Emotional and behavioral features associated with subclinical hypothyroidism in children and adolescents with Down syndrome

Background

Subclinical hypothyroidism (SH) is particularly frequent in individuals with Down syndrome (DS). Despite the amount of evidence suggesting SH is associated with psychopathological symptoms and sleep problems in general population, poor is known about the emotional and behavioral features associated with SH in children with DS.

Objective

The first aim of the current study was to investigate differences in emotional and behavioral profiles between a group of children with DS exhibiting co-occurring SH and a group of age and BMI-matched children with DS without co-occurring SH. The second aim of the present study was to investigate differences in sleep disturbances between these groups.

Methods

We included in this retrospective study 98 participants with DS aged 3-18 years with the aim to explore differences in emotional/behavioral problems as well as in sleep difficulties between children with DS with or without co-occurring SH.

Results

Participants with co-occurring SH exhibited significantly higher scores at several scales of the Conners' Parent Rating Scales Long Version - Revised. However, they did not exhibit more sleep problems than control group.

Conclusion

These results provide specific indications for psychological and neuropsychiatric evaluation of children with DS with suspected or diagnosed SH, highlighting the importance of a multidisciplinary approach in clinical care for children and adolescents with DS.

Investigations on learning and memory function in extended one-generation reproductive toxicity studies - when considered needed and based on what?

To justify investigations on learning and memory (L&M) function in extended one-generation reproductive toxicity studies (EOGRTS; Organization for Economic Co-operation and Development (OECD) test guideline (TG) 443) for registration under Registration, Evaluation, Authorization, and Restriction of Chemical (REACH), the European Chemicals Agency has referred to three publications based on which the Agency concluded that "perturbation of thyroid hormone signaling in offspring affects spatial cognitive abilities (learning and memory)" and "Therefore, it is necessary to conduct spatial learning and memory tests for F1 animals". In this paper, the inclusion of the requested L&M tests in an EOGRTS is challenged. In addition, next to the question on the validity of rodent models in general for testing thyroid hormone-dependent perturbations in brain development, the reliability of the publications specifically relied upon by the agency is questioned as these contain numerous fundamental errors in study methodology, design, and data reporting, provide contradicting results, lack crucial information to validate the results and exclude confounding factors, and finally show no causal relationship. Therefore, in our opinion, these publications cannot be used to substantiate, support, or conclude that decreases in blood thyroid (T4) hormone level on their own would result in impaired L&M in rats and are thus not adequate to use as fundament to ask for L&M testing as part of an EOGRTS.

Early postnatal hypothyroidism reduces juvenile play behavior, but prenatal hypothyroidism compensates for these effects

Perinatal hypothyroidism causes long-lasting effects on behavior, including hyperactivity, cognitive delays/deficits, and a reduction in anxiety. Although there is some evidence that hypothyroidism during fetal development in humans has been associated with later autism spectrum disorder diagnosis or autism-like traits, the relationships between early thyroid hormones and social behaviors are largely unknown. Previously, we found that a moderate dose of the hypothyroid-inducing drug methimazole during embryonic and postnatal development dramatically increased juvenile play in male and female rats. The goal of the current study was to determine the extent to which thyroid hormones act in prenatal or postnatal development to organize later social behaviors. Subjects were exposed to methimazole in the drinking water during prenatal (embryonic day 12 to birth), postnatal (birth to postnatal day 23), or pre- and postnatal development; control animals received regular drinking water throughout the experiment. They were tested for play behavior as juveniles (P30-32). We found an interaction between pre- and postnatal methimazole administration such that postnatal hypothyroidism decreased some play behaviors, whereas sustained pre- and postnatal hypothyroidism restored play to control levels. The effects were similar in males and females. To our knowledge, this is the first report of an interaction between pre- and postnatal hypothyroidism on later behavior. The complexity of the timing of these effects may help explain why epidemiological studies have not consistently found a relationship between gestational hypothyroidism and later behavior.

Experimental Modeling Of Hypothyroidism: Principles, Methods, Several Advanced Research Directions In Cardiology

Hypothyroidism is one of the most common pathological conditions in modern clinical practice. Due to the fact that the targets of thyroid hormones are virtually all organs and tissues, the morphological and clinical manifestations arising with a deficiency of thyroid hormones are quite diverse. Experimental models of hypothyroidism in laboratory animals are widely used for preclinical study of the fundamental pathophysiological mechanisms underlying hypothyroidism, as well as for assessing the effectiveness of treatment-and-prophylactic effects. Currently, several groups of effective models of hypothyroidism have been developed: dietary, surgical, medicamentous, genetic, radioactive and immunological. Each of the specified models is based on different principles, has advantages and disadvantages, and can be used depending on the goals and objectives of the experiment. In this review, we will consistently consider hypothyroidism modeling methods and indicate some promising areas of their use in cardiology.

Neurotoxicity and Behavioral Alterations Following Subchronic Administration of Aqueous Extract of Erythrophleum Ivorense Stem Bark in Mice

Introduction:

Erythrophleum Ivorense (EI) is a tree found across tropical Africa. The bark of EI is widely used as hunting poisons for animals and ordeal poison in humans. Eating this plant causes paralysis, respiratory distress, and amnesia. In folklore, these behavioral changes have been attributed to guilt in victims; nonetheless, no scientific evidence supports this claim. Thus, the mechanism of neurotoxicity and behavioral alteration of this plant should be investigated.

Methods:

A total of 48 BALB/c male mice were randomly divided into four groups. The three experimental groups were administered an aqueous extract of EI in a single daily dose of 5, 10, and 15 mg/kg bodyweight for 28 days, while the control group received distilled water. Afterward, the motor coordination, learning, memory, and grip strength of the mice were accessed with wire grip, Morris water maze, and inverted wire mesh grid grip tests. Histological staining of brain sections was also carried out.

Results:

At all tested doses, the aqueous extract of EI caused a significant reduction in hanging latency, significantly increased escape latency, and decreased duration of the target platform in the Morris water maze test compared to control. Reduced grip strength was also observed in the test groups compared to the control. Histology revealed dysmorphic and disoriented Purkinje cells and loss of this cell layer of the cerebellum.

Conclusion:

Erythrophleum ivorense administration altered motor coordination, learning and memory, and grip strength in mice dose-dependently. It also caused disruption of granule cells layer, loss of Purkinje cells, and altered cerebellar anatomy leading to motor deficits in mice.

