Effects of an anti‐thyroid drug, methimazole, administration to rat dams on the cerebellar cortex development in their pups

Potential Application of Marine Algae and Their Bioactive Metabolites in Brain Disease Treatment: Pharmacognosy and Pharmacology Insights for Therapeutic Advances

Seaweeds, also known as edible marine algae, are an abundant source of phytosterols, carotenoids, and polysaccharides, among other bioactive substances. Studies conducted in the past few decades have demonstrated that substances derived from seaweed may be able to pass through the blood-brain barrier and act as neuroprotectants. According to preliminary clinical research, seaweed may also help prevent or lessen the symptoms of cerebrovascular illnesses by reducing mental fatigue, preventing endothelial damage to the vascular wall of brain vessels, and regulating internal pressure. They have the ability to control neurotransmitter levels, lessen neuroinflammation, lessen oxidative stress, and prevent the development of amyloid plaques. This review aims to understand the application potential of marine algae and their influence on brain development, highlighting the nutritional value of this "superfood" and providing current knowledge on the molecular mechanisms in the brain associated with their dietary introduction.

Towards a science-based testing strategy to identify maternal thyroid hormone imbalance and neurodevelopmental effects in the progeny-part III: how is substance-mediated thyroid hormone imbalance in pregnant/lactating rats or their progeny related to neurodevelopmental effects?

This review investigated which patterns of thyroid- and brain-related effects are seen in rats upon gestational/lactational exposure to 14 substances causing thyroid hormone imbalance by four different modes-of-action (inhibition of thyroid peroxidase, sodium-iodide symporter and deiodinase activities, enhancement of thyroid hormone clearance) or to dietary iodine deficiency. Brain-related parameters included motor activity, cognitive function, acoustic startle response, hearing function, periventricular heterotopia, electrophysiology and brain gene expression. Specific modes-of-action were not related to specific patterns of brain-related effects. Based upon the rat data reviewed, maternal serum thyroid hormone levels do not show a causal relationship with statistically significant neurodevelopmental effects. Offspring serum thyroxine together with offspring serum triiodothyronine and thyroid stimulating hormone appear relevant to predict the likelihood for neurodevelopmental effects. Based upon the collated database, thresholds of ≥60%/≥50% offspring serum thyroxine reduction and ≥20% and statistically significant offspring serum triiodothyronine reduction indicate an increased likelihood for statistically significant neurodevelopmental effects; accuracies: 83% and 67% when excluding electrophysiology (and gene expression). Measurements of brain thyroid hormone levels are likely relevant, too. The extent of substance-mediated thyroid hormone imbalance appears more important than substance mode-of-action to predict neurodevelopmental impairment in rats. Pertinent research needs were identified, e.g. to determine whether the phenomenological offspring thyroid hormone thresholds are relevant for regulatory toxicity testing. The insight from this review shall be used to suggest a tiered testing strategy to determine whether gestational/lactational substance exposure may elicit thyroid hormone imbalance and potentially also neurodevelopmental effects.

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.

Testing for heterotopia formation in rats after developmental exposure to selected in vitro inhibitors of thyroperoxidase

The thyroperoxidase (TPO) enzyme is expressed by the thyroid follicular cells and is required for thyroid hormone synthesis. In turn, thyroid hormones are essential for brain development, thus inhibition of TPO in early life can have life-long consequences for brain function. If environmental chemicals with the capacity to inhibit TPO in vitro can also alter brain development in vivo through thyroid hormone dependent mechanisms, however, remains unknown. In this study we show that the in vitro TPO inhibiting pesticide amitrole alters neuronal migration and induces periventricular heterotopia; a thyroid hormone dependent brain malformation. Perinatal exposure to amitrole reduced pup serum thyroxine (T4) concentrations to less than 50% of control animals and this insufficiency led to heterotopia formation in the 16-day old pup's brain. Two other in vitro TPO inhibitors, 2-mercaptobenzimidazole and cyanamide, caused reproductive toxicity and had only minor sporadic effects on the thyroid hormone system; consequently, they did not cause heterotopia. This is the first demonstration of an environmental chemical causing heterotopia, a brain malformation until now only reported for rodent studies with the anti-thyroid drugs propylthiouracil and methimazole. Our results highlight that certain TPO-inhibiting environmental chemicals can alter brain development through thyroid hormone dependent mechanisms. Improved understanding of the effects on the brain as well as the conditions under which chemicals can perturb brain development will be key to protect human health.

