Regulation of phosphosignaling pathways involved in transcription of cell cycle target genes by TRH receptor activation in GH1 cells

Thyrotropin-releasing hormone (TRH) is known to activate several cellular signaling pathway, but the activation of the TRH receptor (TRH-R) has not been reported to regulate gene transcription. The aim of this study was to identify phosphosignaling pathways and phosphoprotein complexes associated with gene transcription in GH1 pituitary cells treated with TRH or its analog, taltirelin (TAL), using label-free bottom-up mass spectrometry-based proteomics. Our detailed analysis provided insight into the mechanism through which TRH-R activation may regulate the transcription of genes related to the cell cycle and proliferation. It involves control of the signaling pathways for β-catenin/Tcf, Notch/RBPJ, p53/p21/Rbl2/E2F, Myc, and YY1/Rb1/E2F through phosphorylation and dephosphorylation of their key components. In many instances, the phosphorylation patterns of differentially phosphorylated phosphoproteins in TRH- or TAL-treated cells were identical or displayed a similar trend in phosphorylation. However, some phosphoproteins, especially components of the Wnt/β-catenin/Tcf and YY1/Rb1/E2F pathways, exhibited different phosphorylation patterns in TRH- and TAL-treated cells. This supports the notion that TRH and TAL may act, at least in part, as biased agonists. Additionally, the deficiency of β-arrestin2 resulted in a reduced number of alterations in phosphorylation, highlighting the critical role of β-arrestin2 in the signal transduction from TRH-R in the plasma membrane to transcription factors in the nucleus.

Thyrotropin-releasing hormone stimulates NR4A3 expression in the pituitary thyrotrophs of proestrus rats

The secretion of several hypothalamic peptide hormones is activated during the preovulatory period. Hypothalamic thyrotropin-releasing hormone (TRH) is one such hormone with reproductive and/or metabolic significance. However, it remains unclear whether thyroid-stimulating hormone (TSH)-producing thyrotrophs are produced during the preovulatory period. We previously found a transient increase in the expression of the nuclear receptor NR4A3, a well-known immediate early gene, in the proestrus afternoon in the anterior pituitary glands of rats. To investigate the relationship between TRH secretion and pituitary NR4A3 expression during proestrus, we used proestrus and thyroidectomized rats to identify NR4A3-expressing cells and examined the regulation of Nr4a3 gene expression via the hypothalamus-pituitary-thyroid (HPT) axis. The percentage of NR4A3-expressing cells increased in thyrotrophs at 14:00 h of proestrus. Incubation of rat primary pituitary cells with TRH transiently stimulated Nr4a3 expression. Thyroidectomy to attenuate the negative feedback effects led to increased serum TSH levels and Nr4a3 gene expression in the anterior pituitary, whereas thyroxine (T4) administration conversely suppressed Nr4a3 expression. Additionally, the administration of T4 or TRH antibodies significantly suppressed the increase in Nr4a3 expression at 14:00 h of proestrus. These results demonstrate that pituitary NR4A3 expression is regulated by the HPT axis, and that TRH stimulates thyrotrophs and induces NR4A3 expression during the proestrus afternoon. This suggests the potential involvement of NR4A3 in the regulation of the HPT axis during pre- and post-ovulatory periods.

Thyrotropin-releasing hormone induces Ca2+ increase in a subset of vagal nodose ganglion neurons

Thyrotropin-releasing hormone (TRH) plays a central role in metabolic homeostasis, and single-cell sequencing has recently demonstrated that vagal sensory neurons in the nodose ganglion express thyrotropin-releasing hormone receptor 1 (TRHR1). Here, in situ hybridization validated the presence of TRHR1 in nodose ganglion (NG) neurons and immunohistochemistry showed that the receptor is expressed at the protein level. However, it has yet to be demonstrated whether TRHR1 is functionally active in NG neurons. Using NG explants transduced with a genetically encoded Ca²⁺ indicator (GECI), we show that TRH increases Ca²⁺ in a subset of NG neurons. TRH-induced Ca²⁺ transients were briefer compared to those induced by CCK-8, 2-Me-5-HT and ATP. Blocking Na⁺ channels with TTX or Na⁺ substitution did not affect the TRH-induced Ca²⁺ increase, but blocking Gq signaling with YM-254890 abolished the TRH-induced response. Field potential recordings from the vagus nerve in vitro showed an increase in response to TRH, suggesting that TRH signaling produces action potentials in NG neurons. These observations indicate that TRH activates a small group of NG neurons, involving Gq pathways, and we hypothesize that these neurons may play a role in gut-brain signaling.

Effects of iodine excess on serum thyrotropin-releasing hormone levels and type 2 deiodinase in the hypothalamus of Wistar rats

Iodine is an important element in thyroid hormone biosynthesis. Thyroid function is regulated by the hypothalamic-pituitary-thyroid axis. Excessive iodine leads to elevated thyroid-stimulating hormone (TSH) levels, but the mechanism is not yet clear. Type 2 deiodinase (Dio2) is a Se-containing protease that plays a vital role in thyroid function. The purpose of this study was to explore the role of hypothalamus Dio2 in regulating TSH increase caused by excessive iodine and to determine the effects of iodine excess on thyrotropin-releasing hormone (TRH) levels. Male Wistar rats were randomised into five groups and administered different iodine dosages (folds of physiological dose): normal iodine, 3-fold iodine, 6-fold iodine, 10-fold iodine and 50-fold iodine. Rats were euthanised at 4, 8, 12 or 24 weeks after iodine administration. Serum TRH, TSH, total thyroxine (TT4) and total triiodothyronine (TT3) were determined. Hypothalamus tissues were frozen and sectioned to evaluate the expression of Dio2, Dio2 activity and monocarboxylate transporter 8 (MCT8). Prolonged high iodine intake significantly increased TSH expression (P < 0·05) but did not affect TT3 and TT4 levels. Prolonged high iodine intake decreased serum TRH levels in the hypothalamus (P < 0·05). Dio2 expression and activity in the hypothalamus exhibited an increasing trend compared at each time point with increasing iodine intake (P < 0·05). Hypothalamic MCT8 expression was increased in rats with prolonged high iodine intake (P < 0·05). These results indicate that iodine excess affects the levels of Dio2, TRH and MCT8 in the hypothalamus.