Toxicological outcome of exposure to psychoactive drugs carbamazepine and diazepam on non-target insect Nauphoeta cinerea

The continuous detection of human pharmaceuticals during environmental biomonitoring is a global concern because of the menaces they may exert on non-target organisms. Carbamazepine (CBZ) and diazepam (DZP) are commonly prescribed psychotropic drugs which have been reported to coexist in the environment globally. Nauphoeta cinerea is a common insect with high ecological impact. This study elucidated the influence of co-exposure to DZP (0.5 and 1.0 μg kg^-1 diet) and CBZ (1.5 and 3.0 μg kg^-1 diet) for 42 days on the behavior and biochemical responses in Nauphoeta cinerea. Results showed that DZP alone did not induce adverse effect on the behavior and antioxidant status in the exposed insects. However, exposure to CBZ alone and binary mixtures of DZP and CBZ significantly decreased locomotor and exploratory accomplishments evidenced by decreased mobile episodes, total mobile time, maximum speed, total distance traveled, absolute turn angle, body rotation and path efficiency in comparison with control. The decline observed in the exploratory activities of insects fed with CBZ alone and the mixtures was confirmed by track plots and heat maps. Further, acetylcholinesterase and antioxidant enzyme activities decreased significantly whereas reactive oxygen and nitrogen species, nitric oxide and lipid peroxidation levels increased significantly in the hemolymph, head and midgut of insects exposed to CBZ alone and the mixtures. Collectively, CBZ alone and binary mixtures of CBZ and DZP caused neurotoxicity via induction of inflammatory and oxidative stress in insects. Nauphoeta cinerea may be a potential non-target insect model for monitoring ecotoxicological hazard of pharmaceuticals.

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.

Phycocyanin alleviates ICV-STZ induced cognitive and molecular deficits via PI3-Kinase dependent pathway

In this study, the effect of Phycocyanin (Pc) to ameliorate the cognitive dysfunction in experimental model of Alzheimer's disease (AD) was evaluated. Intracerebroventricular (ICV) induction of Streptozotocin (STZ) (3 mg/kg) was done bilaterally twice in rats on alternative days. Rats were injected with Pc (50, 100 mg/kg; i. p.) for 28 days daily for behavioural and cholinergic activity assessment. As the effect was only significant at 100 mg/kg, later molecular experiments were performed using the same only. STZ induction led to increased activity of hippocampal cholinesterases and BAX and decreased activity of BCL-2 and ChAT. It enhanced TNF-α, and NF-κB in rat's brain and reduced BDNF and IGF-1 levels. Dysfunctional insulin signaling and decreased gene expressions of PI3-K, AKT was also observed. However, Pc treatment significantly prevented STZ-induced increased activity of hippocampal cholinesterases and BAX as well as increased the levels of BCL-2 and ChAT. Neuroinflammation was significantly attenuated and BDNF and IGF-1 levels were upregulated. Further, Pc also alleviated dysfunctional insulin signaling as evidenced by increased gene expression of IRS-1, PI3-K, AKT. In conclusion, our study demonstrated the immense potential of Pc in attenuating STZ-induced cognitive decline and it may be further explored as a therapeutic agent in managing AD.

Gestational hypothyroidism elicits more pronounced lipid dysregulation in mice than pre-pregnant hypothyroidism

Thyroid hormone is crucial for regulating lipid and glucose metabolism, which plays essential role in maintaining the health of pregnant women and their offspring. However, the current literature is just focusing on the development of offspring born to the untreated mothers with hypothyroidism, rather than mothers themselves. Additionally, the interaction between hypothyroidism and pregnancy, and its impact on the women's health are still elusive. Therefore, this study was designed to compare the metabolic differences in dams with hypothyroidism starting before pregnancy and after pregnancy. Pre-pregnant hypothyroidism was generated in 5-week-old female C57/BL/6J mice using iodine-deficient diet containing 0.15% propylthiouracil for 4 weeks, and the hypothyroidism was maintained until delivery. Gestational hypothyroidism was induced in dams after mating, using the same diet intervention until delivery. Compared with normal control, gestational hypothyroidism exhibited more prominent increase than pre-pregnant hypothyroidism in plasma total cholesterol and low-density lipoprotein cholesterol, and caused hepatic triglycerides accumulation. Similarly, more significant elevations of protein expressions of SREBP1c and p-ACL, while more dramatic inhibition of CPT1A and LDL-R levels were also observed in murine livers with gestational hypothyroidism than those with pre-pregnant hypothyroidism. Moreover, the murine hepatic levels of total cholesterol and gluconeogenesis were dramatically and equally enhanced in two hypothyroid groups, while plasma triglycerides and protein expressions of p-AKT, p-FoxO1 and APOC3 were reduced substantially in two hypothyroid groups. Taken together, our current study illuminated that gestational hypothyroidism may elicit more pronounced lipid dysregulation in dams than dose the pre-pregnant hypothyroidism.

The effects of concurrent treatment of silymarin and lactulose on memory changes in cirrhotic male rats

Introduction: Chronic liver disease frequently accompanied by hepatic encephalopathy (HE). Changes in the permeability of the blood-brain barrier in HE, make an easier entrance of ammonia among other substances to the brain, which leads to neurotransmitter disturbances. Lactulose (LAC), causes better defecation and makes ammonia outreach of blood. Silymarin (SM) is a known standard drug for liver illnesses. The purpose of this research was to determine the results of LAC and SM combined treatment, on the changes in memory of cirrhotic male rats. Methods: The cirrhotic model established by treatment with thioacetamide (TAA) for 18 weeks. Cirrhotic rats randomized to four groups (n = 7): TAA group (received drinking water), LAC group (2 g/kg/d LAC in drinking water), SM group (50 mg/kg/d SM by food), SM+ LAC group (similar combined doses of both compounds) for 8 weeks. The control group received drinking water. The behavior examined by wire hanging (WH), passive avoidance (PA), and open field (OF) tests.

Results: Our findings showed that treatment with SM+LAC effectively increased PA latency, compared with the control group. The results showed that the administration of LAC and SM+LAC affected the number of lines crossed, the total distance moved and velocity in the OF tests.

Conclusion: SM and LAC have anti-inflammatory effects that are memory changing. It may be due to their useful effects. These results indicated that SM+LAC restored memory disturbance and irritated mood in the cirrhotic rats. Comparable neuroprotection was never previously informed. Such outcomes are extremely promising and indicate the further study of SM+LAC.