Thyroid hormones during the perinatal period are necessary to respiratory network development of newborn rats

Thyroid hormones (THs) are essential for foetal brain development. Because the gestating mother is the main source of THs to the foetus, maternal hypothyroidism and/or premature birth compromise neurological outcomes in the offspring. Respiratory instability and recurrent apneas due to immaturity of the respiratory control network are major causes of morbidity in infants. Inadequate TH supply may be sufficient to delay perinatal maturation of the respiratory control system; however, this hypothesis remains untested. To address this issue, maternal hypothyroidism was induced by adding methimazole (MMI; 0.02% w/v) to the drinking water of pregnant dams from conception to postpartum day 4 (P4). The effect of TH supplementation on respiratory function was tested by injecting levothyroxine (L-T4) in newborns at P1. Respiratory function was assessed by plethysmography (in vivo) and recording of phrenic output from medullary preparations (in vitro). By comparison with controls, TH deficiency increased the frequency of apneas and decreased basal ventilation in vivo and prevented the age-dependent increase in phrenic burst frequency normally observed in vitro. The effects of TH deficiency on GABAergic modulation of respiratory activity were measured by bath application of muscimol (GABA_A agonist) or bicuculline (GABA_A antagonist). The phrenic burst frequency responses to GABAergic agents were consistently greater in preparations from TH deficient pups. L-T4 supplementation reversed part of the respiratory anomalies related to MMI treatment in vitro. We conclude that TH deficiency during the perinatal period is sufficient to delay maturation of the respiratory control network development. Excessive GABAergic inhibition may contribute to this effect.

Effects of a rat model of gestational hypothyroidism on forebrain dopaminergic, GABAergic, and serotonergic systems and related behaviors

We investigated the effects of maternal hypothyroidism on forebrain dopaminergic, GABAergic, and serotonergic systems and related behavior in adult rat offspring. Experimental gestational hypothyroidism (EGH) was induced by administering 0.02% methimazole (MMI) to pregnant rats from gestational day 9 to delivery. Neurotransmitter-related protein and gene expression were evaluated in offspring forebrain at postnatal day (P) 120. Exploratory behavior, contextual fear conditioning, locomotion, and 30-day reserpine Parkinson induction were assessed from P75-P120. Protein and gene expression assessments of medial prefrontal cortex showed group differences in dopaminergic, GABAergic, and serotonergic receptors, catabolic enzymes, and transporters. Striatum of MMI offspring showed an isolated decrease in the dopaminergic enzyme, tyrosine hydroxylase. MMI exposure increased GABA and dopamine receptor expression in amygdala. MMI offspring also had decreased state anxiety and poor contextual fear conditioning. We found that baseline locomotion was not changed, but reserpine treatment significantly reduced locomotion only in MMI offspring. Our results indicated that restriction of maternal thyroid hormones reduced dopaminergic, GABAergic, and serotoninergic forebrain components in offspring. Tyrosine hydroxylase deficiency in the striatum may underlie enhanced reserpine induction of Parkinson-like movement in these same offspring. Deficits across different neurotransmitter systems in medial prefrontal cortex and amygdala may underlie decreased state anxiety-like behavior and reduced fear conditioning in offspring, but no changes in trait anxiety-like behavior occurred with maternal MMI exposure. These findings strongly support the hypothesis that adequate delivery of maternal thyroid hormones to the fetus is crucial to the development of the central nervous system critical for emotion and motor regulation.

Repeated potassium iodide exposure during pregnancy impairs progeny's brain development

Protracted radioiodine release may require repeated intake of potassium iodide (KI) to protect thyroid gland. It is well established that iodine excess inhibits transiently the thyroid function. As developing fetus depends on maternal thyroid hormones (TH) supply, more knowledge is needed about the plausible effects that repeated KI intake can cause in this sensitive population, especially that even subtle variation of maternal thyroid function may have persistent consequences on progeny brain processing. The aim of this study is to assess the consequences of repeated intake of KI during pregnancy on the progeny's thyroid function and brain development. To do so pregnant Wistar rats received KI over eight days, and then thirty days after the weaning, male progeny was subjected to behavior test. Pituitary and thyroid hormones level, anti-thyroid antibodies level, organs morphology, gene expression and global DNA methylation were assessed. Thirty days after the weaning, KI-exposed male progeny showed an uncommon hormonal status, characterized by a decrease of both thyroid-stimulating hormone (-28%) and free thyroxine (-7%) levels. Motor coordination was altered in KI-exposed male progeny. At the cerebellar level, we observed a decrease of mRNA expression of DCX (-42%) and RC3 (-85%); on the other hand, at the cortical level, mRNA expression of MBP (+71%), MOBP (+90%) and Kcna1 (+42%) was increased. To conclude, repeated KI prophylaxis is not adequate during pregnancy since it led to long-term irreversible neurotoxicity in the male progeny.

