Pituitary Prolactin Secretion Research Articles

Network pharmacology analysis and molecular mechanism of paeoniflorin and its metabolite in prolactinoma cells.

Prolactinoma was the most common functionalpituitary neuroendocrine tumor tissue type, which was caused by excessive proliferation of pituitary prolactin (PRL) cells. Drug therapy of dopamine receptoragonists was generally considered as the prior treatment for prolactinoma patients. However, there were still prolactinoma patients who were resistant to dopamine agonists. Studies have been reported that paeoniflorin can inhibit the secretion of PRL in prolactinoma cells lacking dopamine D2 receptor (D2R) expression, and paeoniflorin can be metabolized into albiflorin by intestinal flora in rats. The effect of albiflorin on prolactinoma has not been reported yet. In this study, network pharmacology was used to analyze the mechanism of paeoniflorin and its metabolite albiflorin as multi-target therapy for prolactinoma, and the experimental verification was carried out. In order to clarify the complex relationship among paeoniflorin, albiflorin and prolactinoma, we constructed a component-target-disease network, and further constructed interaction network, MMP9, EGFR, FGF2, FGFR1 and LGALS3 were screened as the core targets. Kyoto encyclopedia of genes and genomes (KEGG) analysis showed that paeoniflorin and albiflorin may be involved in various pathways in the treatment of prolactinoma, included relaxin signaling pathway and PI3K-Akt signaling pathway. Molecular docking analysis showed that paeoniflorin and albiflorin had good binding activity with MMP9. Western blotting results showed that paeoniflorin and albiflorin could significantly reduce the expression of MMP9, and ELISA results showed that paeoniflorin and albiflorin could significantly reduce the concentration of PRL in GH3 cells, and the reduce degree of albiflorin was stronger than paeoniflorin at 50μM, which indicated that albiflorin might be a potential drug to treat prolactinoma, which can regulate prolactinoma through MMP9 and reduce the concentration of PRL. Our study provided a new therapeutic strategy for prolactinoma.

Hormonal regulation of mammary gland development and lactation.

Lactation is critical to infant short-term and long-term health and protects mothers from breast cancer, ovarian cancer and type 2 diabetes mellitus. The mammary gland is a dynamic organ, regulated by the coordinated actions of reproductive and metabolic hormones. These hormones promote gland development from puberty onwards and induce the formation of a branched, epithelial, milk-secreting organ by the end of pregnancy. Progesterone withdrawal following placental delivery initiates lactation, which is maintained by increased pituitary secretion of prolactin and oxytocin, and stimulated by infant suckling. After weaning, local cytokine production and decreased prolactin secretion trigger large-scale mammary cell loss, leading to gland involution. Here, we review advances in the molecular endocrinology of mammary gland development and milk synthesis. We discuss the hormonal functions of the mammary gland, including parathyroid hormone-related peptide secretion that stimulates maternal calcium mobilization for milk synthesis. We also consider the hormonal composition of human milk and its associated effects on infant health and development. Finally, we highlight endocrine and metabolic diseases that cause lactation insufficiency, for example, monogenic disorders of prolactin and prolactin receptor mutations, maternal obesity and diabetes mellitus, interventions during labour and delivery, and exposure to endocrine-disrupting chemicals such as polyfluoroalkyl substances in consumer products and other oestrogenic compounds.

Microglial NLRP3 inflammasome activation-mediated inflammation promotes prolactinoma development.

