Thyroid hormone modulation of brain in vivo tyrosine hydroxylase activity and kinetics in the female catfish Heteropneustes fossilis

Testosterone Treatment Mimics Seasonal Downregulation of Dopamine Innervation in the Auditory System of Female Midshipman Fish

In seasonally breeding vertebrates, hormones coordinate changes in nervous system structure and function to facilitate reproductive readiness and success. Steroid hormones often exert their effects indirectly via regulation of neuromodulators, which in turn can coordinate the modulation of sensory input with appropriate motor output. Female plainfin midshipman fish (Porichthys notatus) undergo increased peripheral auditory sensitivity in time for the summer breeding season, improving their ability to detect mates, which is regulated by steroid hormones. Reproductive females also show differences in catecholaminergic innervation of auditory circuitry compared with winter, non-reproductive females as measured by tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholaminergic synthesis. Importantly, catecholaminergic input to the inner ear from a dopaminergic-specific forebrain nucleus is decreased in the summer and dopamine inhibits the sensitivity of the inner ear, suggesting that gonadal steroids may alter auditory sensitivity by regulating dopamine innervation. In this study, we gonadectomized non-reproductive females, implanted them with estradiol (E2) or testosterone (T), and measured TH immunoreactive (TH-ir) fibers in auditory nuclei where catecholaminergic innervation was previously shown to be seasonally plastic. We found that treatment with T, but not E2, reduced TH-ir innervation in the auditory hindbrain. T-treatment also reduced TH-ir fibers in the forebrain dopaminergic cell group that projects to the inner ear, and likely to the auditory hindbrain. Higher T plasma in the treatment group was correlated with reduced-ir TH terminals in the inner ear. These T-treatment induced changes in TH-ir fibers mimic the seasonal downregulation of dopamine in the midshipman inner ear and provide evidence that steroid hormone regulation of peripheral auditory sensitivity is mediated, in part, by dopamine.

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

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

Differential effects of hypo- and hyperthyroidism on remodeling of contacts between neurons expressing the neuropeptide EI and tyrosine hydroxylase in hypothalamic areas of the male rat

The Neuropeptide EI (NEI, glutamic acid- isoleucine amide) participates in neuroendocrine function. Previously we demonstrated that NEI concentration is regulated by thyroid hormones in discrete hypothalamic areas in rats. We observed that the thyroid status affects the dopaminergic regulation of the pituitary hormones. In this study we explored possible interactions between NEI and tyrosine hydroxylase (TH) containing elements in selected hypothalamic areas of male rats. Neuronal somas, terminals and boutons were assessed by confocal microscopy, in hypo- and hyperthyroid animals. We observed a remodeling of the contacts between the TH and NEI immunoreactive elements in the incerto-hypothalamic area (IHy, also known as rostromedial zona incerta) according to thyroid function. However, in the dorsolateral zone of the peduncular part of the lateral hypothalamus (DL-PLH) the thyroid hormones affect the dendritic trees of the neurons without perturbing the overall NEI/TH contacts. Also, we demonstrated that TRH Receptor 1 (TRH-R1) is colocalized in NEI immunoreactive neurons in the peduncular part of the lateral hypothalamus (PLH) and NEI precursor mRNA expression increased by hypothyroidism indicating that NEI neurons are responsive to the feedback mechanisms of the Hypothalamic Pituitary-Thyroid Axis (HPT). In conclusion, the hypothyroid status seems to increase the interactions between the NEI neurons and the dopaminergic pathways while hyperthyroidism either decreases or displays no effects. Altogether these observations support the participation of the IHy and PLH NEI as a modulating component of the HPT suggesting that altered neuroendocrine, behavioral and cognitive dysfunctions induced by dysthyroidism could be in part mediated by NEI.

Critical role of TRPC1 in thyroid hormone-dependent dopaminergic neuron development

Thyroid hormones play a crucial role in midbrain dopaminergic (DA) neuron development. However, the underlying molecular mechanisms remain largely unknown. In this study, we revealed that thyroid hormone treatment evokes significant calcium entry through canonical transient receptor potential (TRPC) channels in ventral midbrain neural stem cells and this calcium signaling is essential for thyroid hormone-dependent DA neuronal differentiation. We also found that TRPC1 is the dominant TRPC channel expressed in ventral midbrain neural stem cells which responds to thyroid hormone. In addition, thyroid hormone increases TRPC1 expression through its receptor alpha 1 during DA neuron differentiation, and, importantly, produces calcium signals by activating TRPC1 channels. In vivo and in vitro gene silencing experiments indicate that TRPC1-mediated calcium signaling is required for thyroid hormone-dependent DA neuronal differentiation. Finally, we confirmed that the activation of OTX2, a determinant of DA neuron development and the expression of which is induced by thyroid hormone, is dependent on TRPC1-mediated calcium signaling. These data revealed the molecular mechanisms of how thyroid hormone regulates DA neuron development from ventral midbrain neural stem cells, particularly endowing a novel physiological relevance to TRPC1 channels.

