ToxSci Advance Access originally published online on April 7, 2008
Toxicological Sciences 2008 104(1):107-112; doi:10.1093/toxsci/kfn074
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Published by Oxford University Press 2008.
Suppression of the Steroid-Primed Luteinizing Hormone Surge in the Female Rat by Sodium Dimethyldithiocarbamate: Relationship to Hypothalamic Catecholamines and GnRH Neuronal Activation
Endocrinology Branch, Reproductive Toxicology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711
1 To whom correspondence should be addressed. Fax: (919) 541-5138. E-mail: goldman.jerome{at}epa.gov.
Received February 8, 2008; accepted March 27, 2008
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
In female rodents, hypothalamic norepinephrine (NE) has a role in stimulating the secretion of gonadotropin-releasing hormone (GnRH) that triggers the ovulatory surge of luteinizing hormone (LH). NE synthesis from dopamine (DA) is catalyzed by dopamine-β-hydroxylase (DβH) which contains a copper cofactor. Sodium dimethyldithiocarbamate (DMDC) is a pesticide with metal chelating properties that has been found to reduce DβH activity. The resultant decrease in NE causes a suppression of both the LH surge and ovulation. The present study examined the dose-related impact of DMDC on hypothalamic GnRH neuronal activation indicated by the nuclear presence of the early gene product c-fos. It represents an essential link between effects on NE and suppression of the surge. Ovariectomized (OVX), estradiol-, and progesterone-primed Sprague-Dawley rats were given a single ip injection of 0, 3.6, 7.1, 14.2, or 28.4 mg/kg DMDC in separate groups of females to assess tissue GnRH/c-fos immunostaining, hypothalamic catecholamines, and serial blood samplings for LH. A dose-related decline in hypothalamic NE and increase in DA at 2 h after DMDC administration were consistent with a decrease in c-fos–positive GnRH neurons, with an almost complete absence of c-fos at the two highest doses. The effects correlated well with a suppression of the surge, although the percentage decrease in c-fos neurons at 7.1 mg/kg only attenuated the surge peak, not the overall amount of circulating LH. The present data offer further evidence that the impact of DMDC on the LH surge is central in origin and in doing so defines the toxic pathway for this effect on ovulation.
Key Words: sodium dimethyldithiocarbamate; gonadotropin-releasing hormone; luteinizing hormone; norepinephrine; c-fos.
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Sodium dimethyldithiocarbamate (DMDC) is a metabolite of the pesticide thiram that itself has been employed in a variety of pesticidal applications as insecticide, fungicide, miticide, and microbicide. A dithiocarbamate, it is able to function as a metal chelator and has also found use in metal finishing operations and wastewater treatments to enhance the precipitation of metals (Andrus, 2000
; Matlock et al., 2002). This metal chelating property has been found to underlie many of the adverse physiological effects of DMDC, given that a large number of enzymes rely on metal cofactors for their activity.
In the rodent, noradrenergic neuronal input to the hypothalamus is an important component of those mechanisms involved in the secretion of gonadotropin-releasing hormone (GnRH) (e.g., Drouva et al., 1982; Helena et al., 2002; Kalra and Kalra, 1983; Kalra and McCann, 1974). In turn, GnRH triggers the ovulatory surge of luteinizing hormone (LH) from the pituitary into the general circulation, an event in the female rat that is initiated on the day of proestrus, typically a few hours before the onset of the dark portion of the photoperiod. The neurotransmitter norepinephrine (NE) released from these noradrenergic neurons is converted from dopamine (DA) by the enzyme dopamine-β-hydroxylase (DβH), which requires a copper cofactor for its activity. There is now a body of evidence demonstrating that DMDC and related dithiocarbamates are able to suppress DβH activity, thereby decreasing NE synthesis and elevating its DA precursor (e.g., Lippman and Lloyd, 1969; Maj and Vertulani, 1969; Przewlocka et al., 1975). In the rat, this effect is consistent with an abolition of the LH surge and the absence of normal ovulation (Goldman et al., 1994, 1997). The present study focuses on the impact of increasing doses of DMDC on the activation of hypothalamic GnRH neurons as indicated by the presence in nuclei of the early gene product c-fos (Lee et al., 1990; Rubin et al., 1994; Tsukahara, 2006). It is hypothesized that a significant diminution in the percentage of c-fos–positive GnRH neurons in response to this toxicant will show a comparable decrease in the magnitude of the LH surge, thereby providing an essential link between the effects on hypothalamic NE and the suppression of the surge.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Animals.
