Oestradiol Microimplants in the Ventromedial Preoptic Area Inhibit Secretion of Luteinizing Hormone via Dopamine Neurones in Anoestrous Ewes

Anderson, Greg M.; Connors, John M.; Hardy, Steven L.; Valent, Miroslav; Goodman, Robert L.

doi:10.1046/j.1365-2826.2001.00726.x

Cited by 47 publications

(47 citation statements)

References 56 publications

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“…E 2 -containing microimplants placed in the MPOA also suppressed pulsatile GnRH/LH secretion during anestrus, and sulpiride (a dopamine antagonist) disrupted this suppression [22]. It was reported that the ERα-expressing neurons predominate in this region [37, 40].…”

Section: Discussionmentioning

confidence: 99%

“…Expression of ERβ has been found in GnRH neurons, however, until now, only in rodents [16, 17]. Considerable evidence indicates that the positive or negative effects of E 2 on the GnRH neuronal system in sheep are mediated by interneurons and/or the glial matrix [18, 19, 20, 21, 22]. E 2 has also been shown to be a most potent drug stimulating prolactin (PRL) release.…”

Section: Introductionmentioning

confidence: 99%

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Genistein, a Phytoestrogen, Effectively Modulates Luteinizing Hormone and Prolactin Secretion in Ovariectomized Ewes during Seasonal Anestrus

Romanowicz

Misztal²,

Barcikowski³

2004

Neuroendocrinology

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Through binding with estrogen receptors, phytoestrogens, plant-derived estrogen-like compounds, affect numerous reproductive functions. It is not known whether these compounds are capable of evoking effective changes in luteinizing hormone (LH) and prolactin (PRL) secretion in ewes by acting directly within the central nervous system (CNS). The hypothesis studied was that genistein, infused for several hours into the third ventricle, could immediately affect LH and PRL secretion in ovariectomized (OVX) ewes during seasonal anestrus. Two doses of genistein, 1 µg/100 µl/h (total 4 µg, n = 7) and 10 µg/100 µl/h (total 40 µg, n = 7), were infused intracerebroventricularly from 12.00 to 16.00 h and blood samples were collected from 8.00 to 20.00 h at 10-min intervals. Randomly selected ewes were infused with a vehicle (control, n = 5). The mean plasma LH concentration in control ewes was significantly (p < 0.01) higher during infusion of the vehicle than before the infusion. It remained on an insignificantly changed level after the infusion. The frequency of LH pulses in control ewes did not differ significantly before, during, or after vehicle infusion. In ewes infused with a lower dose of genistein, plasma LH concentrations decreased significantly (p < 0.001) after the infusion, as compared with the values noted before and during genistein infusion. Only a tendency towards a decrease in LH pulse frequency occurred after infusion of a lower dose of genistein. In ewes infused with a higher dose of genistein, the plasma LH concentration decreased significantly (p < 0.01) after phytoestrogen administration as compared with the values noted before and during infusion. The frequency of LH pulses was also significantly (p < 0.01) lower after genistein administration. Because the changes in PRL secretion were more dynamic in response to genistein infusion, the statistical analysis included 2-hour periods. The mean plasma PRL concentration in control animals was significantly enhanced (p < 0.01) only during the first 2-hour period of sampling. After that it decreased and remained on an unchanged level up to the end of sampling. Similar changes in PRL secretion were observed in both experimental groups before genistein infusion. In contrast, significant (p < 0.01 to p < 0.001) increases in PRL concentration were noted regularly during and shortly after the genistein infusion in either low-dose or high-dose genistein-infused ewes, compared with the concentrations noted before genistein treatment. Plasma PRL concentrations during and after genistein infusion in both experimental groups were also significantly higher than the control (p < 0.01 to p < 0.001). The presented data demonstrate that genistein, a phytoestrogen, may effectively modulate LH and PRL secretion in OVX ewes by acting within the CNS.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Genistein, a Phytoestrogen, Effectively Modulates Luteinizing Hormone and Prolactin Secretion in Ovariectomized Ewes during Seasonal Anestrus

Romanowicz

Misztal²,

Barcikowski³

2004

Neuroendocrinology

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“…We stereotaxically implanted an 18-gauge stainless steel guide tube (n ϭ 10, experiment 2) into the third ventricle using sterile techniques and gas anesthesia (4 parts oxygen: 1 part nitrous oxide, supplemented with halothane at 1-4%) as previously described (27). Briefly, a 2-cm diameter hole was drilled in the skull, the sagittal sinus ligated, and radioopaque dye injected into one lateral ventricle.…”

Section: Experiments 2: the Effects Of Ofq Or An Agonist For The Orl-1mentioning

confidence: 99%

“…Concentrations of LH were determined in duplicate 100-or 200-l aliquots by RIA, using a modification of a previously described method (27). Values are expressed in terms of the ovine standard, NIH S24.…”

Section: Riasmentioning

confidence: 99%

Orphanin FQ: Evidence for a Role in the Control of the Reproductive Neuroendocrine System

