Tachykinins and the control of prolactin secretion

Polymorphisms in genes of melatonin biosynthesis and signaling support the light-at-night hypothesis for breast cancer

Light-at-night triggers the decline of pineal gland melatonin biosynthesis and secretion and is an IARC-classified probable breast-cancer risk factor. We applied a large-scale molecular epidemiology approach to shed light on the putative role of melatonin in breast cancer. We investigated associations between breast-cancer risk and polymorphisms at genes of melatonin biosynthesis/signaling using a study population of 44,405 women from the Breast Cancer Association Consortium (22,992 cases, 21,413 population-based controls). Genotype data of 97 candidate single nucleotide polymorphisms (SNPs) at 18 defined gene regions were investigated for breast-cancer risk effects. We calculated adjusted odds ratios (ORs) and 95% confidence intervals (CI) by logistic regression for the main-effect analysis as well as stratified analyses by estrogen- and progesterone-receptor (ER, PR) status. SNP-SNP interactions were analyzed via a two-step procedure based on logic regression. The Bayesian false-discovery probability (BFDP) was used for all analyses to account for multiple testing. Noteworthy associations (BFDP < 0.8) included 10 linked SNPs in tryptophan hydroxylase 2 (TPH2) (e.g. rs1386492: OR = 1.07, 95% CI 1.02-1.12), and a SNP in the mitogen-activated protein kinase 8 (MAPK8) (rs10857561: OR = 1.11, 95% CI 1.04-1.18). The SNP-SNP interaction analysis revealed noteworthy interaction terms with TPH2- and MAPK-related SNPs (e.g. rs1386483R ∧ rs1473473D ∧ rs3729931D: OR = 1.20, 95% CI 1.09-1.32). In line with the light-at-night hypothesis that links shift work with elevated breast-cancer risks our results point to SNPs in TPH2 and MAPK-genes that may impact the intricate network of circadian regulation.

Adverse effects of antiepileptic drugs on hormones of the hypothalamic-pituitary-gonadal axis in males: A review

The HPG axis is critical in the maintenance of spermatogenesis and sexual function in males. The GnRH-releasing neurons of the hypothalamus are the axis's main hierarchical element. These neurons make connections with different areas of the brain to regulate the release of GnRH. Neurotransmitters have a critical in the connections between these neurons. So, neurotransmitters can inhibit or stimulate the release of GnRH by affecting GnRH-releasing neurons. In neurological disorders, neurotransmitter's activities inevitably change; therefore, these changes can affect the HPG axis via affecting GnRH-releasing neurons, just like in epilepsy. Many investigations have attracted attention to be decreased fertility potential in males with epilepsy. It has been stated that changes in the HPG axis hormone levels have been found in these patients. Moreover, it has also been observed that sperm quality decreased in patients. It has been emphasized that a decrease in sperm quality may be related to both epilepsy and AEDs. It has been shown that AEDs caused decreased sperm quality by impairing the HPG axis, so they act like endocrine-disrupting chemicals. AEDs can affect fertility and cause additive adverse effects in terms of sperm quality together with epilepsy. Therefore, it is crucial to investigate the adverse reproductive effects of AEDs, which are frequently used during reproductive ages, and determine the role of the HPG axis on potential reproductive pathologies.

Tachykinins, new players in the control of reproduction and food intake: A comparative review in mammals and teleosts

In vertebrates, the tachykinin system includes tachykinin genes, which encode one or two peptides each, and tachykinin receptors. The complexity of this system is reinforced by the massive conservation of gene duplicates after the whole-genome duplication events that occurred in vertebrates and furthermore in teleosts. Added to this, the expression of the tachykinin system is more widespread than first thought, being found beyond the brain and gut. The discovery of the co-expression of neurokinin B, encoded by the tachykinin 3 gene, and kisspeptin/dynorphin in neurons involved in the generation of GnRH pulse, in mammals, put a spotlight on the tachykinin system in vertebrate reproductive physiology. As food intake and reproduction are linked processes, and considering that hypothalamic hormones classically involved in the control of reproduction are reported to regulate also appetite and energy homeostasis, it is of interest to look at the potential involvement of tachykinins in these two major physiological functions. The purpose of this review is thus to provide first a general overview of the tachykinin system in mammals and teleosts, before giving a state of the art on the different levels of action of tachykinins in the control of reproduction and food intake. This work has been conducted with a comparative point of view, highlighting the major similarities and differences of tachykinin systems and actions between mammals and teleosts.

