Effect of Cyanotoxins on the Hypothalamic–Pituitary–Gonadal Axis in Male Adult Mouse

Background

Microcystins LR (MC-LR) are hepatotoxic cyanotoxins that have been shown to induce reproductive toxicity, and Hypothalamic–Pituitary–Gonadal Axis (HPG) is responsible for the control of reproductive functions. However, few studies have been performed to evaluate the effects of MC-LR on HPG axis. This study aimed to investigate the MC-LR-induced toxicity in the reproductive system of mouse and focus on the HPG axis.

Methods

Adult male C57BL/6 mice were exposed to various concentrations of MC-LR (0, 3.75, 7.50, 15.00 and 30.00 µg/kg body weight per day) for 1 to 14 days, and it was found that exposure to different concentrations of MC-LR significantly disturbed sperm production in the mice testes in a dose- and time-dependent manner. To elucidate the associated possible mechanisms, the serum levels of testosterone, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were assessed. Meanwhile, PCR assays were employed to detect alterations in a series of genes involved in HPG axis, such as FSH, LH, gonadotropin-releasing hormone (GnRH) and their complement receptors. Furthermore, the effect of MC-LR on the viability and testosterone production of Leydig cells were tested in vitro. Results: MC-LR significantly impaired the spermatogenesis of mice possibly through the direct or indirect inhibition of GnRH synthesis at the hypothalamic level, which resulted in reduction of serum levels of LH that lead to suppression of testosterone production in the testis of mice.

Conclusions

MC-LR may be a GnRH toxin that would disrupt the reproductive system of mice.     

Antidepressant-like Effect of Bacopaside I in Mice Exposed to Chronic Unpredictable Mild Stress by Modulating the Hypothalamic–Pituitary–Adrenal Axis Function and Activating BDNF Signaling Pathway

Preliminary studies conducted in our laboratory have confirmed that Bacopaside I (BS-I), a saponin compound isolated from Bacopa monnieri, displayed antidepressant-like activity in the mouse behavioral despair model. The present investigation aimed to verify the antidepressant-like action of BS-I using a mouse model of behavioral deficits induced by chronic unpredictable mild stress (CUMS) and further probe its underlying mechanism of action. Mice were exposed to CUMS for a period of 5 consecutive weeks to induce depression-like behavior. Then, oral gavage administrations with vehicle (model group), fluoxetine (12 mg/kg, positive group) or BS-I (5, 15, 45 mg/kg, treated group) once daily were started during the last two weeks of CUMS procedure. The results showed that BS-I significantly ameliorated CUMS-induced depression-like behaviors in mice, as characterized by an elevated sucrose consumption in the sucrose preference test and reduced immobility time without affecting spontaneous locomotor activity in the forced swimming test, tail suspension test and open field test. It was also found that BS-I treatment reversed the increased level of plasma corticosterone and decreased mRNA and protein expressions of glucocorticoid receptor induced by CUMS exposure, indicating that hypothalamic–pituitary–adrenal (HPA) axis hyperactivity of CUMS-exposed mice was restored by BS-I treatment. Furthermore, chronic administration of BS-I elevated expression levels of brain-derived neurotrophic factor (BDNF) (mRNA and protein) and activated the phosphorylation of extracellular signal-regulated kinase and cAMP response element-binding protein in the hippocampus and prefrontal cortex in mice subjected to CUMS procedure. Taken together, these results indicated that BS-I exhibited an obvious antidepressant-like effect in mouse model of CUMS-induced depression that was mediated, at least in part, by modulating HPA hyperactivity and activating BDNF signaling pathway.     

