Biochemical Indices of Catecholaminergic Neuronal Activity in the Median Eminence during the Estrous Cycle of the Rat

Demarest, Keith T.; Johnston, Craig A.; Moore, Kenneth E.

doi:10.1159/000123124

Cited by 28 publications

(18 citation statements)

References 12 publications

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“…Although decreases in TIDA neuronal activity have been reported at [26,35] or prior to [ 15,19] the time of elevated PRL levels, it is difficult to compare these data with ours due to varia tions in experimental protocols, frequency of sampling and light schedules for the rats. In support of a functional DA input to the anterior pituitary at this time, we showed that treatment with «-MPT ( fig.…”

Section: Discussionmentioning

confidence: 58%

“…This surge is similar in profile, but lower in magnitude to the proestrous PRL surge in adult cycling rats [15,24,30]. Surprisingly, at the peak of the PRL release, the activity of DA neurons in the SME and PP were increased or unchanged, res pectively.…”

Section: Discussionmentioning

confidence: 79%

“…O f major importance are the tuberoinfundibular dopaminergic (T1DA) neurons with cell bodies in the arcuate nucleus and nerve ter minals in the stalk-median eminence (SME) [9]. DA neuronal activity in the SME has been extensively studied in both cycling Received: May 17, 1988 Accepted after revision: September 1, 1988 [1,7,15,35] and PMSG-treated rats [19,26], However, a clear consensus relating the dynamics of these neurons during the periovulatory period and the rise and fall of PRL secretion has not yet emerged. The second system is comprised of the tuberohypophysial dopaminergic (THDA) neurons with cell bodies in the arcuate nucleus and terminals in the neural and intermed iate lobes of the posterior pituitary (PP) [9].…”

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confidence: 99%

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Differential Alterations in Dopamine Turnover Rates in the Stalk-Median Eminence and Posterior Pituitary during the Preovulatory Prolactin Surge

1989

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The relative contributions of dopamine (DA) and prolactin-releasing factor (PRF) in generating the preovulatory prolactin (PRL) surge were investigated. Immature female rats were injected with pregnant mare’s serum gonadotropin (PMSG) on day 28. Jugular blood was collected hourly on days 30 and 31. PRL levels were low in the morning of day 30, rose 10–12 times to peak levels from 14.00 to 16.00 h, reached a prolonged plateau from 18.00 to 24.00 h, and reduced to basal levels in the morning of day 31. All PMSG-treated rats ovulated an average of 13–14 ova. PRL levels in age-matched control rats were low throughout this time, and no oviductal ova were present. DA turnover rates in the stalk-median eminence (SME) and posterior pituitary (PP) were determined from the decline in tissue DA after injecting α-methyl-p-tyrosine (α-MPT), a competitive inhibitor of tyrosine hydroxylase. DA turnover rates increased or were unaltered in the SME and PP, respectively, during the peak PRL phase as compared to presurge rates. In contrast, DA turnover rates were significantly reduced in both tissues during the plateau phase. The turnover rate in the SME, but not the PP, was increased in the morning of day 31. DA turnover rates in control rats never changed. Injection of α-MPT to PMSG-treated rats increased PRL levels at all times examined except during the plateau phase. Blood PRL levels were also determined in PMSG-treated rats following posterior pituitary lobectomy or sham lobectomy. The PRL surge was similar in both groups and all rats ovulated. These data suggest that the peak PRL surge occurs in spite of high DA activity and the presence of DA input to the anterior pituitary, and is therefore sustained by a non-dopaminergic mechanism. The prolongation of the PRL surge likely results from the decreased activity of DA neurons in both the SME and PP and its termination is caused by increased DA activity in the SME only. There is no evidence for a PRF input from the PP during the preovulatory PRL surge in PMSG-treated rats, but a hypothalamic PRF might be involved.