After arrival, 60-day-old female Sprague-Dawley rats (Charles River Laboratories, Raleigh, NC) were housed one per cage under controlled temperature (22 ± 2°C), humidity (40–50%), and lighting conditions (1410 h light:dark photoperiod, lights on 0500 h), with ad libitum access to food and water. All animal care, handling, and treatment procedures conformed to National Institutes of Health standards for laboratory animal research and were approved by the Institutional Animal Care and Use Committee at the National Health and Environmental Effects Research Laboratory.
Treatment.
After a 1-week acclimation period, vaginal smears were taken on a daily basis for two additional weeks. Those females exhibiting normal 4- or 5-day estrous cycles were weighed and assigned to treatment groups, such that group mean body weights were comparable. Animals were bilaterally OVX under ketamine:xylazine (70:10 mg/kg) anesthesia. At that time, they were implanted with a 6-mm silastic capsule containing estradiol benzoate (Sigma Chemical, St Louis, MO 4 mg/ml in sesame oil) that at 3 days had previously been determined to result in serum concentrations of approximately 50 pg/ml (Goldman et al., 2007). At 1145 h–1200 h on the third day after surgery, females were given sc injections of progesterone (2.5 mg/0.2 ml sesame oil) designed to elicit a full surge of LH. One hour after progesterone administration, the animals were injected ip with DMDC (Aldrich Chemical, Milwaukee, WI, 98% purity) at 0, 3.6, 7.1, 14.2, or 28.4 mg/kg body weight, dosages based upon prior work with the compound (Goldman et al., 2007). The chemical was dissolved in 0.9% sterile saline just prior to dosing and administered in a volume of 0.1 ml/100 g body weight. Control females received saline only. Small 220 µl aliquots of blood were then gently expressed from a nick in a lateral tail vein into small serum separation tubes (Becton Dickinson, Rutherford, NJ) at 1400, 1600, and 1800 h. Animals were then killed at 2000 h and trunk blood taken. Sera from all time points were analyzed for LH in order to determine a dose-related effect on the surge peak and area under the curve (AUC).
Groups of comparably treated animals were killed by decapitation at 1500 h, just prior to the appearance of a rise in LH. The brains were carefully removed and frozen for assessment of hypothalamic catecholamines. While still partially frozen, anterior and posterior hypothalamic areas, along with caudate nuclei, were dissected out, using the following landmarks. A rostral cut was made at the anterior margin of the optic chiasm, while one was placed caudally at the anterior border of the mammillary bodies. Parallel rostrocaudal cuts were then positioned, one on each side, at the hypothalamic sulci. Finally, a horizontal cut was placed at the ventral margin of the anterior commissure. The hypothalamus was further divided into anterior (AH) and posterior (PH) regions by a coronal knife cut at the caudal margin of the optic chiasm. In addition, bilateral portions of caudate tissue were taken from the region anterodorsal to the midline appearance of the anterior commissure and extending to just below the corpus callosum. Catecholamine and tissue protein concentrations were determined as described below.
A third cohort of animals was OVX, steroid primed, and dosed with DMDC, as above, to assess the immunohistochemical presence of nuclear c-fos in identified GnRH neurons. Between 1445 h and 1515 h, females were anesthetized as before with ketamine:xylazine and were perfused intracardially with phosphate-buffered saline followed by 4% paraformaldehyde (Sigma Chemical). Brains were carefully removed and placed in paraformaldehyde (4°C) for an additional 4 h. The brains were then trimmed and transferred to a 25% sucrose solution for at least 18 h (4°C) until submerged. They were then encased in Tissue-Tek OCT compound (Sakura Finetek, Torrance, CA) and kept frozen (– 25°C) until sectioning. Every third 30-µm frozen coronal section was saved from the region just anterior to the organum vasculosum of the lamina terminalis to immediately posterior to the midline appearance of the anterior commissure, encompassing the region containing the great majority of GnRH cell bodies (Gross, 1976; King and Anthony, 1984; Ramirez et al., 1975; Wheaton et al., 1975). Sections were placed in cryoprotectant (Watson et al., 1986) separately within a 24-well microplate and stored covered at – 25°C until staining.