Evolution of thyrotropin-releasing factor extracellular communication units

Thyroid hormones (THs) are ancient signaling molecules that contribute to the regulation of metabolism, energy homeostasis and growth. In vertebrates, the hypothalamus-pituitary-thyroid (HPT) axis links the corresponding organs through hormonal signals, including thyrotropin releasing factor (TRF), and thyroid stimulating hormone (TSH) that ultimately activates the synthesis and secretion of THs from the thyroid gland. Although this axis is conserved among most vertebrates, the identity of the hypothalamic TRF that positively regulates TSH synthesis and secretion varies. We review the evolution of the hypothalamic factors that induce TSH secretion, including thyrotropin-releasing hormone (TRH), corticotrophin-releasing hormone (CRH), urotensin-1-3, and sauvagine, and non-mammalian glucagon-like peptide in metazoans. Each of these peptides is part of an extracellular communication unit likely composed of at least 3 elements: the peptide, G-protein coupled receptor and bioavailability regulator, set up on the central neuroendocrine articulation. The bioavailability regulators include a TRH-specific ecto-peptidase, pyroglutamyl peptidase II, and a CRH-binding protein, that together with peptide secretion/transport rate and transduction coupling and efficiency at receptor level shape TRF signal intensity and duration. These vertebrate TRF communication units were coopted from bilaterian ancestors. The bona fide elements appeared early in chordates, and are either used alternatively, in parallel, or sequentially, in different vertebrate classes to control centrally the activity of the HPT axis. Available data also suggest coincidence between apparition of ligand and bioavailability regulator.

Cardiac Thyrotropin-releasing Hormone Inhibition Improves Ventricular Function and Reduces Hypertrophy and Fibrosis After Myocardial Infarction in Rats

BACKGROUND

Cardiac thyrotropin-releasing hormone (TRH) is a tripeptide with still unknown functions. We demonstrated that the left ventricle (LV) TRH system is hyperactivated in spontaneously hypertensive rats and its inhibition prevented cardiac hypertrophy and fibrosis. Therefore, we evaluated whether in vivo cardiac TRH inhibition could improve myocardial function and attenuate ventricular remodeling in a rat model of myocardial infarction (MI).

METHODS AND RESULTS

In Wistar rats, MI was induced by a permanent left anterior descending coronary artery ligation. A coronary injection of a specific small interfering RNA against TRH was applied simultaneously. The control group received a scrambled small interfering RNA. Cardiac remodeling variables were evaluated one week later. In MI rats, TRH inhibition decreased LV end-diastolic (1.049 ± 0.102 mL vs 1.339 ± 0.102 mL, P < .05), and end-systolic volumes (0.282 ± 0.043 mL vs 0.515 ± 0.037 mL, P < .001), and increased LV ejection fraction (71.89 ± 2.80% vs 65.69 ± 2.85%, P < .05). Although both MI groups presented similar infarct size, small interfering RNA against TRH treatment attenuated the cardiac hypertrophy index and myocardial interstitial collagen deposition in the peri-infarct myocardium. These effects were accompanied by attenuation in the rise of transforming growth factor-β, collagen I, and collagen III, as well as the fetal genes (atrial natriuretic peptide, B-type natriuretic peptide, and beta myosin heavy chain) expression in the peri-infarct region. In addition, the expression of Hif1α and vascular endothelial growth factor significantly increased compared with all groups.

CONCLUSIONS

Cardiac TRH inhibition improves LV systolic function and attenuates ventricular remodeling after MI. These novel findings support the idea that TRH inhibition may serve as a new therapeutic strategy against the progression of heart failure.

Chronic stress inhibits hypothalamus-pituitary-thyroid axis and brown adipose tissue responses to acute cold exposure in male rats

PURPOSE

Cold exposure activates the hypothalamus-pituitary-thyroid (HPT) axis, response blunted by previous acute stress or corticosterone administration. Chronic stressors can decrease serum T3 concentration, and thyrotropin-releasing hormone (Trh) expression in the paraventricular nucleus (PVN), but impact on the response to cold is unknown; this was studied in rats submitted to daily repeated restraint (rRes) that causes habituation of hypothalamus-pituitary-adrenal (HPA) axis response, or to chronic variable stress (CVS) that causes sensitization and hyperreactivity.

METHODS

Wistar male adult rats were submitted to rRes 30 min/day, or to CVS twice a day, for 15 days. On day 16, rats were exposed 1 h to either 5 or 21 °C. Parameters of HPT and HPA axes activity and of brown adipose tissue (BAT) cold response were measured; gene expression in PVN and BAT, by RT-PCR; serum hormone concentration by radioimmunoassay or ELISA.

RESULTS

Compared to naïve animals, Crh and corticosterone concentrations were attenuated at the end of rRes, but increased at the end of CVS treatments. Cold exposure increased mRNA levels of Crh, Trh, and serum concentration of thyrotropin in naïve, but not in rRes or CVS rats; corticosterone increased in all groups. Cold induced expression of thermogenic genes in BAT (Dio2 and Ucp1) in naïve but not in stressed rats; Adrb3 expression was differentially regulated.

CONCLUSION

Both types of chronic stress blunted HPT and BAT responses to cold. Long-term stress effects on noradrenergic and/or hormonal signaling are likely responsible for HPT dysfunction and not the type of chronic stressor.

Plasma prolactin, thyroid-stimulating hormone, melanocyte-stimulating hormone, and adrenocorticotropin responses to thyrotropin-releasing hormone in mares treated with detomidine and butorphanol

Stress or excitement is a concern when performing endocrine tests on fractious horses. Sedation may be a solution; however, perturbation of test results may preclude useful information. Thyrotropin-releasing hormone (TRH) is a known stimulator of prolactin, thyroid-stimulating hormone (TSH), melanocyte-stimulating hormone (MSH), and ACTH. Thyrotropin-releasing hormone-induced ACTH is a diagnostic tool for the assessment of endocrinopathies such as pituitary pars intermedia dysfunction. It is unknown if drugs commonly used for sedation alter endocrine responses. The objective of this study was to assess the effects of detomidine (DET) and butorphanol on endocrine responses to TRH. Nine light horse mares were used in a replicated 3 × 3 Latin square with the following treatments: saline, DET, and detomidine + butorphanol (DET/BUT), all administered intravenously at 0.01 mg/kg BW. A 1-wk washout period was allowed between phases, all of which were performed in December. Blood samples were collected at -10 and 0 min before treatment and 5 and 10 min post-treatment. Administration of 1 mg TRH occurred 10 min post-treatment, and blood sampling continued 5, 10, 20, and 30 min post-TRH. Data were analyzed by ANOVA as a replicated Latin square with repeated sampling. Plasma prolactin increased (P < 0.0001) after TRH in all groups, rapidly peaking at 5 min in drug-treated mares and 40 min in saline-treated mares. The peak prolactin response to TRH was 2-fold higher (P < 0.0001) in saline-treated mares compared with those drug-treated. A peak rise in plasma TSH was observed in DET/BUT-treated mares 10 min after TSH and was greater (P ≤ 0.007) compared with DET- and saline-treated mares. Plasma MSH was stimulated (P = 0.001) by DET and DET/BUT before TRH, and the peak MSH response to TRH was greater (P < 0.0001) in drug-treated mares, although not hastened as observed with prolactin and TSH. A peak rise in ACTH was observed in drug-treated mares 5 min after administration of TRH, whereas a peak rise was observed in control mares 10 min post-TRH and was almost 2-fold lower (P = 0.05) than the peak observed in DET and DET/BUT-treated mares. Basal ACTH concentrations were not affected by DET or DET/BUT, indicating that sedation with these compounds may be achieved when needing to measure basal plasma ACTH. Treatment with DET and DET/BUT did alter the prolactin, TSH, MSH, and ACTH responses to TRH; therefore, the use of these drugs may not be advisable when assessing endocrine responses to TRH stimulation.

