T. Cabaleiro

Endosulfan effects on pituitary hormone and both nitrosative and oxidative stress in pubertal male rats.

The present study was undertaken to investigate in pubertal male rats possible effects of endosulfan administered throughout lactation and gestation on: (a) pituitary gene expression of prolactin, luteinizing hormone (LH), growth hormone (GH) and thyroid stimulating hormone (TSH); (b) circulating levels of these hormones; and (c) expression of nitric oxide synthase 1 and 2 (NOS1 and NOS2), and heme oxygenase-1 (HO-1) at pituitary level. Endosulfan was administered orally at the doses of 0.61 mg/kg/day or 6.12 mg/kg/day, and possible toxic effects were studied in pubertal male pups (at postnatal day 30). Gene expression was evaluated by RT-PCR and plasma hormone levels by RIA. Exposure to both administered doses down-regulated LH, GH and TSH. Treatment with 0.61 mg endosulfan/kg/day decreased prolactin expression, although its plasmatic concentration was decreased by both administered doses. LH secretion was stimulated by both doses, whereas the highest dose increased GH levels and decreased plasma TSH concentration. Endosulfan up-regulated NOS1 and NOS2. We can conclude that in pubertal male rat, prenatal and lactational exposure to endosulfan modifies expression and release of prolactin, LH, GH and TSH, and pituitary NOS1 and NOS2 mRNA levels, suggesting that nitrosative stress can be implicated in the endocrine toxicity of endosulfan at pituitary level.

Cadmium effects on 24 h changes in glutamate, aspartate, glutamine, GABA and taurine content of rat striatum

This work evaluates the possible changes in 24 h variations of striatal aspartate, glutamate, glutamine, gamma-aminobutyric acid (GABA) and taurine content after oral cadmium treatment. Male rats were submitted to cadmium exposure at two doses (25 and 50 mg/L of cadmium chloride (CdCl(2))) in the drinking water for 30 days. Control rats received cadmium-free water. After the treatment, rats were killed at six different time intervals throughout a 24 h cycle. Differential effects of cadmium on 24 h amino acid fluctuations were observed. Metal exposure modified the daily pattern of the amino acids concentration found in control animals, except for GABA and taurine with the lowest dose used. Exposure to 25 mg/L of CdCl(2) decreased mean content of aspartate, as well as GABA concentration. These results suggest that cadmium exposure affects 24 h changes of the studied amino acids concentration in the striatum, and those changes may be related to alterations in striatal function.

Toxic effects of cadmium on GABA and taurine content in different brain areas of adult male rats

This work assesses the possible changes in gamma amino butyric acid (GABA) and taurine content in the hypothalamus, the median eminence and striatum after the exposure to various doses of cadmium. Cadmium chloride (CdCl2) was administered in the drinking water at the doses of 5, 10, 25, 50 or 100 ppm to adult male rats for 1 month. In the anterior hypothalamus, taurine and GABA content decreased with the dose of 10 ppm of CdCl2 only. Cadmium exposure decreased both GABA and taurine content in mediobasal hypothalamus except for the 50 ppm dose. In posterior hypothalamus GABA and taurine content was not affected by cadmium treatment. As far as the median eminence, 5 or 10 ppm of CdCl2 increased taurine concentration, and at a dose of 5 ppm enhanced GABA content. A significant decrease of GABA and taurine concentration was seen in the striatum at any dose of cadmium used. The concentration of cadmium increased in the hypothalamus and in the striatum in animals receiving CdCl2 in the drinking water at doses of 25, 50 or 100 ppm. The results indicate that cadmium globally decreased GABA and taurine content in the brain areas studied through effects that were not dose dependent.ResumenEn este trabajo se evalúan las posibles alteraciones en el contenido de ácido gamma amino butírico (GABA) y taurina, inducidas por varias dosis de cadmio en el hipotálamo, la eminencia media y el estriado. Para ello, se administró cloruro de cadmio (CdCl2) durante 30 días a ratas macho adultas en el agua de bebida a las dosis de 5, 10, 25, 50 ó 100 ppm. En el hipotálamo anterior, la exposición al cadmio no modificó el contenido de taurina y GABA, aunque la concentración de estos aminoácidos descendió con las dosis de 10 ppm. Tanto el contenido de GABA como el de taurina disminuyeron significativamente en el hipotálamo mediobasal tras la exposición al cadmio, excepto con la dosis de 50 ppm. Sin embargo, en el hipotálamo posterior, la exposición a este metal no alteró los niveles de GABA y taurina. En la eminencia media, las dosis de 5 y 10 ppm aumentaron la concentración de taurina, mientras que el contenido de GABA sólo aumentó con la dosis de 5 ppm. Tras la exposición al cadmio, se observó un descenso en el contenido de GABA y taurina en el estriado con todas las dosis utilizadas. La concentración de cadmio aumentó en el hipotálamo y en el estriado con las dosis de 25, 50 y 100 ppm de CdCl2. Globalmente, según estos resultados, la exposición al cadmio puede conllevar un descenso de GABA y taurina en las regiones cerebrales estudiadas, aunque dichos descenso no parece ser dependiente de las dosis del metal.

Toxic effects of methoxychlor administered subcutaneously on the hypothalamic-pituitary-testicular axis in adult rats.

