid disrupting chemicals. This includes assays to identify adverse cellular effects of the brain by both immunohistochemistry and gene expression, which would compliment serum T4 measures. While additional experiments are needed to test the full utility of these approaches, incorporation of these cellular and molecular assays could enhance chemical evaluation in the regulatory arena.

Regulation of Thyroid-disrupting Chemicals to Protect the Developing Brain

Synthetic chemicals with endocrine disrupting properties are pervasive in the environment and are present in the bodies of humans and wildlife. As thyroid hormones (THs) control normal brain development, and maternal hypothyroxinemia is associated with neurological impairments in children, chemicals that interfere with TH signaling are of considerable concern for children's health. However, identifying thyroid-disrupting chemicals (TDCs) in vivo is largely based on measuring serum tetraiodothyronine in rats, which may be inadequate to assess TDCs with disparate mechanisms of action and insufficient to evaluate the potential neurotoxicity of TDCs. In this review 2 neurodevelopmental processes that are dependent on TH action are highlighted, neuronal migration and maturation of gamma amino butyric acid-ergic interneurons. We discuss how interruption of these processes by TDCs may contribute to abnormal brain circuitry following developmental TH insufficiency. Finally, we identify issues in evaluating the developmental neurotoxicity of TDCs and the strengths and limitations of current approaches designed to regulate them. It is clear that an enhanced understanding of how THs affect brain development will lead to refined toxicity testing, reducing uncertainty and improving our ability to protect children's health.

Transient Hypothyroidism During Lactation Alters the Development of the Corpus Callosum in Rats. An in vivo Magnetic Resonance Image and Electron Microscopy Study

Magnetic resonance imaging (MRI) data of children with late diagnosed congenital hypothyroidism and cognitive alterations such as abnormal verbal memory processing suggest altered telencephalic commissural connections. The corpus callosum (CC) is the major inter-hemispheric commissure that contra-laterally connects neocortical areas. However, in late diagnosed neonates with congenital hypothyroidism, the possible effect of early transient and chronic postnatal hypothyroidism still remains unknown. We have studied the development of the anterior, middle and posterior CC, using in vivo MRI and electron microscopy in hypothyroid and control male rats. Four groups of methimazole (MMI) treated rats were studied. One group, as a model for early transient hypothyroidism, was MMI-treated from postnatal day (P) 0 to P21; some of these rats were also treated with L-thyroxine (T4) from P15 to 21. Another group modeling chronic hypothyroid, were treated with MMI from P0 to 150 and from embryonic day 10 to P170. The results obtained from these groups were compared with same age control rats. The normalized T2 signal obtained using MRI was higher in MMI-treated rats and correlated with a low number and percentage of myelinated axons. The number and density of myelinated axons decreased in transient and chronic hypothyroid rats at P150. The g-ratio (inner to outer diameter ratio) and the estimated conduction velocity of myelinated axons were similar between MMI-treated and controls, but the conduction delay decreased in the posterior CC of MMI-treated rats compared to controls. These data show that early postnatal transient and chronic hypothyroidism alters CC maturation in a way that may affect the callosal transfer of information. These alterations cannot be reversed after delayed T4-treatment. Our data support the findings of neurocognitive delay in late T4-treated children with congenital hypothyroidism.

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

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

A Mini-Review of the Role of Glutamate Transporter in Drug Addiction

Goals: The development of new treatment for drug abuse requires identification of targetable molecular mechanisms. The pathology of glutamate neurotransmission system in the brain reward circuit is related to the relapse of multiple drugs. Glutamate transporter regulates glutamate signaling by removing excess glutamate from the synapse. And the mechanisms between glutamate transporter and drug addiction are still unclear.

Methods: A systematic review of the literature searched in Pubmed and reporting drug addiction in relation to glutamate transporter. Studies were screened by title, abstract, and full text.

Results: This review is to highlight the effects of drug addiction on glutamate transporter and glutamate uptake, and targeting glutamate transporter as an addictive drug addiction treatment. We focus on the roles of glutamate transporter in different brain regions in drug addiction. More importantly, we suggest the functional roles of glutamate transporter may prove beneficial in the treatment of drug addiction.

Conclusion: Overall, understanding how glutamate transporter impacts central nervous system may provide a new insight for treatment of drug addiction.