Prolactinomas have harmful effects on human health, and the pathogenesis is still unknown. Furthermore, 25% of prolactinoma patients do not respond to the therapy of dopamine receptor agonist in the clinic. Thus, it is important to reveal the pathogenesis and develop new therapeutic methods for prolactinomas. Herein, two animal models of prolactinomas, namely oestrogen-treated rats and transgenic D2 dopamine receptor-deficient mice, were used. PET/CT imaging detection showed that translocator protein-mediated microglia activation and inflammation significantly increased in the pituitary glands of prolactinomas rats. Messenger RNA microarrays were used to analyze and compare the differential gene and signal pathways of the pituitary glands between control and prolactinomas rats. Statistical results pertaining to gene enrichment showed that the innate immune response genes were upregulated in the pituitary glands of prolactinoma rats. This suggested that the innate immune response was activated. We analyzed the NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) inflammasome that is one of the most important members of the innate immune system in mammals and found that the expressions of NLRP3, Caspase-1, apoptosis-associated speck-like, interleukin 1B (IL1B) and IL18 proteins of pituitary glands in prolactinomas rats were increased considerably compared with those in control rats. This suggested the activation of the NLRP3 inflammasome during the emergence and evolution of prolactinomas. Immunohistochemistry results also confirmed that the NLRP3 expression was elevated in human prolactinoma tissues, and the microglia marker-ionised calcium binding adaptor molecule-1 was co-located with the NLRP3 protein in prolactinomas by immunofluorescence assay. Finally, compared with the WT mice, NLRP3-/- mice had smaller pituitary glands (weight/body weight) and diminished prolactin (PRL) expressions and secretions. These findings were associated with a reduction in the caspase-1 activation and maturation of IL1B. Furthermore, MCC950 decreased the PRL expression and secretion following the inhibition of NLRP3 inflammasome activation in GH3 cells stimulated with lipopolysaccharide and nigericin. And MCC950 inhibited the pituitary tumor overgrowth and PRL expression and secretion in prolactinoma rats. These data confirm that the microglial NLRP3 inflammasome activation upregulates the inflammatory cytokines IL1/IL18 in the pituitary glands and induces prolactinomas. Our findings showed that microglial NLRP3 inflammasome activation-mediated IL1B-related inflammation promoted the development of prolactinomas and identified the inflammasome as a new therapeutic target for prolactinomas.

Inhibiting MAPK14 showed anti-prolactinoma effect

BackgroundThe specific underlying pathogenesis of prolactinoma has not been clarified yet, to the best of our knowledge. p38 mitogen-activated protein kinase (MAPK) signaling including p38α MAPK (MAPK14), p38β (MAPK11), p38γ (MAPK12) and p38δ (MAPK13) is associated with the development and progression of several types of cancer.MethodsImmunofluorescence analysis was performed on the prolactin (PRL) and MAPK14 expressions of pituitary gland in C57BL/6 mice and human prolactinoma specimen. In the present study, the role of MAPK14 in prolactinoma was determined using estradiol-induced mice and dopamine D2 receptor knockout (DRD2−/−) mice models in C57BL/6 wild-type (WT), MAPK14−/− and DRD2−/−MAPK14+/− mice. GH3 cells were transfected with different sets of MAPK14 small interfering RNA, which to study MAPK14 and PRL expression in GH3 cells.ResultsImmunofluorescence analysis showed that PRL and MAPK14 expression were colocalized and increased in the pituitary gland of mice and human prolactinoma specimen compared with the control specimen. It was shown that PRL and MAPK14 expression was colocalized and increased significantly in the pituitary gland of estradiol-injected prolactinoma mice compared with the control mice. Knockout of MAPK14 significantly inhibited tumor overgrowth, and PRL expression was decreased in estradiol-induced mice. Furthermore, MAPK14 knockout of DRD2−/−MAPK14+/− mice significantly reduced the overgrowth of pituitary gland and PRL production and secretion compared with DRD2−/− mice. MAPK14 knockout using siRNA inhibited PRL production in GH3 cells.ConclusionThese results suggest that MAPK14 serves a promoting role in the formation of prolactinoma, and highlights the potential of MAPK14 as a potential therapeutic target in the treatment of prolactinoma.

Pre- and post-synaptic modulation by GABAB receptors of rat neuroendocrine dopamine neurones.

The secretion of prolactin from the pituitary is negatively controlled by tuberoinfundibular dopamine (TIDA) neurones. The electrical properties of TIDA cells have recently been identified as a modulatory target of neurotransmitters and hormones in the lactotrophic axis. The role of the GABAB receptor in this control has received little attention, yet is of particular interest because it may act as a TIDA neurone autoreceptor. Here, this issue was explored in a spontaneously active rat TIDA in vitro slice preparation using whole-cell recordings. Application of the GABAB receptor agonist, baclofen, dose-dependently slowed down or abolished the network oscillations typical of this preparation. Pharmacological manipulations identify the underlying mechanism as an outward current mediated by G-protein-coupled inwardly rectifying K+ -like channels. In addition to this postsynaptic modulation, we describe a presynaptic modulation where GABAB receptors restrain the release of glutamate and GABA onto TIDA neurones. Our data identify both pre- and postsynaptic modulation of TIDA neurones by GABAB receptors that may play a role in the neuronal network control of pituitary prolactin secretion and lactation.