The implications of hypothalamic abnormalities for schizophrenia

Until a few years ago, the hypothalamus was believed to play only a marginal role in schizophrenia pathophysiology. However, recent findings show that this rather small brain region involved in many pathways found disrupted-in schizophrenia. Gross anatomic abnormalities (volume changes of the third ventricle, the hypothalamus, and its individual nuclei) as well as alterations at the cellular level (circumscribed loss of neurons) can be observed. Further, increased or decreased expression of hypothalamic peptides such as oxytocin, vasopressin, several factors involved in the regulation of appetite and satiety, endogenous opiates, products of schizophrenia susceptibility genes as well as of enzymes involved in neurotransmitter and neuropeptide metabolism have been reported in schizophrenia and/or animal models of the disease. Remarkably, although profound disturbances of the hypothalamus-pituitary-adrenal axis, hypothalamus-pituitary-thyroid axis, and the hypothalamus-pituitary-gonadal axis are typical signs of schizophrenia, there is currently no evidence for alterations in the expression of hypothalamic-releasing and inhibiting factors that control these hormonal axes. Finally, the implications of hypothalamus for disease-related disturbances of the sleep-wakefulness cycle and neuroimmune dysfunctions in schizophrenia are outlined.

The hypothalamus in anxiety disorders

Of all mental disorders, anxiety disorders are currently the strongest contributors to the global burden of disease, with 7.3% of the general population affected worldwide. The hypothalamus is crucial hub of a network of neural structures modulating fear conditioning and extinction and, as such, highly relevant to the pathophysiology of these conditions. Three hypothalamic systems have emerged as particularly relevant in this context. First, the oxytocin system is highly likely to be involved anxiety disorders and in particular in the cognitive and behavioral deficits pertaining to social anxiety disorder. Second, peripheral markers of the hypothalamic-pituitary-adrenal axis appear altered in patients with panic disorder and generalized anxiety disorder, which may denote aberrant functioning of their central corticotropin-releasing hormone system. Furthermore, cortisol seems to augment the effects of exposure therapy in patients with specific phobia. Third, the integrity of the hypothalamic-pituitary-thyroid axis is likely compromised in panic disorder. Further, cross-disciplinary research efforts are required to shed more light on how, exactly, these hypothalamic systems interact with the neural structures involved in fear conditioning and extinction, which should ultimately open up new avenues for the prevention and treatment of anxiety disorders.

Transient expression of thyrotropin releasing hormone peptide and mRNA in the rat hippocampus following global cerebral ischemia/reperfusion injury

INTRODUCTION

The role of extra-hypothalamic thyrotropin-releasing hormone (TRH) has been investigated by pharmacological studies using TRH or its analogues and found to produce a wide array of effects in the central nervous system.

METHODS

Immunofluorescence, In situ labeling of DNA (TUNEL), in situ hybridization chain reaction and quantitative real-time polymerase chain reaction were used in this study.

RESULTS

We found that the granular cells of the dentate gyrus expressed transiently a significant amount of TRH-like immunoreactivity and TRH mRNA during the 6-24 h period following global cerebral ischemia/reperfusion injury. TUNEL showed that apoptosis of neurons in the CA1 region occurred from 48 h and almost disappeared at 7 days. TRH administration 30 min before or 24 h after the injury could partially inhibit neuronal loss, and improve the survival of neurons in the CA1 region.

CONCLUSION

These data suggest that endogenous TRH expressed transiently in the dentate gyrus of the hippocampus may play an important role in the survival of neurons during the early stage of ischemia/reperfusion injury and that delayed application of TRH still produced neuroprotection. This delayed application of TRH has a promising therapeutic significance for clinical situations.

Ameliorating effect of rovatirelin on the ataxia in rolling mouse Nagoya

Rovatirelin is a newly synthetized thyrotropin-releasing hormone (TRH) analog. This study aimed to investigate the effect of rovatirelin on motor function using rolling mouse Nagoya (RMN), a mouse model of hereditary ataxia, and compare it with that of taltirelin, which is clinically used to treat spinocerebellar degeneration in Japan. We also examined the effect of rovatirelin on glucose metabolism in various brain regions of RMN using autoradiography (ARG). Rovatirelin (1, 3, 10, and 30 mg/kg) dose-dependently reduced the fall index in RMN, and its effect was more potent than that of taltirelin (3, 10, 30, and 100 mg/kg). No attenuation of the effect was observed by repeated daily administration for 2 weeks. Furthermore, the reduction in the fall index by rovatirelin persisted for 2 weeks after completing treatment. In the ARG study, rovatirelin induced a significantly elevated uptake of glucose in the prefrontal cortex, nucleus accumbens shell, nucleus accumbens core, striatum, anterior cingulate cortex, secondary motor area, pretectal area, ventral tegmental area, black pars compacta, locus coeruleus, nucleus cerebellaris middle nucleus, medial nucleus of the vestibular nerve, fourth/fifth lobule, and third lobule. Furthermore, rovatirelin increased cerebellar mRNA level of brain derived neurotrophic factor. These results suggest that rovatirelin activates the cerebellum and other parts of the central nervous system to improve motor function in spinocerebellar ataxia (SCA) model animals, and its action is more potent than that of taltirelin. Therefore, rovatirelin can be a potential alternative to the traditionally used therapeutics for SCA.

Differential regulation of thyrotropin-releasing hormone mRNA expression in the paraventricular nucleus and dorsomedial hypothalamus in OLETF rats

Thyrotropin-releasing hormone (TRH) plays an important role in the regulation of energy balance. While the regulation of TRH in the paraventricular nucleus (PVN) in response to changes of energy balance has been well studied, how TRH is regulated in the dorsomedial hypothalamus (DMH) in maintaining energy homeostasis remains unclear. Here, we assessed the effects of food restriction and exercise on hypothalamic Trh expression using Otsuka Long-Evens Tokushima Fatty (OLETF) rats. Sedentary ad lib fed OLETF rats (OLETF-SED) became hyperphagic and obese. These alterations were prevented in OLETF rats with running wheel access (OLETF-RW) or food restriction in which their food was pair-fed (OLETF-PF) to the intake of lean control rats (LETO-SED). Evaluation of hypothalamic gene expression revealed that Trh mRNA expression was increased in the PVN of OLETF-SED rats and normalized in OLETF-RW and OLETF-PF rats compared to LETO-SED rats. In contrast, the expression of Trh in the DMH was decreased in OLETF-SED rats relative to LETO-SED rats. This alteration was reversed in OLETF-RW rats as seen in LETO-SED rats, but food restriction resulted in a significant increase in DMH Trh expression in OLETF-PF rats compared to LETO-SED rats. Strikingly, while Trh mRNA expression was decreased in the PVN of intact rats in response to acute food deprivation, food deprivation resulted in increased expression of Trh in the DMH. Together, these results demonstrate the differential regulation of Trh expression in the PVN and DMH in OLETF rats and suggest that DMH TRH also contributes to hypothalamic regulation of energy balance.