Effects of Maternal Prenatal Multi-Micronutrient Supplementation on Growth and Development until 3 Years of Age

At present, there is insufficient evidence on whether prenatal multi-micronutrient (MM) supplementation can be an antenatal nutritional intervention or not. This study aimed to explore the sustained effect of prenatal MM supplementation on early childhood health. A total of 939 mother–offspring pairs were followed up in the study between 2015 to 2018 in Changsha, China. Information was mainly collected through household surveys at the ages of 1, 3, 6, 8, 12, 18, 24, and 36 months. General linear models and generalized estimating equation models were used to estimate the effects of maternal prenatal MM compared with IFA supplementation on infant growth and development. Offspring of women who used prenatal MM compared with IFA supplements had lower weight-for-age z score (WAZ) (adjusted β: −0.23, 95% CI: (−0.40, −0.06)) and weight-for-length z score (WLZ) (adjusted β: −0.20, 95% CI: (−0.37, −0.02)) at 3 months old, but a reduced risk of obesity at birth (aRR: 0.30, 95% CI: 0.11–0.78) and being overweight at 3 months old (aRR: 0.52, 95% CI: 0.32–0.84). Moreover, offspring of women who used prenatal MM compared with IFA supplements had significantly higher scores for communication (adjusted β: 0.41, 95% CI: 0.61–0.21), gross motor (adjusted β: 0.68, 95% CI: 0.49–0.88), fine motor (adjusted β: 1.64, 95% CI: 1.45–1.84), problem solving (adjusted β: 0.29, 95% CI: 0.10–0.49), and personal–social (adjusted β: 0.90, 95% CI: 0.70–1.10) skills at 36 months old. Prenatal MM supplementation could result in better infant growth in the first few months of life and improve development scores at the age of 3 years compared with IFA supplementation.

Coordinated transcriptional regulation by thyroid hormone and glucocorticoid interaction in adult mouse hippocampus-derived neuronal cells

The hippocampus is a well-known target of thyroid hormone (TH; e.g., 3,5,3’-triiodothyronine—T₃) and glucocorticoid (GC; e.g., corticosterone—CORT) action. Despite evidence that TH and GC play critical roles in neural development and function, few studies have identified genes and patterns of gene regulation influenced by the interaction of these hormones at a genome-wide scale. In this study we investigated gene regulation by T₃, CORT, and T₃ + CORT in the mouse hippocampus-derived cell line HT-22. We treated cells with T₃, CORT, or T₃ + CORT for 4 hr before cell harvest and RNA isolation for microarray analysis. We identified 9 genes regulated by T₃, 432 genes by CORT, and 412 genes by T₃ + CORT. Among the 432 CORT-regulated genes, there were 203 genes that exhibited an altered CORT response in the presence of T₃, suggesting that T₃ plays a significant role in modulating CORT-regulated genes. We also found 80 genes synergistically induced, and 73 genes synergistically repressed by T₃ + CORT treatment. We performed in silico analysis using publicly available mouse neuronal chromatin immunoprecipitation-sequencing datasets and identified a considerable number of synergistically regulated genes with TH receptor and GC receptor peaks mapping within 1 kb of chromatin marks indicative of hormone-responsive enhancer regions. Functional annotation clustering of synergistically regulated genes reveal the relevance of proteasomal-dependent degradation, neuroprotective effect of growth hormones, and neuroinflammatory responses as key pathways to how TH and GC may coordinately influence learning and memory. Taken together, our transcriptome data represents a promising exploratory dataset for further study of common molecular mechanisms behind synergistic TH and GC gene regulation, and identify specific genes and their role in processes mediated by cross-talk between the thyroid and stress axes in a mammalian hippocampal model system.