Secretion and Function of Pituitary Prolactin in Evolutionary Perspective.

The hypothalamo-pituitary system developed in early vertebrates. Prolactin is an ancient vertebrate hormone released from the pituitary that exerts particularly diverse functions. The purpose of the review is to take a comparative approach in the description of prolactin, its secretion from pituitary lactotrophs, and hormonal functions. Since the reproductive and osmoregulatory roles of prolactin are best established in a variety of species, these functions are the primary subjects of discussion. Different types of prolactin and prolactin receptors developed during vertebrate evolution, which will be described in this review. The signal transduction of prolactin receptors is well conserved among vertebrates enabling us to describe the whole subphylum. Then, the review focuses on the regulation of prolactin release in mammals as we have the most knowledge on this class of vertebrates. Prolactin secretion in response to different reproductive stimuli, such as estrogen-induced release, mating, pregnancy and suckling is detailed. Reproduction in birds is different from that in mammals in several aspects. Prolactin is released during incubation in avian species whose regulation and functional significance are discussed. Little information is available on prolactin in reptiles and amphibians; therefore, they are mentioned only in specific cases to explain certain evolutionary aspects. In turn, the osmoregulatory function of prolactin is well established in fish. The different types of pituitary prolactin in fish play particularly important roles in the adaptation of eutherian species to fresh water environments. To achieve this function, prolactin is released from lactotrophs in hyposmolarity, as they are directly osmosensitive in fish. In turn, the released prolactin acts on branchial epithelia, especially ionocytes of the gill to retain salt and excrete water. This review will highlight the points where comparative data give new ideas or suggest new approaches for investigation in other taxa.

The effects of extended photoperiod and warmth on hair growth in ponies and horses at different times of year.

Photoperiod is considered the most dominant environmental cue allowing animals to anticipate and adapt to seasonal changes. In seasonally breeding mammals, changes in daylength alter pineal melatonin secretion and pituitary prolactin secretion. During the seasonal transition to shorter winter daylengths, increased production of melatonin and declining prolactin are associated with triggering winter coat growth in many animals. Similarly, studies have shown that artificial extension of photoperiod suppresses melatonin secretion and lifts prolactin inhibition to activate moulting. Four longitudinal cohort studies were conducted to determine if extended photoperiod and warmth, provided by mobile light masks and rugs (horse blankets), could reverse the onset of winter coat growth, maintain the summer coat and accelerate winter coat shedding in horses and in ponies. Studies began at dates corresponding to the autumnal equinox, one month post-summer solstice, one month pre-winter solstice and one month post-winter solstice, respectively. To extend photoperiod to approximately 15h of light, commercially available head-worn light masks provided low intensity blue light to one eye until 11pm daily. Coat condition and shedding rate were scored and hair samples collected, measured and weighed bi-weekly. Data from control and treatment groups were analysed by repeated measures ANOVA. Results revealed that extended photoperiod 1) did not reverse winter coat growth when initiated at the autumnal equinox, 2) effectively maintained the summer coat in stabled horses when initiated one month post-summer solstice, 3) accelerated shedding in outdoor living horses when initiated one month pre-winter solstice and 4) did not accelerate shedding in indoor or outdoor living ponies when initiated one month post-winter solstice. To successfully manage equine coat growth while also preserving optimal thermoregulation in both competition and breeding stock correct timing of light application is crucial and requires careful monitoring of environmental temperature. Further studies are needed where variations in breed and management are considered.

Patterns of prolactin secretion

Prolactin is pleotropic in nature affecting multiple tissues throughout the body. As a consequence of the broad range of functions, regulation of anterior pituitary prolactin secretion is complex and atypical as compared to other pituitary hormones. Many studies have provided insight into the complex hypothalamic-pituitary networks controlling prolactin secretion patterns in different species using a range of techniques. Here, we review prolactin secretion in both males and females; and consider the different patterns of prolactin secretion across the reproductive cycle in representative female mammals with short versus long luteal phases and in seasonal breeders. Additionally, we highlight changes in the pattern of secretion during pregnancy and lactation, and discuss the wide range of adaptive functions that prolactin may have in these important physiological states.