Catecholamine determinations.
Catecholamine concentrations were quantified by high-performance liquid chromatography (HPLC) and electrochemical detection. Weighed hypothalamic and caudate fragments were sonicated over ice as 1:11 dilutions in cold HPLC mobile phase and a 10 µl aliquot removed for tissue protein determination (Smith et al., 1985), using materials obtained from Pierce Chemical (Rockford, IL). The mobile phase consisted of 115mM dibasic sodium phosphate (Fisher Chemical, Fairlawn, NJ), 0.19mM EDTA (Mallinckrodt, Paris, KY), 3mM 1-heptanesulfonic acid, sodium salt (Eastman Kodak, Rochester, NY), and 8% acetonitrile (Burdick & Jackson, Muskegon, MI) in HPLC grade water previously filtered and deionized through a Hydro PicoPure purification system (Durham, NC). Samples were then centrifuged (10 min., 13,000 rpm, 4°C) and each supernatant drawn off and filtered (Gelman Acrodisc LC13, 0.2 µM, Ann Arbor, MI) before being further diluted 1:2.5 in previously filtered mobile phase for HPLC injection. The HPLC system consisted of a Waters Model 515 isocratic pump (Milford, MA), Waters Model 717-Plus refrigerated autosampler, Waters µBondapak C18 (3.9 x 300 mm) reversed phase column, and an ESA Coulochem II 5200A electrochemical detector (Bedford, MA) with ESA model 5014 analytical and model 5021 conditioning cells. A flow rate of 1.5 ml/min was employed for all separations. NE standards for calibration were obtained from Sigma Chemical, and dihydroxybenzylamine was included as an internal standard, with the recovery averaging 95%.
Immunohistochemistry.
Free-floating sections were transferred to mesh bottom wells and subjected to a double-staining procedure for c-fos and GnRH. Unless otherwise stated, all steps were carried out at 4°C, and each series of washes encompassed six 10-min rinses with 0.05M tris-buffered saline (TBS). Sections were initially washed of cryoprotectant before placement in a 3% hydrogen peroxide solution (45 min). Another series of washes was followed by a blocking solution of 10% normal goat serum and further TBS washing. The sections were then placed in c-fos antibody (Ab-5, EMD Biosciences, 1:80K) and incubated at 4°C for 48 h. They were subsequently washed with TBS and incubated with anti-rabbit IgG (2 h, room temperature) and then with avidin-biotin complex solution (90 min, room temperature, ABC Elite kit, Vector Laboratories, Burlingame, CA). After a TBS wash series, the c-fos antibody–peroxidase complex was stained with a solution of 3,3-diaminobenzidine HCl (DAB), H2O2, and NiSO4 (Vector Laboratories, 11–14 min) to visualize a black nuclear reaction product. Tissues were then washed (6x) with TBS and incubated at 4°C for 48 h in a 1:40K dilution of GnRH antibody (LR-2, kindly provided by Dr R. Benoit, McGill University). The subsequent procedure followed the same steps used for c-fos, except that DAB visualization of GnRH was performed for 3–4 min without the addition of NiSO4, yielding a brown reaction product. The staining specificity for c-fos and GnRH was determined in separate sections by elimination of antibodies for each. The sections were then positioned on slides and allowed to dry before being taken through graded alcohols and xylene. They were subsequently coverslipped under Permount mounting medium (Fisher Chemicals).
Hormonal assay.
LH was determined by radioimmunoassay with materials obtained from the National Hormone and Peptide Program through Dr A. F. Parlow, Harbor-University of California-Los Angeles Medical Center, Torrance, CA. Chloramine-T 125I tracer iodination was performed in-house, and LH assays were conducted according to recommendations provided by the supplier, with the sensitivity optimized by a 24-h coincubation of sample and first antibody prior to the addition of tracer. The assay sensitivity averaged 0.084 ng/ml, with respective intra- and interassay coefficients of variation being 5.8 and 7.0%.
