Luteinizing hormone-releasing hormone (LHRH) receptors in the neuroendocrine-immune network. Biochemical bases and implications for reproductive physiopathology

GDM Alters Expression of Placental Estrogen Receptor α in a Cell Type and Gender-Specific Manner

OBJECTIVE

The nuclear receptor estrogen receptor α (ERα) is one of the key players in energy balance, insulin resistance, and trophoblast differentiation. We tested the hypothesis that gestational diabetes mellitus (GDM) alters expression of placental ERα in a cell type-specific manner and that this regulation may involve epigenetic changes.

STUDY DESIGN

Expression of ERα was analyzed by immunohistochemistry using the semiquantitative immunoreactive score in 80 placentas (40 GDM/40 controls). Quantitative real-time polymerase chain reaction (PCR) measured ERα messenger RNA (mRNA) in decidual tissue. Methylation-specific PCR was performed to analyze cytosine-phosphatidyl-guanine-island methylation of the ERα promoter.

RESULTS

Expression of ERα protein is upregulated (P = .011) in GDM in extravillous trophoblasts but not in syncytiotrophoblast. Gestational diabetes mellitus downregulated ERα in decidual vessels only in pregnancies with male but not female fetuses. Furthermore, mRNA of the ERα encoding gene estrogen receptor gene 1 (ESR1) was increased (+1.77 fold) in GDM decidua when compared to controls (P = .024). In parallel, the promoter of ESR1 was methylated only in decidua of healthy control individuals but not in GDM.

CONCLUSION

Gestational diabetes mellitus affects expression of placental ERα in a cell type-dependent way, on epigenetic level. These data link GDM with epigenetic deregulations of ERα expression and open new insights into the intrauterine programming hypothesis of GDM.

The compensatory expression of reproductive hormone receptors in the thymus of the male rat following active immunization against GnRH

To determine whether hormone-receptor signaling pathways in the thymus are altered by active immunization against gonadotrophin-releasing hormone I (GnRH), 3-week-old Sprague-Dawley male rats received GnRH-tandem-OVA peptides (200 μg/ml), and the effects were compared to a control group. Serum testosterone, LH and FSH concentrations were markedly reduced, with severe testicular atrophy, compared to controls, demonstrating effective blockade of the pituitary-gonadal axis. The reduction in LH and FSH concentrations in the thymus of immunized animals was lower than that observed in the serum, where a significant difference (P<0.001) in concentration was observed between both groups. Concentrations of GnRH were increased in the thymus of immunized rats. In thymic tissue, GnRHR, FSHR and LHR demonstrated stronger immunostaining, and AR weaker staining, in the immunized group compared to controls. Reproductive hormone receptor mRNA expression was consistent with protein variations in the immunized thymus. Compared to controls, GnRHR gene levels were significantly increased (P<0.05), however, AR mRNA expression were greatly decreased with immune week-age (P<0.05). Both FSHR and LHR mRNA expression levels were significantly higher in the treated group than in controls in the first three samples (P<0.05). When GnRHR was blocked by an antagonist in thymocytes, all reproductive hormone receptor gene expressions were significantly increased (P<0.001). In summary, these findings suggest that active immunization against GnRH can up-regulate GnRH receptor and gonadotropin receptor signaling, by stimulating thymic autocrine and paracrine function, whereas the androgen receptor is down-regulated due to a lack of testosterone secretion in the thymus.

Immune function in hypopituitarism: time to reconsider?

Hypopituitarism is not currently considered as a potential cause of immune disruption in humans. Accumulating data from in vitro and animal models support a role for the pituitary gland in immune regulation. Furthermore, the increased mortality risk noted in patients with adult hypopituitarism remains poorly explained and immune dysfunction could conceivably contribute to this observation. In a recent issue of Clinical & Experimental Immunology, we presented new data relating to immune status in adults with treated, severe hypopituitarism. We observed humoral immune deficiency in a significant proportion, despite stable pituitary replacement, including growth hormone (GH). This was especially evident in those with low pretreatment IGF-I levels and appeared independent of anticonvulsant use or corticosteroid replacement. These observations require substantiation with future studies. In this short review, we summarize existing data relating to the effects of pituitary hormones on immune function and discuss potential clinical implications surrounding the hypothesis of immune dysregulation in severe hypopituitarism.