The Role of Melatonin in Ewes Reproduction: a Review

This review was assigned to illustrate the melatonin (MLT) effect on reproduction in sheep (ewes). However, the pathway by which MLT charge the seasonal reproduction are imperfectly understood in sheep, the researchers consents that MLT regulates reproduction under influence of day length (photoperiod) to guarantee that birth happen in appropriate date of the year, it’s called neuro-endocrine process. This mechanism mediates by the pineal hormone (MLT). The major role of MLT in ewes is to translate the photo signals into endocrine pulses (gonadotropin-releasing hormone (GnRH) secretion) at the end of the retino-pineal pathway. In sheep, the MLT receptors distributed in premammillary hypothalamus (PMH), pituitary gland and Suprachiasmatic nucleus (SCN), therefore, many brain loci are participating for MLT pathways to modify the seasonal reproduction. Melatonin stimulates GnRH secretion through effect in different regions and neurons in hypothalamus such as a pre-mammillary nucleus, Arcuate and several factors like kisspeptin, RF-amide related peptide-3 (RFRP-3) and Tyrosine Hydroxylase (TH). In addition, its indirectly control prolactin (PRL) output via an effect on Tuberalin release, which is mediate the mechanism of MLT activity on pituitary PRL secretion and regulate his seasonal cyclicity. The alter in day length is the principle ecological factor that control the breeding in seasonal domestic animals. Several reproductive activities are related to short days and begin during autumn when the day becomes short and a decline in temperature (short-day breeder). While expanding in the duration of light lead to a cessation in reproduction activities during late winter and early spring. In conclusion, according to the major physiological role of MLT, it can be used in different aspects in ewes reproduction industry such as induce oestrus, increment the ovulation rate and In vitro embryo production.

Identification of a novel somatic mutation of POU6F2 by whole-genome sequencing in prolactinoma.

BackgroundPituitary adenomas (PAs) are one of the most common intracranial tumors; approximately half of PAs are prolactin (PRL)‐secreting PAs (prolactinomas). The genetic alterations prevalent in prolactinomas are unknown.MethodsHere, we present a patient with an extremely aggressive and giant prolactinoma accompanied by serious destruction of the surrounding bone mass. This patient exhibited resistance to dopaminergic drugs. Through whole‐genome sequencing, we identified two novel somatic mutations in the POU6F2 gene (NM_001166018.2: c. 839 C>T; NM_001166018.2: c. 875A>G).ResultsThis report is the first to identify these somatic mutations in the POU6F2 gene in a prolactinoma. We found that these two mutations obviously decreased the expression level of POU6F2. Inhibition of POU6F2 activity increased the cell proliferation and PRL secretion in rat pituitary cells, but proliferation and PRL secretion were decreased in cells with POU6F2 overexpression.Conclusions POU6F2 might play a crucial role in the development of prolactinomas and may be a promising target for developing new therapies against prolactinomas.

Dopamine Release Dynamics in the Tuberoinfundibular Dopamine System.