Seasonal reproductive state determines gene expression in the hypothalamus of a latitudinal migratory songbird during the spring and autumn migration

We investigated gonadal effects on hypothalamic transcription of genes in sham-operated and castrated redheaded buntings photostimulated into spring and autumn migratory states. RNA-Seq results showed testes-dependent differences between spring and autumn migratory states. In particular, differentially expressed genes enriched G-protein-coupled receptor and calcium-ion signaling pathways during spring and autumn states, respectively. qPCR assay showed attenuated gabra5, ttr, thra and thrb expressions, suggesting reduced GABA and thyroid hormone effects on photo-sexual response in spring. In spring castrates, reduced npy, tac1 and nrcam and increased ank3 expression suggested testicular effects on the appetite, prolactin release and neuronal functions, whereas in autumn castrates, reduced rasgrp1, grm5 and grin1, and increased mras expression suggested testicular effects on the ras, G-protein and glutamate signaling pathways. Castration-induced reciprocal switching of pomc and pdyn expressions suggested effects on the overall homeostasis in both seasons. These results demonstrate transcriptome-wide changes, with season-dependent roles of testes in songbird migration.

The role of neurokinin A and its receptor in the regulation of prolactin secretion by the anterior pituitary of cyclic pigs

In pigs, plasma prolactin concentration markedly changes during the oestrous cycle and the regulation of its secretion is very complex. The contribution of neurokinins in this process has not been sufficiently delineated. The aim of the study was to examine the effects of neurokinin A (NKA) on prolactin synthesis and secretion in cyclic gilts. The expression of NKA precursor (Ppta) and receptor (Tacr2) genes as well as NKA and TACR proteins content in the porcine pituitaries (days 2-3, 9-10, 12-13, 15-16 and 19-20 of the cycle) was determined. Furthermore, the in vitro influence of NKA on the expression of prolactin (Prl), dopamine receptor (D2r), TRH receptor (Trhr) genes and prolactin secretion by the porcine pituitary cells (days 9-10, 15-16 and 19-20 of the cycle) was assessed. The expression of Ppta and Tacr2 as well as NKA and TACR proteins in the pituitary tissue has been changing throughout the oestrous cycle. NKA affected in vitro the expression of studied genes and prolactin secretion depending on the stage of the cycle, dose of NKA and/or duration of the cell incubation. Altogether, the study indicates that NKA is engaged in the modulation of prolactin secretion in the pig during the oestrous cycle.

15 years on the Editorial Board of PEPTIDES

In this article, part of an issue of PEPTIDES celebrating the many years of dedication of Dr. A.J. Kastin as Editor-in-Chief of the journal, I describe how I first met him and how our friendship and collaboration developed. In 1970 I joined Dr. A.V. Schally's team at the Endocrine and Polypeptide Laboratories of Tulane University and the V.A. Hospital and it was at that time that I met Dr. Kastin for the first time. In 1984 I joined Dr. Schally's team for the second time and I began publishing part of my research findings in PEPTIDES. Afterward many more results from the research work were also published in PEPTIDES. I became a member of the Editorial Board of the same journal in 1999. It was going to be a very interesting experience. Some of my observations as a reviewer for PEPTIDES are described in the present article. Finally, I expressed my warmest congratulations to Dr. A.J. Kastin for the outstanding job that he carried out as Editor-in-Chief of PEPTIDES.

Lack of sensorial innervation in the newborn female rats affects the activity of hypothalamic monoaminergic system and steroid hormone secretion during puberty

There is evidence that sensory innervation plays a role regulating ovarian functions, including fertility.Since sensory denervation by means of capsaicin in newborn female rats results in a lower response togonadotropins, the present study analyzed the effects that sensory denervation by means of capsaicin in neonatal rats has on the concentration of monoamines in the anterior(AH) and medium (MH) hypothalamus, and on steroid hormone levels in serum. Groups of newborn female rats were injected subcutaneously with capsaicin and killed at 10, 20, and 30 days of age and on the first vaginal estrous.The concentrations of noradrenaline, dopamine, serotonin(5-HT), and their metabolites in the AH and MH were measured using HPLC, and the levels of estradiol (E),progesterone (P), testosterone (T), FSH, and luteinizing hormone using radioimmunoanalysis. The results show thatat 20 days of age, capsaicin-treated rats have lowernoradrenergic and serotonergic activities in the AH, and that the dopaminergic activity was lower in the MH. These results suggest that the sensorial system connections within the monoaminergic systems of the AH and MH are different.Capsaicin-treated animals had lower T, E, and P levels than in the control group, suggesting that the lower activity in the AH monoaminergic system and lower hormonesecretion could be explained by the blockade of information mediated by the sensory innervation (probably substance P), mainly between the ovary and the AH.