Thymus as a target tissue of glucocorticoid action: what are the consequences of glucocorticoids thymectomy?

Glucocorticoids represent the most powerful endogenous anti-inflammatory and immunosuppressive effectors, interfering with virtually every step of immunoinflammatory responses. Glucocorticoids are often the most effective therapy in the prevention or suppression of inflammation and other immunologically mediated processes, but their use is limited by systemic side effects induced by the over-production of reactive oxygen species, causing dysregulation of physiological processes. The thymus is an organ with both endocrine and immune functions. Glucocorticoids induce thymocyte apoptosis, causing a profound reduction in thymic mass and volume and inducing hormonal thymectomy. The clinical aspects of glucocorticoid thymectomy are not under enough investigation. These unwanted systemic side effects may be the consequence of prolonged therapeutic application of glucocorticoids and prolonged or chronic activation of the hypothalamic-pituitary adrenal axis, which may lead to increased and prolonged secretion of glucocorticoids. This review will discuss the metabolic effects of glucocorticoids in the context of thymic physiology asthe primary sex hormone-responsive organ.

Gonadotropin-releasing hormone agonist administration affects the thymopoiesis in adult female rats independently on gonadal hormone production

PROBLEM

In addition to having an indirect effect on the T-cell development by controlling the production of ovarian steroids, an accumulating body of evidence suggest that GnRH analogue (GnRH-A) administration may exert a thymopoietic regulatory effect that is not mediated by ovarian hormones.

METHOD OF STUDY

In non-ovariectomized (non-OVX) and OVX adult female AO rats treated s.c. with GnRH-A or saline (controls), over 14 days, were estimated the thymic cellularity and thymocyte expression of CD4/CD8/TCRalphabeta by stereological analysis and three-color flow cytometry, respectively.

RESULTS

GnRH-A in both groups of rats diminished the thymic cellularity. In non-OVX rats GnRH-A increased the relative numbers of immature cells (CD4-8-TCRalphabeta(-), CD4-8-TCRalphabeta(low) and CD4+8-TCRalphabeta(low)), and reduced those of positively selected CD4+8+TCRalphabeta(high) and mature (CD4-8+TCRalphabeta(high), CD4(+8)-TCRalphabeta(high)) cells, suggesting decelerated expression of TCRalphabeta followed by less efficient positive selection and further maturation of the selected cells. Differently, in OVX rats GnRH-A decreased the percentage of immature (CD4-8-TCRalphabeta(-), CD4+8+ TCRalphabeta(-)) cells and increased those of all TCRalphabeta(high) subsets, suggesting an increased rate of early thymocyte differentiation, more efficient positive selection and further maturation of the selected cells.

CONCLUSIONS

The effect of GnRH-A administration is affected by the presence of ovarian steroids.

Major molecular differences between mammalian sexes are involved in drug metabolism and renal function

Many anatomical differences exist between males and females; these are manifested on a molecular level by different hormonal environments. Although several molecular differences in adult tissues have been identified, a comprehensive investigation of the gene expression differences between males and females has not been performed. We surveyed the expression patterns of 13,977 mouse genes in male and female hypothalamus, kidney, liver, and reproductive tissues. Extensive differential gene expression was observed not only in the reproductive tissues, but also in the kidney and liver. The differentially expressed genes are involved in drug and steroid metabolism, osmotic regulation, or as yet unresolved cellular roles. In contrast, very few molecular differences were observed between the male and female hypothalamus in both mice and humans. We conclude that there are persistent differences in gene expression between adult males and females. These molecular differences have important implications for the physiological differences between males and females.

Immunomodulatory actions of gonadal steroids may be mediated by gonadotropin-releasing hormone

Estrogens are considered to be immunostimulatory, whereas androgens are considered to be immunosuppressive. We hypothesized that the divergent actions of gonadal steroids on the immune system may be mediated indirectly, via their potent divergent feedback effects on the hypothalamic hormone GnRH, which is itself immunostimulatory. We used the GnRH-deficient HPG/Bm mouse in an effort to disentangle the effects of gonadal steroids from the effects of GnRH. We randomized GnRH-deficient mice and their GnRH-sufficient littermates to receive androgens, estrogens, or GnRH. We subsequently measured B and T cell proliferative responses to mitogen and serum IgG levels. We demonstrate that estrogens exert stimulatory effects on B cell proliferation and serum IgG levels in the presence of GnRH but not in the absence of GnRH. Testosterone exerts suppressive effects on B cell function in the presence of GnRH but not in its absence. Androgens and estrogens exerted divergent actions on T cell function irrespective of the presence and absence of GnRH, although responses were markedly attenuated in GnRH-deficient mice. Our data suggest that the immunostimulatory effects of estrogen and the immunosuppressive effects of androgens on B cell function may be mediated indirectly via GnRH.