et al. 2007

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Orphanin FQ (OFQ), also known as nociceptin, is a member of the endogenous opioid peptide family that has been functionally implicated in the control of pain, anxiety, circadian rhythms, and neuroendocrine function. In the reproductive system, endogenous opioid peptides are involved in the steroid feedback control of GnRH pulses and the induction of the GnRH surge. The distribution of OFQ in the preoptic area and hypothalamus overlaps with GnRH, and in vitro evidence suggests that OFQ can inhibit GnRH secretion from hypothalamic fragments. Using the sheep as a model, we examined the potential anatomical colocalization between OFQ and GnRH using dual-label immunocytochemistry. Confocal microscopy revealed that approximately 93% of GnRH neurons, evenly distributed across brain regions, were also immunoreactive for OFQ. In addition, almost all GnRH fibers and terminals in the external zone of the median eminence, the site of neurosecretory release of GnRH, also colocalized OFQ. This high degree of colocalization suggested that OFQ might be functionally important in controlling reproductive endocrine events. O RPHANIN FQ (OFQ), also known as nociceptin, is a member of the family of endogenous opioid peptides, which also includes ␤-endorphin, enkephalins, and dynorphin (1). Whereas sharing some homology with dynorphin, OFQ does not exhibit appreciable binding affinity for classical opioid receptors (1, 2); rather it functions as an endogenous ligand for the opioid receptor like (ORL)-1 receptor (1). OFQ cells are present in the preoptic area, anterior hypothalamus, and arcuate nucleus of the hypothalamus of the rat (3) and human (4). Functionally, OFQ has been implicated in a variety of systems including pain (5), anxiety (6), cardiovascular function (7), food intake (8), circadian rhythms (9), and cognition (10). There is also evidence that OFQ may play a role in neuroendocrine function: intracerebroventricular delivery of OFQ in the rat stimulates GH and prolactin (11, 12) and has been reported to both stimulate (13) and inhibit (14) corticosterone secretion. Sinchak et al. (15) have shown that OFQ delivered into the ventromedial nucleus facilitates lordosis in female rats in a dose-dependent manner. However, there has been relatively little attention to the possible role of OFQ in reproductive neuroendocrine function, specifically in the control of GnRH secretion.GnRH neurons, and their projections to the median eminence, control the secretion of pituitary LH and thus comprise the final common pathway for the neuroendocrine control of reproduction (16). Endogenous opioid peptides are important regulators of the GnRH system, controlling both the preovulatory surge (17) and pulsatile secretion (18) of GnRH. OFQ has been shown to inhibit forskolin-induced GnRH secretion in a dose-dependent manner from rat hypothalamic fragments (19). OFQ cells in the preoptic area and anterior hypothalamus overlap the site of a majority of GnRH perikarya (20 -22). In addition, OFQ fibers and ORL-1 receptors are present in high abund...

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“…This suggests that DA receptors may be involved in the VIP modulation of GnRH secretion in the septo-preoptic area and may influence interactions involved in mediating the photoperiodic response in birds. In mammals, it has been suggested that the dopaminergic system interacts with photoperiodic regulation of LH secretion [69, 70]. …”

Section: Discussionmentioning

confidence: 99%

Expression of D<sub>1</sub> and D<sub>2</sub> Dopamine Receptors in the Hypothalamus and Pituitary during the Turkey Reproductive Cycle: Colocalization with Vasoactive Intestinal Peptide

et al. 2003

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The regulation of avian prolactin (PRL) secretion and PRL gene expression is influenced by hypothalamic vasoactive intestinal peptide (VIP), the PRL-releasing factor in avian species. Recent evidence indicates that D₁ and D₂ dopamine (DA) receptors play a pivotal role in VIP and PRL secretion. The differential expression of DA receptors located on hypothalamic VIP neurons and anterior pituitary cells may affect the degree of prolactinemia observed during the turkey reproductive cycle. The relative expression of D_1D and D₂ DA receptor subtype mRNA was quantitated using in situ hybridization histochemistry (ISH). D_1D and D₂ DA receptor mRNA was found expressed throughout the hypothalamus and pituitary. The expression of D_1D DA receptor mRNA in the hypothalamus was found to be 6.8-fold greater than that of D₂ DA receptor mRNA. Higher D_1D DA receptor mRNA content was found in the anterior hypothalamus (3.6-fold), the ventromedial nucleus (2.0-fold), the infundibular nuclear complex (INF; 1.9-fold), and the medial preoptic nucleus (1.5-fold) of laying hens as compared to that of reproductively quiescent non-photostimulated hens. The levels seen in incubating hyperprolactinemic hens were essentially the same as in laying hens, except for the INF where levels were 52% higher. During the photorefractory stage (hypoprolactinemia), the D_1D DA receptor mRNA was at its lowest level in all areas tested. No differences were observed in hypothalamic D₂ DA receptor mRNA abundance throughout the reproductive cycle, except for an increase in D₂ DA receptor mRNA within the INF of photorefractory hens. Also, a marked reduction in D₂ DA receptor mRNA was observed in the pituitary of incubating hens. Pituitary D_1D DA receptor levels did not change when birds entered the incubating phase. Double ISH revealed that D_1D and D₂ DA receptor mRNAs were co-expressed within neurons expressing VIP mRNA, predominantly within the lateral hypothalamus and INF. D_1D DA receptor mRNA was more highly expressed than D₂ DA receptor mRNA. The present findings clearly demonstrate that the expression of stimulatory D₁ DA receptor mRNA in the hypothalamus increases in hyperprolactinemic incubating hens, whereas inhibitory D₂ DA receptor mRNA increases in the pituitary of hypoprolactinemic photorefractory hens.

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Oestradiol Microimplants in the Ventromedial Preoptic Area Inhibit Secretion of Luteinizing Hormone via Dopamine Neurones in Anoestrous Ewes

Cited by 47 publications

References 56 publications

Genistein, a Phytoestrogen, Effectively Modulates Luteinizing Hormone and Prolactin Secretion in Ovariectomized Ewes during Seasonal Anestrus

Genistein, a Phytoestrogen, Effectively Modulates Luteinizing Hormone and Prolactin Secretion in Ovariectomized Ewes during Seasonal Anestrus

Orphanin FQ: Evidence for a Role in the Control of the Reproductive Neuroendocrine System

Expression of D<sub>1</sub> and D<sub>2</sub> Dopamine Receptors in the Hypothalamus and Pituitary during the Turkey Reproductive Cycle: Colocalization with Vasoactive Intestinal Peptide

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