Neurobehavioural and biochemical responses associated with exposure to binary waterborne mixtures of zinc and nickel in rats

Environmental and occupational exposure to metal mixtures due to various geogenic and anthropogenic activities poses a health threat to exposed organisms. The outcome of systemic interactions of metals is a topical area of research because it may cause either synergistic or antagonistic effect. The present study investigated the impact of co-exposure to environmentally relevant concentrations of waterborne nickel (75 and 150 μg NiCl ₂ L^-1) and zinc (100 and 200 μg ZnCl₂ L^-1) mixtures on neurobehavioural performance of rats. Locomotor, motor and exploratory activities were evaluated using video-tracking software during trial in a novel arena and thereafter, biochemical and histological analyses were performed using the cerebrum, cerebellum and liver. Results indicated that zinc significantly (p < 0.05) abated the nickel-induced locomotor and motor deficits as well as improved the exploratory activity of exposed rats as verified by track plots and heat map analyses. Moreover, zinc mitigated nickel-mediated decrease in acetylcholinesterase activity, elevation in biomarkers of liver damage, levels of reactive oxygen and nitrogen species as well as lipid peroxidation in the exposed rats when compared with control. Additionally, nickel mediated decrease in antioxidant enzyme activities as well as the increase in tumour necrosis factor alpha, interleukin-1 beta and caspase-3 activity were markedly abrogated in the cerebrum, cerebellum and liver of rats co-exposed to nickel and zinc. Histological and histomorphometrical analyses evinced that zinc abated nickel-mediated neurohepatic degeneration as well as quantitative reduction in the widest diameter of the Purkinje cells and the densities of viable granule cell layer of dentate gyrus, pyramidal neurones of cornu ammonis 3 and cortical neurons in the exposed rats. Taken together, zinc abrogated nickel-induced neurohepatic damage via suppression of oxido-inflammatory stress and caspase-3 activation in rats.

Erythropoietin ameliorates harmaline-induced essential tremor and cognition disturbances

There are conflicting reports concerning the association of motor disabilities with increased risk of mental disorders. This investigation will provide a good understanding about defining the possible association between tremor and risk of anxiety and cognitive alterations. Beside, a secondary objective of the current study was to determine the effect of erythropoietin (EPO) on harmaline-induced motor and cognitive impairments. Male Wistar rats were used for the present study. The animal model of Esential tremor (ET) was established by the intraperitoneal injection of harmaline. EPO (5000 U/kg, i.p.) administered to the animals 1 h prior to harmaline injection. Exploratory, balance, anxiety related behaviors and cognitive function were assessed using footprint, open field, wire grip, rotarod and shuttle box tests. Findings demonstrated EPO ameliorated tremor scores that was induced by harmaline. Harmaline impaired cognitive functions of the treated rats, whereas EPO showed a promising effect against the cognitive impairments induced by harmaline. EPO can be offered as a potential neuroprotective agent in the treatment of patients with ET that manifest locomotor and cognitive impairments; however, further studies are needed to clarify the exact mechanisms.

Critical Period Regulation by Thyroid Hormones: Potential Mechanisms and Sex-Specific Aspects

Adequate perinatal levels of thyroid hormones (THs) are required for normal brain function and development. Studies in non-mammalian species suggest that TH might be involved in the regulation of critical periods (CPs) of heightened plasticity. Yet, it is largely unknown what mechanisms controlling such CPs might be under TH regulation. Here, we briefly review the influence of TH in early life across evolution. We discuss possible links between TH and known circuit and/or molecular mechanisms determining the timing of CPs of heightened brain plasticity. We focus on the role of parvalbumin-positive (PV) interneurons since their maturation defines CP onset and closure. Specifically, abnormal PV circuits are associated with low perinatal levels of TH, possibly because thyroid hypofunction may increase oxidative stress and/or dysregulate Otx2-mediated maturation of neuroprotective perineuronal nets. In addition, the level of cholinergic transmission is important for CP plasticity. Potentially, TH levels could affect gain changes in cholinergic transmission that can alter brain development. We believe that understanding how TH impacts CPs of circuit refinement will shed light onto the principles underlying normal developmental trajectories. Given that the thyroid gland expresses estrogen and androgen receptors, its activity can potentially be regulated differently between the sexes, contributing to sexually dimorphic behaviors.

The Effect of Perinatal Gadolinium-Based Contrast Agents on Adult Mice Behavior

OBJECTIVES

The aim of this study was to examine the effects of perinatal exposure to gadolinium (Gd)-based contrast agents (GBCAs) on the behavior of adulthood offspring.

MATERIALS AND METHODS

Pregnant Balb/C mice (n = 5 per group) were intravenously injected with gadoterate meglumine (Magnescope, macrocyclic GBCA), gadodiamide (Omniscan, linear GBCA), or vehicle from pregnancy day 15 to 19, corresponding to embryonic day 15 to 19 of the fetus, at 2 mmol/kg body weight per day. Brain samples from dams and pups were collected on postpartum day 28. The total Gd concentration was quantified by inductively coupled plasma-mass spectrometry (dams, n = 3; gadoterate meglumine-treated pups group, n = 9; and gadodiamide-treated pups group, n = 10). Behavioral testing of offspring was started on postpartum day 70 (control group, n = 22; gadoterate meglumine-treated group, n = 23; and gadodiamide-treated group, n = 20).

RESULTS

Higher levels of Gd retention were observed in dams and pups in the gadodiamide-treated group. Perinatal exposure to GBCAs caused anxiety-like behavior, disrupted motor coordination, impaired memory function, stimulated tactile sensitivity, and decreased muscle strength, particularly in the gadodiamide-treated group.

CONCLUSIONS

In the present study, we showed that Gd was transferred to pups and was retained in their brain during postnatal development. Gadolinium retention may lead to impaired brain development. These findings indicate that the use of GBCAs in pregnant women should be avoided because it may have adverse effects on the fetus, particularly on brain development.