The reproductive system at the neuroendocrine-immune interface: focus on LHRH, estrogens and growth factors in LHRH neuron-glial interactions

Bidirectional communication between the neuroendocrine and immune systems plays a pivotal role in health and disease. Signals generated by the hypothalamic-pituitary-gonadal (HPG) axis (i.e. luteinizing hormone-releasing hormone, LHRH, and sex steroids) are major players coordinating the development immune system function. Conversely, products generated by immune system activation exert powerful and longlasting effects on HPG axis activity. In the central nervous system (CNS), one chief neuroendocrine-immune (NEI) compartment is represented by the astroglial cell population and its mediators. Of special interest, the major supporting cells of the brain and the thymus, astrocytes and thymic epithelial cells, share a similar origin and a similar set of peptides, transmitters, hormones and cytokines functioning as paracrine/autocrine regulators. This may explain some fundamental analogies in LHRH regulation of both cell types during ontogeny and in adult life. Hence, the neuropeptide LHRH significantly modulates astrocyte and thymic cell development and function. Here we focus this work on LHRH neuron-glial signaling cascades which dictate major changes during LHRH neuronal differentiation and growth as well as in response to hormonal manipulations and pro-inflammatory challenges. The interplay between LHRH, growth factors, estrogens and pro-inflammatory mediators will be discussed, and the potential physiopathological implications of these findings summarized. The overall study highlights the plasticity of this intersystem cross-talk and emphasize neuron-glial interactions as a key regulatory level of neuroendocrine axes activity.

Type II gonadotropin-releasing hormone receptor transcripts in human sperm

GnRH regulates reproduction via the well-characterized mammalian pituitary GnRH receptor (type I). In addition, two homologous genes for a second form of the GnRH receptor (type II) are present in the human genome, one on chromosome 14 and the second on chromosome 1. The chromosome 14 gene is ubiquitously transcribed at high levels in the antisense orientation but lacks exon 1, required to encode a full-length receptor. In comparison, the chromosome 1 gene contains all three exons. The issue of whether this gene is transcribed in any human tissue(s), and whether these transcripts encode a functional receptor protein, remains unresolved. We have directly addressed this by screening a panel of human RNAs by hybridization and RT-PCR. These analyses showed that, unlike the chromosome 14 gene, chromosome 1 gene expression is limited and of low abundance. Exon 1-containing transcripts were detected by in situ hybridization in mature sperm and in human postmeiotic testicular cells. Further sequence analysis revealed that although all the potential coding segments were present, the human transcripts, like the gene, contain a stop codon within the coding region and a frame-shift relative to other mammalian GnRH receptors. Although this suggests that the human gene may be a transcribed pseudogene, a functional type II GnRH receptor cDNA has recently been cloned from monkeys. Given the well-established role of GnRH in spermatogenesis and reported evidence of type II GnRH receptor immunoreactivity in human tissues, it is possible that the chromosome 1 gene is functional.

Developmental expression of three different prepro-GnRH (gonadotrophin-releasing hormone) messengers in the brain of the European sea bass (Dicentrarchus labrax)