Thyroid Hormone and Thyrotropin Concentrations and Responses to Thyrotropin-Stimulating Hormone in Horses with PPID Compared with Age-Matched Normal Horses

Glucocorticoids are known to exert inhibitory action on the hypothalamic-pituitary-thyroid axis. With recent evidence that free plasma cortisol and urinary excretion of cortisol metabolites may be increased in horses with pituitary pars intermedia dysfunction (PPID), it is important to further examine thyroid function in horses with PPID. To test the hypothesis that serum thyrotropin (TSH) concentrations are decreased in horses with PPID, baseline serum thyroid hormone and TSH concentrations, and responses to TSH-releasing hormone (TRH), were compared between 12 horses diagnosed as having PPID and 14 age-matched normal horses. Horses with PPID had resting serum concentrations of free thyroxine by equilibrium dialysis (fT4D) and TSH that were significantly lower than serum concentrations of fT4D and TSH in age-matched normal horses. Serum concentrations of total T4 and total and free triiodothyronine (T3) were also lower in horses with PPID compared with normal horses, but the differences did not reach statistical significance. Thyroid hormone and TSH responses to TRH administration were not different between horses with PPID and normal horses. In conclusion, serum fT4D concentrations are decreased in horses with PPID without an appropriate increase in serum TSH concentrations. Normal serum thyroid hormone and TSH concentration responses to exogenous TRH administration support the theory that increased glucocorticoid activity in horses with PPID may exert prolonged tonic suppression, but not complete inhibition, of TRH and subsequent TSH release, similar to what has been observed in other species.

The forgotten effects of thyrotropin-releasing hormone: Metabolic functions and medical applications

Thyrotropin-releasing hormone (TRH) causes a variety of thyroidal and non-thyroidal effects, the best known being the feedback regulation of thyroid hormone levels. This was employed in the TRH stimulation test, which is currently little used. The role of TRH as a cancer biomarker is minor, but exaggerated responses to TSH and prolactin levels in breast cancer led to the hypothesis of a potential role for TRH in the pathogenesis of this disease. TRH is a rapidly degraded peptide with multiple targets, limiting its suitability as a biomarker and drug candidate. Although some studies reported efficacy in neural diseases (depression, spinal cord injury, amyotrophic lateral sclerosis, etc.), therapeutic use of TRH is presently restricted to spinocerebellar degenerative disease. Regulation of TRH production in the hypothalamus, patterns of expression of TRH and its receptor in the body, its role in energy metabolism and in prolactin secretion are addressed in this review.

TRH Neurons and Thyroid Hormone Coordinate the Hypothalamic Response to Cold

Thyroid hormone (TH) plays a key role in regulating body temperature in mammals. Cold exposure stimulates the hypothalamus-pituitary-thyroid (HPT) axis at the hypothalamic level by activating hypophysiotropic thyrotropin-releasing hormone (TRH)-producing neurons, ultimately resulting in increased plasma TH concentrations. Importantly, the local TH metabolism within various cold-responsive organs enables tissue-specific action of TH on heat production and adaption to cold independently of the circulating TH levels. In addition to these neuroendocrine effects, TRH neurons in the hypothalamus also have neural connections with brown adipose tissue (BAT), probably contributing to regulation of thermogenesis by the autonomic nervous system. Recent studies have demonstrated that intrahypothalamic TH has profound metabolic effects on BAT, the liver, and the heart that are mediated via the autonomic nervous system. These effects originate in various hypothalamic nuclei, including the paraventricular nucleus (PVN), the ventromedial nucleus, and recently reported neurons in the anterior hypothalamic area, indicating a potential central function for TH on thermoregulation. Finally, although robust stimulation of the thermogenic program in BAT was shown upon TH administration in the ventromedial hypothalamus, the physiological relevance of these neurally mediated effects of TH is unclear at present. This review provides an overview of studies reporting the role of TH in cold defense, with a focus on recent literature evidencing the centrally mediated effects of TRH and TH.

Possible involvement of thyrotropin-releasing hormone receptor 3 in the release of prolactin in the metamorphosing bullfrog larvae

In amphibians, thyrotropin (TSH), corticotropin (ACTH) and prolactin (PRL) are regarded as the major pituitary hormones involved in metamorphosis, their releasing factors being corticotropin-releasing factor (CRF), arginine vasotocin (AVT), and thyrotropin-releasing hormone (TRH), respectively. It is also known that thyrotropes and corticotropes are equipped with CRF type-2 receptor and AVT V1b receptor, respectively. As for PRL cells, information about the type of receptor for TRH (TRHR) through which the action of TRH is mediated to induce the release of PRL is lacking. In order to fill this gap, an attempt was made to characterize the TRHR subtype existing in the PRL cells of the anterior pituitary gland of the bullfrog, Rana catesbeiana. We cloned cDNAs for three types of bullfrog TRHRs, namely TRHR1, TRHR2 and TRHR3, and confirmed that all of them are functional receptors for TRH by means of reporter gene assay. Analyses with semi-quantitative reverse transcription-PCR and in situ hybridization revealed that TRHR3 mRNA is expressed in the anterior lobe and that the signals reside mostly in the PRL cells. It was also noted that the expression levels of TRHR3 mRNA in the anterior pituitary as well as in the PRL cells of metamorphosing tadpoles elevate as metamorphosis progresses. Since the pattern of changes in TRHR3 mRNA levels in the larval pituitary is almost similar to that previously observed in the pituitary PRL mRNA and plasma PRL levels, we provide a view that TRHR3 mediates the action of TRH on the PRL cells to induce the release of PRL that is prerequisite for growth and metamorphosis in amphibians.

The potential role of thyrotropin-releasing hormone in colonic dysmotility induced by water avoidance stress in rats

OBJECTIVE

This study sought to investigate the effect and underlying mechanism of thyrotrophin releasing hormone (TRH) on colonic contractile disorders induced by chronic water avoidance stress (WAS).

METHODS

Male SD rats were exposed to daily 1-h WAS or sham WAS for 10 consecutive days. The presence of TRH in the serum and colonic mucosa were determined using enzyme immunoassay kits. Immunohistochemistry and western blotting were performed to detect the expression of TRH receptor 1 (TRH-R1). The contractions of proximal colonic smooth muscle were studied in an organ bath system. The whole-cell patch-clamp technique was used to record the currents of both L-type calcium currents (I_Ca,L) and large conductance Ca²⁺-activated K⁺ (BK_Ca) channels in colonic smooth muscle cells (SMCs) isolated from adult rats.