Role of Neurokinin B and Dynorphin A in pituitary gonadotroph and somatolactotroph cell lines

The role of Neurokinin B (NKB) and Dynorphin A (Dyn) in the regulation of the hypothalamic pituitary axis is an important area of recent investigation. These peptides are critical for the rhythmic release of GnRH, which subsequently stimulates the secretion of the gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The present study utilized the gonadotroph cell line LβT2 and the somatolactotroph GH3 cell line to examine the possible role of these peptides in pituitary hormone secretion. The NKB receptor (NK3R) and the Dyn receptor (the κ-opiate receptor (KOR)) were both detected in LβT2 cells and GH3 cells. NKB, by itself, failed to increase gonadotropin LHβ and FSHβ promoter activities and did not modulate the effects of GnRH on gonadotropin promoter activity. In GH3 cells, NKB significantly increased TRH-induced PRL promoter activity although NKB alone did not have an effect on basal PRL promoter activity. Dyn had no effect on gonadotropin promoters alone or in combination with GnRH stimulation. PRL promoters stimulated by TRH were not significantly changed by Dyn. TRH-induced PRL promoter activity was further increased in the presence of higher concentrations of NKB, whereas Dyn did not have a significant effect on the PRL promoter even at a high concentration. In addition, TRH-induced ERK (Extracelluar signal-regulated kinase) activation was enhanced in the presence of NKB. Our current study demonstrated that NKB had a stimulatory effect on PRL expression in a PRL-producing cell, but had no effect on gonadotropin secretion from a gonadotroph cell line.

Identification of Eya3 and TAC1 as long-day signals in the sheep pituitary

Seasonally breeding mammals such as sheep use photoperiod, encoded by the nocturnal secretion of the pineal hormone melatonin, as a critical cue to drive hormone rhythms and synchronize reproduction to the most optimal time of year. Melatonin acts directly on the pars tuberalis (PT) of the pituitary, regulating expression of thyrotropin, which then relays messages back to the hypothalamus to control reproductive circuits. In addition, a second local intrapituitary circuit controls seasonal prolactin (PRL) release via one or more currently uncharacterized low-molecular-weight peptides, termed "tuberalins," of PT origin. Studies in birds have identified the transcription factor Eya3 as the first molecular response activated by long photoperiod (LP). Using arrays and in situ hybridization studies, we demonstrate here that Eya3 is the strongest LP-activated gene in sheep, revealing a common photoperiodic molecular response in birds and mammals. We also demonstrate TAC1 (encoding the tachykinins substance P and neurokinin A) to be strongly activated by LP within the sheep PT. We show that these PRL secretagogues act on primary pituitary cells and thus are candidates for the elusive PT-expressed tuberalin seasonal hormone regulator.

A direct neuronal connection between the subparafascicular and ventrolateral arcuate nuclei in non-lactating female rats. Could this pathway play a role in the suckling-induced prolactin release?

The neuronal pathways, through which prolactin secretion is regulated during lactation, have still not been fully explored. Studies indicate that the suckling stimulus travels through the spinal cord, the brain stem, and then reaches the hypothalamus. The focus of this present experiment is to further explore the neuronal connections between the brain stem and the arcuate nucleus that may be involved in suckling-induced prolactin release. Ante- and retrograde tracing techniques were used. To chemically characterize the explored neurons neuropeptide immunohistochemistry was applied. Previous studies have indicated that the peripeduncular nucleus is a relay of the suckling stimulus in the midbrain, conveying the information to the hypothalamus. In our experiments, we have found an additional cell group in the subparafascicular parvocellular nucleus located just behind the posterior thalamus that projects to the arcuate neurons. The injection of the retrograde tracer into the ventrolateral part of the arcuate nucleus labeled cells in the lateral subdivision of the subparafascicular parvocellular nucleus. Anterograde tracing from the subparafascicular parvocellular nucleus resulted in fiber labeling in the arcuate nucleus in close apposition with dynorphin immunopositive neurons. Double labeling revealed that a subpopulations of the subparafascicular parvocellular neurons projecting to the arcuate nucleus contained tuberoinfundibular peptide of 39 residues or calcitonin gene-related peptide. The presented findings suggest that the ascending fibers from the subparafascicular parvocellular nucleus might be in the pathway involved in the suckling-induced prolactin release.