Effect of hyperthyroidism on circulating prolactin and hypothalamic expression of tyrosine hydroxylase, prolactin signaling cascade members and estrogen and progesterone receptors during late pregnancy and lactation in the rat

Hyperthyroidism (HyperT) compromises pregnancy and lactation, hindering suckling-induced PRL release. We studied the effect of HyperT on hypothalamic mRNA (RT-qPCR) and protein (Western blot) expression of tyrosine hydroxylase (TH), PRL receptor (PRLR) and signaling pathway members, estrogen-α (ERα) and progesterone (PR) receptors on late pregnancy (days G19, 20 and 21) and early lactation (L2) in rats. HyperT advanced pre-partum PRL release, reduced circulating PRL on L2 and increased TH mRNA (G21 and L2), p-TH, PRLR mRNA, STAT5 protein (G19 and L2), PRLR protein (G21) and CIS protein (G19). PRs mRNAs and protein decreased on G19 but afterwards PRA mRNA (G20), PRB mRNA (G21) and PRA mRNA and protein (L2) increased. ERα protein increased on G19 and decreased on G20. Thus, the altered hypothalamic PRLR, STAT5, PR and ERα expression in hyperthyroid rats may induce elevated TH expression and activation, that consequently, elevate dopaminergic tone during lactation, blunting suckling-induced PRL release and litter growth.

Molecular cloning and characterization of brain and ovarian cytochrome P450 aromatase genes in the catfish Heteropneustes fossilis: Sex, tissue and seasonal variation in, and effects of gonadotropin on gene expression

Cytochrome P450 aromatase (Cyp19arom) is the rate-limiting enzyme controlling estrogen biosynthesis, coded by Cyp19a1 in most gnathostomes. Most teleosts have two forms expressed differentially in ovary (cyp19a1a) and neural tissue (cyp19a1b). In this study, full length cDNAs of 2006 bp and 1913 bp with ORFs of 1575 bp and 1488 bp were isolated from the brain and ovary, respectively, of the catfish Heteropneustes fossilis, an air-breathing species with high aquaculture potential. The ORFs encode predicted proteins of 495 and 524 amino acid residues, respectively. The proteins show 62% identity with each other and cluster in two distinct clades (the brain type and ovary type) in the teleost taxon, separated from the tetrapod type. In the in situ localization study, both cyp19a1a and cyp19a1b transcripts were localized in the brain but the signal intensity was higher for the brain type paralog. The transcript signals were observed in the radial glial cells and in neuronal populations of the dorso-lateral region of the telencephalon, pre-tectum, hypothalamus and medulla oblongata. In the ovary, both paralogs were expressed in the follicular layer with a high signal intensity of the ovarian type (cyp19a1a). The differential expression of the gene paralogs was evident from qPCR analysis. Cyp19a1b has relatively a high abundance in the female brain, followed by other peripheral tissues (gonads, liver, gill, kidney and muscle). On the other hand, cyp19a1a has relatively a high transcript abundance in the ovary and female brain, followed by the testis and male brain, and female liver and muscle. The expression was low in male liver and muscle, and the lowest in the gill and kidney. The expression of the two paralogs exhibit brain regional differences; both types have relatively a high transcript abundance in telencephalon-preoptic area with the cyp19a1b expression higher in females than males. In hypothalamus, the expression of both types is higher in males than females. In medulla, the expression of the cyp19a1b is higher than cyp19a1a, and the transcript abundance of the ovarian type is higher in females than males. The expression of the gene paralogs elicits significant seasonal variations in the ovary and brain. In both tissues, the expression increases from the resting to preparatory phases, and decreases through the prespawning phase to low levels in spawning phase. In vivo and/or in vitro treatments with human chorionic gonadotropin (hCG) stimulated the expression of the gene paralogs in the brain and ovary, time-dependently. In conclusion, both paralogs have an overlapping distribution at different levels of the brain-pituitary-gonad axis and may function as a single functional unit as far as the estrogen synthesis is concerned.