In this study, we have analyzed the ontogenic expression of three gonadotrophin-releasing hormones (GnRH) systems expressed in the brain of a perciform fish, the European sea bass, using in situ hybridization. The riboprobes used correspond to the GnRH-associated peptide (GAP) coding regions of the three prepro-GnRH cDNAs cloned from the same species: prepro-salmon GnRH, prepro-seabream GnRH and prepro-chicken GnRH II. On day 4 after hatching, the first prepro-chicken GnRH-II mRNA-expressing cells appeared in the germinal zone of the third ventricle. They increased in number and size from 10 to 21 days, reaching at day 30 their adult final position, within the synencephalic area, at the transitional zone between the diencephalon and the mesencephalon. First prepro-salmon GnRH mRNA-expressing cells became evident on day 7 arising from the olfactory placode and migrating towards the olfactory nerve. On day 10, this cell group reached the olfactory bulb, being evident in the ventral telencephalon and preoptic area from days 15 and 45, respectively. Weakly labeled prepro-seabream GnRH mRNA-expressing cells were first detected at 30 days in the olfactory area and ventral telencephalon. On day 45, prepro-seabream GnRH mRNA-expressing cells were also present in the preoptic region reaching the ventrolateral hypothalamus on day 60. The results obtained in sea bass indicate that sGnRH and sbGnRH cells have a common origin in an olfactory primordium suggesting that both forms might arise from a duplication of a single ancestral gene, while cGnRH-II cells develop from a synencephalic primordium.

Neuroendocrine-immune (NEI) circuitry from neuron-glial interactions to function: Focus on gender and HPA-HPG interactions on early programming of the NEI system

Bidirectional communication between the neuroendocrine and immune systems during ontogeny plays a pivotal role in programming the development of neuroendocrine and immune responses in adult life. Signals generated by the hypothalamic-pituitary-gonadal axis (i.e. luteinizing hormone-releasing hormone, LHRH, and sex steroids), and by the hypothalamic-pituitary-adrenocortical axis (glucocorticoids (GC)), are major players coordinating the development of immune system function. Conversely, products generated by immune system activation exert a powerful and long-lasting regulation on neuroendocrine axes activity. The neuroendocrine-immune system is very sensitive to preperinatal experiences, including hormonal manipulations and immune challenges, which may influence the future predisposition to several disease entities. We review our work on the ongoing mutual regulation of neuroendocrine and immune cell activities, both at a cellular and molecular level. In the central nervous system, one chief compartment is represented by the astroglial cell and its mediators. Hence, neuron-glial signalling cascades dictate major changes in response to hormonal manipulations and pro-inflammatory triggers. The interplay between LHRH, sex steroids, GC and pro-inflammatory mediators in some physiological and pathological states, together with the potential clinical implications of these findings, are summarized. The overall study highlights the plasticity of this intersystem cross-talk for pharmacological targeting with drugs acting at the neuroendocrine-immune interface.

Gender, neuroendocrine-immune interactions and neuron-glial plasticity. Role of luteinizing hormone-releasing hormone (LHRH)

Signals generated by the hypothalamic-pitutary-gonadal (HPG) axis powerfully modulate immune system function. This article summarizes some aspects of the impact of gender in neuroendocrine immunomodulation. Emphasis is given to the astroglial cell compartment, defined as a key actor in neuroendocrine immune communications. In the brain, the principal hormones of the HPG axis directly interact with astroglial cells. Thus, luteinizing hormone releasing hormone, LHRH, influences hypothalamic astrocyte development and growth, and hypothalamic astrocytes direct LHRH neuron differentiation. Hormonally induced changes in neuron-glial plasticity may dictate major changes in CNS output, and thus actively participate in sex dimorphic immune responses. The impact of gender in neuroimmunomodulation is further underlined by the sex dimorphism in the expression of genes encoding for neuroendocrine hormones and their receptors within the thymus, and by the potent modulation exerted by circulating sex steroids during development and immunization. The central role of glucocorticoids in the interactive communication between neuroendocrine and immune systems, and the impact of gender on hypothalamic-pituitary-adrenocortical (HPA) axis modulation is underscored in transgenic mice expressing a glucocorticoid receptor antisense RNA.

Neurobiological mechanisms of the onset of puberty in primates

An increase in pulsatile release of LHRH is essential for the onset of puberty. However, the mechanism controlling the pubertal increase in LHRH release is still unclear. In primates the LHRH neurosecretory system is already active during the neonatal period but subsequently enters a dormant state in the juvenile/prepubertal period. Neither gonadal steroid hormones nor the absence of facilitatory neuronal inputs to LHRH neurons is responsible for the low levels of LHRH release before the onset of puberty in primates. Recent studies suggest that during the prepubertal period an inhibitory neuronal system suppresses LHRH release and that during the subsequent maturation of the hypothalamus this prepubertal inhibition is removed, allowing the adult pattern of pulsatile LHRH release. In fact, y-aminobutyric acid (GABA) appears to be an inhibitory neurotransmitter responsible for restricting LHRH release before the onset of puberty in female rhesus monkeys. In addition, it appears that the reduction in tonic GABA inhibition allows an increase in the release of glutamate as well as other neurotransmitters, which contributes to the increase in pubertal LHRH release. In this review, developmental changes in several neurotransmitter systems controlling pulsatile LHRH release are extensively reviewed.

