Taurine Promotes Axonal Regeneration after a Complete Spinal Cord Injury in Lampreys.

Taurine is one of the most abundant free amino acids in the brain. It is well known that taurine protects the brain from further damage after a traumatic event. However, only a few ex vivo studies have looked at the possible role of taurine in the regulation of axon regeneration after injury. Here, we aimed to reveal the possible role for taurine in the modulation of axonal regeneration following a complete spinal cord injury (SCI) using lampreys as an animal model. The brainstem of lampreys contains several individually identifiable descending neurons that differ greatly in their capacity for axonal regeneration after SCI. This offers a convenient model to promote or inhibit axonal regrowth in the same in vivo preparation. First, we carried out high performance liquid chromatography experiments to measure taurine levels in the spinal cord following SCI. Our results revealed a statistically significant increase in taurine levels 4 weeks post-lesion, which suggested that taurine might have a positive effect on axonal regrowth. Based on these results, we decided to apply an acute taurine treatment at the site of injury to study its effect on axon regeneration. Results from these experiments show that an acute taurine treatment enhances axonal regeneration following SCI in lampreys. This offers a novel way to try to promote axon regeneration after nervous system injuries in mammalian models.

The hypothalamic-pituitary-gonadal axis is target of cadmium toxicity. An update of recent studies and potential therapeutic approaches.

This review presents an overview of neuroendocrine disruption induced by cadmium on the hypothalamic-pituitary-gonadal (HHG) axis. This review focuses on a number of hypotheses: (1) the HHG axis is a physiological target on cadmium toxicity; (2) cadmium could induce chronotoxicity on this neuroendocrine axis by disrupting the daily pattern of the HHG axis activity; (3) cadmium exposure throughout life could contribute to the oxidative stress and the circadian rhythms disruption induced by aging on the HHG; and (4) cadmium induces oxidative stress in the HHG axis so antioxidants could prevent or reduce cadmium toxicity in this system. Cadmium disrupts the regulatory mechanisms of this physiological axis, by altering neurotransmitters involved in this regulation at the hypothalamic level, altering gonadotropin hormone secretion, and by affecting testicular or ovarian structure and activity. These effects are age-dependent and they could be related to the circadian rhythms of this physiological axis. Several antioxidant agents could have a protective action against the neuroendocrine toxicity of cadmium on the reproductive system. A comprehensive view of the physiological axis may provide a better understanding about the neuroendocrine toxicity of cadmium on the reproductive system, so this perspective is recommended for undertaking further studies.

Neurotoxic effects induced by endosulfan exposure during pregnancy and lactation in female and male rat striatum.

Possible neurotoxic effects induced by endosulfan exposure during pregnancy and lactation in striatum of Sprague-Dawley female and male offspring rats have been evaluated. Dams were treated orally with 0.61 or 6.12mg of endosulfan/kg/day from the beginning of gestation until weaning. At postnatal day 60 offspring were sacrificed. We studied variations of norepinephrine, dopamine and serotonin content in striatum by High Performance Liquid Chromatography (HPLC) in these animals. Dopamine and serotonin metabolism was also determined. Endosulfan inhibits the striatal aminergic systems in adult male rats by decreasing norepinephrine and serotonin concentration and dopamine and serotonin metabolism. However, in adult female rats, only a diminution of norepinephrine content and an increase of dopamine and serotonin content were observed after endosulfan administration at the dose of 6.12mg/kg/day, whereas the concentration and the metabolism of these biogenic amines were not with the dose of 0.61mg/kg/day. Gender differences emerge in the striatal aminergic system susceptibility to endosulfan exposure during the early life stages, being the neurotoxic effects of this organochlorine insecticide higher in male than in female rats.

Modulatory effects of melatonin on cadmium-induced changes in biogenic amines in rat hypothalamus.