Environmental exposure to perchlorate: A review of toxicology and human health

Perchlorate pharmacology and toxicology studies date back at least 65 years in the peer-reviewed literature. Repeated studies in animals and humans have demonstrated perchlorate's mechanism of action, dose-response, and adverse effects over a range of doses. The first measurable effect of perchlorate is inhibition of iodine uptake to the thyroid gland. Adequate levels of thyroid hormones are critical for the development of the fetal nervous system. With sufficient dose and exposure duration, perchlorate can reduce thyroid hormones in the pregnant or non-pregnant woman via this mechanism. The developing fetus is the most sensitive life stage for chemical agents that affect iodide uptake to the thyroid. Perchlorate has a half-life of eight hours, is not metabolized, does not bioaccumulate, is not a mutagen or carcinogen, and is not reprotoxic or immunotoxic. More recently, epidemiological and biomonitoring studies have been published in the peer-reviewed literature characterizing the thyroidal effects of perchlorate and other goitrogens. While the results from most populations report no consistent association, a few studies report thyroidal effects at environmentally relevant levels of perchlorate. We reviewed the literature on health effects of perchlorate at environmental exposure levels, with a focus on exposures during pregnancy and neurodevelopmental effects. Based on the studies we reviewed, health effects are expected to only occur at doses substantially higher than environmental levels.

Perinatal hypothyroidism increases play behaviors in juvenile rats

Thyroid hormones play an instrumental role in the development of the central nervous system. During early development, the fetus is dependent on maternal thyroid hormone production due to the dysfunction of its own thyroid gland. Thus, maternal thyroid dysfunction has been shown to elicit significant abnormalities in neural development, neurochemistry, and behavior in offspring. Previous reports have suggested that human maternal hypothyroidism may increase the chances of having children with autism spectrum disorder and attention-deficit/hyperactivity disorder. However, very few studies have evaluated social behaviors in animal models of perinatal hypothyroidism. To evaluate the possibility that hypothyroidism during development influences the expression one of the most commonly observed non-reproductive social behaviors, juvenile play, we used the validated rat model of perinatal hypothyroidism by methimazole administration (MMI; 0.025% in drinking water) from GD12-PD23. Control animals had regular drinking water. During adolescence (PD33-35), we tested subjects for juvenile play behavior by introducing them to a same-sex, unfamiliar (since weaning) littermate for 30min. Play behaviors and other behaviors (sleep, social contact, locomotion) were then scored. MMI-treated subjects played more than twice as much as control animals, and the increase in some behaviors was particularly dramatic in males. Locomotor and other affiliative social behaviors were unaffected. These data suggest that perinatal hypothyroidism may alter the organization of the neural networks regulating play behaviors, but not other social behaviors. Moreover, this implicates perinatal hypothyroidism as a potential etiological factor in the development of neurobehavioral disorders, particularly those characterized by heightened social interactions and impulsivity.

In Utero and Postnatal Propylthiouracil-Induced Mild Hypothyroidism Impairs Maternal Behavior in Mice

Thyroid hormones (THs) play crucial roles in general and brain development. Even if the hypothyroidism is mild, it may alter brain function, resulting in irreversible behavioral alterations. Although various behavioral analyses have been conducted, the effects of propylthiouracil (PTU) treatment during in utero and postnatal periods on maternal behavior have not yet been studied. The present study examined in mice whether THs insufficiency during development induce behavioral changes. Pregnant C57BL/6j mice were divided into three groups, and each group was administered different dosages of PTU (0, 5, or 50 ppm) in drinking water during in utero and postnatal periods (from gestational day 14 to postnatal day 21). First, locomotor activity and cognitive function were assessed in the offspring at 10 weeks. Next, female offspring were mated with normal mice and they and their offspring were used to assess several aspects of maternal behavior (identifying first pup, returning all pups to nest, time spent nursing, and licking pups). As expected, locomotor and cognitive functions in these mice were disrupted in a PTU dose-dependent manner. On postpartum day 2, dams who had been exposed 50 ppm PTU during in utero and postnatal periods displayed a significantly longer time identifying the first pup and returning all three pups back to the nest, less time nursing, and decreased licking behavior. The decrease in maternal behavior was significantly correlated with a decrease in cognition. These results indicate that insufficiency of THs during in utero and postnatal periods impairs maternal behavior, which may be partly induced by impaired cognitive function.

Modulation of sphingosine-1-phosphate receptor ameliorates harmaline-induced essential tremor in rat

Essential tremor (ET) is one of the most common movement disorders with unknown etiology. Despite lack of effective clinical treatments, some potential therapeutic factors and modulation of some neurotransmitters have been utilized to ameliorate motor symptoms in the animal models of tremor. In the current study, male Wistar rats (n=10 in each group) weighing 40-60g were divided into vehicle control groups (saline or DMSO), saline/DMSO+harmaline (30mg/kg, i.p.)+fingolimod (FTY720) (1mg/kg, i.p, 1h before harmaline injection) groups. Open field, rotarod, wire grip and foot print tests were used to evaluate motor function. The results demonstrated that administration of FTY720 can improve harmaline-induced tremor in rats. Moreover, FTY720 ameliorated gait disturbance. The results showed that FTY720 can recover step width, left and right step length; however, FTY720 failed to recover mobility duration. FTY720 also improved falling time and time spent in wire grip and rotarod, respectively. The current study provides the first evidence for the effectiveness of FTY720 on motor function in the harmaline model of ET. Furthermore, neuroprotective effects of FTY720 demonstrated in this study offer sphingosine-1-phosphate receptor (S1PR) modulators as a potential neuroprotective candidate against substance-induced tremor and a possible strategy for the treatment of patients with tremor.

Memory Deficit Recovery after Chronic Vanadium Exposure in Mice

Vanadium is a transitional metal with an ability to generate reactive oxygen species in the biological system. This work was designed to assess memory deficits in mice chronically exposed to vanadium. A total of 132 male BALB/c mice (4 weeks old) were used for the experiment and were divided into three major groups of vanadium treated, matched controls, and animals exposed to vanadium for three months and thereafter vanadium was withdrawn. Animals were tested using Morris water maze and forelimb grip test at 3, 6, 9, and 12 months of age. The results showed that animals across the groups showed no difference in learning but had significant loss in memory abilities after 3 months of vanadium exposure and this trend continued in all vanadium-exposed groups relative to the controls. Animals exposed to vanadium for three months recovered significantly only 9 months after vanadium withdrawal. There was no significant difference in latency to fall in the forelimb grip test between vanadium-exposed groups and the controls in all age groups. In conclusion, we have shown that chronic administration of vanadium in mice leads to memory deficit which is reversible but only after a long period of vanadium withdrawal.