In vivo modulation of the distribution of thymocyte subsets by female sex steroid hormones

This study examined the effects of the principal ovarian steroids, 17 beta-estradiol (E) and progesterone (P), on the thymic structure and on the intrathymic development of T-cells. Adult female rats were ovariectomized (OVX) and treated for 14 days with physiological doses of either E or P; controls received an equivalent volume of vehicle. Ovariectomy produced a marked increase (vs. sham-operated controls) in thymus weight, which was associated with an increase in the volume and cellularity of both the medulla and cortex. Treatment of OVX rats with E reduced the thymic weight to value, which was significantly lower than that of sham-operated controls decreasing the volume of cortex below level in sham-OVX rats, and reversing the effect of ovariectomy on the volume of medulla. P only prevented the increases in thymus weight and cortical volume induced by OVX. However, unlike E, it had no discernable effect on the medullary volume. E treatment reduced the cellularity of the cortex and medulla to values, which were lower than those of sham-OVX rats, while P only reversed the effects of OVX on the cellularity of both the compartments. Ovariectomy also had a profound effect on the thymocyte profile, increasing the proportion of CD4+8+TCR alpha beta- cells and producing a corresponding decrease in the relative proportions of all TCR alpha beta high cell subsets. The decrease in the latter was opposed by treatment with E or P. However, the sensitivity of the less mature cells (except CD4-8-TCR alpha beta-, the percentage of which was reduced by both hormones) to the two hormones differed. E reduced the relative proportion of CD4-8+TCR alpha beta-, CD4-8+TCR alpha beta low and CD4+8+TCR alpha beta- cells, while P increased the percentage of CD4-8+TCR alpha beta low cells. The results suggest that E and P affect both the lymphoid and nonlymphoid compartments of the thymus, and that while P increases the volume of the nonlymphoid component of the medulla, E has the opposite effect. The finding that ovariectomy decreased while E and P increased the relative proportion of the most mature thymocytes, which include CD4-8-TCR alpha beta high cells that are believed to harbour potentially autoreactive cell clones, is particularly interesting and may relate to the high propensity of autoimmune diseases in females.

Immortalized hypothalamic luteinizing hormone-releasing hormone (LHRH) neurons induce a functional switch in the growth factor responsiveness of astroglia: involvement of basic fibroblast growth factor

Recent evidence indicates that astroglial-derived growth factors (GFs) participate in the development of luteinizing hormone-releasing hormone (LHRH) neurons, but it is still unknown whether LHRH neurons may exert a reciprocal modulation of glial cell function. Using immortalized hypothalamic LHRH (GT1-1) neurons in co-culture with glial cells, we have recently shown that basic fibroblast growth factor (bFGF) plays a prominent role in the glial-induced acquisition of the mature LHRH phenotype by GT1-1 cells. We have resorted to this model and combined biochemical and morphological approaches to study whether the response of glial cells to a number of GFs (including bFGF, insulin-like growth factor I, IGF-I, epidermal growth factor, EGF and insulin) expressed during LHRH neuron differentiation, is modulated by co-culture with pure LHRH neurons. Pre-treatment of hypothalamic astrocytes with an inactive ('priming') dose of bFGF for 12 h powerfully increased astroglia proliferative response to IGF-I (10 ng/ml), EGF (10 g/ml) and insulin (10 microg/ml), inducing a 65-100% increase in the [3H]thymidine incorporation compared to untreated cultures. When astroglial cells and developing GT1-1 neurons were co-cultured for 5 days in vitro (DIV), the [3H]thymidine incorporation was significantly higher than in astroglial cells cultured without neurons. Application of the different GFs to the co-culture for either 12 or 24 h further stimulated DNA synthesis to various extent according to the GF applied and the time of application. Localization of the proliferating cells by dual immunohistochemical staining, followed by cell counting and bromodeoxiuridine (BrdU) labeling index calculation, revealed that the incorporation of BrdU was restricted to the nuclei of LHRH-immunopositive neurons. Such changes were accompanied by extensive morphological alterations of astroglial and LHRH fiber networks, whereas neutralization of bFGF activity in GT1-1 neuron-glial co-cultures by a bFGF-antibody, dramatically counteracted the observed effects. The functional switch of astroglia proliferative response to GFs coupled to the potent morphological and functional modifications of developing glia and pure LHRH neurons observed in vitro, support a bidirectional interaction between immortalized LHRH neurons and astroglial cells and identify bFGF as a key player in this crosstalk.