RESULTS

Enzyme immunoassay revealed that TRH was present in both serum and colonic mucosa and that this expression increased in the WAS group. Immunohistochemistry revealed that the TRH-R1 level increased in colons devoid of mucosa and submucosa from the stressed rats as compared with the control group. TRH increased the spontaneous contractions of the longitudinal muscle and circular muscle strips in a dose-dependent manner in vitro. The effect was also confirmed in an vivo experiment, where an intraperitoneal injection of TRH in rats significantly increased fecal pellet output during a 24-h period as compared with the control group. Furthermore, intraperitoneal injection of a non-specific TRH receptor antagonist, chlordiazepoxide and a TRH-R1 antibody, partially decreased the fecal pellets of WAS rats during the 10-day stress period. Furthermore, TRH increased the peak current of L-type channels in colonic smooth muscle cells (SMCs) at a membrane potential of 0 mV, while the current of large conductance Ca²⁺-activated K⁺ (BK_Ca) channels was not changed following the addition of TRH.

CONCLUSION

TRH may be involved in the dysmotility induced by chronic stress and may have some potential clinical therapeutic use in regulating gut motility.

Gene expression of thyrotropin- and corticotrophin-releasing hormones is regulated by environmental salinity in the euryhaline teleost Sparus aurata

In euryhaline teleosts, the hypothalamus-pituitary-thyroid and hypothalamus-pituitary-interrenal axes (HPT and HPI, respectively) are regulated in response to environmental stimuli such as salinity changes. However, the molecular players participating in this physiological process in the gilthead seabream (Sparus aurata), a species of high value for aquaculture, are still not identified and/or fully characterized in terms of gene expression regulation. In this sense, this study identifies and isolates the thyrotropin-releasing hormone (trh) mRNA sequence from S. aurata, encoding prepro-Trh, the putative factor initiating the HPT cascade. In addition, the regulation of trh expression and of key brain genes in the HPI axis, i.e., corticotrophin-releasing hormone (crh) and corticotrophin-releasing hormone-binding protein (crhbp), was studied when the osmoregulatory status of S. aurata was challenged by exposure to different salinities. The deduced amino acid structure of trh showed 65-81% identity with its teleostean orthologs. Analysis of the tissue distribution of gene expression showed that trh mRNA is, though ubiquitously expressed, mainly found in brain. Subsequently, regulation of gene expression of trh, crh, and crhbp was characterized in fish acclimated to 5-, 15-, 40-, and 55-ppt salinities. In this regard, the brain gene expression pattern of trh mRNA was similar to that found for the crh gene, showing an upregulation of gene expression in seabream acclimated to the highest salinity tested. Conversely, crhbp did not change in any of the groups tested. Our results suggest that Trh and Crh play an important role in the acclimation of S. aurata to hypersaline environments.

Administration of Thyrotropin-Releasing Hormone in the Hypothalamic Paraventricular Nucleus of Male Rats Mimics the Metabolic Cold Defense Response

BACKGROUND

Cold exposure increases thyrotropin-releasing hormone (TRH) expression primarily in the hypothalamic paraventricular nucleus (PVN). The PVN is a well-known hypothalamic hub in the control of energy metabolism. TRH terminals and receptors are found on PVN neurons. We hypothesized that TRH release in the PVN plays an important role in the control of thermogenesis and energy mobilization during cold exposure.

METHODS

Male Wistar rats were exposed to a cold environment (4°C) or TRH retrodialysis in the PVN for 2 h. We compared the effects of cold exposure and TRH administration in the PVN on plasma glucose, corticosterone, and thyroid hormone concentrations, body temperature, locomotor activity, as well as metabolic gene expression in the liver and brown adipose tissue.

RESULTS

Cold exposure increased body temperature, locomotor activity, and plasma corticosterone concentrations, but blood glucose concentrations were similar to that of room temperature control animals. TRH administration in the PVN also promptly increased body temperature, locomotor activity and plasma corticosterone concentrations. However, TRH administration in the PVN markedly increased blood glucose concentrations and endogenous glucose production (EGP) compared to saline controls. Selective hepatic sympathetic or parasympathetic denervation reduced the TRH-induced increase in glucose concentrations and EGP. Gene expression data indicated increased gluconeogenesis in liver and lipolysis in brown adipose tissue, both after cold exposure and TRH administration.

CONCLUSIONS

We conclude that TRH administration in the rat PVN largely mimics the metabolic and behavioral changes induced by cold exposure indicating a potential link between TRH release in the PVN and cold defense.

Role of TRH/UCN3 neurons of the perifornical area/bed nucleus of stria terminalis region in the regulation of the anorexigenic POMC neurons of the arcuate nucleus in male mice and rats

Two anorexigenic peptides, thyrotropin-releasing hormone (TRH) and urocortin 3 (UCN3), are co-expressed in a continuous neuronal group that extends from the perifornical area to the bed nucleus of stria terminalis, raising the possibility that this cell group may be involved in the regulation of energy homeostasis. In this study, therefore, we tested the hypothesis that the TRH/UCN3 neurons regulate food intake by influencing feeding-related neuropeptide Y (NPY) and/or proopiomelanocortin (POMC) neurons in the arcuate nucleus (ARC). Triple-labeled immunofluorescent preparations demonstrated that only very few NPY neurons (4.3 ± 1.3%) were contacted by double-labeled TRH/UCN3 axons in the ARC. In contrast, more than half of the POMC neurons (52.4 ± 8.5%) were contacted by double-labeled axons. Immuno-electron microscopy demonstrated that the UCN3 axons established asymmetric synapses with POMC neurons, indicating the excitatory nature of these synaptic specializations. Patch clamp electrophysiology revealed that TRH and UCN3 have antagonistic effects on the POMC neurons. While UCN3 depolarizes and increases the firing rate of POMC neurons, TRH prevents these effects of UCN3. These data demonstrate that TRH/UCN3 neurons in the perifornical/BNST region establish abundant synaptic associations with the POMC neurons in the ARC and suggest a potentially important role for these neurons in the regulation of food intake through an antagonistic interaction between TRH and UCN3 on the electrophysiological properties of POMC neurons.

The Mechanism of Negative Transcriptional Regulation by Thyroid Hormone: Lessons From the Thyrotropin β Subunit Gene

Thyroid hormone (T3) activates (positive regulation) or represses (negative regulation) target genes at the transcriptional level. The molecular mechanism of the former has been elucidated in detail; however, the mechanism for negative regulation has not been established. The best example of the gene that is negatively regulated by T3 is the thyrotropin (thyroid-stimulating hormone) β subunit (TSHβ) gene. Analogous to the T3-responsive element (TRE) in positive regulation, a negative TRE (nTRE) has been postulated in the TSHβ gene. However, TSHβ promoter analysis, performed in the presence of transcription factors Pit1 and GATA2, which are determinants of thyrotroph differentiation in the pituitary, revealed that the nTRE is dispensable for inhibition by T3. We propose a tethering model in which the T3 receptor is tethered to GATA2 via protein-protein interaction and inhibits GATA2-dependent transactivation of the TSHβ gene in a T3-dependent manner.