Hexabromocyclododecane (HBCD) induced changes in the liver proteome of eu- and hypothyroid female rats

Hexabromocyclododecane (HBCD) is a brominated flame retardant known for its low acute toxicity as observed in animal experiments. However, HBCD exposure can affect liver functioning and thyroid hormone (TH) status. As exact mechanisms are unknown and only limited toxicological data exists, a gel-based proteomic approach was undertaken. In a eu- and hypothyroid female rat model, rats were exposed to 3 and 30 mg/kg bw/day HBCD for 7 days via their diet, and exposure was related to a range of canonical endpoints (hormone status, body weight) available for these animals. Alterations in the liver proteome under HBCD exposure were determined in comparison with patterns of control animals, for both thyroid states. This revealed significantly changed abundance of proteins involved in metabolic processes (gluconeogenesis/glycolysis, amino acid metabolism, lipid metabolism), but also in oxidative stress responses, in both euthyroid and hypothyroid rats. The results provide a more detailed picture on the mechanisms involved in these alterations, e.g. at the protein level changes of the proposed influence of HBCD on the lipid metabolism. Present results show that proteomic approaches can provide further mechanistic insights in toxicological studies.

The Effect of a Mutation in the Thyroid Stimulating Hormone Receptor (TSHR) on Development, Behaviour and TH Levels in Domesticated Chickens

The thyroid stimulating hormone receptor (TSHR) has been suggested to be a “domestication locus” in the chicken, due to a strong selective sweep over the gene found in domesticated chickens, differentiating them from their wild ancestor the Red Junglefowl (RJF). We investigated the effect of the mutation on development (incubation time), behaviour and thyroid hormone levels in intercross chickens homozygous for the mutation (d/d), wild type homozygotes (w/w) or heterozygotes (d/w). This allowed an assessment of the effect of genotype at this locus against a random mix of RJF and WL genotypes throughout the rest of the genome, controlling for family effects. The d/d genotype showed a longer incubation time, less fearful behaviours, lower number of aggressive behaviours and decreased levels of the thyroid hormone T4, in comparison to the w/w genotype. The difference between TSHR genotypes (d/d vs. w/w) in these respects mirrors the differences in development and behaviour between pure domesticated White Leghorns and pure RJF chickens. Higher individual T3 and T4 levels were associated with more aggression. Our study indicates that the TSHR mutation affects typical domestication traits, possibly through modifying plasma levels of thyroid hormones, and may therefore have been important during the evolution of the domestic chicken.

Pistachio supplementation attenuates motor and cognition impairments induced by cisplatin or vincristine in rats

Background:

A large number of natural products and dietary components have been evaluated as potential chemoprotective agents. In the present investigation we report the effects of treatment with the dietary antioxidant, pistachio, on cisplatin- or vincristine-induced neurotoxicity in male Wistar rats.

Materials and Methods:

Dietary pistachio (10%) was assessed for its neuroprotective effects through the alteration in performance of hippocampus- and cerebellum-related behaviors following chronic cisplatin (5 mg/kg) or vincristine (0.2 mg/kg) treatment in male rats. We also evaluated the effects of cisplatin, vincristine, and pistachio administration on nociception. Six behavioral tasks were used: open field, rotarod, grasping, Morris water maze (MWM), hot plate, and motor nerve conductive velocity (MNCV).

Results:

We showed that the exposure of adolescent rats to cisplatin or vincristine resulted in a significant decrease in explorative behaviors and memory retention. Pistachio consumption somewhat improved memory and motor abilities in cisplatin- or vincristine-treated rats, while pistachio alone did not show any significant changes in these abilities compared to saline. Cisplatin and vincristine increased the latency of response to nociception, and pistachio did not reverse this effect.

Conclusion:

We conclude that pistachio in the diet following anticancer drugs such as cisplatin and vincristine might have a protective effect against anticancer drug-induced disruptions in motor and cognitive function. However, further studies are needed to elucidate the exact mechanisms of this protective effect of pistachio.

Congenital hypothyroidism: a clinical update of long-term outcome in young adults

Congenital hypothyroidism (CH) is the most common congenital endocrine disorder. The early treatment of CH patients has successfully improved the prognosis and management of this disorder. Optimal treatment and management throughout the patient's life, beginning in the neonatal period, are required to ensure long-term health. Affected patients should be offered assessments of associated medical conditions and provided with accurate information about their condition throughout their lives, but particularly during the transition from pediatric to adult services. This review provides a summary of current knowledge about the long-term outcomes of these patients and appropriate management into early adulthood. We carried out a systematic search of the Medline database to identify relevant articles. Despite major improvements in prognosis, the impact of CH is clearly not uniform, and management should take into account a broader range of relevant indicators, including CH severity, associated comorbid conditions and the adequacy of treatment during childhood and adulthood. The early diagnosis and management of associated medical conditions, and better educational strategies to improve compliance with treatment, should improve the long-term prognosis. Further studies are required to explore changes with aging.

Adult onset-hypothyroidism: alterations in hippocampal field potentials in the dentate gyrus are largely associated with anaesthesia-induced hypothermia

Thyroid hormone (TH) is essential for a number of physiological processes and is particularly critical during nervous system development. The hippocampus is strongly implicated in cognition and is sensitive to developmental hypothyroidism. The impact of TH insufficiency in the foetus and neonate on hippocampal synaptic function has been fairly well characterised. Although adult onset hypothyroidism has also been associated with impairments in cognitive function, studies of hippocampal synaptic function with late onset hypothyroidism have yielded inconsistent results. In the present study, we report hypothyroidism induced by the synthesis inhibitor propylthiouracil (10 p.p.m., 0.001%, minimum of 4 weeks), resulted in marginal alterations in excitatory postsynaptic potential (EPSP) and population spike (PS) amplitude in the dentate gyrus measured in vivo. No effects were seen in tests of short-term plasticity, and a minor enhancement of long-term potentiation of the EPSP slope was observed. The most robust synaptic alteration evident in hypothyroid animals was an increase in synaptic response latency, which was paralleled by a failure to maintain normal body temperature under anaesthesia, despite warming on a heating pad. Latency shifts could be reversed in hypothyroid animals by increasing the external heat source and, conversely, synaptic delays could be induced in control animals by removing the heat source, with a consequent drop in body and brain temperature. Thermoregulation is TH- dependent, and anaesthesia necessary for surgical procedures posed a thermoregulatory challenge that was differentially met in control and hypothyroid animals. Minor increases in field potential EPSP slope, decreases in PS amplitudes and increased latencies are consistent with previous reports of hypothermia in naive control rats. We conclude that failures in thyroid-dependent temperature regulation rather than direct action of TH in synaptic physiology are responsible for the observed effects. These findings stand in contrast to the synaptic impairments observed in adult offspring following developmental TH insufficiency, and emphasise the need to control for the potential unintended consequences of hypothermia in the interpretation of hypothyroid-induced changes in physiological systems, most notably synaptic transmission.

