Neurotransmitters Involved in Mediating the Steroid-Dependent Suppression of Pulsatile Luteinizing Hormone Secretion in Anestrous Ewes: Effects of Receptor Antagonists*

Meyer, S.; Goodman, Robert L.

doi:10.1210/endo-116-5-2054

Cited by 114 publications

(80 citation statements)

References 32 publications

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“…For example, i.v. injection of pimozide, a D2-like antagonist, stimulated LH secretion in intact and OVX+E ewes during the anestrus season (Meyer & Goodman 1985, 1986. In the ram, s.c. injection of sulpiride during long days stimulated LH secretion, whereas s.c. injection of bromocriptine, a D2-like agonist, reduced LH secretion During the period 0-5 h, only vehicle (Ringer's lactate) was infused.…”

Section: Discussionmentioning

confidence: 99%

“…The action of dopamine can be mediated by two major types of dopaminergic receptors, D1-like and D2-like (Kebabian & Calne 1979). Although the implication of D2-like receptors in the control of LH secretion has been shown in several physiological conditions in sheep (Meyer & Goodman 1985, Curlewis et al 1991, Havern et al 1991, Anderson et al 1997, the nature of the receptors involved in the ME is not known. Indeed, effects on LH secretion of D2-like receptor analogs delivered in the ME were observed, but dose-dependent comparisons of the effects of specific analogs of each type of receptor have not been performed in this site.…”

Section: Introductionmentioning

confidence: 99%

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Implication of D2-like dopaminergic receptors in the median eminence during the establishment of long-day inhibition of LH secretion in the ewe

Bertrand

Thiéry²,

Picard³

et al. 1999

Journal of Endocrinology

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In ewes, photoperiod modulates LH release and dopaminergic terminals in the median eminence (ME) have a critical role in the establishment of long-day inhibition of LH secretion. This study was undertaken to determine the type of dopaminergic receptors, D1-like or D2-like, that mediate the action of dopamine on LH secretion at the ME level in this situation. This was assessed, in ovariectomized and estradiol-treated ewes, with the use of reverse microdialysis in the ME in three experiments: first, when LH secretion was stimulated by short days, by determining the response to three doses (0·01, 0·1 or 1 mg/ml) of a D1-like (SKF38393) and a D2-like (quinpirole) agonist; secondly, during early long-day inhibition of LH secretion, by determining the ability of SKF38393 and quinpirole (1 mg/ml) to mimic the inhibitory effects of dopamine, after a blockade of its synthesis with -methyl-paratyrosine ( MPT; 2 mg/ml); and thirdly, during early long-day inhibition of LH secretion, by determining the response to three doses (0·009, 0·09 or 0·9 mg/ml) of a D1-like (SCH23390) and a D2-like (sulpiride) antagonist.In none of the conditions was effect of the D1-like analogs on LH secretion found, compared with the control treatments. In contrast, the D2-like analogs caused changes in LH secretion. First, with short days, quinpirole in the highest dose significantly reduced mean LH concentration (P<0·05) and LH pulse frequency (P<0·01). Secondly, with long days, addition of quinpirole to MPT caused a significant decrease in LH secretion relative to MPT alone (P<0·05). Thirdly, with long days, sulpiride at the highest dose significantly increased mean LH concentration (during the first 3 h of treatment, P<0·05) and LH pulse frequency (P<0·05). Prolactin secretion was also determined in these experiments, and D2-like agonist and antagonist caused an inhibition and a stimulation of prolactin secretion, respectively. These results demonstrate that, in the ME, inhibitory action of dopamine on LH secretion, critical for the initiation of long-dayinduced inhibition, is mediated by D2-like, not D1-like, dopaminergic receptors.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Implication of D2-like dopaminergic receptors in the median eminence during the establishment of long-day inhibition of LH secretion in the ewe

Bertrand

Thiéry²,

Picard³

et al. 1999

Journal of Endocrinology

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“…Recent studies suggest that inhibitions of LH secretion are mediated through monoaminergic pathways (8,9), while it was shown in our laboratory that the mechanisms could involve the A15 dopaminergic nucleus of the retrochiasmatic area (10). The failure to demonstrate annual changes in receptor sensitivity to amines (8,9) led these investigators to postulate the existence of seasonal modifications in the activity of the aminergic systems.…”

mentioning

confidence: 89%

“…The failure to demonstrate annual changes in receptor sensitivity to amines (8,9) led these investigators to postulate the existence of seasonal modifications in the activity of the aminergic systems.…”

mentioning

confidence: 99%

Monoamine Content of the Stalk‐Median Eminence and Hypothalamus in Adult Female Sheep as Affected by Daylength