Effect of Intracerebroventricular Administration of Apelin-13 on the Hypothalamus–Pituitary–Thyroid Axis and Peripheral Uncoupling Proteins

Apelin, a ligand for G protein-coupled APJ receptor, is a peptide hormone. Although apelin and APJ receptors are determined in hypothalamus and thyroid gland its role in the hypothalamus–pituitary–thyroid (HPT) axis and mechanism of action on energy metabolism is not clear. This suggests that apelin may play a role in the HPT axis and energy metabolism. This study was designed to determine possible effects of centrally administered apelin-13 on the HPT axis and energy metabolism. A total of 40 adult male Sprague Dawley rats were divided into four groups (n?=?10 each group). Intact rats served as control group while the sham group received vehicle of apelin. Apelin-13 was injected intracerebroventricularly at the doses of 1 and 10 nmol, for 7 days in the rats in the experimental group. At the end of the experimental protocol, animals were decapitated and brain, blood, white and brown adipose tissues samples were collected. There was no significant difference between the groups in terms of hypothalamic TRH mRNA levels. Serum TSH levels were significantly higher in all groups compared to the control group (p?<?0.05). Serum fT3 and fT4 levels were significantly lower in apelin-13 administered groups (p?<?0.05). Moreover, apelin-13 administered groups had lower levels of UCP1 mRNA in white and brown adipose tissues. UCP3 mRNA expression in muscle tissue was also lower in apelin-13 treated groups (p?<?0.05). These results indicates that apelin-13 exhibits a decreasing effect on energy consumption through a mechanism involving the peripheral rather than central arms of the HPT axis.     

Chronic Stress Suppresses the Expression of Cutaneous Hypothalamic–Pituitary–Adrenocortical Axis Elements and Melanogenesis

Chronic stress can affect skin function, and some skin diseases might be triggered or aggravated by stress. Stress can activate the central hypothalamic–pituitary–adrenocortical (HPA) axis, which causes glucocorticoid levels to increase. The skin has HPA axis elements that react to environmental stressors to regulate skin functions, such as melanogenesis. This study explores the mechanism whereby chronic stress affects skin pigmentation, focusing on the HPA axis, and investigates the role of glucocorticoids in this pathway. We exposed C57BL/6 male mice to two types of chronic stress, chronic restraint stress (CRS) and chronic unpredictable mild stress (CUMS). Mice subjected to either stress condition showed reduced melanogenesis. Interestingly, CRS and CUMS triggered reductions in the mRNA expression levels of key factors involved in the HPA axis in the skin. In mice administered corticosterone, decreased melanin synthesis and reduced expression of HPA axis elements were observed. The reduced expression of HPA axis elements and melanogenesis in the skin of stressed mice were reversed by RU486 (a glucocorticoid receptor antagonist) treatment. Glucocorticoids had no significant inhibitory effect on melanogenesis in vitro. These results suggest that, high levels of serum corticosterone induced by chronic stress can reduce the expression of elements of the skin HPA axis by glucocorticoid-dependent negative feedback. These activities can eventually result in decreased skin pigmentation. Our findings raise the possibility that chronic stress could be a risk factor for depigmentation by disrupting the cutaneous HPA axis and should prompt dermatologists to exercise more caution when using glucocorticoids for treatment.     

The Hypothalamic–Pituitary–Adrenal Axis and Serotonin Metabolism in Individual Brain Nuclei of Mice with Genetic Disruption of the NK1 Receptor Exposed to Acute Stress

Mice lacking the substance P (SP) neurokinin-1 (NK1) receptor (NK1R?/?mice) were used to investigate whether SP affects serotonin (5-HT) function in the brain and to assess the effects of acute immobilisation stress on the hypothalamic–pituitary–adrenocortical (HPA) axis and 5-HT turnover in individual brain nuclei. Basal HPA activity and the expression of hypothalamic corticotropin-releasing hormone (CRH) in wild-type (WT)- and NK1R?/? mice were identical. Stress-induced increases in plasma ACTH concentration were considerably higher in NK1R?/? mice than in WT mice while corticosterone concentrations were equally elevated in both mouse lines. Acute stress did not alter the expression of CRH. In the dorsal raphe nucleus (DRN), basal 5-HT turnover was increased in NK1R?/? mice and a 15 min stress further magnified 5-HT utilisation in this region. In the frontoparietal cortex, medial prefrontal cortex, central nucleus of amygdala, and the hippocampal CA1 region, stress increased 5-HT and/or 5-hydroxyindoleacetic acid (5-HIAA) concentrations to a similar extent in WT and NK1R?/? mice. 5-HT turnover in the hypothalamic paraventricular nucleus was not affected by stress, but stress induced similar increases in 5-HT and 5-HIAA in the ventromedial and dorsomedial hypothalamic nuclei in WT and NK1R?/? mice. Our findings indicate that NK1 receptor activation suppresses ACTH release during acute stress but does not exert sustained inhibition of the HPA axis. Genetic deletion of the NK1 receptor accelerates 5-HT turnover in DRN under basal and stress conditions. No differences between the responses of serotonergic system to acute stress in WT and NK1R?/? mice occur in forebrain nuclei linked to the regulation of anxiety and neuroendocrine stress responses.     