Mild Maternal Hypothyroxinemia During Pregnancy Induces Persistent DNA Hypermethylation in the Hippocampal Brain-Derived Neurotrophic Factor Gene in Mouse Offspring

BACKGROUND

Thyroid hormones are essential for normal development of the central nervous system (CNS). Experimental rodents have shown that even a subtle thyroid hormone insufficiency in circulating maternal thyroid hormones during pregnancy may adversely affect neurodevelopment in offspring, resulting in irreversible cognitive deficits. This may be due to the persistent reduced expression of the hippocampal brain-derived neurotrophic factor gene Bdnf, which plays a crucial role in CNS development. However, the underlying molecular mechanisms remain unclear.

METHODS

Thiamazole (MMI; 0.025% [w/v]) was administered to dams from two weeks prior to conception until delivery, which succeeded in inducing mild maternal hypothyroxinemia during pregnancy. Serum thyroid hormone and thyrotropin levels of the offspring derived from dams with mild maternal hypothyroxinemia (M offspring) and the control offspring (C offspring) were measured. At 70 days after birth, several behavior tests were performed on the offspring. Gene expression and DNA methylation status were also evaluated in the promoter region of Bdnf exon IV, which is largely responsible for neural activity-dependent Bdnf gene expression, in the hippocampus of the offspring at day 28 and day 70.

RESULTS

No significant differences in serum thyroid hormone or thyrotropin levels were found between M and C offspring at day 28 and day 70. M offspring showed an impaired learning capacity in the behavior tests. Hippocampal steady-state Bdnf exon IV expression was significantly weaker in M offspring than it was in C offspring at day 28. At day 70, hippocampal Bdnf exon IV expression at the basal level was comparable between M and C offspring. However, it was significantly weaker in M offspring than in C offspring after the behavior tests. Persistent DNA hypermethylation was also found in the promoter region of Bdnf exon IV in the hippocampus of M offspring compared to that of C offspring, which may cause the attenuation of Bdnf exon IV expression in M offspring.

CONCLUSIONS

Mild maternal hypothyroxinemia induces persistent DNA hypermethylation in Bdnf exon IV in offspring as epigenetic memory, which may result in long-term cognitive disorders.

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.

Aluminium and Acrylamide Disrupt Cerebellum Redox States, Cholinergic Function and Membrane-Bound ATPase in Adult Rats and Their Offspring

Accumulation of aluminium and acrylamide in food is a major source of human exposure. Their adverse effects are well documented, but there is no information about the health problems arising from their combined exposure. The aim of the present study was to examine the possible neurotoxic effects after co-exposure of pregnant and lactating rats to aluminium and acrylamide in order to evaluate redox state, cholinergic function and membrane-bound ATPases in the cerebellum of adult rats and their progeny. Pregnant female rats have received aluminium (50 mg/kg body weight) via drinking water and acrylamide (20 mg/kg body weight) by gavage, either individually or in combination from the 14th day of pregnancy until day 14 after delivery. Exposure to these toxicants provoked an increase in malondialdehyde (MDA) and advanced oxidation protein product (AOPP) levels and a decrease in SOD, CAT, GPx, Na⁺K⁺-ATPase, Mg²⁺-ATPase and AChE activities in the cerebellum of mothers and their suckling pups. A reduction in GSH, NPSH and vitamin C levels was also observed. These changes were confirmed by histological results. Interestingly, co-exposure to these toxicants exhibited synergism based on physical and biochemical variables in the cerebellum of mothers and their progeny.

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

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

Aberrant Cerebellar Development in Mice Lacking Dual Oxidase Maturation Factors

BACKGROUND

Thyroid hormone (TH) plays a key role in the developing brain, including the cerebellum. TH deficiency induces organizational changes of the cerebellum, causing cerebellar ataxia. However, the mechanisms causing these abnormalities are poorly understood. Various animal models have been used to study the mechanism. Lacking dual oxidase (DUOX) and its maturation factor (DUOXA) are major inducers of congenital hypothyroidism. Thus, this study examined the organizational changes of the cerebellum using knockout mice of the Duoxa gene (Duoxa-/-).