Thiéry

1991

J Neuroendocrinology

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In the ewe, plasma luteinizing hormone and prolactin concentrations exhibit seasonal variations. During long days, inhibition of pulsatile luteinizing hormone secretion is mediated by monoamines. In a model of ovariectomized ewes bearing a subcutaneous oestradiol implant, we previously showed that the steroid-dependent inhibition of luteinizing hormone involves the A15 dopaminergic nucleus of the retrochiasmatic area. In the present work, we compared the aminergic activities of tele-diencephalic structures in groups of ovariectomized ewes under artificial illumination for short versus long days (8 versus 16 h/day of light, respectively). Half the animals in each group were bearing a subcutaneous oestradiol implant. Using high-performance liquid chromatography and electrochemical detection, we measured the levels of amines and amine metabolites in 'punches' of tissues from regions containing luteinizing hormone-releasing hormone axon terminals or cell bodies and catecholaminergic structures. Concurrently, we checked the pulsatile luteinizing hormone release and plasma prolactin concentration to assess the ability of our model to mimic seasonal changes in the hormonal status.As expected, ovariectomized ewes with a subcutaneous oestradiol implant showed an inhibition of the pulsatile luteinizing hormone release under long days. A higher concentration of plasma prolactin was also observed under long days, without any effect of the steroid treatment. Under this light regimen, statistically significant higher contents of dopamine than under short days were found in the stalk-median eminence. Larger contents of homovanillic acid, a dopamine metabolite, and 4-hydroxy-3-methoxyphenylethyleneglycol (MHPG), a noradrenaline metabolite were observed in the infundibular nucleus, while the catecholamines themselves remained unchanged. Furthermore, oestradiol also significantly increased the content of MHPG in the latter structure. During long days, animals without oestradiol treatment exhibited a significant lower content of noradrenaline in the A15 nucleus, without any alteration of the dopamine content. Daylength or oestradiol treatment had no significant effects on the levels of amines or amine metabolites in the preoptic or septa1 areas. Thus, our results in the ewe underline the role played by the medial basal hypothalamus in the catecholaminergic regulation of seasonal changes in hormone release and suggest modifications in the turnover of the neurotransmitters in some structures.In the ewe, which is a short day breeder, annual variations in the secretion of luteinizing hormone (LH) and prolactin (PRL) accompany seasonal changes in reproductive activity (1 -3). The seasonal effect on LH (4, 5 ) and PRL secretion (6) has also been demonstrated in the ovariectomized ewe. During the period corresponding to anoestrus in the intact animals, the frequency of LH pulses in the ovariectomized females was slightly lower than during the breeding season, (steroid-independent inhibition), but the effect was fully expressed wh...

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“…The [49]. Similarly, pimozide caused a temporary increase in LH secretion in long-day exposed (photo-inhibited) OVX + E ewes [33].…”

Section: Sites Of Action Of Melatoninmentioning

confidence: 94%

Melatonin and the seasonal control of reproduction

Malpaux

Thiéry²,

Chemineau³

1999

Reprod. Nutr. Dev.

115

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-Many mammalian species from temperate latitudes exhibit seasonal variations in breeding activity which are controlled by the annual photoperiodic cycle. Photoperiodic information is conveyed through several neural relays from the retina to the pineal gland where the light signal is translated into a daily cycle of melatonin secretion: high at night, low in the day. The length of the nocturnal secretion of melatonin reflects the duration of the night and it regulates the pulsatile secretion of gonadotropin-releasing hormone (GnRH)

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Neurotransmitters Involved in Mediating the Steroid-Dependent Suppression of Pulsatile Luteinizing Hormone Secretion in Anestrous Ewes: Effects of Receptor Antagonists*

Cited by 114 publications

References 32 publications

Implication of D2-like dopaminergic receptors in the median eminence during the establishment of long-day inhibition of LH secretion in the ewe

Implication of D2-like dopaminergic receptors in the median eminence during the establishment of long-day inhibition of LH secretion in the ewe

Monoamine Content of the Stalk‐Median Eminence and Hypothalamus in Adult Female Sheep as Affected by Daylength

Melatonin and the seasonal control of reproduction

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