Distribution of GABAergic Neurons and VGluT1 and VGAT Immunoreactive Boutons in the Ferret (Mustela putorius) Piriform Cortex and Endopiriform Nucleus. Comparison With Visual Areas 17, 18 and 19

We studied the cellular organization of the piriform network [comprising the piriform cortex (PC) and endopiriform nucleus (EP)] of the ferret (Mustela putorius)-a highly excitable region prone to seizures-and, more specifically, the distribution and morphology of different types of gamma-aminobutyric acid (GABA)ergic neurons, and the distribution and ratio of glutamatergic and GABAergic boutons, and we compared our findings to those in primary visual area 17, and secondary areas 18 and 19. We accomplished this by using cytochrome oxidase and immunohistochemistry for mature neuronal nuclei (NeuN), GABAergic neurons [glutamic acid decarboxylase-67 (GAD67), calretinin (CR) and parvalbumin (PV)], and for excitatory (vesicular glutamate transporter 1; VGluT1) and inhibitory (vesicular GABA transporter; VGAT) boutons. In the ferret, the cellular organization of the piriform network is similar to that described in other species such as cats, rats and opossums although some differences also exist. GABAergic immunolabeling showed similarities between cortical layers I-III of the PC and visual areas, such as the relative distribution of GABAergic neurons and the density and area of VGluT1- and VGAT-immunoreactive boutons. However, multiple differences between the piriform network and visual areas (layers I-VI) were found, such as the percentage of GABAergic neurons with respect to the total number of neurons and the ratio of VGluT1- and VGAT-immunoreactive boutons. These findings are relevant to better understand the high excitability of the piriform network.

Adult-onset hypothyroidism increases ethanol consumption

RATIONALE

Only in Europe it can be estimated that more than 20 million of people would be affected by hypothyroidism in some moment of their life. Given that ethanol consumption is so frequent, it would be reasonable to ask what the consequences of ethanol consumption in those individuals affected by hypothyroidism are.

OBJECTIVES

To study the interaction between hypothyroidism and ethanol consumption.

METHODS

We study ethanol consumption in a rat model of methyl-mercaptoimidazole-induced-adult-onset hypothyroidism and thyroid T4/T3 hormone supplementation. Also, we studied the effects of ethanol on motor activity, memory, and anxiety.

RESULTS

We found that hypothyroidism increased the voluntary ethanol consumption and that this was enhanced by thyroid hormone supplementation. Hypothyroidism was associated with motor hyperactivity which was prevented either by T4/T3 supplementation or ethanol. The relationship between hypothyroidism, ethanol, and anxiety was more complex. In an anxiogenic context, hypothyroidism and T4/T3 supplementation would increase immobility, an anxiety-like behavior, while in a less anxiogenic context would decrease rearing, a behavior related to anxiety. Regarding memory, acute ethanol administration did not alter episodic-like memory in hypothyroid rats. Gene expression of enzymes involved in the metabolism of ethanol, i.e., Adh1 and Aldh2, were altered by hypothyroidism and T4/T3 supplementation.

CONCLUSIONS

Our results suggest that hypothyroid patients would need personalized attention in terms of ethanol consumption. In addition, they point that it would be useful to embrace the thyroid axis in the study of ethanol addiction, including as a possible therapeutic target for the treatment of alcoholism and its comorbid disorders.

Dentate Gyrus Immaturity in Schizophrenia

Hippocampal abnormalities have been heavily implicated in the pathophysiology of schizophrenia. The dentate gyrus of the hippocampus was shown to manifest an immature molecular profile in schizophrenia subjects, as well as in various animal models of the disorder. In this position paper, we advance a hypothesis that this immature molecular profile is accompanied by an identifiable immature morphology of the dentate gyrus granule cell layer. We adduce evidence for arrested maturation of the dentate gyrus in the human schizophrenia-affected brain, as well as multiple rodent models of the disease. Implications of this neurohistopathological signature for current theory regarding the development of schizophrenia are discussed.

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

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

Transient Hypothyroidism During Lactation Arrests Myelination in the Anterior Commissure of Rats. A Magnetic Resonance Image and Electron Microscope Study