METHODS

The morphological, behavioral, and electrophysiological changes were analyzed in wild type (Wt) and Duoxa-deficient (Duoxa-/-) mice from postnatal day (P) 10 to P30. To detect the changes in the expression levels of presynaptic proteins, Western blot analysis was performed.

RESULTS

The proliferation and migration of granule cells was delayed after P15 in Duoxa-/- mice. However, these changes disappeared by P25. Although the cerebellar structure of Duoxa-/- mice was not significantly different from that of Wt mice at P25, motor coordination was impaired. It was also found that the amplitude of paired-pulse facilitation at parallel fiber-Purkinje cell synapses decreased in Duoxa-/- mice, particularly at P15. There were no differences between expression levels of presynaptic proteins regulating neurotransmitter release at P25.

CONCLUSIONS

These results indicate that the anatomical catch-up growth of the cerebellum did not normalize its function because of the disturbance of neuronal circuits by the combined effect of hypothyroidism and functional disruption of the DUOX/DUOXA complex.

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.

Impact of mild thyroid hormone deficiency in pregnancy on cognitive function in children: lessons from the Generation R Study

Animal models and epidemiological studies suggest that mild maternal thyroid hormone deficiency in early gestation has adverse consequences on the cognitive abilities of the children. However, methodological problems, lack of a consistent definition for mild thyroid hormone deficiency, and short follow-up of the children reduce the confidence in the conclusion of existing studies. In this review, we summarize the main findings of a series of studies performed in Generation R, a population-based birth cohort in Rotterdam, the Netherlands. In this iodine sufficient region, we aimed to investigate the relation between mild maternal thyroid hormone deficiency in early gestation and children's verbal and nonverbal cognitive function and executive function. We discuss the main findings of these studies, present recommendations for clinicians and formulate suggestions for future research.

Effects of maternal exposure to thiamazole on behavioral development in infant cynomolgus monkeys

Thiamazole, an anti-hyperthyroidism agent, was administered orally to pregnant cynomolgus monkeys at doses of 2.0 and 3.5 mg/kg per day from GD 120 to GD 150 to investigate effects on behavioral development of their infants. Swelling of the throat region due to enlargement of the thyroid glands was observed at birth in thiamazole-treated infants, and it returned to normal around postnatal day (PND) 30. At necropsy of infants at 12 months of age, thyroidal weight in the thiamazole groups was increased. This finding suggested the likelihood that administration of thiamazole to maternal animals during the late gestational period induced thyroid goiter in fetal/infant monkeys through placental transfer of thiamazole. No clear changes were noted in thyroid histopathology or serum thyroid hormone levels in maternal animals or infants, but goiter formation might have been indicative of exposure to high thyroid stimulating hormone (TSH) and low T3 or T4 in utero from maternal treatment with thiamazole. Age-related changes were observed in the control in behavioral development tests, while infants at 3.5 mg/kg showed no age-related decrease in contact behavior and no increase in exploratory activity on PND 90 or PND 170. In addition, the number of eye contacts between PND 210 and PND 240 was less frequent. This indicated that maternal exposure to thiamazole induced mental retardation-like behaviors in infants. Thiamazole may directly inhibit thyroid hormone synthesis in the fetus by placental transfer. From these results, it was speculated that oral administration of thiamazole to maternal animals during the late gestational period induced retardation of behavioral development in their infants.

Effects of cobalt on membrane ATPases, oxidant, and antioxidant values in the cerebrum and cerebellum of suckling rats

Chronic overexposure to cobalt (Co) may result in neurotoxic effects, but the mechanism of Co-induced neurotoxicity is not yet well established. Our study was conducted to determine whether Co is associated to the induction of central nervous system damage in pregnant rats and their progeny. Twelve pregnant female rats were randomly divided into 2 groups: group I served as controls and group II received Co (350 mg/L, orally). Treatments started from the 14th day of pregnancy until day 14 after delivery. Co concentration in plasma was higher in the treated groups than in the controls. Exposure to Co also increased the levels of MDA, PCO, H2O2, and AOPP, while Na(+)K(+)-ATPase and Mg(2+)-ATPase, AChE, and BuChE activities decreased in the cerebrum and cerebellum of suckling pups. A smear without ladder formation on agarose gel was also shown in the cerebrum and cerebellum, indicating random DNA degradation. A reduction in GPx, SOD, CAT, GSH, NPSH, and vitamin C values was observed. The changes were confirmed by histological results. In conclusion, these data showed that the exposure of pregnant and lactating rats to Co resulted in the development of oxidative stress and the impairment of defense systems in the cerebrum and cerebellum of their suckling pups.