Suppression of Hypothalamic–Pituitary–Adrenal Axis by Acute Heroin Challenge in Rats During Acute and Chronic Withdrawal from Chronic Heroin Administration

It is known that heroin dependence and withdrawal are associated with changes in the hypothalamic–pituitary–adrenal (HPA) axis. The objective of these studies in rats was to systematically investigate the level of HPA activity and response to a heroin challenge at two time points during heroin withdrawal, and to characterize the expression of associated stress-related genes 30 min after each heroin challenge. Rats received chronic (10-day) intermittent escalating-dose heroin administration (3 × 2.5 mg/kg/day on day 1; 3 × 20 mg/kg/day by day 10). Hormonal and neurochemical assessments were performed in acute (12 h after last heroin injection) and chronic (10 days after the last injection) withdrawal. Both plasma ACTH and corticosterone levels were elevated during acute withdrawal, and heroin challenge at 20 mg/kg (the last dose of chronic escalation) at this time point attenuated this HPA hyperactivity. During chronic withdrawal, HPA hormonal levels returned to baseline, but heroin challenge at 5 mg/kg decreased ACTH levels. In contrast, this dose of heroin challenge stimulated the HPA axis in heroin naïve rats. In the anterior pituitary, pro-opiomelanocortin (POMC) mRNA levels were increased during acute withdrawal and retuned to control levels after chronic withdrawal. In the medial hypothalamus, however, the POMC mRNA levels were decreased during acute withdrawal, and increased after chronic withdrawal. Our results suggest a long-lasting change in HPA abnormal responsivity during chronic heroin withdrawal.     

Honokiol Exerts Antidepressant Effects in Rats Exposed to Chronic Unpredictable Mild Stress by Regulating Brain Derived Neurotrophic Factor Level and Hypothalamus–Pituitary–Adrenal Axis Activity

Honokiol (HNK), the main active component of Magnolia officinalis, has shown a variety of pharmacological activities. In the present study, we measured the antidepressant-like effects of HNK in a rat model of chronic unpredictable mild stress (CUMS) and explored its possible mechanisms. The antidepressant-like effects of HNK were assessed in rats by an open field test (OFT), sucrose preference test (SPT) and forced swimming test (FST). Then, serum levels of corticotrophin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and corticosterone (CORT) and hippocampal brain-derived neurotrophic factor (BDNF) and glucocorticoid receptor α (GRα) levels were assessed to explore the possible mechanisms. We identified that HNK treatment (2, 4, and 8 mg/kg) alleviated the CUMS-induced behavioural deficits. Treatment with HNK also normalized the CUMS-induced hyperactivity of the limbic hypothalamic–pituitary–adrenal (HPA) axis, as indicated by reduced CRH, ACTH and CORT serum levels. In addition, HNK increased the expression of GRα (mRNA and protein) and BDNF (mRNA and protein) in the hippocampus. These data confirmed the antidepressant-like effects of HNK, which may be related to its normalizing the function of the HPA axis and increasing the BDNF level in the hippocampus.     

