Biomedical subjects

Sergio R Ojeda

Publications and source records attributed to Sergio R Ojeda.

At least 19 recordsLinked to original sources

PubMed2006

Deletion of the Ttf1 gene in differentiated neurons disrupts female reproduction without impairing basal ganglia function.

Thyroid transcription factor 1 (TTF1) [also known as Nkx2.1 (related to the NK-2 class of homeobox genes) and T/ebp (thyroid-specific enhancer-binding protein)], a homeodomain gene required for basal forebrain morphogenesis, remains expressed in the hypothalamus after birth, suggesting a role in neuroendocrine function. Here, we show an involvement of TTF1 in the control of mammalian puberty and adult reproductive function. Gene expression profiling of the nonhuman primate hypothalamus revealed that TTF1 expression increases at puberty. Mice in which the Ttf1 gene was ablated from differentiated neurons grew normally and had normal basal ganglia/hypothalamic morphology but exhibited delayed puberty, reduced reproductive capacity, and a short reproductive span. These defects were associated with reduced hypothalamic expression of genes required for sexual development and deregulation of a gene involved in restraining puberty. No extrapyramidal impairments associated with basal ganglia dysfunction were apparent. Thus, although TTF1 appears to fulfill only a morphogenic function in the ventral telencephalon, once this function is satisfied in the hypothalamus, TTF1 remains active as part of the transcriptional machinery controlling female sexual development.

Animals↗

PubMed2006

FSH regulates acetycholine production by ovarian granulosa cells.

BACKGROUND: It has been previously shown that cultured granulosa cells (GCs) derived from human ovarian preovulatory follicles contain choline acetyltransferase (ChAT), the enzyme responsible for acetylcholine (ACh) synthesis. They also produce ACh and express functional muscarinic ACh receptors. ACh can act on GCs to increase proliferation, disrupt gap junctional communication, alter intracellular calcium levels, as well as expression of transcription factors, suggesting an unrecognized role of ACh in GC function. To gain further insights into the possible role of ACh in the ovary, we examined ChAT expression in the gland before and after birth, as well as in adults, and studied the regulation of ACh production by FSH. METHODS: ChAT immunohistochemistry was performed using ovarian samples of different species and ages (embryonic, postnatal and adult rats and mice, including embryonic ovaries from mice null for ChAT, neonatal and adult rhesus monkeys and adult humans). ACh was measured by HPLC and/or a fluorescence based method in rat ovaries and in a FSH receptor-expressing cell line (rat GFSHR-17) cultured with or without FSH. RESULTS: In adult rat, as well as in all other species, ovarian ChAT immunoreactivity is associated with GCs of antral follicles, but not with other structures, indicating that GCs are the only ovarian source of ACh. Indeed ACh was clearly detected in adult rat ovaries by two methods. ChAT immunoreactivity is absent from embryonic and/or neonatal ovaries (mouse/rat and monkey) and ovarian development in embryonic mice null for ChAT appears normal, suggesting that ACh is not involved in ovarian or follicular formation. Since ChAT immunoreactivity is present in GCs of large follicles and since the degree of the ChAT immunoreactivity increases as antral follicles grow, we tested whether ACh production is stimulated by FSH. Rat GFSHR-17 cells that stably express the FSH receptor, respond to FSH with an increase in ACh production. CONCLUSION: ACh and ChAT are present in GCs of growing follicles and FSH, the major driving force of follicular growth, stimulates ACh production. Since ACh stimulates proliferation and differentiation processes in cultured GCs, we suggest that ACh may act in the growing ovarian follicle as a local mediator of some of the actions ascribed to FSH.

Acetylcholine↗

PubMed2006

Quantitative proteomics identifies a change in glial glutamate metabolism at the time of female puberty.