The relationship between neuronal impulse activity and neurotransmitter release remains elusive. This issue is especially poorly understood in the neuroendocrine system, with its particular demands on periodically voluminous release of neurohormones at the interface of axon terminals and vasculature. A shortage of techniques with sufficient temporal resolution has hindered real-time monitoring of the secretion of the peptides that dominate among the neurohormones. The lactotropic axis provides an important exception in neurochemical identity, however, as pituitary prolactin secretion is primarily under monoaminergic control, via tuberoinfundibular dopamine (TIDA) neurons projecting to the median eminence (ME). Here, we combined electrical or optogenetic stimulation and fast-scan cyclic voltammetry to address dopamine release dynamics in the male mouse TIDA system. Imposing different discharge frequencies during brief (3 s) stimulation of TIDA terminals in the ME revealed that dopamine output is maximal at 10 Hz, which was found to parallel the TIDA neuron action potential frequency distribution during phasic discharge. Over more sustained stimulation periods (150 s), maximal output occurred at 5 Hz, similar to the average action potential firing frequency of tonically active TIDA neurons. Application of the dopamine transporter blocker, methylphenidate, significantly increased dopamine levels in the ME, supporting a functional role of the transporter at the neurons' terminals. Lastly, TIDA neuron stimulation at the cell body yielded perisomatic release of dopamine, which may contribute to an ultrafast negative feedback mechanism to constrain TIDA electrical activity. Together, these data shed light on how spiking patterns in the neuroendocrine system translate to vesicular release toward the pituitary and identify how dopamine dynamics are controlled in the TIDA system at different cellular compartments.SIGNIFICANCE STATEMENT A central question in neuroscience is the complex relationship between neuronal discharge activity and transmitter release. By combining optogenetic stimulation and voltammetry, we address this issue in dopamine neurons of the neuroendocrine system, which faces particular spatiotemporal demands on exocytotic release; large amounts of neurohormone need to be secreted into the portal capillaries with precise timing to adapt to physiological requirements. Our data show that release is maximal around the neurons' default firing frequency. We further provide support for functional dopamine transport at the neurovascular terminals, shedding light on a long-standing controversy about the existence of neuroendocrine transmitter reuptake. Finally, we show that dopamine release occurs also at the somatodendritic level, providing a substrate for an ultrashort autoregulatory feedback loop.

Milk yield, lactation parameters and prolactin secretion characteristics in sheep treated with melatonin implants during pregnancy and lactation in long-day conditions

In a temperate climate zone, sheep lambing during long days (summer) produce less milk and have shorter lactation than those naturally lambing during short days (winter). We investigated whether artificially induced and prolonged increase in melatonin concentration in sheep lambed during long days would improve milk yield and lactation parameters through changes in pituitary prolactin (PRL) secretion. In addition, the relative mRNA levels of PRL and PRL-receptor (PRL-R) were determined in the mammary gland. Sheep (n = 36) were randomly divided into three groups: lambed in January (short day – SD treatment group), lambed in June (long day – LD treatment group), and lambed in June and treated with the subcutaneous melatonin implants (in May and then in August, LDM treatment group). After lamb weaning, milk yield, the number of milking days and the total length of lactation (days) were monitored individually. Plasma melatonin and PRL concentrations were determined in samples collected from 18 sheep (6 of each group): 6 weeks before parturition, day after weaning and then during lactation, every 28 days. A mammary gland biopsy was performed in these sheep 3–4 days before parturition. Milk yield was higher in the SD group, than in the LD (P < 0.05) and LDM (P < 0.001) groups. Both the number of milking days and total length of lactation were higher in the SD (P < 0.001) and LDM (P < 0.05) groups than in the LD group. The PRL and melatonin secretion profiles varied in all groups, reflecting the characteristics of the endogenous circannual rhythm. An additional increase in plasma PRL concentration occurred in LDM sheep, compared to LD sheep (P < 0.01). Statistical differences were found neither in the relative levels of PRL mRNA nor PRL-R mRNA in the mammary gland between the SD and LD groups, however both transcripts contents decreased (P < 0.05) in the LDM group. In conclusions: 1) alterations in milk yield and lactational parameters in sheep are affected by changes in the secretory PRL profile during the established lactation; 2) PRL refractoriness to melatonin develops in lactating sheep with extended melatonin treatment, which increases only a number of milking days, with no positive effect on milk yield; 3) The sheep mammary gland is qualitatively at the same level of preparation, in both short and long days, for the synthesis and perception of PRL during the periparturient period; 4) Artificially elevated plasma melatonin concentration before parturition causes a decrease in abundance of both PRL and PRL-R transcripts in the mammary gland.

Inflammation and LPS-Binding Protein Enable the Stimulatory Effect of Endotoxin on Prolactin Secretion in the Ovine Anterior Pituitary: Ex Vivo Study.