Developmental neurotoxicity of 3,3',4,4'-tetrachloroazobenzene with thyroxine deficit: Sensitivity of glia and dentate granule neurons in the absence of behavioral changes

Thyroid hormones (TH) regulate biological processes implicated in neurodevelopmental disorders and can be altered with environmental exposures. Developmental exposure to the dioxin-like compound, 3,3',4,4'-tetrachloroazobenzene (TCAB), induced a dose response deficit in serum T4 levels with no change in 3,5,3'- triiodothyronine or thyroid stimulating hormone. Female Sprague-Dawley rats were orally gavaged (corn oil, 0.1, 1.0, or 10 mg TCAB/kg/day) two weeks prior to cohabitation until post-partum day 3 and male offspring from post-natal day (PND)4-21. At PND21, the high dose showed a deficit in body weight gain. Conventional neuropathology detected no neuronal death, myelin disruption, or gliosis. Astrocytes displayed thinner and less complex processes at 1.0 and 10 mg/kg/day. At 10 mg/kg/day, microglia showed less complex processes, unbiased stereology detected fewer hippocampal CA1 pyramidal neurons and dentate granule neurons (GC) and Golgi staining of the cerebellum showed diminished Purkinje cell dendritic arbor. At PND150, normal maturation of GC number and Purkinje cell branching area was not observed in the 1.0 mg/kg/day dose group with a diminished number and branching suggestive of effects initiated during developmental exposure. No effects were observed on post-weaning behavioral assessments in control, 0.1 and 1.0mg/kg/day dose groups. The demonstrated sensitivity of hippocampal neurons and glial cells to TCAB and T4 deficit raises support for considering additional anatomical features of brain development in future DNT evaluations.

Sensitive periods for hormonal programming of the brain

During sensitive periods, information from the external and internal environment that occurs during particular phases of development is relayed to the brain to program neural development. Hormones play a central role in this process. In this review, we first discuss sexual differentiation of the brain as an example of hormonal programming. Using sexual differentiation, we define sensitive periods, review cellular and molecular processes that can explain their restricted temporal window, and discuss challenges in determining the precise timing of the temporal window. We then briefly review programming effects of other hormonal systems and discuss how programming of these systems interact with sexual differentiation.

Maternal mobile phone exposure adversely affects the electrophysiological properties of Purkinje neurons in rat offspring

Electromagnetic field (EMF) radiations emitted from mobile phones may cause structural damage to neurons. With the increased usage of mobile phones worldwide, concerns about their possible effects on the nervous system are rising. In the present study, we aimed to elucidate the possible effects of prenatal EMF exposure on the cerebellum of offspring Wistar rats. Rats in the EMF group were exposed to 900-MHz pulse-EMF irradiation for 6h per day during all gestation period. Ten offspring per each group were evaluated for behavioral and electrophysiological evaluations. Cerebellum-related behavioral dysfunctions were analyzed using motor learning and cerebellum-dependent functional tasks (Accelerated Rotarod, Hanging and Open field tests). Whole-cell patch clamp recordings were used for electrophysiological evaluations. The results of the present study failed to show any behavioral abnormalities in rats exposed to chronic EMF radiation. However, whole-cell patch clamp recordings revealed decreased neuronal excitability of Purkinje cells in rats exposed to EMF. The most prominent changes included afterhyperpolarization amplitude, spike frequency, half width and first spike latency. In conclusion, the results of the present study show that prenatal EMF exposure results in altered electrophysiological properties of Purkinje neurons. However, these changes may not be severe enough to alter the cerebellum-dependent functional tasks.

Experimental hypothyroidism during pregnancy affects nociception and locomotor performance of offspring in rats

BACKGROUND

Thyroid hormones (THs) play a crucial role in the development of several organic systems. An adequate support of maternal THs may be required to ensure a normal nociceptive function of offspring into adulthood. We investigated the impact of experimental gestational hypothyroidism (EGH) on nociceptive threshold and motor performance in the offspring at different post-natal days (PND) in both male and female rats.

METHODS

EGH was induced by the administration of 0.02% methimazole (MMI) in the drinking water from the ninth day of gestation until birth. The offspring from MMI-treated dams (OMTDs) or from water-treated dams (OWTDs) were assessed for thermal and mechanical nociception using the tail-flick test and von Frey filaments, respectively. Both rota-rod and grip strength were used to assess motor function.

RESULTS

OMTD had reduced thermal (p<0.05) but not mechanical threshold at all studied ages (60 and 120 PND). Sixty-day-old OMTD presented reduced latency to the tail-flick test (p=0.01). Grip strength in 120-day-old OMTD was reduced (p<0.01). However, only male OMTD presented a lower locomotor performance on the rota-rod test when analysed on the 60th PND (p<0.01).

CONCLUSIONS

EGH promotes hypersensitivity to noxious thermal but not mechanical stimulus. Moreover, motor force is similarly reduced in male and female OMTDs, whereas motor performance is reduced only in mature male OMTD, suggesting the presence of a protective factor in females.

Developmentally-induced hypothyroidism alters the expression of Egr-1 and Arc genes and the sensitivity to cannabinoid agonists in the hippocampus. Possible implications for memory and learning

We analyzed the role of the cannabinoid system in the cognitive deficits caused by developmentally-induced hypothyroidism. We studied in control and hypothyroid rats the effect of a cannabinoid agonist on spatial memory, hippocampal phosphorylation of CREB and expression of early genes. Our results show that, 1-basal hippocampal expression of early genes and spatial learning are decreased in hypothyroid rats; 2-hypothyroid rats are very sensitive to cannabinoid agonists. Low dose of cannabinoid agonist ineffective in controls altered spatial memory, CREB's phosphorylation and early gene expression in hypothyroids. These effects are not due a change in CB1 receptor (CB1R) content. 3-Treatment of hypothyroid rats with thyroid hormones normalized the biochemical and behavioral responses to cannabinoid agonists but did not correct the low basal levels of early gene transcripts and the deficits in spatial learning. All these data suggest that the hippocampal deregulation of early genes expression could play an important role in the basal cognitive deficits of hypothyroid rats.