Mammalian puberty requires activation of luteinizing hormone-releasing hormone (LHRH) neurons. In turn, these neurons are controlled by transsynaptic and glia-to-neuron communication pathways, which employ diverse cellular proteins for proper function. We have now used a high throughput relative quantitative proteomics technique to identify such proteins. We selected the method of two-dimensional liquid chromatography tandem mass spectrometry (2DLC-MS/MS) and cleavable isotope-coded affinity tags (cICAT), to both identify and quantify individual proteins within a complex protein mixture. The proteins used derived from the hypothalamus of juvenile (25-day-old) and peripubertal (first proestrus, LP) female rats, and their identity was established by analyzing their mass spectra via database searching. Five proteins involved in glutamate metabolism were detected and two of them appeared to be differentially expressed. They were selected for further analysis, because of their importance in controlling glutamate synthesis and degradation, and their preferential expression in astroglial cells. One, glutamate dehydrogenase (GDH) catalyzes glutamate synthesis; its hypothalamic content detected by 2DLC-MS/MS increases at first proestrus. The other, glutamine synthetase (GS), catalyzes the metabolism of glutamate to glutamine; its content decreases in proestrus. Western blot analysis verified these results. Because these changes suggested an increased glutamate production at puberty, we measured glutamate release from hypothalamic fragments from juvenile 29-day old rats, and from rats treated with PMSG to induce a premature proestrus surge of luteinizing hormone (LH). To determine the net output of glutamate in the absence of re-uptake we used the excitatory amino acid transporter (EAAT) inhibitor l-trans-pyrrolidine-2,4-dicarboxylic acid (PDC). PDC elicited significantly more glutamate- and LHRH-release from the proestrus hypothalamus. Thus, an increase excitatory drive to the LHRH neuronal network provided by glutamatergic inputs of glial origin, is an event contributing to the pubertal activation of LHRH secretion.

Age Factors↗

PubMed2006

Hypothalamic tumor necrosis factor-alpha converting enzyme mediates excitatory amino acid-dependent neuron-to-glia signaling in the neuroendocrine brain.

Glial erbB1 receptors play a significant role in the hypothalamic control of female puberty. Activation of these receptors by transforming growth factor alpha (TGFalpha) results in production of prostaglandin E2, which then stimulates luteinizing hormone releasing hormone (LHRH) neurons to secrete LHRH, the neuropeptide controlling sexual development. Glutamatergic neurons set in motion this glia-to-neuron signaling pathway by transactivating erbB1 receptors via coactivation of AMPA receptors (AMPARs) and metabotropic glutamate receptors (mGluRs). Because the metalloproteinase tumor necrosis factor alpha converting enzyme (TACE) releases TGFalpha from its transmembrane precursor before TGFalpha can bind to erbB1 receptors, we sought to determine whether TACE is required for excitatory amino acids to activate the TGFalpha-erbB1 signaling module in hypothalamic astrocytes, and thus facilitate the advent of puberty. Coactivation of astrocytic AMPARs and mGluRs caused extracellular Ca2+ influx, a Ca2+/protein kinase C-dependent increase in TACE-like activity, and enhanced release of TGFalpha. Within the hypothalamus, TACE is most abundantly expressed in astrocytes of the median eminence (ME), and its enzymatic activity increases selectively in this region at the time of the first preovulatory surge of gonadotropins. ME explants respond to stimulation of AMPARs and mGluRs with LHRH release, and this response is prevented by blocking TACE activity. In vivo inhibition of TACE activity targeted to the ME delayed the age at first ovulation, indicating that ME-specific changes in TACE activity are required for the normal timing of puberty. These results suggest that TACE is a component of the neuron-to-glia signaling process used by glutamatergic neurons to control female sexual development.

ADAM Proteins↗

PubMed2006

Voltage-dependent K+ channel acts as sex steroid sensor in endocrine cells of the human ovary.

Molecular targets of rapid non-genomic steroid actions are not well known compared to those of the classical transcription pathway, but ion channels have recently been identified to be steroid-sensitive. Especially, in the ovary, the very organ producing high amounts of sex steroids, their rapid actions are not well examined. We now identified a yet unknown target for sex steroids, a voltage-dependent K+ channel (Kv4.2) that contributes to a transient outward K+ current (I(A)) in human granulosa cells (GCs). Sex steroid hormones at concentrations typical for the ovary (1 microM) blocked Kv4.2 thereby attenuating I(A) by about 25% within seconds. We also found both Kv4.2 (KCND2) mRNA and protein in endocrine cells of the human and rhesus macaque ovary, emphasizing the physiological relevance of this channel. Therefore, we propose a role as fast-responding steroid sensor for the Kv4.2 channel. The direct regulation of K+ channel activity by sex steroids might represent a yet unknown mechanism of rapid steroid action in close proximity to the site of steroid production in the primate ovary. Our data might also be important for Kv4 channels in the brain and the cardiovascular system where rapid steroid effects are discussed in the context of prevention of cell death.

4-Aminopyridine↗

PubMed2006

Neuroendocrine mechanisms controlling female puberty: new approaches, new concepts.