Basic fibroblast growth factor (bFGF) acts on both neurons and glia to mediate the neurotrophic effects of astrocytes on LHRH neurons in culture

Luteinizing hormone-releasing hormone (LHRH) neurons play a pivotal role in the neuroendocrine control of mammalian reproduction. Astrocytes were shown to be involved in the regulation of LHRH neuronal function, but little is known about the contribution of astroglial-derived factors in the regulation of LHRH neuron development. In order to gain insight into the mechanisms regulating the development of these cells, at morphological and biochemical levels we characterized the neurotrophic effects exerted by young astrocytes (maintained in culture for 8 days in vitro) and old astrocytes (maintained 26 days) on the differentiation, proliferation, and phenotypic expression of immortalized hypothalamic LHRH (GT(1-1)) neurons in vitro. Culturing GT(1-1) cells in the presence of young glia for different time intervals caused a marked acceleration in the acquisition of their neuronal phenotype. At all times examined, GT(1-1) cells cocultured with young glia exhibited a significantly greater extension of processes/cell, larger number of processes/cell and greater surface area of growth cones than GT(1-1) cells grown over nonglial adhesive substrates (polylysine). By contrast, when GT(1-1) neurons were cocultured with old glia, the length of neuronal processes and the growth cone surface area were significantly lower than in control GT(1-1) neurons cultured in the absence of glia. At 3 days in vitro (DIV), GT(1-1) neurons cocultured with young glia exhibited a 50% lower incorporation of [(3)H]thymidine than GT(1-1) neurons cultured without glia. By contrast, in the presence of old glia [(3)H]thymidine incorporation was significantly higher in cells cocultured with glia than in GT(1-1) neurons cultured alone. Localization of the proliferating cells by dual immunohistochemical staining revealed that the incorporation of bromodeoxiuridine (BrdU) was restricted to nuclei of GT(1-1) neurons when these were cocultured with young glia, but associated with both neurons and astrocytes in the presence of old glia. At the functional level, coculture of GT(1-1) neurons with young glia increased the spontaneous release of LHRH as compared to GT(1-1) neurons grown in the absence of glia. By contrast, in the presence of old glia LHRH release in the medium was significantly lower than in controls. Conditioned medium of young glia (ACM-Y) induced significant neurotrophic and functional effects on GT(1-1) cells, but these effects were 50% less potent than the coculture itself. Heat denaturation of ACM-Y totally abolished its neurotrophic and functional properties, indicating that they involved a peptide factor. Suppression of bFGF activity in ACM-Y reduced its neurotrophic activity by approximately 40%, but did not affect its LHRH release-promoting effects. By contrast, neutralization of endogenous bFGF activity in GT(1-1) neurons cocultured with young glia counteracted both neurotrophic and functional effects of young glia. Treatment of old glia with bFGF rescued its neurotrophic and functional effects on GT(1-1) cells. Moreover, the ACM of aged bFGF-treated old glia was the most powerful neurotrophic stimulus for GT(1-1) neurons. These results suggest that: 1) soluble peptidic factors, including bFGF, and mechanism(s) requiring coculture are responsible for the highly potent neurotrophic and functional effects of young glia; 2) the inhibitory effects of old glia on neurite outgrowth and LHRH release are mediated in part by soluble inhibitory molecules and in part by factors requiring coculture with old glia; 3) old glia may revert to a growth-supporting state when treated with bFGF and this functional shift involves a diffusible molecule with potent neurotrophic and functional effects on immortalized LHRH neurons. (c) 2000 Wiley-Liss, Inc.