Hypothalamo–Pituitary System Controls the Development of Humoral Immune Response during Prenatal Ontogenesis in Rats

We studied the influence of the neuroendocrine system on the development of humoral immune response to sheep erythrocytes in rat fetuses. The removal of brain in utero by decapitation of 18-day fetuses induced a fourfold increase in the number of antibody-forming cells in the liver, as compared to the unoperated fetuses. After the removal of the forebrain, including hypothalamus (encephalectomy), the number of antibody-forming cells was comparable to that in unoperated fetuses. The observed increase in the number of antibody-forming cells in the liver was not due to a disturbed migration of precursors of B-lymphocytes in the spleen, since their content in the spleen was also four times that in the encephalectomized and unoperated fetuses. The increased number of antibody-forming cells in decapitated fetuses could be due to an enhanced proliferative activity of the lymphocytes in the liver of these fetuses. It has been proposed that humoral immunity is controlled by the hypothalamo–pituitary–adrenal system already during prenatal development; the adrenocorticotropic hormone and glucocorticoids appear to be involved in this regulation.     

Modeling Endocrine Control of the Pituitary–Ovarian Axis: Androgenic Influence and Chaotic Dynamics

Mathematical models of the hypothalamus-pituitary-ovarian axis in women were first developed by Schlosser and Selgrade in 1999, with subsequent models of Harris-Clark et al. (Bull. Math. Biol. 65(1):157–173, 2003) and Pasteur and Selgrade (Understanding the dynamics of biological systems: lessons learned from integrative systems biology, Springer, London, pp. 38–58, 2011). These models produce periodic in-silico representation of luteinizing hormone (LH), follicle stimulating hormone (FSH), estradiol (E2), progesterone (P4), inhibin A (InhA), and inhibin B (InhB). Polycystic ovarian syndrome (PCOS), a leading cause of cycle irregularities, is seen as primarily a hyper-androgenic disorder. Therefore, including androgens into the model is necessary to produce simulations relevant to women with PCOS. Because testosterone (T) is the dominant female androgen, we focus our efforts on modeling pituitary feedback and inter-ovarian follicular growth properties as functions of circulating total T levels. Optimized parameters simultaneously simulate LH, FSH, E2, P4, InhA, and InhB levels of Welt et al. (J. Clin. Endocrinol. Metab. 84(1):105–111, 1999) and total T levels of Sinha-Hikim et al. (J. Clin. Endocrinol. Metab. 83(4):1312–1318, 1998). The resulting model is a system of 16 ordinary differential equations, with at least one stable periodic solution. Maciel et al. (J. Clin. Endocrinol. Metab. 89(11):5321–5327, 2004) hypothesized that retarded early follicle growth resulting in “stockpiling” of preantral follicles contributes to PCOS etiology. We present our investigations of this hypothesis and show that varying a follicular growth parameter produces preantral stockpiling and a period-doubling cascade resulting in apparent chaotic menstrual cycle behavior. The new model may allow investigators to study possible interventions returning acyclic patients to regular cycles and guide developments of individualized treatments for PCOS patients.     

Noise Induces Hypothyroidism and Gonadal Dysfunction Via Stimulation of Pineal–Adrenal Axis in Chicks

Noise is a world-wide problem that causes nervous, endocrine and cardiovascular disorders, and eventually health hazards in humans and animals. Objective of the current work is to investigate endocrine interaction in noise stress, which subsequently affects other endocrine functions including gonads in a poultry bird like chicks. Gravimetric, ultrastructural and hormonal status of the endocrine organs were examined to ascertain the effects of noise stress. Acute noise at 60 dB had no effect, but at 80 and 100 dB each for 3 h, increased pineal and serum serotonin, and adrenal and serum corticosterone, epinephrine and norepinephrine concentrations, without any change in thyroid or gonadal hormones. Chronic noise exposure at 60, 80 and 100 dB each for 6 h, daily for 7 days, drastically disturbed normal behavior, and quantum of food consumption and water intake. Chronic exposure also significantly decreased body weight including thyroid, ovary and testis weight, and increased adrenal weight. Noise stress caused ultrastructural changes leading to stimulations of pinealocytes (with abundance of rough endoplasmic reticulum and mitochondria), adrenocortical cells (enlarged nuclei and abundance of smooth endoplasmic reticulum) and adrenomedullary cells (enlarged nuclei with presence of chromaffin granules) were observed in noise stress. Additionally, pineal and serum serotonin, N-acetyl serotonin and melatonin, and adrenal and serum corticosterone, epinephrine and norepinephrine levels were significantly elevated following chronic noise exposure. Contrarily, thyroid activity was suppressed with atrophied thyroid follicles followed by declined levels of serum T₃ and T₄ with elevation of TSH level. Simultaneously, serum 17β-estradiol (E₂) and testosterone (T) concentrations were also significantly declined in all the doses of chronic noise. These changes were dose dependent of noise exposure. The findings suggest that (a) adrenal and pineal glands respond primarily to noise and secondarily act on other endocrine organs including gonads in chicks, (b) adrenal directly and/or indirectly causes thyroid and gonadal dysfunctions via pineal following noise exposure in chicks.     