Prolactin is a hormone that plays an important role in the regulation of many physiological processes including lactation, reproduction, fat metabolism, and immune response. The secretion of prolactin could be disturbed by an immune stress commonly accompanying infection. This study was designed to determine the influence of bacterial endotoxin—lipopolysaccharide (LPS)—on prolactin gene (PRL) expression and prolactin release from the ovine anterior pituitary (AP) explants collected from saline- and LPS-treated ewes in the follicular phase. The expressions of toll-like receptor 4 (TLR4) and proinflammatory cytokines interleukin- (IL-) 1β, IL-6, and tumor necrosis factor- (TNF-) α genes were also assayed. The results of the study showed that LPS stimulates prolactin secretion and IL-6 gene expression in the AP explants, but its action on lactotrophs depends on the immunological status of animal. It was demonstrated that an important role in enhancing the effect of LPS on the pituitary in the saline-treated ewes is played by LPS-binding protein (LBP)- “adapter molecule” for LPS binding to the cell surface receptor CD14 and then to TLR4. Also, it was found that bacterial endotoxin acting on the anterior pituitary cells may enhance prolactin secretion, and this effect of LPS could be mediated by IL-6 which is known as prolactin-releasing factor. Identification of the neuroendocrine and immune interactions in the regulation of prolactin secretion could be helpful in developing newer and more effective treatments for dysfunctions connected with disorders in this hormone secretion.

Role of Oxytocin in Prolactin Secretion during Late Pregnancy

Background/Aims: During late pregnancy, the blockade of progesterone action by mifepristone (Mp) treatment induces a dopaminergic tone fall that enables naloxone (NAL) administration to release pituitary prolactin (PRL). We determined whether oxytocin (OT), which stimulates PRL secretion acting directly on anterior pituitary lactotrophs, mediates the stimulatory action of Mp and NAL on PRL secretion during late pregnancy. Methods: On day 19 of pregnancy, circulating and pituitary OT and PRL levels were measured by radioimmunoassay, 10, 20, and 30 min after NAL (given at 17:30 h) in rats pretreated with Mp (at 08:00 h). Pituitary OT receptor (OTR) expression in Mp-treated rats was evaluated by RT-PCR. Activation of OT neurons in Mp-NAL-treated rats was measured counting double immunoreactive neurons for Fos and OT (Fos-OT-ir) in supraoptic nuclei (SON), and medial (PaMM) and lateral magnocellular divisions of paraventricular nuclei. Results: Elevated serum OT and decreased pituitary OT were observed 10 min after NAL administration in both vehicle- and Mp-treated rats. This PRL increase was prevented by previous i.p. administration of an OTR antagonist, but intracerebroventricular OT administration was ineffective. Mp increased pituitary OTR expression at 18:00 h. Only Mp-NAL increased Fos-OT-ir neurons in the PaMM and SON. Conclusions: These findings suggest that PRL secretion induced by Mp-NAL treatment is preceded by OT release. These results, together with the activation of hypothalamic OT neurons and the higher expression of pituitary OTR, support the hypothesis that, during late pregnancy, OT may act at the pituitary level to facilitate PRL secretion if the inhibitory action of progesterone is blocked.

A pilot phase II trial of cabergoline in the treatment of metastatic breast cancer.

e12568 Background: The prolactin receptor can be overexpressed in breast cancer, and pre-clinical data indicate that it contributes to the pathobiology of breast cancer. Cabergoline is a potent dopamine receptor agonist of D2 receptors and has a direct inhibitory effect on pituitary prolactin secretion resulting in reduced serum prolactin levels. Methods: A pilot phase II study of cabergoline in patients with metastatic breast cancer was conducted with primary end point of best overall response rate (ORR) among patients with measurable disease. Eligible patients had metastatic breast cancer, any receptors status was allowed, and there was no limit of prior lines of therapy. Both measurable and unmeasurable diseases (RECIST 1.1) were allowed. Cabergoline 1mg orally, twice weekly (1 cycle = 4 weeks) was given until disease progression or unacceptable toxicity. Immunohistochemistry prolactin receptor staining was performed on available baseline tumor tissue, and serum prolactin levels were serially assessed. Results: A total of 20 women were enrolled, 19 of whom were evaluable for response (one patient died on C1D7 of unrelated causes). Mean age was 62 (range 42-83); 15 (75%) were Caucasian; mean number of prior lines of therapy 5 (range 0-14). Tumor receptor statuses were distributed as follows: HR+/HER2+ 1(5%), HR+/HER2- 18 (80%), HR-/HER2+ 1 (5%). Analysis was performed after a median follow-up of 6.8 months (0.2-26.2). Best ORR was 8.3% among 12 patients with measurable disease. Results for secondary endpoints were as follows: 4-month CBR = 26% (including patients with measurable and non-measurable disease), median PFS = 1.9 months, and median OS = 10.4 months. Most common treatment related AEs were nausea (30%), fatigue (25%), and elevation in alkaline phosphatase (15%). The highest-grade AE was a single grade 3 treatment-related pain in extremity. Nine patients had sufficient baseline tissue for analysis, there was no correlation between baseline tumor prolactin receptor expression and clinical benefit ( p= 0.24). Additional correlative work is ongoing. Conclusions: Cabergoline was well tolerated and associated with modest anti-tumor activity. Clinical trial information: NCT01730729.