Statistical analyses.
Surge concentrations of serum LH in response to DMDC were analyzed for statistical significance by repeated measures ANOVA under the general linear models procedure of the Statistical Analysis System package. Since the time of appearance of a surge peak can vary among animals, the four sampled values for each animal were collectively shifted so that analyses could be performed on the peaks (or highest LH concentration), along with groups designated as – 6, – 4, – 2, + 2, + 4, and + 6 h from the peak. Chi-square analysis was used to evaluate effects of the treatment on the time of appearance of the LH peak. AUC for these animals was computed using MedCalc software (Mariakerke, Belgium) and the data analyzed by the Kruskal-Wallis nonparametric ANOVA, followed by Dunn's multiple comparison test. The percentages of identified GnRH neurons with nuclei stained for c-fos were determined without knowledge of the treatment group. Arcsine transformations were then conducted on these percentage data before being analyzed by ANOVA. Catecholamine data were also evaluated for statistical significance by ANOVA. For comparisons against control groups, Dunnett's post hoc procedure was performed on all parametric analyses.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Table 1 shows that a single administration of DMDC was able to decrease hypothalamic NE in a dose-related manner within both anterior and posterior fragments. Posterior hypothalamic DA concentrations were concurrently elevated, an effect consistent with a suppression in DβH activity. In contrast, caudate DA was unaffected as the region is without DβH activity and is virtually absent of detectable NE.
|
The influence of DMDC on the steroid-induced LH surge is presented as a comparison of both the peak amplitude of the surge (Fig. 1) and AUC over the four sampling times (Fig. 2). The two lower doses of 3.6 and 7.1 mg/kg had no statistically significant effects on the AUC. However, there was a significant attenuation in the peak concentration at 7.1 mg/kg. The rise in LH at 14.2 and 28.4 mg/kg was completely abolished, and this was reflected in the dramatically reduced AUC. For the 0, 3.6, and 7.1 groups that did exhibit a surge, Figure 3A presents a comparison of individual data points for the peak concentrations, along with the preceding and subsequent 2-h collections. The results indicated that LH concentrations at the pre- or postpeak sampling times for these two lowest DMDC doses were elevated, indicating a general broadening of the time over which the rise in LH was present. Moreover, while all females in both the 0- and 3.6-mg/kg treatments had LH peaks at 1600 h (Fig. 3B), results from the 7.1 group showed that four of seven animals had a significant shift in peaks to the 1800 h sampling time.
|
|
|
Assessments of the effect of DMDC on the percentage of GnRH neurons that were positive for c-fos showed that no effects were present at 3.6 mg/kg, although a modest but significant decline was apparent in response to the 7.1-mg/kg treatment (Fig. 4). Compared to the controls, sections from both the 14.2- and 28.4-mg/kg groups exhibited a dramatic decrease in the presence of GnRH nuclear c-fos (Fig. 5), with very few if any positively stained nuclei, an effect comparable to the full blockade of the surge at these dosages.
|
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Previous data had established that various dithiocarbamates, as a consequence of their effect on catecholamine metabolism, are able to suppress the LH surge and ovulation (Goldman et al., 1994
, 1997; Kalra and McCann, 1974; Stoker et al., 1993). However, the actual impact of these compounds on GnRH neuronal activity had been inferred from the relationships among catecholamine alterations, circulating LH, and the impact on retrieved oviductal oocytes. For this class of compounds, the present study represents the first dose-related assessment of the extent of proestrous GnRH neuronal activation as it relates to both the impact on hypothalamic catecholamines and the dynamics of the LH surge.
It had been well established that the dithiocarbamates are able to suppress the activity of DβH by virtue of their ability to form a chelate complex with the Cu2+ cofactors required for activity of the enzyme (e.g., Brodde et al., 1977; Caroldi and de Paris, 1995; de Paris and Caroldi, 1995). Present effects, showing a depletion of hypothalamic NE and a rise in DA within a 2-h period, along with the lack of an effect within the DA-rich, but DβH-absent, caudate nucleus, were consistent with such a mechanism. In addition to these changes seen in rodents, a comparable alteration in DA metabolism has also been reported in humans exposed to elevated dithiocarbamate levels (Kaskevich, 1985).