Astrocyte–Endotheliocyte Axis in the Regulation of the Blood–Brain Barrier

Neurochemical Research - The evolution of blood–brain barrier paralleled centralisation of the nervous system: emergence of neuronal masses required control over composition of the...     

Chronic Piromelatine Treatment Alleviates Anxiety,Depressive Responses and Abnormal Hypothalamic–Pituitary–Adrenal Axis Activity in Prenatally Stressed Male and Female Rats

The prenatal stress (PNS) model in rodents can induce different abnormal responses that replicate the pathophysiology of depression. We applied this model to evaluate the efficacy of piromelatine (Pir), a novel melatonin analog developed for the treatment of insomnia, in male and female offspring. Adult PNS rats from both sexes showed comparable disturbance associated with high levels of anxiety and depressive responses. Both males and females with PNS demonstrated impaired feedback inhibition of the hypothalamic–pituitary–adrenal (HPA) axis compared to the intact offspring and increased glucocorticoid receptors in the hippocampus. However, opposite to female offspring, the male PNS rats showed an increased expression of mineralocorticoid receptors in the hippocampus. Piromelatine (20 mg/kg, i.p., for 21 days injected from postnatal day 60) attenuated the high anxiety level tested in the open field, elevated plus-maze and light–dark test, and depressive-like behavior in the sucrose preference and the forced swimming tests in a sex-specific manner. The drug reversed to control level stress-induced increase of plasma corticosterone 120 min later in both sexes. Piromelatine also corrected to control level the PNS-induced alterations of corticosteroid receptors only in male offspring. Our findings suggest that the piromelatine treatment exerts beneficial effects on impaired behavioral responses and dysregulated HPA axis in both sexes, while it corrects the PNS-induced changes in the hippocampal corticosteroid receptors only in male offspring.

     

The Effect of Iron–Vitamin C Co-supplementation on Biomarkers of Oxidative Stress in Iron-Deficient Female Youth

There is no study that assessed the effect of co-supplementation of iron and vitamin C on biomarkers of oxidative stress in non-anemic iron-deficient females. We investigated the effects of iron vs. iron?+?vitamin C co-supplementation on biomarkers of oxidative stress in iron-deficient girls. In a double-blind randomized controlled clinical trial, performed among 60 non-anemic iron-deficient girls, participants were randomly assigned to receive either 50 mg/day elemental iron supplements or 50 mg/day elemental iron?+?500 mg/day ascorbic acid for 12 weeks. Fasting blood samples were taken at baseline, weeks 6 and 12 for assessment of biomarkers of oxidative stress. Compared with the baseline levels, both iron and iron?+?vitamin C supplementation resulted in a significant reduction in serum malondialdehyde (MDA) levels (P _time?<?0.001) and remarkable elevation in serum total antioxidant capacity (TAC; P _time?<?0.001) and vitamin C levels (P _time?=?0.001); however, comparing the two groups we failed to find an additional effect of iron?+?vitamin C supplementation to that of iron alone on serum TAC and MDA levels (P _group was not statistically significant). Iron?+?vitamin C supplementation influenced serum vitamin C levels much more than that by iron alone (P _group?<?0.01). We also found a significant interaction term between time and group about serum vitamin C levels while this interaction was not significant about serum TAC and MDA levels. In conclusion, we found that iron supplementation with/without vitamin C improve biomarkers of oxidative stress among non-anemic iron-deficient females and may strengthen the antioxidant defense system by decreasing reactive oxygen species. Co-supplementation of iron?+?vitamin C has no further effect on oxidative stress compared with iron alone.     