This study was undertaken to examine whether cadmium oral exposure modifies biogenic amine concentration at hypothalamic level in adult male rats, and to investigate the possible modulatory effects of melatonin against cadmium-induced changes on these neurotransmitters. For this purpose, rats were exposed to cadmium (25 mg/l of CdCl(2) in the drinking water) with or without melatonin (30 µg/rat/day intraperitoneally) for 30 days. Norepinephrine (NE), dopamine (DA), serotonin (5-HT), 3,4-dihydroxyphenyl acetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) were quantified by high performance liquid chromatography (HPLC). Oral cadmium administration led to decrease of NE, DA, and 5-HT content and DA turnover within the three hypothalamic regions examined, and therefore an inhibition of 5-HT turnover at posterior hypothalamus. Sensitivity to melatonin was specific to the hypothalamic region evaluated. Thus, the anterior hypothalamus was not nearly sensitive to exogenously administered melatonin, whereas the neurohormone decreased the content of these amines in the mediobasal hypothalamus, and melatonin increased it in the posterior hypothalamic region. Melatonin effectively prevented some cadmium-induced alterations on hypothalamic amine concentration. This is the case of DA in the anterior and posterior hypothalamus, and 5-HT metabolism in the posterior hypothalamic region. In conclusion, the obtained results indicate that melatonin treatment may be effective modulating some neurotoxic effects induced by cadmium exposure, and, more to the point, a possible role of this indolamine as a preventive agent for environmental or occupational cadmium contamination.

Cadmium chronotoxicity at pituitary level: effects on plasma ACTH, GH, and TSH daily pattern.

Cadmium is an endocrine disruptor that has been shown to induce chronotoxic effects. The present study was designed to evaluate the possible cadmium effects on the daily secretory pattern of adrenocorticotropin hormone (ACTH), growth hormone (GH), and thyroid-stimulating hormone (TSH) in adult male Sprague-Dawley rats. For this purpose, animals were treated with cadmium at two different doses [25 and 50 mg/l cadmium chloride (CdCl(2))] in the drinking water for 30 days. Control age-matched rats received cadmium-free water. After the treatment, rats were killed at six different time intervals throughout a 24-h cycle. Cadmium exposure modified the 24-h pattern of plasma ACTH and GH levels, as the peak of ACTH content between 12:00 and 16:00 h in controls appeared at 12:00 h in the group treated with the lowest dose used, while it appeared between 16:00 and 20:00 h in rats exposed to 50 mg/l CdCl(2). In addition, the peak of GH content found at 04:00 h in controls moved to 16:00 h in rats exposed to 25 mg/l CdCl(2), and the highest dose used abolished 24-h changes of GH secretion. The metal treatment did not modify ACTH secretory pattern. Exposure to cadmium also increased ACTH and TSH medium levels around the clock with both doses used. These results suggest that cadmium modifies ACTH and TSH medium levels around the clock, as well as disrupted ACTH and GH secretory pattern, thus confirming the metal chronotoxicity at pituitary level.

Daily pattern of pituitary glutamine, glutamate, and aspartate content disrupted by cadmium exposure.

Cadmium is a neurotoxic heavy metal and is considered endocrine disruptor. In this work, we investigate the effects of cadmium on the 24 h changes of aspartate, glutamate, and glutamine content in the pituitary. Adult male Sprague-Dawley rats were treated with 25 or 50 mg/l of cadmium chloride (CdCl(2)) in the drinking water for 30 days. Metal exposure with the lowest dose induced the disappearance of the nocturnal peak of anterior pituitary amino acid content, and the appearance of a peak of glutamine concentration during the resting phase of the photoperiod. After exposure to 50 mg/l of CdCl(2), the peaks of anterior pituitary amino acid content at 12:00 and 00:00 h disappeared, and two minimal values at these same hours and a peak at 08:00 h appeared. In the posterior pituitary, cadmium treatment with the lowest dose induced the appearance of a peak of aspartate and glutamate concentration at 12:00 h, and the disappearance of the peak of glutamine content at 16:00 h. After exposure to 50 mg/l of CdCl(2) aspartate and glutamate daily pattern presented two maximal values between 00:00 and 04:00 h, and the metal abolished glutamine daily pattern. These results suggest that cadmium disrupted aspartate, glutamate, and glutamine daily pattern in the pituitary.

Relationship between blood concentrations of heavy metals and cytogenetic and endocrine parameters among subjects involved in cleaning coastal areas affected by the 'Prestige' tanker oil spill.