The effect of restricted nutrition on uterine macrophage populations in mice

The abundant macrophage populations present in the endometrium are implicated in the tissue remodelling events and immunological changes necessary for pregnancy. Using two regimens of restricted nutrition (95 and 88% of ad libitum intake for 19 days), we have shown that moderately reduced food consumption can dramatically alter the number of endometrial macrophages and their immunoaccessory function in mice. Restricted nutrition also interfered with the estrous cycle, but the effects on endometrial macrophages were more extensive and qualitatively different than could be explained by diminished ovarian steroid hormone activity. Significantly less F4/80+ and Ia+ cells were found in the endometrium of food restricted mice than in ad libitum mice at the same estrous cycle stage. In the more severely restricted mice the losses were even greater than those seen after ovariectomy. In ad libitum fed animals, uterine but not peritoneal macrophages showed an ovarian hormone-dependent inhibitory phenotype in a splenocyte mitogenesis assay. Macrophages derived from both locations exhibited greater immunostimulatory activity following restricted nutrition. We conclude that endometrial macrophage populations are influenced by nutritional status and this may be mediated through both steroid hormone-dependent and -independent mechanisms. Nutritionally induced aberrations in the number or behaviour of endometrial macrophages during the estrous cycle or in early pregnancy could have important implications for the quality of the pre- and peri-implantation environment and the maternal immune response to pregnancy.

Luteinizing hormone-releasing hormone is a primary signaling molecule in the neuroimmune network

The brain-pituitary-reproductive axis and the brain thymus-lymphoid axis are linked by an array of internal mechanisms of communication that use similar signals (neurotransmitters, peptides, growth factors, hormones) acting on similar recognition targets. Moreover, such communication networks form the basis and control each step and every level of reproductive physiology. This presentation highlights the extent to which endocrine, neural, glial, or immunologically competent cells may achieve their specific functions using common mechanisms, but employing them to different degrees. In particular, this work will focus on LHRH, the chief hormone orchestrating reproductive events. Within the thymus LHRH plays a unique role of immunomodulator, contributing to the sex-dependent changes in immune responsiveness during the estrous-menstrual cycle as well as pregnancy. From the recent cloning and sequencing of lymphocyte LHRH, the expression of LHRH receptor mRNA in lymphocyte, the transduction mechanisms involved, and the steroidogenic sensitivity of the intralymphocyte LHRH system. It would appear that this peptide may act as an immunological response modifier in the brain-pituitary-lymphoid-gonadal axis. The interplay between neuronal, endocrine, and immune compartments is further emphasized in the study of LHRH-astroglial interactions. Astrocytes are able to manufacture a wide variety of signaling agents and can secrete immunoregulatory molecules that influence immune cells, as well as the glial cells themselves. Astroglia and the immortalized hypothalamic LHRH (GT1-1) neurons communicate with an array of mechanisms, via soluble mediators as well as cell-to-cell contacts. Manipulation of astroglial-derived cytokines and nitric oxide (NO) in GT1-1 neuron-astroglia cocultures, underscores a potential cross-talk between different intra/inter-cellular mediators in the dynamic control of LHRH release. Further studies aimed to disclose at a biochemical and a molecular level such bidirectional, informative network will give us new insights into more general issues concerned with the malfunction of the neuroendocrine-immune axis.

Changes in lymphoid tissue after treatment with a gonadotropin releasing hormone antagonist in the neonatal marmoset (Callithrix jacchus)

PROBLEM

The effect of neonatal treatment with a gonadotropin releasing hormone (GnRH) antagonist on the morphology and distribution of lymphocytes in lymphoid tissue of the infant marmoset was examined.

METHOD OF STUDY

From a screened panel of antihuman antibodies for specific immune cells, antibodies for the CD20 and CD3 antigens showed excellent reactivity with marmoset tissue. Five sets of marmoset twins were treated with either the GnRH antagonist or a vehicle from birth, and were euthanized at 7 to 9 (3 sets) or 16 to 20 weeks (2 sets) of age. The spleen, thymus, and inguinal lymph nodes from each animal were processed for immunocytochemistry, and the number of cells expressing the CD20 and CD3 antigens were quantified.