At 14.2 and 28.4 mg/kg DMDC, the marked declines in hypothalamic NE paralleled quite nicely the near absence of GnRH c-fos and the complete suppression of the LH surge. In contrast, 3.6 mg/kg showed no significant alterations in any of the measures. It is at the mid-range dose of 7.1 mg/kg that some end points begin to inflect. While NE in both anterior and posterior hypothalamic regions showed small but statistically nonsignificant shifts downward, the peak of the LH surge was significantly lower. This decrease in the peak was not matched by a correspondingly diminished AUC, indicating that at this dose there was a broadening of the surge window, which became evident when data from individual animals were plotted from the period extending 2 h prior to 2 h after the LH peak. Moreover, the 7.1-mg/kg treatment showed that in 57% of animals, a significant delay occurred in the time of appearance of the peak. It would then appear that a dosage of DMDC, one that only showed a statistically nonsignificant decrease in hypothalamic NE, was still capable of producing a significant decline in c-fos–positive GnRH neurons, which in turn affected the observed modification in the LH surge. It is possible that this temporal shift in the surge peak in response to 7.1 mg/kg was linked to a corresponding delay in the augmentation of GnRH activity, so that the number of c-fos–positive neurons would have continued to rise past the 1500 h perfusion. The appearance of such shifts in LH may correspond to a delay in oocyte release, something that our lab had previously observed following toxicant exposure (Goldman et al., 1993). Consequently, an evaluation of oocyte numbers at a designated time on the morning of estrus in response to prior chemical insult may not necessarily reflect an impairment of the ovulatory process but merely a delay in ovulation.
Relationships among estradiol, noradrenergic input to the hypothalamus, and the generation of the LH surge have been known for some time. Along with previous studies showing the impact on the LH surge from a chemical depletion of NE (Hancke and Wuttke, 1979; Kalra and McCann, 1974; Simpkins et al., 1979) or surgical ablation of noradrenergic input from locus coeruleus to the rat hypothalamus (Franci and Antunes-Rodrigues, 1985; Helena et al., 2002), there is additional evidence of a close relationship between a generated pattern of NE pulses and a concordant responsiveness of GnRH secretion (Pau et al., 1998, 2000). Moreover, the expression of message in locus coeruleus for the NE precursor tyrosine hydroxylase is increased following estradiol treatment (Curran-Rauhut and Petersen, 2003; Serova et al., 2002). A similar effect in locus coeruleus, following an iv infusion of estradiol, was seen in OVX rhesus macaques, along with an augmentation in hypothalamic NE secretion (Pau et al., 2000). Thus, in the present study using steroid-primed OVX females, the correspondence among hypothalamic catecholamine concentrations, the impact of DMDC on GnRH neuronal c-fos and a suppression of the LH surge, strongly implicate a depletion in NE as the causal factor.
In summary, this study incorporated hypothalamic catecholamine concentrations, assessments of GnRH neuronal activation, and the succeeding impact on the LH surge. In doing so, it represents the first demonstration of parallel dose relationships among these three measures following a single exposure to an environmental toxicant known to target the synthesis of a neurotransmitter critical to normal regulatory activity within the female reproductive system. Coupled with the previously reported blockade of ovulation by DMDC, the present data define the toxic pathway through which this compound impairs normal reproductive function.
|
NOTES |
|---|
Disclaimer: The research described in this article has been reviewed by the National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.
|
ACKNOWLEDGMENTS |
|---|
The authors wish to thank Faye Poythress, Svetlana Kilmon, and Al Moore (New Year Tech) for their excellent contributions in furnishing animal husbandry support and in providing daily vaginal lavages. Svetlana also assisted in translating the Cyrillic text for one of the citations. We appreciate Brian Grey's assistance with imaging, and Janet Ferrell and Emily Gibson (all US EPA) also gave their time assisting in collection of blood samples for LH analysis.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Andrus ME. A review of metal precipitation chemicals for metal-finishing applications. Met. Finish. (2000) 98:20–23.