The sinking of the 'Prestige' oil tanker in front of the Galician coast (NW of Spain) in November 2002 offered a unique opportunity to analyze intermediate cytogenetic and endocrine effects among people exposed to the complex mixture of substances that oil constitutes, including several toxic heavy metals. In this work we evaluated the relationship between exposure to heavy metals (blood concentrations of aluminium, cadmium, nickel, lead and zinc) and genotoxic parameters (sister chromatid exchanges, micronucleus test and comet assay) or endocrine parameters (plasmatic concentrations of prolactin and cortisol) in subjects exposed to 'Prestige' oil during cleaning tasks developed after the spillage. Concentrations of lead were significantly related to the comet assay even after adjusting by age, sex and smoking. Cortisol concentrations were significantly influenced by aluminium, nickel (both, inversely) and cadmium (positively). Women had clearly higher concentrations of prolactin and cortisol, even when adjusting by age, smoking, cadmium, aluminium or nickel. Plasmatic cortisol was jointly influenced by gender, smoking and aluminium or nickel (all p<0.05). In women there was a strong relationship between concentrations of cadmium and prolactin (beta=0.37, p=0.031). When the effects of cadmium, aluminium and nickel on cortisol were simultaneously assessed, only the latter two metals remained statistically significant. Among parameters analysed, cortisol appeared to be the most sensitive to the effects of metal exposure. Plasma levels of cortisol deserve further evaluation as a potentially relevant biomarker to assess the effects of exposure to heavy metals.

Effects of in utero and lactational exposure to endosulfan in prefrontal cortex of male rats.

The possible neurotoxic effects of the organochlorine pesticide endosulfan have been evaluated on male offspring rats exposed in utero and during lactation. Dams were treated with 0.61mg or 6.12mg endosulfan/(kgday) from the gestation beginning until the weaning. Male offspring rats were sacrificed at post-natal days (PND) 15, 30 and 60, and possible alterations in the content and metabolism of biogenic amines and amino acids were determined in prefrontal cortex using high-performance liquid chromatography (HPLC). Globally, endosulfan induced an increase in amino acid content in prefrontal cortex at PND 15 and PND 30. However, the levels of GABA at PND 15 and those of glutamine at PND 30 were not modified. At PND 60, a significant reduction in the content of GABA and taurine was observed, while the concentration of glutamate, aspartate and glutamine remained constant. Endosulfan did not modify norepinephrine and dopamine content, but serotonin concentration was increased at PND 30 and PND 60 and serotoninergic and dopaminergic metabolism was also modified. These results suggest that pre- and post-natal exposure to endosulfan affects biogenic amines and amino acids in prefrontal cortex, and those variations could be related to several alterations in the functions in which the prefrontal cortex is involved.

Biomonitoring of human exposure to prestige oil: effects on DNA and endocrine parameters.

Since 1960, about 400 tankers spilled more than 377765 tons of oil, with the Prestige accident (Galician coast, NW Spain, November 2002) the most recent. Taking into account the consistent large number of individuals exposed to oil that exists all over the world, it seems surprising the absence in the literature of studies focused on the chronic effects of this exposure on human health. In this work we evaluated the level of DNA damage by means of comet assay, and the potential endocrine alterations (prolactin and cortisol) caused by Prestige oil exposure in a population of 180 individuals, classified in 3 groups according to the tasks performed, and 60 controls. Heavy metals in blood were determined as exposure biomarkers, obtaining significant increases of aluminum, nickel and lead in the exposed groups as compared to controls. Higher levels of genetic damage and endocrine alterations were also observed in the exposed population. DNA damage levels were influenced by age, sex, and the use of protective clothes, and prolactin concentrations by the last two factors. Surprisingly, the use of mask did not seem to protect individuals from genetic or endocrine alterations. Moreover, polymorphisms in genes encoding for the main enzymes involved in the metabolism of oil components were analyzed as susceptibility biomarkers. CYP1A1-3'UTR and EPHX1 codons 113 and 139 variant alleles were related to higher damage levels, while lower DNA damage was observed in GSTM1 and GSTT1 null individuals.

Initial study on the effects of Prestige oil on human health.