Mct8 and trh co-expression throughout the hypothalamic paraventricular nucleus is modified by dehydration-induced anorexia in rats

Thyrotropin-releasing hormone (TRH) is a neuropeptide with endocrine and neuromodulatory effects. TRH from the paraventricular hypothalamic nucleus (PVN) participates in the control of energy homeostasis; as a neuromodulator TRH has anorexigenic effects. Negative energy balance decreases PVN TRH expression and TSH concentration; in contrast, a particular model of anorexia (dehydration) induces in rats a paradoxical increase in TRH expression in hypophysiotropic cells from caudal PVN and high TSH serum levels, despite their apparent hypothalamic hyperthyroidism and low body weight. We compared here the mRNA co-expression pattern of one of the brain thyroid hormones' transporters, the monocarboxylate transporter-8 (MCT8) with that of TRH in PVN subdivisions of dehydration-induced anorexic (DIA) and control rats. Our aim was to identify whether a low MCT8 expression in anorexic rats could contribute to their high TRH mRNA content.We registered daily food intake and body weight of 7-day DIA and control rats and analyzed TRH and MCT8 mRNA co-expression throughout the PVN by double in situ hybridization assays. We found that DIA rats showed increased number of TRHergic cells in caudal PVN, as well as a decreased percentage of TRH-expressing neurons that co-expressed MCT8 mRNA signal. Results suggest that the reduced proportion of double TRH/MCT8 expressing cells may be limiting the entry of hypothalamic triiodothyronine to the greater number of TRH-expressing neurons from caudal PVN and be in part responsible for the high TRH expression in anorexia rats and for the lack of adaptation of their hypothalamic-pituitary-thyroid axis to their low food intake.

Established Stem Cell Model of Spinal Muscular Atrophy Is Applicable in the Evaluation of the Efficacy of Thyrotropin-Releasing Hormone Analog

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder characterized by the degeneration of spinal motor neurons. This disease is mainly caused by mutation or deletion of the survival motor neuron 1 (SMN1) gene. Currently, no effective treatment is available, and only symptomatic treatment can be provided. Our purpose in the present study was to establish a human SMA-derived induced pluripotent stem cell (SMA-iPSC) disease model and assay a therapeutic drug in preparation for the development of a novel treatment of SMA. We generated iPSCs from the skin fibroblasts of a patient with SMA and confirmed that they were pluripotent and undifferentiated. The neural differentiation of SMA-iPSCs shortened the dendrite and axon length and increased the apoptosis of the spinal motor neurons. In addition, we found activated astrocytes in differentiated SMA-iPSCs. Using this model, we confirmed that treatment with the thyrotropin-releasing hormone (TRH) analog, 5-oxo-l-prolyl-l-histidyl-l-prolinamide, which had marginal effects in clinical trials, increases the SMN protein level. This increase was mediated through the transcriptional activation of the SMN2 gene and inhibition of glycogen synthase kinase-3β activity. Finally, the TRH analog treatment resulted in dendrite and axon development of spinal motor neurons in differentiated SMA-iPSCs. These results suggest that this human in vitro disease model stimulates SMA pathology and reveal the potential efficacy of TRH analog treatment for SMA. Therefore, we can screen novel therapeutic drugs such as TRH for SMA easily and effectively using the human SMA-iPSC model. Significance: Platelet-derived growth factor (PDGF) has recently been reported to produce the greatest increase in survival motor neuron protein levels by inhibiting glycogen synthase kinase (GSK)-3β; however, motor neurons lack PDGF receptors. A human in vitro spinal muscular atrophy-derived induced pluripotent stem cell model was established, which showed that the thyrotropin releasing hormone (TRH) analog promoted transcriptional activation of the SMN2 gene and inhibition of GSK-3β activity, resulting in the increase and stabilization of the SMN protein and axon elongation of spinal motor neurons. These results reveal the potential efficacy of TRH analog treatment for SMA.

Calcium signaling properties of a thyrotroph cell line, mouse TαT1 cells

TαT1 cells are mouse thyrotroph cell line frequently used for studies on thyroid-stimulating hormone beta subunit gene expression and other cellular functions. Here we have characterized calcium-signaling pathways in TαT1 cells, an issue not previously addressed in these cells and incompletely described in native thyrotrophs. TαT1 cells are excitable and fire action potentials spontaneously and in response to application of thyrotropin-releasing hormone (TRH), the native hypothalamic agonist for thyrotrophs. Spontaneous electrical activity is coupled to small amplitude fluctuations in intracellular calcium, whereas TRH stimulates both calcium mobilization from intracellular pools and calcium influx. Non-receptor-mediated depletion of intracellular pool also leads to a prominent facilitation of calcium influx. Both receptor and non-receptor stimulated calcium influx is substantially attenuated but not completely abolished by inhibition of voltage-gated calcium channels, suggesting that depletion of intracellular calcium pool in these cells provides a signal for both voltage-independent and -dependent calcium influx, the latter by facilitating the pacemaking activity. These cells also express purinergic P2Y1 receptors and their activation by extracellular ATP mimics TRH action on calcium mobilization and influx. The thyroid hormone triiodothyronine prolongs duration of TRH-induced calcium spikes during 30-min exposure. These data indicate that TαT1 cells are capable of responding to natively feed-forward TRH signaling and intrapituitary ATP signaling with acute calcium mobilization and sustained calcium influx. Amplification of TRH-induced calcium signaling by triiodothyronine further suggests the existence of a pathway for positive feedback effects of thyroid hormones probably in a non-genomic manner.

ERK and RSK are necessary for TRH-induced inhibition of r-ERG potassium currents in rat pituitary GH3 cells

The transduction pathway mediating the inhibitory effect that TRH exerts on r-ERG channels has been thoroughly studied in GH3 rat pituitary cells but some elements have yet to be discovered, including those involved in a phosphorylation event(s). Using a quantitative phosphoproteomic approach we studied the changes in phosphorylation caused by treatment with 1μM TRH for 5min in GH3 cells. The activating residues of Erk2 and Erk1 undergo phosphorylation increases of 5.26 and 4.87 fold, respectively, in agreement with previous reports of ERK activation by TRH in GH3 cells. Thus, we studied the possible involvement of ERK pathway in the signal transduction from TRH receptor to r-ERG channels. The MEK inhibitor U0126 at 0.5μM caused no major blockade of the basal r-ERG current, but impaired the TRH inhibitory effect on r-ERG. Indeed, the TRH effect on r-ERG was also reduced when GH3 cells were transfected with siRNAs against either Erk1 or Erk2. Using antibodies, we found that TRH treatment also causes activating phosphorylation of Rsk. The TRH effect on r-ERG current was also impaired when cells were transfected with any of two different siRNAs mixtures against Rsk1. However, treatment of GH3 cells with 20nM EGF for 5min, which causes ERK and RSK activation, had no effect on the r-ERG currents. Therefore, we conclude that in the native GH3 cell system, ERK and RSK are involved in the pathway linking TRH receptor to r-ERG channel inhibition, but additional components must participate to cause such inhibition.