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.

Role of reactive oxygen species and NADPH-oxidase in the development of rat cerebellum

Experimental evidence suggests that reactive oxygen species (ROS) could participate in the regulation of some physiological conditions. In the nervous system, ROS have been suggested to act as signaling molecules involved in several developmental processes including cell differentiation, proliferation and programmed of cell death. Although ROS can be generated by several sources, it has been suggested that NADPH oxidase (NOX) could be critical in the production of ROS acting as a signal in some of these events. It has been reported that ROS production by NOX enzymes participate in neuronal maturation and differentiation during brain development. In the present study, we found that during rat cerebellar development there was a differential ROS generation at different ages and areas of the cerebellum. We also found a differential expression of NOX homologues during rat cerebellar development. When we treated developing rats with an antioxidant or with apocynin, an inhibitor of NOX, we found a marked decrease of the ROS levels in all the cerebellar layers at all the ages tested. Both treatments also induced a significant change in the cerebellar foliation as well as an alteration in motor behavior. These results suggest that both ROS and NOX have a critical role during cerebellar development.

Experimental gestational hypothyroidism evokes hypertension in adult offspring rats

Gestational hypothyroidism is a prevalent disorder in pregnant women. We aimed to investigate the impact of experimental gestational hypothyroidism (EGH) on cardiovascular and autonomic nervous systems (ANS) in the offspring of rats. EGH was induced with methimazole (MMI) 0.02% in drinking water from day 9 of gestation until birth. Sixty day old offspring from MMI-treated dams (OMTD, n=13) or water-treated dams (OWTD, n=13) had femoral arteries surgically assessed for the measurements of heart rate (HR), mean (MAP), systolic (SAP) and diastolic arterial pressure (DAP), and spontaneous baroreflex sensitivity (BRS). To investigate the balance of ANS, we established the high (HF) and low frequency (LF) bands of pulse interval (PI) and LF band of SAP spectrum. OMTD had increased MAP (130.2 ± 2.0 vs 108.8 ± 3.0 mmHg, p<0.001), SAP (157.3 ± 2.9 vs 135.7 ± 4.5mm Hg, p<0.001) and DAP (109.7 ± 1.9 vs 88.4 ± 2.6 mmHg, p<0.001) when compared to OWTD, and had lower HR (355.1 ± 8.9 vs 386.8 ± 9.2 bpm, p<0.05). After spectral analysis of PI and SAP, only LF band of SAP spectrum was higher (7.2 ± 0.8 vs 4.0 ± 0.6 mmHg(2), p<0.01) in OMTD under spontaneous condition. Despite bradycardia, EGH promotes spontaneous hypertension in 60 day old offspring, probably due to increased sympathetic modulation of vessels, which is suggested by the higher LF of SAP. These findings suggest a critical role of maternal THs in the development of fetal cardiovascular and autonomic nervous systems.

Formation of excess sublobules in the cerebellum of hypothyroid rats

Cerebellar folia may increase in number in hypothyroid rats (Lauder et al., 1974; Hasebe et al., 2008a). In this study, we aimed to confirm the formation of an excess sublobule and to determine whether excess sublobules are consistently formed in conserved positions in hypothyroid rats. Instead of the foliation pattern partitioned by cerebellar fissures, we employed the bifurcation pattern of the internal granular layer for investigation of complexity of the cerebellar cortex in hypothyroid rats. The basic foliation pattern of the cerebellum was intact in hypothyroid rats, but lobules III to IX frequently showed an increase in the number of sublobules. The excess sublobules were mainly found in the folia and along the shallow region of the fissure. In other words, the excess sublobules were not located in random locations but rather in specific locations. The area in the internal granular layer of lobules V to IX was significantly larger than that in control rats. From the increased area of the internal granular layer it may be inferred that internal granular cells increase in number than those in normal rats. In our study, regions within the cerebellum that show an excess of sublobules correlate with regions that show an intermediate to late-forming internal granular layer (Altman, 1969). Our observations fit with the view that excess sublobules are formed by the external granular layer showing prolonged cell proliferation and hypothyroidism predominantly has an adverse impact on the intermediate to late phases in development of the internal granular layer.