RESULTS

Control twins exhibited high plasma levels of testosterone, characteristic of the neonatal period, whereas testosterone concentrations were reduced (P = 0.001) to detection limits in the GnRH antagonist-treated twins. Microscopic evaluation suggested that treatment reduced the volume and cellularity of the thymic cortex, resulting in a decrease in the cortical-to-medullary ratio. Treatment reduced (P = 0.046) the number of thymocytes expressing the B-cell antigen (CD20) and marginally lowered (P = 0.067) the number expressing the T-cell antigen (CD3) in the thymic medulla. In the spleens of treated animals, periarterial lymphatic sheaths were less prominent on microscopic examination, and there were marginally fewer (P = 0.064) CD3+ cells. Numbers of CD20+ lymphocytes in the peripheral white pulp of the spleen and in the germinal centers of the lymph nodes, or CD3+ cells in the paracortex and germinal centers of the lymph nodes, were not altered by treatment.

CONCLUSION

Neonatal treatment with a GnRH antagonist may alter maturational processes for B and T cells in the thymus and spleen of the marmoset and may deprive the immune system of its normal sensitivity to GnRH at a potentially critical time in development.

Second gene for gonadotropin-releasing hormone in humans

Gonadotropin-releasing hormone (GnRH) is a decapeptide widely known for its role in regulating reproduction by serving as a signal from the hypothalamus to pituitary gonadotropes. In addition to hypothalamic GnRH (GnRH-I), a second GnRH form (pGln-His-Trp-Ser-His-Gly-Trp-Tyr-Pro-Gly; GnRH-II) with unknown function has been localized to the midbrain of many vertebrates. We show here that a gene encoding GnRH-II is expressed in humans and is located on chromosome 20p13, distinct from the GnRH-I gene that is on 8p21-p11.2. The GnRH-II genomic and mRNA structures parallel those of GnRH-I. However, in contrast to GnRH-I, GnRH-II is expressed at significantly higher levels outside the brain (up to 30x), particularly in the kidney, bone marrow, and prostate. The widespread expression of GnRH-II suggests it may have multiple functions. Molecular phylogenetic analysis shows that this second gene is likely the result of a duplication before the appearance of vertebrates, and predicts the existence of a third GnRH form in humans and other vertebrates.

Effects of long-term gonadotrophin-releasing hormone analog treatment on growth, growth hormone (GH) secretion, GH receptors, and GH-binding protein in the rat

Long-acting gonadotropin-releasing hormone (GnRH) analogs (GnRH-a) suppress gonadal steroid production and are used in precocious puberty, resulting in an arrest of pubertal development, a slower epiphyseal maturation, and a deceleration of growth, but an increased final height. However, the way that GnRH-a affect growth is not clear. GnRH-a treatment might not only affect gonadal steroid production but might also modulate the GH axis and thereby affect growth. We used a rat model to investigate the long-term effects of prepubertally started GnRH-a treatment (triptorelin) on growth, spontaneous GH secretion, hepatic GH receptors (GHR), and GH-binding protein (GHBP) and compared it with surgical gonadectomy. Triptorelin affected most parameters in the same direction as surgical gonadectomy but to a lesser extent. In females, growth was enhanced by triptorelin, baseline GH secretion was decreased, and hepatic GHR and GHBP were decreased. Apart from these effects on the GH axis, reduction of the direct inhibiting effect of estrogen on growth could be responsible for the triptorelin-induced growth. In males, triptorelin treatment enhanced body weight gain and slightly enhanced gain in length. GH peak amplitude was the only parameter of GH secretion affected and decreased, whereas GHR or GHBP were not affected. This stimulation of weight gain by long-term triptorelin treatment in male rats, which is opposite the effect of surgical gonadectomy, could indicate an interference of GnRH-a in the hormonal regulation of food intake and body weight control. We conclude that triptorelin treatment affected growth and the GH-GHR-GHBP axis in rats, more markedly in females than in males. However, triptorelin was not as effective as surgical gonadectomy.

Circadian melatonin and young-to-old pineal grafting postpone aging and maintain juvenile conditions of reproductive functions in mice and rats

Chronic, night administration of melatonin to aging mice and transplantation of a young pineal gland into the thymic rudiment of older mice and rats have been studied with the aim of evaluating their effects on aging of gonadal, sexual, and reproductive functions. Both melatonin administration and young-to-old pineal grafting positively affect size and function of testes and maintenance of juvenile hippocampal and testicular LHRH-receptors and beta-adrenergic receptors in the tests of old rats and mice. These results demonstrate that a pineal-directed circadian function and cyclicity is fundamental for the regulation of sexual, reproductive physiology, and that proper intervention with melatonin may potentially postpone aging of both neural and gonadal sexual function.