Effect of pH on the Content of Glycolipids in Aureobasidium pullulans S–l

When Aureobasidium pullulans was cultivated with initial pH 6.0 and pH 2.5 in shaking flasks, only a slight difference was observed in the content of lipids in cells. On the other hand, when cultured with initial pH 2.5 in a jar fermenter, the content of lipids in mycelia was larger than that with initial pH 6.0. The content of sugars in the lipids showed a similar tendency. Glucolipids were easily hydrolyzed with dilute acid into glucose, glucooligo- saccharide and lipids.     

Effect of Exogenous ABA on the Salt Tolerance of Corn Seedlings Under Salt Stress

The exogenous ABA in different concentrations was used to spray Zea mays L. (cv. Luyu 11) seedlings under different salinity. The growth status, osomotic potential and osmotic regulatory activity, the contents of Na+ and K+, soluble sugars and proline were determined at different time after treatment. The results were shown as follows: The exogenous ABA gave an increase in salt resistance and dry weight of corn seedlings under different salinity, this increase was as a result of inhanced osmotic adjustment activity and exclusion of sodium ions from the shoot through the action of exogenous ABA, resulting an accumulation of sodium in the roots. Moreover, the decrease of osmotic potential and the increase of osmotic regulatory activity were for reasons of enhancement of organic osmotors, instead inorganic, e.g. Na+ and K+ osmotors. The mechanism of sodium exclusion from the shoot was also discussed.     

Effect of nutrients on the accumulation of glutamyl endopeptidase in the culture liquid ofBacillus intermedius 3–19

The effect of nutrients and growth conditions on the accumulation of glutamyl endopeptidase in the culture liquid ofBacillus intermedius 3–19 was studied. Glucose and other readily metabolizable carbon sources were found to suppress the production of the enzyme, whereas inorganic phosphate and ammonium cations enhanced it. Protein substrates, such as casein, gelatin, and hemoglobin, did not affect enzyme production. Some bivalent cations (Ca²⁺, Mg²⁺, Co²⁺) increased the production of glutamyl endopeptidase, but others (Zn²⁺, Fe²⁺, Cu²⁺) acted in the opposite way. The rate of enzyme accumulation in the culture liquid increased as the growth rate of the bacterium decreased, so that the maximum enzyme activity was observed in the stationary growth phase. Based on the results of this investigation, an optimal medium for the maximum production of glutamyl endopeptidase byB. intermedius 3–19 was elaborated.     

Effect of α-p-chlorophenoxyisobutyrate on the metabolism of isoprenoid compounds in the rat

1. Feeding of alpha-p-chlorophenoxyisobutyrate (CPIB) to rats increased ubiquinone concentration in the liver but not in other tissues. The increase was progressive with the time of feeding and related to the concentration of CPIB in the diet. 2. Incorporation of [1-(14)C]acetate, but not of [2-(14)C]mevalonate, into sterols in the liver in vivo or by liver slices in vitro was decreased on feeding the rats with CPIB. However, incorporation of mevalonate into ubiquinone increased. 3. CPIB, when added in low concentrations to liver slices, had no effect on isoprene synthesis from acetate; higher concentrations, however, were inhibitory. 4. No activation of ubiquinone synthesis from mevalonate was observed when CPIB was added to the liver slices synthesizing ubiquinone. 5. The increase in ubiquinone in CPIB-fed animals appears to be due to increased synthesis in the initial stages and to decreased catabolism in the later stages. 6. An inverse relationship was found between the concentration of ubiquinone in the liver and the serum sterol concentration in CPIB-fed rats.