This study was undertaken to evaluate the effects of methoxychlor MTX at the hypothalamic-pituitary-testicular axis in adult male rats. This global objective comprises three major aims: (1) to analyze the possible differential MTX effects in norepinephrine and serotonin concentration an in serotoninergic metabolism in anterior, mediobasal and posterior hypothalamus and median eminence; (2) to evaluate effects induced by MTX exposure on gonadotropins and testosterone; 93 to elucidate whether the regulatory interactions in the hypothalamic-pituitary-testicular axis are modified by this pesticide. Animals were administered subcutaneously 25mg/kg/day of MTX for 1 month. MTX increased norepinephrine and serotonin content in anterior hypothalamus (P < or = 0.05), but decreased serotonin concentration in posterior hypothalamus (P < or = 0.05). MTX diminished serotonin turnover in anterior hypothalamus (P < or = 0.01) and decreased plasma LH (P < or = 0.001) and testosterone (P < or = 0.05) levels but those of FSH remained unmodified. We can conclude that MTX exposure: (1) could exert differential effects in norepinephrine and serotonin concentration an in serotoninergic metabolism in anterior, mediobasal and posterior hypothalamus and median eminence, being the anterior hypothalamus the most sensitive region to the pesticide; (2) could inhibit LH and testosterone secretion without changing FSH; (3) four potential pathways might be involved in MTX effects on testosterone secretion (changing LH secretion; modifying serotonin and norepinephrine at the hypothalamic level; alterating the direct neural pathway between brain and testes; and/or by a direct effect in testes).

Cadmium chloride exposure modifies amino acid daily pattern in the mediobasal hypothalamus in adult male rat.

The present study was conducted to investigate the possible effects of cadmium exposure on the daily pattern of aspartate, glutamate, glutamine, gamma‐aminobutyric acid (GABA) and taurine levels in the mediobasal hypothalamus of adult male rats. For this purpose, animals were treated with cadmium at two different exposure doses (25 and 50 mg l−1 of cadmium chloride, CdCl2) in the drinking water for 30 days. Control age‐matched rats received CdCl2‐free water. After the treatment, rats were killed at six different time intervals throughout a 24 h cycle. CdCl2 exposure modified the amino acid daily pattern, as it decreased aspartate, glutamate, GABA and taurine levels at 12:00 h with both exposure doses employed. In addition, the treatment with 25 mg l−1 of CdCl2 induced the appearance of minimal values at 16:00 h and maximal values between 04:00 and 08:00 h for glutamate, and a peak of glutamine content at 20:00 h. The heavy metal also decreased GABA medium levels around the clock in the mediobasal hypothalamus. However, CdCl2 did not alter the metabolic correlation between glutamate, aspartate, glutamine and GABA observed in control animals. These results suggest that CdCl2 induced several alterations in aspartate, glutamate, glutamine, GABA and taurine daily pattern in the mediobasal hypothalamus and those changes may be related to alterations in hypothalamic function. Copyright

Toxic effects of methoxychlor in rat striatum: modifications in several neurotransmitters

Neurotoxic effects of methoxychlor (MTX) are poorly understood at present. This study was undertaken to evaluate the possible effects of MTX in norepinephrine, dopamine and amino acid contents and serotonin turnover in rat striatum. For this purpose, adult male Sprague-Dawley rats were administered 25 mg/kg/day of MTX in sesame oil or vehicle only for 30 days. The neurotransmitters of interest were measured in the striatum by HPLC. MTX decreased norepinephrine and 5-hydroxyindole acetic acid (5-HIAA) content and serotonin turnover (measured as 5-HIAA/serotonin ratio), and increased glutamate and GABA concentrations. However, the content of serotonin, aspartate, glutamine and taurine was not modified by MTX exposure. These data suggest that MTX exposure inhibits norepinephrine synthesis and serotonin metabolism. The inhibitory effect on norepinephrine could be explained, at least in part, by the increase of both GABA and glutamate contents. Further studies are needed to understand the effects of MTX on serotonin. Also a disruptive effect of MTX on the metabolisms of glutamate, aspartate, glutamine and GABA emerges.ResumenLos efectos neurotóxicos del metoxicloro (MTX) no son bien conocidos. Este trabajo se Ilevó a cabo para evaluar los posibles efectos de este pesticida en el contenido de norepinefrina, dopamina y aminoácidos, así como en el metabolismo serotoninérgico en cuerpo estriado. Para ello, a ratas macho adultas de la cepa Sprague-Dawley se les administró 25 mg/kg/día de MTX durante 30 días. A los animales del grupo control se administró aceite de sésamo, ya que éste era el vehículo en el que se administró el MTX en los animales tratados. La concentración estriatal de los neurotransmisores estudiados se determinó mediante HPLC. El MTX disminuyó el contenido de norepinefrina y de ácido 5-hidroxiidolacético (5-HIAA) y la tasa metabólica de serotonina (medida como la ratio 5-HIAA/serotonina), y aumentó las concentraciones de glutamato y GABA. Sin embargo, el contenido de serotonina, aspartato, glutamina y taurina no se modificó tras la exposición a MTX. Estos datos sugieren que la exposición a MTX inhibe la síntesis de norepinefrina y el metabolismo de serotonina. El efecto inhibitorio sobre la norepinefrina podría ser explicado, al menos en parte, por el incremento tanto del contenido de GABA como de glutamato. No obstante, se necesitan más estudios para entender los efectos del MTX sobre la serotonina. También se observa un efecto disruptor del MTX sobre el metabolismo del glutamato, aspartato, glutamina y GABA.

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 Nω-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 Nω-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.