Multiple-scale neuroendocrine signals connect brain and pituitary hormone rhythms

Small assemblies of hypothalamic "parvocellular" neurons release their neuroendocrine signals at the median eminence (ME) to control long-lasting pituitary hormone rhythms essential for homeostasis. How such rapid hypothalamic neurotransmission leads to slowly evolving hormonal signals remains unknown. Here, we show that the temporal organization of dopamine (DA) release events in freely behaving animals relies on a set of characteristic features that are adapted to the dynamic dopaminergic control of pituitary prolactin secretion, a key reproductive hormone. First, locally generated DA release signals are organized over more than four orders of magnitude (0.001 Hz-10 Hz). Second, these DA events are finely tuned within and between frequency domains as building blocks that recur over days to weeks. Third, an integration time window is detected across the ME and consists of high-frequency DA discharges that are coordinated within the minutes range. Thus, a hierarchical combination of time-scaled neuroendocrine signals displays local-global integration to connect brain-pituitary rhythms and pace hormone secretion.

Hypocretin/Orexin Peptides Excite Rat Neuroendocrine Dopamine Neurons through Orexin 2 Receptor-Mediated Activation of a Mixed Cation Current

Hypocretin/Orexin (H/O) neurons of the lateral hypothalamus are compelling modulator candidates for the chronobiology of neuroendocrine output and, as a consequence, hormone release from the anterior pituitary. Here we investigate the effects of H/O peptides upon tuberoinfundibular dopamine (TIDA) neurons – cells which control, via inhibition, the pituitary secretion of prolactin. In whole cell recordings performed in male rat hypothalamic slices, application of H/O-A, as well as H/O-B, excited oscillating TIDA neurons, inducing a reversible depolarising switch from phasic to tonic discharge. The H/O-induced inward current underpinning this effect was post-synaptic (as it endured in the presence of tetrodotoxin), appeared to be carried by a Na+-dependent transient receptor potential-like channel (as it was blocked by 2-APB and was diminished by removal of extracellular Na+), and was a consequence of OX2R receptor activation (as it was blocked by the OX2R receptor antagonist TCS OX2 29, but not the OX1R receptor antagonist SB 334867). Application of the hormone, melatonin, failed to alter TIDA membrane potential or oscillatory activity. This first description of the electrophysiological effects of H/Os upon the TIDA network identifies cellular mechanisms that may contribute to the circadian rhythmicity of prolactin secretion.

Levosulpiride and Serum Prolactin Levels.

Levosulpiride is the levorotatory enantiomer of sulpiride used in dyspeptic syndromes of various etiologies. The prokinetic effect of levosulpiride is mediated through the blockade of enteric inhibitory dopaminergic type 2 (D2) receptors. The antagonism of central D2 receptors leads to both therapeutic (e.g. antiemetic effect due to D2 receptor blockade in the chemoreceptor trigger zone) and adverse (including hyperprolactinemia) effects. Dopamine is the main endogenous inhibitor of prolactin synthesis and secretion in the anterior pituitary. Levosulpiride causes significant elevation of serum prolactin levels in significant number of patients. The resultant hyperprolactinemia often manifests as distressing menstrual abnormalities and galactorrhoea in females. A significant number of patients who use levosulpiride develop serum prolactin levels of > 200 ng/mL that goes against the classical textbook teaching where pituitary tumor is supposed to be the mostly likely cause. Careful drug history in patients presenting with high serum prolactin levels will be of great help in reaching the exact diagnosis and avoiding unnecessary brain imaging.