Neuroprotective effects of the 17β-estradiol against ethanol-induced neurotoxicity and oxidative stress in the developing male rat cerebellum: biochemical, histological and behavioral changes

During particular periods of central nervous system (CNS) development, exposure to ethanol can decrease regional brain growth and can result in selective loss of neurons. Unfortunately, there are few effective means of attenuating damage in the immature brain. In this study, the possible antioxidant and neuroprotective properties of 17β-estradiol against ethanol-induced neurotoxicity was investigated. 17β-estradiol (600 μg/kg) was injected subcutaneously in postnatal day (PD) 4 and 5, 30 min prior to intraperitoneal injection of ethanol (6g/kg) in rat pups. Ninety minutes after injection of ethanol, the activities of several antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (Gpx) in vermis of cerebellum were assayed. Thiobarbituric acid reactive substance (TBARS) levels were also measured as a marker of lipid peroxidation. Behavioral studies, including rotarod and locomotor activity tests were performed in PD 21-23 and histological study was performed after completion of behavioral measurements in postnatal day 23. The results of the present work demonstrated that ethanol could induce lipid peroxidation, increase TBARS levels and decrease glutathione peroxidase levels in pup cerebellum. We also observed that ethanol impaired performance on the rotarod and locomotor activities of rat pups. However, treatment with 17β-estradiol significantly attenuated motoric impairment, the lipid peroxidation process and restored the levels of antioxidants. Histological analysis also indicated that ethanol could decrease vermis Purkinje cell count and 17β-estradiol prevented this toxic effect. These results suggest that ethanol may induce lipid peroxidation in the rat pups cerebellum while treatment with 17β-estradiol improves motor deficits by protecting the cerebellum against ethanol toxicity.

Changes in growth hormone (GH), GH receptor, and GH signal transduction in hippocampus of congenital hypothyroid rats

Recent studies have shown that, like thyroid hormone (TH), growth hormone (GH) plays a critical role in development of the brain. However, it is still unclear whether the functions of the two hormones are locally orchestrated in the brain or whether TH has a permissive effect on GH in the central nervous system as it does in the periphery. To address this question, the present study investigated the changes in local expression of GH and GH receptor (GHR) and the activity of GH signaling molecules in the hippocampus of congenitally hypothyroid (CHT) rats. As demonstrated by morphometric measurements and the Y-maze test, CHT rats had decreased neurons and weaker Nissl staining in the stratum pyramidal/granule in the hippocampus and a reduced acquisition of safe place recognition memory. Analyses of QPCR and Western blot revealed a substantially decreased hippocampal expression of GH and GHR, accompanied by a corresponding decrease in phosphorylation of JAK2 and STAT5 in the CHT rats. These changes were, at least in part, corrected by systemic supplement of T3. The findings provide the first direct evidence suggesting that the functional autocrine and paracrine regulation of GH in the CNS is orchestrated by TH.

Expression of sonic hedgehog regulates morphological changes of rat developing cerebellum in hypothyroidism

Although thyroid hormones are crucial for cerebellar development, and several thyroid hormone-dependent genes are known to be correlated with morphological development of the cerebellum, the precise mechanisms of morphological cerebellar changes in hypothyroidism (HT) remain unknown. To investigate these mechanisms in experimental rat HT induced by the anti-thyroid drug methimazole (MMI-HT rat), we carried out gene expression analysis (sonic hedgehog (Shh), reelin, and Bax) using quantitative real-time PCR. Histological examination revealed cerebellar abnormalities, including reductions in the thickness of the molecular layer and delayed disappearance of the external granular layer (EGL), as well as excess bulges or sublobules in the internal granular layer (IGL). At Postnatal Day (P) 6, Shh expression in MMI-HT rat was comparable to that in controls, thus suggesting that Shh expression was sufficient to form the lobes in the initial phase. However, Shh expression decreased in the later phases, as compared with age-matched controls. This demonstrated that stronger and sustained signaling is necessary for partitioning of the cardinal lobes into lobes and sublobes. Although reelin expression was not clearly different from that in controls, Bax expression decreased at P 15. The attrition of Bax at P 15 as well as Shh in the later phase may be related to irregularities in the IGL and the relatively large numbers of internal granular cells. Taken together, these results suggest that Shh expression is related to the morphological cerebellar changes in experimental hypothyroidism and that sustained signaling by Shh may play a key role in normal development, particularly lobulation, in the cerebellum.