Thyroid hormone deficiency at early postnatal ages affects the cytoarchitecture and function of neocortical and telencephalic limbic areas, leading to impaired associative memory and in a wide spectrum of neurological and mental diseases. Neocortical areas project interhemispheric axons mostly through the corpus callosum and to a lesser extent through the anterior commissure (AC), while limbic areas mostly project through the AC and hippocampal commissures. Functional magnetic resonance data from children with late diagnosed congenital hypothyroidism and abnormal verbal memory processing, suggest altered ipsilateral and contralateral telencephalic connections. Gestational hypothyroidism affects AC development but the possible effect of transient and chronic postnatal hypothyroidism, as occurs in late diagnosed neonates with congenital hypothyroidism and in children growing up in iodine deficient areas, still remains unknown. We studied AC development using in vivo magnetic resonance imaging and electron microscopy in hypothyroid and control male rats. Four groups of methimazole (MMI) treated rats were studied. One group was MMI-treated from postnatal day (P) 0 to P21; some of these rats were also treated with L-thyroxine (T4) from P15 to P21, as a model for early transient hypothyroidism. Other rats were MMI-treated from P0 to P150 and from embryonic day (E) 10 to P170, as a chronic hypothyroidism group. The results were compared with age paired control rats. The normalized T2 signal using magnetic resonance image was higher in MMI-treated rats and correlated with the number and percentage of myelinated axons. Using electron microscopy, we observed decreased myelinated axon number and density in transient and chronic hypothyroid rats at P150, unmyelinated axon number increased slightly in chronic hypothyroid rats. In MMI-treated rats, the myelinated axon g-ratio and conduction velocity was similar to control rats, but with a decrease in conduction delays. These data show that early postnatal transient and chronic hypothyroidism alters AC maturation that may affect the transfer of information through the AC. The alterations cannot be recovered after delayed T4-treatment. Our data support the neurocognitive delay found in late T4-treated children with congenital hypothyroidism.

Maternal hypothyroxinaemia in early pregnancy and problem behavior in 5-year-old offspring

INTRODUCTION

There is evidence, though not consistent, that offspring born to mothers with subtle decreases in thyroid function early in their pregnancies may be at risk of cognitive impairments and attention problems. However, other types of problem behavior have not been addressed thus far. We tested whether maternal thyroid function in early pregnancy is associated with several types of problem behavior in offspring at age 5-6 years.

METHODS

This was a longitudinal study that included the data of 2000 mother-child pairs from the Amsterdam Born Children and their Development study. At a median gestational age of 12.9 (interquartile range: 11.9-14.1) weeks, maternal blood was sampled for assessment of free T4 and TSH. Overall problem behavior, hyperactivity/inattention, conduct problems, emotional problems, peer relationship problems and prosocial behavior were measured at age 5-6 years using the Strengths and Difficulties Questionnaire, which was filled out by both parents and teachers.

RESULTS

Maternal hypothyroxinaemia <5th percentile was associated with a 1.70 (95% confidence interval (CI): 1.01-2.86) increased odds of teacher-reported hyperactivity/inattention after adjustment for confounders. By increasing the cut-off level to <10th percentile, the odds ratio became 1.47 (95% CI: 0.99-2.20). There were no associations between maternal thyroid function parameters and hyperactivity/inattention as reported by parents, nor with teacher or parent reports of other types of problem behavior.

CONCLUSIONS

Our results partially confirm previous observations, showing that early disruptions in the maternal thyroid hormone supply may be associated with ADHD symptoms in offspring. Our study adds that there is no evidence for an effect on other types of problem behavior.

Thyroid hormones and learning-associated neuroplasticity

Thyroid hormones (THs) are crucial for brain development and maturation in all vertebrates. Especially during pre- and perinatal development, disruption of TH signaling leads to a multitude of neurological deficits. Many animal models provided insight in the role of THs in brain development, but specific data on how they affect the brain's ability to learn and adapt depending on environmental stimuli are rather limited. In this review, we focus on a number of learning processes like spatial learning, fear conditioning, vocal learning and imprinting behavior and on how abnormal TH signaling during development shapes subsequent performance. It is clear from multiple studies that TH deprivation leads to defects in learning on all fronts, and interestingly, changes in local expression of the TH activator deiodinase type 2 seem to have an important role. Taking into account that THs are regulated in a very space-specific manner, there is thus increasing pressure to investigate more local TH regulators as potential factors involved in neuroplasticity. As these learning processes are also important for proper adult human functioning, further elucidating the role of THs in developmental neuroplasticity in various animal models is an important field for advancing both fundamental and applied knowledge on human brain function.