The influence of equol on the hypothalamic-pituitary-thyroid axis and hepatic lipid metabolic parameters in adult male rats

AIMS

Equol, the principal active metabolite of soy-derived phytoestrogen daidzein, has well-known estrogenic actions. Results of several studies indicate that equol may also have anti-androgenic activities. However, mechanisms of action of equol on hypothalamic-pituitary-thyroid axis (HPTA) and hepatic lipid metabolism in adult male rats have not been determined yet.

MAIN METHODS

Equol at two doses of 100 and 250mg/kgbodyweight(BW)/day was orally gavaged for 5days to groups of 4-month-old male rats. As a positive anti-androgenic control group, animals received 100mg of pure anti-androgenic drug flutamide/kgBW/day. Circulating concentrations of thyroid hormones and lipids, and expression levels of genes underlying HPTA function were determined by radioimmunoassay and TaqMan® real-time reverse transcription polymerase chain reaction, respectively.

KEY FINDINGS

Flutamide significantly decreased relative prostate weight, whereas equol did not. Both equol and flutamide caused a significant increase in relative liver weights, and decreases in plasma levels of total tetraiodothyronine (T4) and triiodothyronine (T3), whereas free T4 and T3 concentrations were not reduced. Equol caused the marked down-regulation of hypothalamic thyrotropin-releasing hormone mRNA expression, whereas flutamide did not. Equol as well as flutamide significantly down-regulated the expression levels of pituitary thyrotropin beta-subunit mRNA, without altering thyrotropin secretion. Equol caused reductions in plasma levels of total cholesterol, high- and low-density lipoproteins and triglycerides, whereas flutamide exerted opposite effects.

SIGNIFICANCE

This is the first study to reveal that in male rats equol did not affect HPTA function and liver lipid metabolism through the anti-androgenic pathway, however, the intrinsic estrogenic actions of equol were observed.

Identification of thyrotropin-releasing hormone as hippocampal glutaminyl cyclase substrate in neurons and reactive astrocytes

Recently, Aβ peptide variants with an N-terminal truncation and pyroglutamate modification were identified and shown to be highly neurotoxic and prone to aggregation. This modification of Aβ is catalyzed by glutaminyl cyclase (QC) and pharmacological inhibition of QC diminishes Aβ deposition and accompanying gliosis and ameliorates memory impairment in transgenic mouse models of Alzheimer's disease (AD). QC expression was initially described in the hypothalamus, where thyrotropin-releasing hormone (TRH) is one of its physiological substrates. In addition to its hormonal role, a novel neuroprotective function of TRH following excitotoxicity and Aβ-mediated neurotoxicity has been reported in the hippocampus. Functionally matching this finding, we recently demonstrated QC expression by hippocampal interneurons in mouse brain. Here, we detected neuronal co-expression of QC and TRH in the hippocampus of young adult wild type mice using double immunofluorescence labeling. This provides evidence for TRH being a physiological QC substrate in hippocampus. Additionally, in neocortex of aged but not of young mice transgenic for amyloid precursor protein an increase of QC mRNA levels was found compared to wild type littermates. This phenomenon was not observed in hippocampus, which is later affected by Aβ pathology. However, in hippocampus of transgenic - but not of wild type mice - a correlation between QC and TRH mRNA levels was revealed. This co-regulation of the enzyme QC and its substrate TRH was reflected by a co-induction of both proteins in reactive astrocytes in proximity of Aβ deposits. Also, in primary mouse astrocytes a co-induction of QC and TRH was demonstrated upon Aβ stimulation.

Hypothalamic-pituitary thyroid axis alterations in female mice with deletion of the neuromedin B receptor gene

Neuromedin B, a peptide highly expressed at the pituitary, has been shown to act as autocrine/paracrine inhibitor of thyrotropin (TSH) release. Here we studied the thyroid axis of adult female mice lacking neuromedin B receptor (NBR-KO), compared to wild type (WT) littermates. They exhibited slight increase in serum TSH (18%), with normal pituitary expression of mRNA coding for α-glycoprotein subunit (Cga), but reduced TSH β-subunit mRNA (Tshb, 41%), lower intra-pituitary TSH content (24%) and increased thyroid hormone transporter MCT-8 (Slc16a2, 44%) and thyroid hormone receptor β mRNA expression (Thrb, 39%). NBR-KO mice exhibited normal thyroxine (T4) and reduced triiodothyronine (T3) (30%), with no alterations in the intra-thyroidal content of T4 and T3 or thyroid morphological changes. Hypothalamic thyrotropin-releasing hormone (TRH) mRNA (Trh) was increased (68%), concomitant with a reduction in type 2 deiodinase mRNA (Dio2, 30%) and no changes in MCT-8 and thyroid hormone receptor mRNA expression. NBR-KO mice exhibited a 56% higher increase in serum TSH in response to an acute single intraperitoneal injection of TRH concomitant with a non-significant increase in pituitary TRH receptor (Trhr) mRNA at basal state. The phenotype of female NBR-KO mice at the hypothalamus-pituitary axis revealed alterations in pituitary and hypothalamic gene expression, associated with reduced serum T3, and higher TSH response to TRH, with apparently normal thyroid morphology and hormonal production. Thus, results confirm that neuromedin B pathways are importantly involved in secretory pathways of TSH and revealed its participation in the in vivo regulation of gene expression of TSH β-subunit and pituitary MCT8 and Thrb and hypothalamic TRH and type 2 deiodinase.

Behavioural phenotyping of male growth hormone-releasing hormone (GHRH) knockout mice

OBJECTIVE

GH-releasing hormone (GHRH) is a key regulator of GH secretion. The role of GH in anxiety is somewhat contradictory. The aim of this study is to elucidate the consequences of lack of GHRH on emotional behaviour in a mouse model of GH deficiency due to removal of the GHRH gene (GHRH knock out, GHRHKO).

DESIGN

Homozygous GHRHKO and wild type male mice were utilized for this study. The emotional behaviour was measured through a battery of behavioural tests (locomotor activity/open field, light-dark exploration, elevated plus maze, forced swim test, tail suspension test). To correlate the emotional behaviour with brain neurochemistry, we evaluated thyrotropin-releasing hormone (TRH) gene expression in hypothalamic tissue by real-time PCR, and the levels of norepinephrine (NE), dopamine (DA) and serotonin (5-hydroxytryptamine, 5-HT) in prefrontal cortex by HPLC analysis.

RESULTS

GHRHKO mice showed increased exploratory activity. In the open field test (P<0.005), light-dark box (P<0.005) and elevated plus maze (P<0.05), GHRHKO mice demonstrated a decrease in anxiety-related behaviour. In addition, GHRHKO mice showed reduced immobility time with respect to control in forced swim test and tail suspension test (P<0.0001). The gene expression of hypothalamic TRH (P<0.05) was increased, while NE levels in prefrontal cortex were decreased compared to control (P<0.05).

CONCLUSION

These results suggest that in male mice GHRH deficiency brings about an increased physical activity and decreased anxiety- and depression-related behaviour, possibly related to increased TRH and decreased NE levels in the brain.