Thyroid Hormone-Otx2 Signaling Is Required for Embryonic Ventral Midbrain Neural Stem Cells Differentiated into Dopamine Neurons

Midbrain dopamine (DA) neurons are essential for maintaining multiple brain functions. These neurons have also been implicated in relation with diverse neurological disorders. However, how these neurons are developed from neuronal stem cells (NSCs) remains largely unknown. In this study, we provide both in vivo and in vitro evidence that the thyroid hormone, an important physiological factor for brain development, promotes DA neuron differentiation from embryonic ventral midbrain (VM) NSCs. We find that thyroid hormone deficiency during development reduces the midbrain DA neuron number, downregulates the expression of tyrosine hydroxylase (TH) and the dopamine transporter (DAT), and impairs the DA neuron-dependent motor behavior. In addition, thyroid hormone treatment during VM NSC differentiation in vitro increases the production of DA neurons and upregulates the expression of TH and DAT. We also found that the thyroid hormone enhances the expression of Otx2, an important determinant of DA neurogenesis, during DA neuron differentiation. Our in vitro gene silencing experiments indicate that Otx2 is required for thyroid hormone-dependent DA neuron differentiation from embryonic VM NSCs. Finally, we revealed both in vivo and in vitro that the thyroid hormone receptor alpha 1 is expressed in embryonic VM NSCs. Furthermore, it participates in the effects of thyroid hormone-induced Otx2 upregulation and DA neuron differentiation. These data demonstrate the role and molecular mechanisms of how the thyroid hormone regulates DA neuron differentiation from embryonic VM NSCs, particularly providing new mechanisms and a potential strategy for generating dopamine neurons from NSCs.

Modulation of lipocalin-type prostaglandin D2 synthase expression in catfish seminal vesicles by thyroid disrupting agents and hormones

Thyroid hormones play crucial role in several biological processes including reproduction. Disruption of normal thyroid status by environmental contaminants can cause severe impairment in reproductive functions. In our previous study, we reported down-regulation of a protein in seminal vesicular fluid of air-breathing catfish, Clarias gariepinus during experimentally induced hyperthyroidism. N-terminal amino acid sequence analysis followed by search in sequence database denoted it to be lipocalin-type prostaglandin D2 synthase (ptgds-b). In the present study, we cloned full-length cDNA of ptgds-b based on the N-terminal amino acid sequence. Surprisingly, Northern blot as well as RT-PCR analysis demonstrated the presence of ptgds-b transcript predominantly in seminal vesicles and developing testis. Further, ptgds-b mRNA significantly decreased in seminal vesicles following L-thyroxine overdose while there was an increased expression of ptgds-b after depletion of thyroid hormone by thiourea and withdrawal of the treatments reverted this effect. Treatment of catfish with human chorionic gonadotropin and estradiol significantly reduced ptgds-b expression. Taken together, we report ptgds-b as a thyroid hormone regulated protein in the seminal vesicles in addition to gonadotropin and estradiol. Further studies might explain the exclusive presence of ptgds-b in seminal vesicles and developing testis yet present data evaluated it as a putative biomarker for thyroid hormone disruption.

Propylthiouracil-induced hypothyroidism during lactation alters leucine and mannose metabolism in rat cerebellar slices

Thyroid hormone deficiency during perinatal development results in significant alterations in neurological functions. The relationship between such events and brain metabolism is not completely understood. The aim of this study was to investigate the effects of hypothyroidism on leucine, mannose, glucose and lactate metabolism in rat cerebellar slices. Experimental hypothyroidism was induced by exposing mothers and pups to propylthiouracil (PTU) until weaning - postnatal day 21. Metabolic analyses were performed in postnatal day 10 (PND10) and 21 (PND21) animals. A matching group of animals received the same oral treatment also after weaning until adulthood PND60 with T3 supplement during lactation (P1-P21). In PND21 animals, PTU treatment significantly increased the rate of leucine oxidation to CO2, although glucose and lactate oxidations were not affected. PTU treatment also increased the oxidation of leucine to CO2 at PND60 (adult animals). PND10 hypothyroidism animals showed a decrease in conversion of mannose to glycolipids and glycoprotein compared with the control group. However, PTU treatment increased the conversion of mannose to glycolipids and glycoprotein in PND21 animals. The replacement of T3 normalized mannose and leucine metabolism in adult rats. These results indicate that deficits in thyroid hormones during lactation could delay or alter brain development and metabolism.