Brodde OE, Nagel M, Schumann HJ. Mechanism of inhibition of dopamine beta-hydroxylase evoked by FLA-63. An in vitro study. Arch. Int. Pharmacodyn. Ther. (1977) 228:184–190.[Web of Science][Medline]
Caroldi S, de Paris P. Comparative effects of two dithiocarbamates, disulfiram and thiram, on adrenal catecholamine content and on plasma dopamine-beta-hydroxylase activity. Arch. Toxicol. (1995) 69:690–693.[CrossRef][Web of Science][Medline]
Curran-Rauhut MA, Petersen SL. Oestradiol-dependent and -independent modulation of tyrosine hydroxylase mRNA levels in subpopulations of A1 and A2 neurones with oestrogen receptor (ER) alpha and ER beta gene expression. J. Neuroendocrinol. (2003) 15:296–303.[CrossRef][Web of Science][Medline]
de Paris P, Caroldi S. In vitro effect of dithiocarbamate pesticides and of CaNa2EDTA on human serum dopamine-beta-hydroxylase. Biomed. Environ. Sci. (1995) 8:114–121.[Medline]
Drouva SV, Laplante E, Kordon C. Alpha1-adrenergic receptor involvement in the LH surge in ovariectomized estrogen-primed rats. Eur. J. Pharmacol. (1982) 81:341–344.[CrossRef][Web of Science][Medline]
Franci JA, Antunes-Rodrigues J. Effect of locus ceruleus lesion on luteinizing hormone secretion under different experimental conditions. Neuroendocrinology (1985) 41:44–51.[Web of Science][Medline]
Goldman JM, Murr AS, Buckalew AR, Ferrell JM, Cooper RL. Moderating influence of the drinking water disinfection by-product dibromoacetic acid on a dithiocarbamate-induced suppression of the luteinizing hormone surge in female rats. Reprod. Toxicol. (2007) 23:541–549.[CrossRef][Web of Science][Medline]
Goldman JM, Parrish MB, Cooper RL, McElroy WK. Blockade of ovulation in the rat by systemic and ovarian intrabursal administration of the fungicide sodium dimethyldithiocarbamate. Reprod. Toxicol. (1997) 11:185–190.[CrossRef][Web of Science][Medline]
Goldman JM, Stoker TE, Cooper RL, McElroy WK, Hein JF. Blockade of ovulation in the rat by the fungicide sodium N-methyldithiocarbamate: Relationship between effects on the luteinizing hormone surge and alterations in hypothalamic catecholamines. Neurotoxicol. Teratol. (1994) 16:257–268.[CrossRef][Web of Science][Medline]
Goldman JM, Stoker TE, Perreault SD, Cooper RL, Crider MA. Influence of the formamidine pesticide chlordimeform on ovulation in the female hamster: Dissociable shifts in the luteinizing hormone surge and oocyte release. Toxicol. Appl. Pharmacol. (1993) 121:279–290.[CrossRef][Web of Science][Medline]
Gross DS. Distribution of gonadotropin-releasing hormone in the mouse brain as revealed by immunohistochemistry. Endocrinology (1976) 98:1408–1417.
Hancke JL, Wuttke W. Effects of chemical lesion of the ventral noradrenergic bundle or the medial preoptic area on preovulatory LH release in rats. Exp. Brain Res. (1979) 35:127–134.[Web of Science][Medline]
Helena CVV, Franci CR, Anselmo-Franci JA. Luteinizing hormone and luteinizing hormone-releasing hormone secretion is under locus coeruleus control in female rats. Brain Res. (2002) 955:245–252.[CrossRef][Web of Science][Medline]
Kalra SP, Kalra PS. Neural regulation of luteinizing hormone secretion in the rat. Endocr. Rev. (1983) 4:311–351.
Kalra SP, McCann SM. Effects of drugs modifying catecholamine synthesis on plasma LH and ovulation in the rat. Neuroendocrinology (1974) 15:79–91.[Web of Science][Medline]
Kaskevich LM. Catecholamine metabolism in persons exposed to dithiocarbamates. Gig. Tr. Prof. Zabol. (1985) 12:50–51.[Medline]
King JC, Anthony ELP. LHRH neurons and their projections in humans and other mammals: Species comparisons. Peptides (1984) 5(Suppl. 1):195–207.[Medline]
Lee W-S, Smith MS, Hoffman GE. Luteinizing hormone-releasing hormone neurons express fos protein during the proestrous surge of luteinizing hormone. Proc. Natl. Acad. Sci. U.S.A. (1990) 87:5163–5167.