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Section: Discussionmentioning

confidence: 58%

Section: Discussionmentioning

confidence: 79%

mentioning

confidence: 99%

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Differential Alterations in Dopamine Turnover Rates in the Stalk-Median Eminence and Posterior Pituitary during the Preovulatory Prolactin Surge

1989

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“…cantly increased by 15 min, compared to aCSF-infused animals, and remained elevated for the duration of the 60min infusion (Fig. 4).…”

Section: Resultsmentioning

confidence: 86%

“…Many of these effects have then been extrapolated to, and demonstrated in, the intact female rat over the estrous cycle (15)(16)(17). We began our investigations on the role of brain A11 in controlling prolactin release using this model with the expectation that the results would help identify physiological conditions where this control was relevant.…”

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confidence: 99%

The Brain Renin‐Angiotensin System and the Regulation of Prolactin Secretion in Female Rats: Influence of Ovarian Hormones

Myers

Steele

1989

J Neuroendocrinology

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This study was designed to investigate the effects of exogenous and endogenous angiotensin II (All) on prolactin release in ovariectomized rats, with and without estrogen and progesterone pretreatment. In the first series of experiments, All or vehicle was injected into the third cerebral ventricle of conscious, freely-moving rats. In both treated and untreated rats, administration of 50 ng All suppressed prolactin levels within 15 min of injection, compared to vehicle-injected rats. In untreated rats, prolactin levels returned to baseline values by 30 min, while in treated rats, prolactin levels remained suppressed for an hour.In the second series of experiments, the involvement of endogenous brain All in tonically suppressing prolactin release was assessed by administering either All receptor blockers (saralasin or sarthran) or an All synthesis inhibitor (enalaprilat, an inhibitor of the conversion of angiotensin I to All). Neither All receptor blockade nor converting enzyme inhibition resulted in any change in prolactin levels in untreated levels in untreated rats. However, following treatment with ovarian steroids, infusion of saralasin or injection of enalaprilat resulted in a significant increase in plasma prolactin titers. During saralasin infusion, prolactin levels were significantly increased by 15 min and continued to be higher than controls at 60 min. After enalaprilat administration, prolactin levels did not rise significantly until 90 min and then remained elevated up to 120 min post-injection. These latter results suggest that at least one h is required for maximal inhibition of angiotensin synthesis in the brain.These data demonstrate that low doses of All suppressed basal prolactin secretion in both untreated and ovarian steroid-treated, ovariectomized rats. However, treated rats appeared to be more sensitive than untreated animals to the prolactin-lowering effects of centrally administered All. The lack of prolactin response in untreated rats when brain All synthesis was inhibited or All receptors were blocked suggests that, in the absence of ovarian steroids, endogenous All was not acting tonically to suppress prolactin secretion. Following exposure to ovarian steroids, however, the endogenous brain All system appeared to be activated and involved in controlling prolactin release.The anterior pituitary gland hormone, prolactin, i s involved in lactation, ovarian and mammillary gland function, pseudopregnancy in female rats, and i s released in response to stress (1). In human males and females, hyperprolactinemia i s associated with impaired sexual behavior and functioning, as well as infertility (2).Prolactin secretion is mainly under tonic inhibitory control by dopamine, derived from the brain tuberoinfundibular system (3). On the other hand, a variety o f peptides (e.g. vasoactive intestinal peptide, thyrotropin-releasing hormone) including angiotensin I1 (AII), have been identified as putative prolactin-releasing factors when applied directly to the anterior pituitary gland (4). Und...

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Hypothalamic Biogenic Amines and the Regulation of Luteinizing Hormone Release in the Rat

Coen

1987

Endocrinology and Physiology of Reproduction

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Biochemical Indices of Catecholaminergic Neuronal Activity in the Median Eminence during the Estrous Cycle of the Rat

Cited by 28 publications

References 12 publications

Differential Alterations in Dopamine Turnover Rates in the Stalk-Median Eminence and Posterior Pituitary during the Preovulatory Prolactin Surge

Differential Alterations in Dopamine Turnover Rates in the Stalk-Median Eminence and Posterior Pituitary during the Preovulatory Prolactin Surge

The Brain Renin‐Angiotensin System and the Regulation of Prolactin Secretion in Female Rats: Influence of Ovarian Hormones

Hypothalamic Biogenic Amines and the Regulation of Luteinizing Hormone Release in the Rat

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