Revisiting thyroid hormones in schizophrenia

Thyroid hormones are crucial during development and in the adult brain. Of interest, fluctuations in the levels of thyroid hormones at various times during development and throughout life can impact on psychiatric disease manifestation and response to treatment. Here we review research on thyroid function assessment in schizophrenia, relating interrelations between the pituitary-thyroid axis and major neurosignaling systems involved in schizophrenia's pathophysiology. These include the serotonergic, dopaminergic, glutamatergic, and GABAergic networks, as well as myelination and inflammatory processes. The available evidence supports that thyroid hormones deregulation is a common feature in schizophrenia and that the implications of thyroid hormones homeostasis in the fine-tuning of crucial brain networks warrants further research.

The menace of endocrine disruptors on thyroid hormone physiology and their impact on intrauterine development

The delivery of the appropriate thyroid hormones quantity to target tissues in euthyroidism is the result of unopposed synthesis, transport, metabolism, and excretion of these hormones. Thyroid hormones homeostasis depends on the maintenance of the circulating 'free' thyroid hormone reserves and on the development of a dynamic balance between the 'free' hormones reserves and those of the 'bound' hormones with the transport proteins. Disturbance of this hormone system, which is in constant interaction with other hormone systems, leads to an adaptational counter-response targeting to re-establish a new homeostatic equilibrium. An excessive disturbance is likely to result, however, in hypo- or hyper- thyroid clinical states. Endocrine disruptors are chemical substances forming part of 'natural' contaminating agents found in most ecosystems. There is abundant evidence that several key components of the thyroid hormones homeostasis are susceptible to the action of endocrine disruptors. These chemicals include some chlorinated organic compounds, polycyclic aromatic hydrocarbons, herbicides, and pharmaceutical agents. Intrauterine exposure to endocrine disruptors that either mimic or antagonize thyroid hormones can produce permanent developmental disorders in the structure and functioning of the brain, leading to behavioral changes. Steroid receptors are important determinants of the consequences of endocrine disruptors. Their interaction with thyroid hormones complicates the effect of endocrine disruptors. The aim of this review is to present the effect of endocrine disruptors on thyroid hormones physiology and their potential impact on intrauterine development.

Thiourea-induced thyroid hormone depletion impairs testicular recrudescence in the air-breathing catfish, Clarias gariepinus

We used thiourea-induced thyroid hormone depletion as a strategy to understand the influence of thyroid hormones on testicular recrudescence of the air-breathing catfish, Clarias gariepinus. Treatment with 0.03% thiourea via immersion for 21 days induced hypothyroidism (thyroid hormone depletion) as evidenced by significantly reduced serum T(3) levels. Thiourea-treated males had narrowed seminiferous lobules with fewer spermatozoa in testis, very little or no secretory fluid, reduced protein and sialic acid levels in seminal vesicles when compared to controls. The histological changes were accompanied by reduction in serum and tissue levels of testosterone (T) and 11-ketotestosterone (11-KT), a potent male specific androgen in fish. Qualitative changes in the localization of catfish gonadotropin-releasing hormone (cfGnRH) and luteinizing hormone (LH, heterologous system) revealed a reduction in the distribution of immunoreactive neuronal cells and fibers in thyroid depleted fish. Interestingly, thiourea-withdrawal group showed physiological and histological signs of recovery after 21 days such as reappearance of spermatozoa and partial restoration of 11-KT and T levels. These data demonstrate that thyroid hormones play a significant role in testicular function of catfish. The mechanism of action includes modulating sex steroids either directly or through the hypothalamo (GnRH)-hypophyseal (LH) axis.

Endocrine control of Anguilla anguilla glass eel dispersal: effect of thyroid hormones on locomotor activity and rheotactic behavior

Dispersal, one of the most important processes in population ecology, is an issue linking physiological and behavioral features. However, the endocrine control of animal dispersal remains poorly understood. Here, we tested whether and how thyroid hormones may influence dispersal in glass eels of Anguilla anguilla, by testing their influence on locomotor activity and rheotactic behavior. Glass eels were caught during their estuarine migration and treated by immersion in either a l-thyroxine (T(4)) or a thiourea (TU) solution. As measured by radioimmunoassay, T(4) and TU treatments induced, respectively, increased and decreased whole-body thyroid hormone levels relative to untreated controls. We tested a total of 960 glass eels distributed into control, and T(4) and TU treatment groups, on their swimming behavior in experimental flume tanks equipped with upstream and downstream traps that allowed us to concurrently measure both the locomotor activity and the rheotactic behavior. Compared to controls, locomotor activity significantly increased among the hyperthyroid, T(4)-treated eels, but significantly decreased among the hypothyroid, TU-treated eels. The results on rheotactic behavior suggested a more complex regulatory mechanism, since TU but not T(4) treatment significantly affected rheotactic behavior. The influence of thyroid hormones on locomotor activity suggests a central role for these hormones in the regulation of mechanisms leading to the colonization of continental habitats by glass eels. Thyroid hormones are also implicated in the control of locomotor activity in mammals and migratory behavior in birds, suggesting that these hormones represent conserved, proximate mediators of dispersal in vertebrates.