Regulation of diapause in carnivores.

Embryonic diapause is an evolutionary strategy to ensure that offspring are born when maternal and environmental conditions are optimal for survival. In many species of carnivores, obligate embryonic diapause occurs in every gestation. In mustelids, the regulation of diapause and reactivation is influenced by photoperiod, which then acts to regulate the secretion of pituitary prolactin. Prolactin in turn regulates ovarian steroid function. Reciprocal embryo transplant studies indicate that this state of embryonic arrest is conferred by uterine conditions and is presumed to be due to a lack of specific factors necessary for continued development. Studies of global gene expression in the mink (Neovison vison) revealed reduced expression of a cluster of genes that regulate the abundance of polyamines in the uterus during diapause, including the rate-limiting enzyme in polyamine production, ornithine decarboxylase (ODC). In addition, in this species, in vivo inhibition of the conversion of ornithine to the polyamine, putrescine, induces a reversible arrest in embryonic development and an arrest in both trophoblast and inner cell mass proliferation in vitro. Putrescine, at 0.5, 2 and 1,000μM concentrations induced reactivation of mink embryos in culture, indicated by an increase in embryo volume, observed within five days. Further, prolactin induces ODC1 expression in the uterus, thereby regulating uterine polyamine levels. These results indicate that pituitary prolactin acts on ovarian and uterine targets to terminate embryonic diapause. In summary, our findings suggest that the polyamines, with synthesis under the control of pituitary prolactin, are the uterine factor whose absence is responsible for embryonic diapause in mustelid carnivores.

Conditional Deletion of the Prolactin Receptor Reveals Functional Subpopulations of Dopamine Neurons in the Arcuate Nucleus of the Hypothalamus.

Tuberoinfundibular dopamine (TIDA) neurons, known as neuroendocrine regulators of prolactin secretion from the pituitary gland, also release GABA within the hypothalamic arcuate nucleus. As these neurons express prolactin receptors (Prlr), prolactin may regulate GABA secretion from TIDA neurons, potentially mediating actions of prolactin on hypothalamic function. To investigate whether GABA is involved in feedback regulation of TIDA neurons, we examined the physiological consequences of conditional deletion of Prlr in GABAergic neurons. For comparison, we also examined mice in which Prlr were deleted from most forebrain neurons. Both neuron-specific and GABA-specific recombination of the Prlr gene occurred throughout the hypothalamus and in some extrahypothalamic regions, consistent with the known distribution of Prlr expression, indicative of knock-out of Prlr. This was confirmed by a significant loss of prolactin-induced phosphorylation of STAT5, a marker of prolactin action. Several populations of GABAergic neurons that were not previously known to be prolactin-sensitive, notably in the medial amygdala, were identified. Approximately 50% of dopamine neurons within the arcuate nucleus were labeled with a GABA-specific reporter, but Prlr deletion from these dopamine/GABA neurons had no effect on feedback regulation of prolactin secretion. In contrast, Prlr deletion from all dopamine neurons resulted in profound hyperprolactinemia. The absence of coexpression of tyrosine hydroxylase, a marker for dopamine production, in GABAergic nerve terminals in the median eminence suggested that rather than a functional redundancy within the TIDA population, the dopamine/GABA neurons in the arcuate nucleus represent a subpopulation with a functional role distinct from the regulation of prolactin secretion. Using a novel conditional deletion of the prolactin receptor, we have identified functional subpopulations in hypothalamic dopamine neurons. Although commonly considered a uniform population of neuroendocrine neurons involved in the control of prolactin secretion, we have shown that approximately half of these neurons express GABA as well as dopamine, but these neurons are not necessary for the feedback regulation of prolactin secretion. The absence of tyrosine hydroxylase in GABAergic nerve terminals in the median eminence suggests that only the non-GABAergic dopamine neurons are involved in the control of pituitary prolactin secretion, and the GABAergic subpopulation may function as interneurons within the arcuate nucleus to regulate other aspects of hypothalamic function.