The big oil tanker Prestige wrecked at 130 miles from the coast of Galicia, on the Northwest of Spain, in November 19, 2002. During the accident over 40,000 tons of oil were spilled, and along the next weeks 22,000 more reached the shore in the way of three black tides. A great number of people participated in the cleaning tasks. The objective of this study was to initially evaluate the damage caused by Prestige oil in exposed individuals both from the cytogenetic and the endocrine points of view. Exposure level was determined by analysing volatile organic compounds in the environment and heavy metals in blood. Cytogenetic damage was determined by sister chromatid exchanges (SCE), and plasmatic prolactin and cortisol levels were used as biomarkers of endocrine toxicity. Finally we have determined the possible influence of GST genetic polymorphisms (GSTM1 and GSTT1 deletion polymorphisms, GSTP1 Ala105Val) on the evaluated effects. The exposed population was classified according to the performed cleaning tasks in three groups: volunteers that collaborated for 1 week (N=25), hired manual workers (N=20) and hired high-pressure cleaner workers (N=23). The control population consisted of 42 individuals. Exposure to Prestige oil caused cytogenetic damage in exposed individuals, being its effect influenced by age, sex, tobacco consumption and GSTM1 polymorphism. With regard to endocrine toxicity, our results showed that xenobiotics present in Prestige oil induced alterations in hormonal status, and thus it may be considered as an endocrine disruptor. Therefore, the selected parameters have shown to be good indicators of toxicity related to exposure to Prestige oil. In addition, data obtained point to the importance of using protective devices in preventing the effects related to the exposure.

In vivo protective effect of melatonin on cadmium-induced changes in redox balance and gene expression in rat hypothalamus and anterior pituitary.

Cadmium (Cd) is widely used in industrial applications and is an important side contaminant of agricultural products. As an endocrine disruptor, Cd modifies pituitary hormone release. It has been shown that this metal causes oxidative stress in primary cultures of anterior pituitary cells. To examine whether Cd induces redox damage in the hypothalamic-pituitary axis in vivo and to evaluate the efficacy of the antioxidant molecule melatonin to prevent Cd activity, rats were exposed to Cd (5 p.p.m. in drinking water) with or without melatonin (3 microg/mL drinking water) for 1 month. In the anterior pituitary, Cd increased lipid peroxidation and mRNA levels for heme oxygenase-1 (HO-1) at both time intervals tested (09:00 and 01:00 hr, beginning of rest span and middle of activity span, respectively). Melatonin administration prevented the Cd-induced increase in both parameters. In the hypothalamus, Cd affected the levels of mRNA for HO-1 by decreasing it in the evening. Melatonin reduced hypothalamic HO-1 gene expression. Cd treatment augmented gene expression of nitric oxide synthase (NOS)1 and NOS2 in the pituitary whereas melatonin decreased it, impairing the activity of Cd. Exposure to Cd increased the levels of hypothalamic NOS1 mRNA at 09:00 hr and decreased the levels of NOS2 mRNA at 01:00 hr, with melatonin treatment preventing Cd effects. Cd treatment decreased plasma thyroid-stimulating hormone levels at both examined times, while melatonin reversed the effect of Cd at 09:00 hr and partially counteracted the effect at 01:00 hr. There were important variations between day and night in the expression of all the genes tested in both tissues. Melatonin treatment was effective reducing all examined effects of Cd, documenting its effectiveness to protect the rat hypothalamic-pituitary axis from the toxic metal effects.

Toxic effects of methoxychlor on the episodic prolactin secretory pattern: possible mediated effects of nitric oxide production.