Preliminary Findings Show Maternal Hypothyroidism May Contribute to Abnormal Cortical Morphology in Offspring

In rodents, insufficient thyroid hormone (TH) gestationally has adverse effects on cerebral cortex development. Comparable studies of humans examining how TH insufficiency affects cortical morphology are limited to children with congenital hypothyroidism or offspring of hypothyroxinemic women; effects on cortex of children born to women with clinically diagnosed hypothyroidism are not known. We studied archived MRI scans from 22 children aged 10-12 years born to women treated for preexisting or de novo hypothyroidism in pregnancy (HYPO) and 24 similar age and sex controls from euthyroid women. FreeSurfer Image Analysis Suite software was used to measure cortical thickness (CT) and a vertex-based approach served to compare HYPO versus control groups and Severe versus Mild HYPO subgroups as well as to perform regression analyses examining effects of trimester-specific maternal TSH on CT. Results showed that relative to controls, HYPO had multiple regions of both cortical thinning and thickening, which differed for left and right hemispheres. In HYPO, thinning was confined to medial and mid-lateral regions of each hemisphere and thickening to superior regions (primarily frontal) of the left hemisphere and inferior regions (particularly occipital and temporal) of the right. The Severe HYPO subgroup showed more thinning than Mild in frontal and temporal regions and more thickening in bilateral posterior and frontal regions. Maternal TSH values predicted degree of thinning and thickening within multiple brain regions, with the pattern and direction of correlations differing by trimester. Notably, some correlations remained when cases born to women with severe hypothyroidism were removed from the analyses, suggesting that mild variations of maternal TH may permanently affect offspring cortex. We conclude that maternal hypothyroidism during pregnancy has long-lasting manifestations on the cortical morphology of their offspring with specific effects reflecting both severity and timing of maternal TH insufficiency.

Differential Pharmacological Regulation of Sensorimotor Gating Deficit in CB1 Knockout Mice and Associated Neurochemical and Histological Alterations

The endocannabinoid system has been widely involved in the pathophysiology of sensorimotor gating deficits. This study aimed to evaluate the pharmacological modulation of the sensorimotor gating impairment induced by cannabinoid CB1 receptor (CB1r) deletion. For this purpose, the prepulse inhibition (PPI) paradigm was used to evaluate the effect of two antipsychotics drugs (risperidone and haloperidol) and a psychostimulant (methylphenidate) on the preattentional deficit presented by CB1KO mice. Furthermore, the effects of the CB1r antagonist AM251 on PPI were evaluated in WT mice. Real-time PCR and immunohistochemical studies were carried out to analyze dopamine transporter (DAT) and α-2C adrenergic receptor (ADRA2C) gene expressions and the distribution of parvalbumin (PV) and cholecystokinin-8 (CCK) immunoreactive (ir) cortical neurons, respectively. Neither risperidone nor haloperidol significantly modified the PPI of WT and CB1KO mice, whereas methylphenidate improved the preattentional deficit of CB1KO mice. In addition, treatment with AM251 (3 mg/kg; i.p.) significantly decreased the PPI of WT animals. The administration of methylphenidate increased DAT and ADRA2C gene expressions in CB1KO mice without producing any effect in WT animals. Immunohistochemical studies revealed that there were no significant changes in CCK immunolabeling between WT and CB1KO mice, whereas the radial distribution of PV-ir neurons was abnormal in CB1KO mice. These data further support the important role of CB1r in sensorimotor gating regulation and the therapeutic usefulness of methylphenidate for the treatment of psychiatric disorders with associated preattentional deficits.

Hippocampal Functioning and Verbal Associative Memory in Adolescents with Congenital Hypothyroidism

Thyroid hormone (TH) is essential for normal development of the hippocampus, which is critical for memory and particularly for learning and recalling associations between visual and verbal stimuli. Adolescents with congenital hypothyroidism (CH), who lack TH in late gestation and early life, demonstrate weak verbal recall abilities, reduced hippocampal volumes, and abnormal hippocampal functioning for visually associated material. However, it is not known if their hippocampus functions abnormally when remembering verbal associations. Our objective was to assess hippocampal functioning in CH using functional magnetic resonance imaging (fMRI). Fourteen adolescents with CH and 14 typically developing controls (TDC) were studied. Participants studied pairs of words and then, during fMRI acquisition, made two types of recognition decisions: in one they judged whether the pairs were the same as when seen originally and in the other, whether individual words were seen before regardless of pairing. Hippocampal activation was greater for pairs than items in both groups, but this difference was only significant in TDC. When we directly compared the groups, the right anterior hippocampus was the primary region in which the TDC and CH groups differed for this pair memory effect. Results signify that adolescents with CH show abnormal hippocampal functioning during verbal memory processing.