Evaluation of destructive effects of exposure to cisplatin during developmental stage: no profound evidence for sex differences in impaired motor and memory performance

We have elucidated the alteration in hippocampal and cerebellum function following chronic cisplatin treatment in male and female rats. Hippocampus and cerebellum related behavioral dysfunction in cisplatin-treated [intraperitoneally, 5 mg/(kg/week) for 5 weeks from 23-day-old] rats were analyzed using explorative, motor function, learning, and memory tasks (grasping, rotarod, open field, and Morris water maze tests). Exposure to cisplatin impaired the motor coordination in male and female rats. Exposure to cisplatin was reflected by a decrease in grasping time compared to vehicle-treated controls (saline) only in male rat while there were not any differences in female rats. When the rearing frequency, total distance moved and velocity of their recorded in open fieldtest, both males and females were dramatically affected by exposure to cisplatin. Compared to the saline, male and female rats trained 5 weeks after cisplatin injection showed significant memory deficits in the Morris water maze test. However, hippocampal and cerebellum functions of male and female rats were profoundly affected by exposure to cisplatin while no sex differences in the most variable were evident.

Profound destructive effects of adolescent exposure to vincristine accompanied with some sex differences in motor and memory performance

Vincristine, an anticancer drug, is known to induce neuronal cell damage. We have elucidated the alteration in performance of the hippocampus and cerebellum following chronic vincristine treatment (0.2 mg·(kg body mass)–1·week–1) in male and female rats. Intraperitoneal injection of vincristine in adolescent rats caused impairment of motor and cognitive behavior. In the probe test, the length of path traveled and percent swimming time for vincristine-treated rats in the correct quadrant was significantly less than for the saline-treated (control) groups. The path length and time latency at the 2nd and 3rd blocks of trials for the male vincristine-treated group was significantly higher than that for the female saline- and the vincristine-treated rats. In the rod test, vincristine exposure impaired the motor coordination in both male and female rats. Exposure to vincristine caused a significant decrease in hanging time in male rats, compared with the saline- and the vincristine-treated female rats, while there were no differences between the female vincristine-treated rats and the saline-treated rats of both sexes. The rearing frequency, total distance moved, and velocity for both male and female rats were dramatically affected by exposure to vincristine. We have observed that the hippocampal and cerebellar functions of male and female rats were profoundly affected by exposure to vincristine, especially the male rats, suggesting a sexual dimorphism in the developing central nervous system that is affected by chemicals such as anticancer drugs.

Selenium and/or iodine deficiency alters hepatic xenobiotic metabolizing enzyme activities in rats

The objective of this study was to investigate the effects of iodine (I(2)) and/or selenium (Se) deficiency on thyroid hormones and hepatic xenobiotic metabolizing enzyme systems using a triple animal model. Three-week-old male Wistar rats were fed for seven weeks. Se deficiency was introduced by a diet containing <0.005 mg/kg Se, and I(2) deficiency was produced by sodium perchlorate containing drinking water. The levels of plasma thyroid hormones [total T(4) (TT(4)), total T(3) (TT(3))], thyroid stimulating hormone (TSH); total microsomal cytochrome P450 (CYP450) and cytochrome b5 (CYP b5) levels; activities of microsomal NADPH-cytochrome P450 reductase (P450R), microsomal aniline hydroxylase (CYP2E1), microsomal 7-ethoxyresorufin O-deethylase (EROD), microsomal 7-pentoxyresorufin O-depentylase (PROD) and cytosolic glutathione S-transferase (GST) were determined. In I(2) deficiency total CYP450 levels, activities of CYP2E1, EROD and GST decreased, and CYP b5 content increased significantly. In Se-deficient rats, total CYP450 level and CYP2E1 activity increased, and EROD and GST activities and CYP b5 level decreased significantly. In combined I(2) and Se deficiency, except for CYP450 content and CYP2E1 activity, all enzyme activities and CYP b5 content decreased significantly compared to control group. Overall results of this study have suggested that metabolism of xenobiotics as well as endogenous compounds is affected by Se and I(2) status.

Nerve growth factor (NGF) immunoreactive neurons in the juvenile rat hippocampus: response to acute and long-term high-light open-field (HL-OF) or forced swim (FS) stress stimulation

This study aimed at examining and comparing the influence of two different stress stimuli on the density (number of cells/mm²) of nerve growth factor (NGF) containing neurons in the hippocampal CA1 and CA3 pyramidal cell layers and the dentate gyrus (DG) granule cell layer in juvenile rats (P28; P-postnatal day). The high-light open-field (HL-OF) test and forced swim (FS) test were employed to investigate the effects of a single, 15-min acute exposure and repeated (15 min daily for 21 days) long-term exposure to stress. In order to detect NGF-ir neurons, immunohistochemical (-ir) techniques were used. In comparison with nonstressed animals, acute and long-term HL-OF or FS stimulation resulted in a marked increase (P<0.001) in the density of NGF-ir containing cells in all the hippocampal structures. The frequency of stress application (acute vs. long-term), however, did not have a substantial impact on the studied parameter, with the exception of the CA3 sector, where a decreased density (P<0.001) of NGF-ir neurons was observed after long-term exposure to FS. It may be concluded that a rise in the density of NGF-ir neurons in the juvenile rat hippocampus after exposure to HL-OF or FS stressors could have affected the activity of the hypothalamic-pituitary-adrenocortical (HPA) stress axis. Prolonged HL-OF or FS stress was probably aggravating enough not to trigger the habituation process. The type of stressor applied (HL-OF vs. FS) was not essentially a factor determining the density of NGF-ir cells in the hippocampus.

The effects of olibanum administered to methimazole-treated dams during lactation on learning and memory of offspring rats

The effect of olibanum administered during lactation to methimazole-treated dams on the learning of offspring was evaluated. The animals were treated for 60 days from the first day of lactation period: group 1--tap water, group 2-0.03% methimazole and groups 3 and 4-0.03% methimazole with 0.25% or 0.125% olibanum, respectively. The serum thyroxin level in the offspring of group 2 was significantly lower than that of group 1. However, there was no difference compared to groups 3 and 4. In a Morris water maze, the distance and time latency to reach the platform in offspring of group 2 was significantly higher than groups 1, 3 and 4. In probe trial, the time spent in target quadrant (Q₁) by offspring of group 2 was lower than groups 1, 3 and 4. It is suggested that impaired learning and memory in the offspring of hypothyroid rats may be prevented by olibanum.

Do two models of acute and chronic stress stimulation influence the amount of nerve growth factor (NGF) and its receptor TrkA in the hippocampal neurons of middle aged rats?