BACKGROUND: This work addresses the issue of whether methoxychlor (MTX) exposure may modify the ultradian secretion of prolactin through changes in the synthesis of nitric oxide (NO) induced by Nomega-nitro-L-arginine methyl ester (L-NAME) in the hypothalamic-pituitary axis. Associated changes in dopamine (DA) content in the anterior (AH), mediobasal (MBH) and posterior hypothalamus (PH) and median eminence (ME) were evaluated. METHODS: Two groups of animals (MTX and MTX+L-NAME treated) received subcutaneous (sc) injections of MTX at a dose of 25 mg/kg/day for one month. The other two groups of animals (control and L-NAME treated) received sc vehicle injections (0.5 mL/day of sesame oil), during the same period of time to be used as controls. Forty hours before the day of the experiment, animals were anaesthetized with intrapritoneal injections of 2.5% tribromoethanol in saline and atrial cannulas were implanted through the external jugular vein. Plasma was continuously extracted in Hamilton syringes coupled to a peristaltic bomb in tubes containing phosphate-gelatine buffer (to increase viscosity). The plasma was obtained by decantation and kept every 7 minutes for the measurement of plasma prolactin levels through a specific radioimmnunoassay and DA concentration by high-pressure liquid chromatography (HPLC). RESULTS: Prolactin release in animals from all experimental groups analyzed was episodic. Mean plasma prolactin levels during the bleeding period, and the absolute pulse amplitude were increased after MTX or Nomega-nitro-L-arginine methyl ester (L-NAME) administration. However MTX and L-NAME did not modify any other parameter studied with the exception of relative pulse amplitude in MTX treated rats. L-NAME administration to rats treated with the pesticide reduced mean plasma prolactin levels and the absolute amplitude of prolactin peaks. Peak duration, frequency and relative amplitude of prolactin peaks were not changed in the group of rats treated with MTX plus L-NAME as compared to either control or MTX treated rats. Whereas MTX decreased DA content in the ME and increased it in the AH, its content did not change in the MBH or PH, as compared to the values found in controls. Also, L-NAME administration decreased DA content in the ME as compared to controls. However, L- NAME administration to MTX exposed rats, markedly increased DA content in the ME as compared to either MTX treated or control rats. L-NAME administration increased DA content in the AH as compared to the values found in non-treated rats. However L-NAME administration to MTX exposed rats did not modify DA content as compared to either MTX treated or control rats. L-NAME administration did not modify DA content at the MBH nor in saline treated nor in MTX treated rats. However, the values of DA in the MBH in MTX plus L-NAME treated animals were statistically decreased as compared to L-NAME treated rats. In the PH, L-NAME administration increased DA content as compared to the values found in non-treated animals. L-NAME administration to MTX exposed rats also increased DA content as compared to either MTX treated or control rats. CONCLUSION: The results suggest the existence of an interaction between MTX and L-NAME in the modulation of the ultradian prolactin secretion at the pituitary levels. The possibility of an indirect effect mediated by changes in DA content at the ME requires further examination.

Differential effects of cadmium on blood lymphocyte subsets.

This work was designed to analyze the possible dose dependent effects of cadmium on the blood lymphocyte subset distribution and if these effects are related to circulating cadmium concentration. For that purpose, adult male rats were exposed for one month to 0, 5, 10, 25, 50 or 100 ppm of cadmium chloride (CdCl2) in the drinking water. B lymphocytes decreased in peripheral blood with the doses of 5 and 10 ppm of CdCl2. From the dose of 25 ppm on, B cells increased. T lymphocytes were increased with the doses of 25, 50 and 100 ppm of CdCl2. The lower doses of the metal induced opposite effects. CD4+ and CD8+ cells decreased with the doses of 5 and 10 ppm whereas they were increased with the dose of 25 ppm of CdCl2 on. From the dose of 10 ppm on, cadmium concentration was increased. The results on the distribution of blood lymphocyte subsets suggest that cadmium inhibits the humoral and cellular immune response with the lower doses of the metal used, and opposite effects were detected with the higher doses, the effect not being dependent on the circulating cadmium.

Effect of nitric oxide on prolactin secretion and hypothalamic biogenic amine contents.

Involvement of nitric oxide (NO) in the episodic secretion of prolactin was studied in conscious freely moving adult rats. Prolactin secretion was pulsatile in all animals of either group during the bleeding period (from 10:30 h to 13:30 h). Administration of N(omega)-nitro-L-arginine methyl ester (L-NAME), a NO synthase inhibitor, increased mean plasma levels of prolactin, and the absolute amplitude of prolactin peaks during the whole bleeding period as compared to values found in the control group. L-NAME increased norepinephrine (170%), dopamine (58.27%) and serotonin contents (30%) in the anterior hypothalamus. In the median eminence, dopamine and serotonin contents decreased (19.79% and 33.9% respectively) after L-NAME as compared to the values found in controls. In addition, norepinephrine content increased in mediobasal hypothalamus (79.6%) of rats treated with L-NAME. The results indicate that changes in NO production may modify the episodic secretion of prolactin. These effects were associated with changes in hypothalamic and median eminence biogenic amines.