Blunted opiate modulation of prolactin response in smoking men and women

Endogenous opioids are integral in modulating drug reward, but it is believed that these may act through several mechanisms including hypothalamic-pituitary-adrenocortical (HPA) and dopamine pathways. This study was developed to examine how nicotine dependence alters endogenous opioid regulation of prolactin response, a peripheral marker of dopaminergic activity. Smokers and nonsmokers completed two sessions during which placebo or 50mg of naltrexone was administered, using a double-blind, counterbalanced design. Blood samples and mood measures were obtained during a resting absorption period, after exposure to two noxious stimuli (cold pressor and thermal pain), and during an extended recovery period. Opioid blockade increased prolactin response, indicating an inhibitory effect of the endogenous opioid system on prolactin, possibly mediated by reduced stimulatory effects of dopamine on this hormone. These responses were attenuated in smokers relative to nonsmokers. There was also a gender disparity in prolactin response, with women showing a stronger response to endogenous opioid modification than men regardless of smoking status. The attenuated effects of opioid blockade may reflect dysregulated opiodergic and dopaminergic effects. Results extend previous reports showing blunted opioid regulation of the HPA response in dependent smokers.

Substance P-immunoreactive cells in the ovine pars tuberalis

The pars tuberalis (PT) is a distinct subdivision of the anterior pituitary gland that plays a central role in regulating seasonal prolactin release. In sheep, there is compelling evidence that seasonal changes in light, transformed into a melatonin signal, are interpreted by the PT to modulate the release of a factor which affects prolactin release. The identity of this factor(s) is unknown but has been preemptively called 'tuberalin'. In the present study, we report on an initial immunocytochemical investigation where we have identified that many ovine PT cells are immunoreactive for the tachykinin substance P (SP). Few cells in the pars distalis immunoreact for SP. The SP-immunoreactive cells did not colocalize with beta-luteinizing hormone. RT-PCR confirmed the presence of preprotachykinin A mRNA in the PT. We hypothesize that SP, and possibly other preprotachykinin A-derived tachykinins, may play a role in the seasonal regulation of prolactin secretion in sheep.

Rethinking the stalk effect: a new hypothesis explaining suprasellar tumor-induced hyperprolactinemia

The pars tuberalis is a distinct subdivision of the pituitary gland but its function remains poorly understood. Suprasellar tumors in this pars tuberalis region are frequently accompanied by hyperprolactinemia. As these tumors do not immunoreact for any of the established pituitary hormones, they are classified as nonsecretory. It has been postulated that these suprasellar tumors induce hyperprolactinemia by compressing the pituitary stalk, resulting in impaired dopamine delivery to the pituitary and, consequently, disinhibition of the lactotropes. An alternative hypothesis proposed is that suprasellar tumors secrete a specific pars tuberalis factor that stimulates prolactin secretion. Hypothesized candidates are the preprotachykinin A derived tachykinins, substance P and/or neurokinin A.

Prolactin and dopamine: what is the connection? A review article

Dopamine (DA) holds a predominant role in the regulation of prolactin (PRL) secretion. Through a direct effect on anterior pituitary lactotrophs, DA inhibits the basally high-secretory tone of the cell. It accomplishes this by binding to D2 receptors expressed on the cell membrane of the lactotroph, activation of which results in a reduction of PRL exocytosis and gene expression by a variety of intracellular signalling mechanisms. The hypothalamic dopaminergic neurons, which provide DA to the anterior pituitary gland, are themselves regulated by feedback from PRL through a 'short-loop feedback mechanism'. A variety of other modulators of prolactin secretion act at the hypothalamic level by either disinhibition of the dopaminergic tone (e.g. serotonin, GABA, oestrogens and opioids) or by reinforcing it (e.g. substance P). All typical antipsychotic medications are associated with sustained hyperprolactinaemia due to their high affinity for the D2 receptor and their slow dissociation from the receptor once bound, but atypicals differ quite dramatically in their propensity to cause prolonged high prolactin levels. Of those atypicals that are associated with prolactin elevation, the main causative factor appears to be a higher peripheral-to-central dopamine receptor potency of either the parent drug or its active metabolite (e.g. risperidone, 9-hydroxy-risperidone and amisulpride). Antipsychotics that easily cross the blood-brain barrier and exhibit fast dissociation from the dopamine receptor once bound do not result in sustained hyperprolactinaemia.