Our study aimed to explore the influence of two different stressors: acute (once for 15 min) and chronic (15 min daily for 21 days) exposure to high light open field (HL-OF) or forced swim (FS) on the density of nerve growth factor (NGF) and tyrosine kinase A (TrkA) immunoreactive neurons in the hippocampal CA1 and CA3 pyramidal cell layers and dentate gyrus (DG) granule cell layer in middle aged (360 days old; P360; P, postnatal day) rats. In contrast to non-stressed animals, acute HL-OF stimulation resulted in an increase (p<0.001) in the density of NGF-ir cells in CA1, CA3, DG, whereas chronic HL-OF produced no changes in all hippocampal regions. The rats which underwent acute and chronic FS tests showed no statistically significant differences in the density of NGF-ir containing cells in the CA1, CA3, and DG subfields compared with control rats. Except for DG, where after 21 days of FS the density of TrkA-ir neurons was found to increase (p<0.05) in comparison to unstressed rats, no changes were noted in the density of TrkA-ir in the studied hippocampal structures as a result of acute and chronic HL-OF or FS exposure. These results indicate that acute HL-OF stress stimulation was the only factor inducing changes in the density of NGF-ir containing neurons in the hippocampal CA1, CA3, and DG of middle aged rats. In respect of the density of NGF-ir and TrkA-ir cells in the hippocampal structures, prolonged exposure to HL-OF or FS stressors did not constitute an aggravating factor for rats in the studied ontogenetic period.

Fenvalerate induced hepatic oxidative stress in selenium- and/or iodine-deficient rats

Considering the potential adverse effects of selenium and iodine deficiencies, and frequency of intensive but improper use of insecticides, this study was designed to evaluate the effects of a pyrethroid insecticide, fenvalerate, on the oxidant/antioxidant status of liver using a rat model of iodine and/or selenium deficiency. The study was conducted on eight groups of 3-week old Wistar rats. Iodine and/or selenium deficiency was introduced by feeding the animals with a diet containing <0.005 mg selenium/kg and/or supplying with 1% sodium perchlorate containing drinking water for a period of 7 weeks. Fenvalerate exposure (100 mg/kg/d, i.p., for the last 7 days) in normal rats increased hepatic glutathione peroxidase activity and lipid peroxidation, decreased glutathione content, but did not change the activities of catalase or any of the superoxide dismutase forms; in iodine-deficient animals caused only the elevation of lipid peroxidation; in selenium-deficient animals and in combined iodine/selenium deficiency decreased glutathione peroxidase, increased catalase activities and lipid peroxidation, and decreased all the forms of superoxide dismutase activity only in combined deficiency. These results suggested that fenvalerate is an oxidant stress inducer in rat liver, and its potential effects on pro-oxidant/antioxidant balance may also be important for human populations, particularly with iodine and/or selenium deficiencies.

Maternal exposure to the CB1 cannabinoid agonist WIN 55212-2 produces robust changes in motor function and intrinsic electrophysiological properties of cerebellar Purkinje neurons in rat offspring

The cerebellum, which controls coordinated and rapid movements, is a potential target for the deleterious effects of drugs of abuse including cannabis (i.e. marijuana, cannabinoids). Prenatal exposure to cannabinoids has been documented to cause abnormalities in motor and cognitive development, but the exact mechanism of this effect at the cellular level has not been fully elucidated. Previous studies indicate that cannabinoids are capable of modulating synaptic neurotransmission. In addition to altering synaptic activity, cannabinoid exposure may also change intrinsic neuronal properties. In the present study several different approaches including behavioral assays, extracellular field potential recordings and whole-cell patch clamp recordings, were used to address whether maternal exposure to the CB1 cannabinoid receptor agonist WIN 55-212-2 (WIN) affects the intrinsic electrophysiological properties of Purkinje neurons. WIN treatment of pregnant rats produced a significant decrease in the rearing frequency, total distance moved and mobility of the offspring, but significantly increased the time of the righting reflex, the grooming frequency and immobility. Neuromotor function, as assessed in the grip test and balance beam test, was also significantly impaired in prenatally WIN-treated group. Prenatal exposure to WIN increased the amplitude of population spikes (PS) recorded from the cerebellar Purkinje cell layer of offspring following synaptic blockage. WIN treatment of pregnant rats also profoundly affected the intrinsic properties of Purkinje neurons in offspring. This treatment increased the firing regularity, firing frequency, amplitude of afterhyperpolarization (AHP), the peak amplitude of action potential and the first spike latency, but decreased significantly the time to peak and duration of action potentials, the instantaneous firing frequency, the rate of rebound action potential and the voltage "sag" ratio. These results raise the possibility that maternal exposure to cannabinoids may profoundly affect the intrinsic membrane properties of cerebellar Purkinje neurons of offspring by altering the membrane excitability through modulation of intrinsic ion channels.

Prenatal induced chronic dietary hypothyroidism delays but does not block adult-type Leydig cell development

Transient hypothyroidism induced by propyl-2-thiouracyl blocks postpartum Leydig cell development. In the present study, the effects of chronic hypothyroidism on the formation of this adult-type Leydig cell population were investigated, using a more physiological approach. Before mating, dams were put on a diet consisting of an iodide-poor feed supplemented with a low dose of perchlorate and, with their offspring, were kept on this diet until death. In the pups at day 12 postpartum, plasma thyroid-stimulating hormone levels were increased by 20-fold, whereas thyroxine and free tri-iodothyronine levels were severely depressed, confirming a hypothyroid condition. Adult-type progenitor Leydig cell formation and proliferation were reduced by 40-60% on days 16 and 28 postpartum. This was followed by increased Leydig cell proliferation at later ages, suggesting a possible slower developmental onset of the adult-type Leydig cell population under hypothyroid conditions. Testosterone levels were increased 2- to 10-fold in the hypothyroid animals between days 21 and 42 postpartum compared with the age-matched controls. Combined with the decreased presence of 5alpha-reductase, this implicates a lower production capacity of 5alpha-reduced androgens. In 84-day-old rats, after correction for body weight-to-testis weight ratio, plasma insulin-like factor-3 levels were 35% lower in the hypothyroid animals, suggestive of a reduced Leydig cell population. This is confirmed by a 37% reduction in the Sertoli cell-to-Leydig cell ratio in hypothyroid rats. In conclusion, we show that dietary-induced hypothyroidism delays but, unlike propyl-2-thiouracyl, does not block the development of the adult-type Leydig cell population.