Methoxychlor modifies the ultradian secretory pattern of prolactin and affects its TRH response.

BACKGROUND: Methoxychlor (MTX) is an insecticide characterized by both estrogenic and antiandrogenic properties that may modify the secretory pattern of prolactin. The objective of the present work was to analyze MTX's effects on changes in the episodic secretion of prolactin induced by thyrotropin-releasing hormone (TRH). MATERIAL/METHODS: Adult male Sprague-Dawley rats (400-420 g body weight) were administered 25 or 50 mg/kg/day of MTX s.c. in sesame oil for 30 days. Control animals received the vehicle only. RESULTS: In animals treated with 50 mg/kg/day of MTX, mean serum prolactin levels and absolute pulse amplitude increased (p< or = 0.05 and p< or = 0.001 respectively). TRH administration (two pulses of 2 Kg) increased both mean serum prolactin levels and the absolute amplitude of the prolactin peaks in all groups studied (p< or = 0.001). The response to TRH was greatly increased in the animals treated with 50 mg/kg/day. TRH reduced the mean life of the hormone in control rats (p< or = 0.01) and in animals treated with 50 mg/kg/day (p< or = 0.001). After TRH administration, the duration of prolactin peaks was increased in the MTX-treated animals (p< or = 0.05 and p< or = 0.001 for 25 and 50 mg/kg/day respectively). TRH reduced the frequency of prolactin pulses in the animals treated with 50 mg/kg/day (p< or = 0.05). CONCLUSIONS: These data suggest that MTX sensitizes the pituitary to TRH, indicating a direct effect of MTX on the pituitary gland.

Are cadmium effects on plasma gonadotropins, prolactin, ACTH, GH and TSH levels, dose-dependent?

It is well established that cadmium affects plasma levels of the pituitary hormones studied. However, whether the effects of the metal are dose dependent needs to be clarify. This work was designed to evaluate the possible changes in plasma levels of gonadotropins, prolactin, ACTH, GH and TSH after oral cadmium exposure in adult male rats. Plasma levels of these hormones were measured in adult male rats exposed to cadmium chloride (CdCl2) in the drinking water at the doses of 5, 10, 25, 50 or 100 ppm for one month. The lower dose of cadmium increased plasma prolactin levels and higher doses of the metal (25 or 50 ppm) decreased them. There was a continuous increase of plasma ACTH levels from the lower to 25 ppm dose of CdCl2 and decreased them after to basal values with the highest dose. Plasma GH levels were increased with the dose of cadmium of 10 ppm, although the doses of 5, 25 and 50 ppm decreased them. Plasma LH levels were only reduced with the dose of 50 ppm of CdCl2, whereas those of FSH increased. Plasma TSH levels were increased with the doses of 5, 25 and 100 ppm of CdCl2. Cadmium concentration increased in pituitary with the doses of 125, 50 and 100 ppm of CdCl2. These data suggest that cadmium differentially affects the secretory mechanisms of the pituitary hormones studied depending on the dose used. The effects of the metal on prolactin and ACTH are dose-dependent.

Oral cadmium exposure throughout puberty does not inhibit secretion of prolactin, GH and ACTH through dopamine metabolism changes in male rat.

This work analyzed possible dopamine-mediated cadmium effects on plasma prolactin, GH and ACTH levels and if these changes were related to metal accumulation. Male rats were treated from day 30 to 60 of life with 50 mg/L of CdCl2 in the drinking water. Cadmium exposure decreased the dopamine (DA) metabolism (DOPAC/DA ratio) in all brain areas studied, and plasma levels of prolactin, GH and ACTH were diminished. The cadmium concentration did not increase nor in hypothalamus nor in the pituitary after the metal exposure. These results suggest that cadmium inhibits the secretion of these pituitary hormones and this inhibitory effect is not mediated by dopamine or the degree of metal accumulation.