First-in-class thyrotropin-releasing hormone (TRH)-based compound binds to a pharmacologically distinct TRH receptor subtype in human brain and is effective in neurodegenerative models

JAK4D, a first-in-class thyrotropin-releasing hormone (TRH)-based compound, is a prospective therapeutic candidate offering a multifaceted approach to treating neurodegeneration and other CNS conditions. The purpose of these studies was to determine the ability of JAK4D to bind to TRH receptors in human brain and to evaluate its neuropharmacological effects in neurodegenerative animal models. Additionally, JAK4D brain permeation was examined in mouse, and initial toxicology was assessed in vivo and in vitro. We report that JAK4D bound selectively with nanomolar affinity to native TRH receptors in human hippocampal tissue and showed for the first time that these receptors are pharmacologically distinct from TRH receptors in human pituitary, thus revealing a new TRH receptor subtype which represents a promising neurotherapeutic target in human brain. Systemic administration of JAK4D elicited statistically significant and clinically-relevant neuroprotective effects in three established neurodegenerative animal models: JAK4D reduced cognitive deficits when administered post-insult in a kainate (KA)-induced rat model of neurodegeneration; it protected against free radical release and neuronal damage evoked by intrastriatal microdialysis of KA in rat; and it reduced motor decline, weight loss, and lumbar spinal cord neuronal loss in G93A-SOD1 transgenic Amyotrophic Lateral Sclerosis mice. Ability to cross the blood-brain barrier and a clean initial toxicology profile were also shown. In light of these findings, JAK4D is an important tool for investigating the hitherto-unidentified central TRH receptor subtype reported herein and an attractive therapeutic candidate for neurodegenerative disorders.

Increased TRH and TRH-like peptide release in rat brain and peripheral tissues during proestrus/estrus

Women are at greater risk for major depression, PTSD, and other anxiety disorders. ERβ-selective agonists for the treatment of these disorders are the focus of pharmacologic development and clinical testing. Estradiol and its metabolites contribute to the neuroprotective effects of this steroid class, particularly in men, due to local conversion of testosterone to estiradiol in key brain regions which are predisposed to neurodegenerative diseases. We have used young adult female Sprague-Dawley rats to assess the role of TRH and TRH-like peptides, with the general structure pGlu-X-Pro-NH2 where "X" can be any amino acid residue, as mediators of the neurobiochemical effects of estradiol. The neuroprotective TRH and TRH-like peptides are coreleased with excitotoxic glutamate by glutamatergic neurons which contribute importantly to the regulation of the estrus cycle. The levels of TRH and TRH-like peptides during proestrus and/or estrus in the 12 brain regions analyzed were significantly decreased (due to accelerated release) 106 times but increased only 25 times when compared to the corresponding levels during diestrus days 1 and 2. These changes, listed by brain region in the order of decreasing number of significant decreases (↓) and/or increases (↑), were: striatum (20↓,1↑), medulla oblongata (16↓,2↑), amygdala (14↓,1↑), cerebellum (13↓,1↑), hypothalamus (12↓,1↑), entorhinal cortex (6↓,6↑), posterior cingulate (10↓,1↑), frontal cortex (3↓,5↑), nucleus accumbens (5↓,3↑), hippocampus (5↓,2↑), anterior cingulate (2↓,1↑), and piriform cortex (1↑). In peripheral tissues the corresponding changes were: ovaries (23↓), uterus (16↓,1↑), adrenals (11↓,3↑), and pancreas (1↓,6↑). We conclude that these peptides may be downstream mediators of some of the therapeutic effects of estrogen.

Effects of ramosetron on gastrointestinal transit of Guinea pig

BACKGROUND/AIMS

A selective 5-hydroxytryptamine (5-HT) type 3 receptor antagonist, ramosetron, inhibits stress-induced abnormal defecation in animals and is currently used as a therapeutic drug for irritable bowel syndrome with diarrhea. The aim of this study is to investigate the effect of ramosetron on altered gastrointestinal (GI) transit.

METHODS

Male guinea pigs weighing approximately 300 g were used. The effect of ramosetron was investigated on altered GI transit induced by thyrotropin-releasing hormone (TRH), 5-HT, or mustard oil (MO). GI transit was evaluated by the migration of charcoal mixture from the pylorus to the most distal point, and expressed as a percentage (%) of charcoal migration (cm) of the total length of total small intestine (cm).

RESULTS

The average charcoal transit was 51.3 ± 20.1% in the control (vehicle) group, whereas in the ramosetron group charcoal moved 56.6 ± 21.9%, 46.9 ± 9.14% and 8.4 ± 5.6% of the total small intestine at the concentrations of 10, 30 and 100 µg/kg, respectively. GI transit after administration of TRH (100 µg/kg), 5-HT (10 mg/kg) or MO (10 mg/kg) was accelerated compared to vehicle (5-HT, 94.9 ± 9.22%; TRH, 73.4 ± 14.7%; MO, 81.0 ± 13.7%). Ramosetron inhibited GI transit altered by 5-HT, TRH or MO.

CONCLUSIONS

Ramosetron modulated GI transit. We suggest that ramosetron may be therapeutically useful for those with accelerated upper GI transit.

Role of thyrotropin-releasing hormone in formation of stress ulcer

AIM: To investigate the role of thyrotropin-releasing hormone (TRH) in the rat ulcer induced by cold-restraint stress and its possible mechanism.

METHODS: The rat model of stress ulcer was constructed by cold-restraint method. The changes of gastric mucosa, gastric juice secretion, and gastric motility were evaluated after injection of TRH or TRH antiserum into the lateral ventricle.

RESULTS: Three hours after the administration of TRH, severe damages were observed in the gastric mucosa of rats fasting for 24 h at room temperature. As compared with the control group, the volume of gastric juice secretion (5.5 ± 0.7 mL/2 h vs 2.7 ± 0.6 mL/2 h, P < 0.01) and total acid output (539.4 ± 50.5 mol HCl/2 h vs 317.7 ± 45.3 mol HCl/2 h, P < 0.05) were increased markedly. Gastric wall mucus secretion was decreased (1.35 ± 0.08 vs 2.21 ± 0.11, P < 0.01), while the frequency of gastric contraction (1.2 ± 0.2 vs 0.4 ± 0.1, P < 0.01), the width of contractive wave (17.2 ± 2.0 vs 8.1 ± 1.1, P < 0.01), and the motility index per minute (90.3 ± 14.2 vs 13.2 ± 3.1, P < 0.01) were elevated significantly. The administration of TRH antiserum significantly inhibited the gastric mucosa damage caused by cold restraint stress (ulcer index: 10.2 ± 3.9 vs 30.3 ± 5.5, P < 0.01).

CONCLUSION: The injection of TRH into the lateral ventricle can induce gastric mucosal ulcer, which is similar to the stress ulcer. The enhancement of TRH synthesis in the brain plays a crucial role in the gastric mucosal damage induced by cold-restraint stress.