Effect of thyroid hormone depletion on monoamines and expression patterns of catfish GnRH in the air-breathing catfish, Clarias gariepinus

Thyroid hormone is known to have profound effect on the efficient functioning of the reproductive system. The GnRH-gondaotropin (GTH) axis is the crucial axis involved in regulation of the various aspects of reproduction like spermatogenesis, synthesis of sex steroids and regulation of courting and spawning behavior. Earlier study from our laboratory has shown that thyroid hormone depletion causes a decrease in GTH and GnRH levels in pituitary and preoptic area, respectively. GnRH secretion in pre-optic area is largely regulated by the monoaminergic system mainly dopamine (DA), epinephrine (E), norepinephrine (NE) and serotonin (5-HT). The expression pattern of catfish GnRH transcripts tends to corroborate our earlier findings. Hence, in the current study we aimed to investigate the levels of monoamines in the preoptic area-hypothalamus (POA-H), so as to determine whether thyroid hormone depletion modulates the monoaminergic neurotransmission thereby affecting GnRH secretion. The levels of NE and L-dopa decreased significantly while that of DA was unaltered following thyroid hormone depletion. DA has an inhibitory effect on GnRH secretion. Findings from the present study suggest that the inhibitory tone is unaltered while the stimulatory tone influencing GnRH neurons in POA-H is decreased during thiourea induced thyroid hormone depletion.

Thyroid hormone modulation of ovarian recrudescence of air-breathing catfish Clarias gariepinus

In the present study, thiourea-induced thyroid hormone depletion and thyroxine (T(4)) 'overdose' were used as a strategy to understand the influence of thyroid hormones on ovarian recrudescence of juvenile (3-months-old), immature (8-months-old) and adult (1-year-old) air-breathing catfish, Clarias gariepinus. Thiourea-induced thyroid hormone depletion in juvenile catfish impaired ovarian development, but no significant effect was observed in immature catfish and during late stage of ovarian recrudescence of mature catfish. T(4) treatment in females undergoing late stages of ovarian recrudescence induced rapid oocyte growth by promoting its early entry into maturational phase as evident from the presence of more number of vitellogenic and post-vitellogenic follicles, decrease in aromatse immunoreactivity and reduced estradiol-17beta levels. Hence, thyroid hormones have an important role to play during early stages of ovarian development and vitellogenesis of catfish and also indicating that thyroid has a stage dependent effect on ovary.

Cyclic AMP-protein kinase a and protein kinase C mediate in vitro T activation of brain tyrosine hydroxylase in the female catfish Heteropneustes fossilis

The present in vitro study demonstrates an involvement of both cAMP-dependent protein kinase A (PKA) and protein kinase C (PKC) signal transduction mechanisms in the triiodothyronone (T(3))-activation of forebrain (telencephalon and hypothalamus) tyrosine hydroxylase (TH) activity in the female catfish Heteropneustes fossilis. Incubations of the enzyme preparations with different concentrations of T(3) (0.15-2.4 ng/ml) stimulated TH activity over the concentrations. Similarly, coincubations of the enzyme preparations with T(3) and cAMP (1.0 mM) or cAMP-elevating drugs such as 1-methyl-3-isobutylxanthine (1.5 mM) or theophylline (1.5 mM) increased TH activity significantly over that of T(3). The stimulatory effect of TH activity with T(3) or cAMP was coincident with a low apparent K(m) and high V(max) for the cofactor, suggesting a higher affinity of the enzyme. Incubation of the enzyme preparations with PKA (H-89) and PKC (calphostin-C) inhibitors decreased basal enzyme activity significantly, with the inhibition being greater in the former group. The incubations of the enzyme preparations with T(3) or T(3) + cAMP, followed by the different inhibitors, also decreased enzyme activity. Although T(3) could not reverse the inhibitory effect of H-89, it could over-ride the effect of calphostin-C to some extent. The suppressive effect of the inhibitors could be related to a high apparent K(m) and low V(max) for the cofactor. The evidence strongly suggests a nongenomic action of T(3) on TH activity via the cell signalling pathways, for which the cAMP-dependent PKA appears to be the major regulatory mechanism.