Lippman W, Lloyd K. Dopamine-β-hydroxylase inhibition by dimethyldithiocarbamate and related compounds. Biochem. Pharmacol. (1969) 18:2507–2516.[CrossRef][Web of Science][Medline]
Maj J, Vertulani J. Effect of some N,N-disubstituted dithiocarbamates on catecholamines level in rat brain. Biochem. Pharmacol. (1969) 18:2045–2047.[CrossRef][Web of Science][Medline]
Matlock MM, Henke KR, Atwood DA. Effectiveness of commercial reagents for heavy metal removal from water with new insights for future chelate designs. J. Haz. Mat. (2002) B92:129–142.[CrossRef][Web of Science][Medline]
Pau KY, Hess DL, Kohama S, Bao J, Pau CY, Spies HG. Oestrogen upregulates noradrenaline release in the mediobasal hypothalamus and tyrosine hydroxylase gene expression in brainstem of ovariectomized rhesus macaques. J. Neuroendocrinol. (2000) 12:899–909.[CrossRef][Web of Science][Medline]
Pau KY, Lee CJ, Cowles A, Yang SP, Hess DL, Spies HG. Possible involvement of norepinephrine transporter activity in the pulsatility of hypothalamic gonadotropin-releasing hormone release: Influence of the gonad. J. Neuroendocrinol. (1998) 10:21–29.[CrossRef][Web of Science][Medline]
Przewlocka B, Sarnek J, Szmigielski A, Niewiadomska A. The effect of some dithiocarbamic acids on dopamine-β-hydroxylase and catecholamines level in rat's brain. Pol. J. Pharmacol. Pharm. (1975) 27:555–559.[Web of Science][Medline]
Ramirez VD, Gautron JP, Epelbaum J, Pattou E, Zamora A, Kordon C. Distribution of LH-RH in subcellular fractions of the basomedial hypothalamus. Mol. Cell. Endocrinol. (1975) 3:339–350.[CrossRef][Web of Science][Medline]
Rubin BS, Lee CE, King JC. A reduced proportion of luteinizing hormone (LH)-releasing hormone neurons express Fos protein during the preovulatory or steroid-induced LH surge in middle-aged rats. Biol. Reprod. (1994) 51:1264–1272.[Abstract]
Serova L, Rivkin M, Nakashima A, Sabban EL. Estradiol stimulates gene expression of norepinephrine biosynthetic enzymes in rat locus coeruleus. Neuroendocrinlogy (2002) 75:193–200.[CrossRef]
Smith PK, Krohn RI, Hermanson GT, Mallia AK, Gartner FH, Provenzano MD, Fugimoto EK, Goeke NM, Olson BJ, Klenk DC. Measurement of protein using bicinchoninic acid. Anal. Biochem. (1985) 150:76–85.[CrossRef][Web of Science][Medline]
Simpkins JW, Advis JP, Hodson CA, Meites J. Blockade of steroid-induced luteinizing hormone release by selective depletion of anterior hypothalamic norepinephrine activity. Endocrinology (1979) 104:506–509.
Stoker TE, Goldman JM, Cooper RL. The dithiocarbamate fungicide thiram disrupts the hormonal control of ovulation in the female rat. Reprod. Toxicol. (1993) 7:211–218.[CrossRef][Web of Science][Medline]
Tsukahara S. Increased fos immunoreactivity in suprachiasmatic nucleus before luteinizing hormone surge in estrogen-treated ovariectomized female rats. Neuroendocrinology (2006) 83:303–312.[CrossRef][Medline]
Watson RE, Wiegand SJ, Clough RW, Hoffman GE. Use of cryoprotectant to maintain long-term peptide immunoreactivity and tissue morphology. Peptides (1986) 7:155–159.[Web of Science][Medline]
Wheaton JE, Krulich L, McCann SM. Localization of luteinizing hormone-releasing hormone in the preoptic area and hypothalamus of the rat using radioimmunoassay. Endocrinology (1975) 97:30–38.
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||