Sexual development and mature reproductive function are controlled by a handful of neurones that, located in the basal forebrain, produce the decapeptide luteinizing hormone releasing hormone (LHRH). LHRH is released into the portal system that connects the hypothalamus to the pituitary gland and act on the latter to stimulate the synthesis and release of gonadotrophin hormones. The pubertal activation of LHRH release requires coordinated changes in excitatory and inhibitory inputs to LHRH-secreting neurones. These inputs are provided by both transsynaptic and glia-to-neurone communication pathways. Using cellular and molecular approaches, in combination with transgenic animal models and high-throughput procedures for gene discovery, we are gaining new insight into the basic mechanisms underlying this dual control of LHRH secretion and, hence, the initiation of mammalian puberty. Our results suggest that the initiation of puberty requires reciprocal neurone-glia communication involving excitatory amino acids and growth factors, and the coordinated actions of a group of transcriptional regulators that appear to represent a higher level of control governing the pubertal process.

Animals↗

PubMed2005

Minireview: the neuroendocrine regulation of puberty: is the time ripe for a systems biology approach?

The initiation of mammalian puberty requires an increase in pulsatile release of GnRH from the hypothalamus. This increase is brought about by coordinated changes in transsynaptic and glial-neuronal communication. As the neuronal and glial excitatory inputs to the GnRH neuronal network increase, the transsynaptic inhibitory tone decreases, leading to the pubertal activation of GnRH secretion. The excitatory neuronal systems most prevalently involved in this process use glutamate and the peptide kisspeptin for neurotransmission/neuromodulation, whereas the most important inhibitory inputs are provided by gamma-aminobutyric acid (GABA)ergic and opiatergic neurons. Glial cells, on the other hand, facilitate GnRH secretion via growth factor-dependent cell-cell signaling. Coordination of this regulatory neuronal-glial network may require a hierarchical arrangement. One level of coordination appears to be provided by a host of unrelated genes encoding proteins required for cell-cell communication. A second, but overlapping, level might be provided by a second tier of genes engaged in specific cell functions required for productive cell-cell interaction. A third and higher level of control involves the transcriptional regulation of these subordinate genes by a handful of upper echelon genes that, operating within the different neuronal and glial subsets required for the initiation of the pubertal process, sustain the functional integration of the network. The existence of functionally connected genes controlling the pubertal process is consistent with the concept that puberty is under genetic control and that the genetic underpinnings of both normal and deranged puberty are polygenic rather than specified by a single gene. The availability of improved high-throughput techniques and computational methods for global analysis of mRNAs and proteins will allow us to not only initiate the systematic identification of the different components of this neuroendocrine network but also to define their functional interactions.

Animals↗

PubMed2005

Leveraging human genomic information to identify nonhuman primate sequences for expression array development.

BACKGROUND: Nonhuman primates (NHPs) are essential for biomedical research due to their similarities to humans. The utility of NHPs will be greatly increased by the application of genomics-based approaches such as gene expression profiling. Sequence information from the 3' end of genes is the key resource needed to create oligonucleotide expression arrays. RESULTS: We have developed the algorithms and procedures necessary to quickly acquire sequence information from the 3' end of nonhuman primate orthologs of human genes. To accomplish this, we identified terminal exons of over 15,000 human genes by aligning mRNA sequences with genomic sequence. We found the mean length of complete last exons to be approximately 1,400 bp, significantly longer than previous estimates. We designed primers to amplify genomic DNA, which included at least 300 bp of the terminal exon. We cloned and sequenced the PCR products representing over 5,500 Macaca mulatta (rhesus monkey) orthologs of human genes. This sequence information has been used to select probes for rhesus gene expression profiling. We have also tested 10 sets of primers with genomic DNA from Macaca fascicularis (Cynomolgus monkey), Papio hamadryas (Baboon), and Chlorocebus aethiops (African green monkey, vervet). The results indicate that the primers developed for this study will be useful for acquiring sequence from the 3' end of genes for other nonhuman primate species. CONCLUSION: This study demonstrates that human genomic DNA sequence can be leveraged to obtain sequence from the 3' end of NHP orthologs and that this sequence can then be used to generate NHP oligonucleotide microarrays. Affymetrix and Agilent used sequences obtained with this approach in the design of their rhesus macaque oligonucleotide microarrays.

Algorithms↗

PubMed2005

Expression of the insulin receptor-related receptor is induced by the preovulatory surge of luteinizing hormone in thecal-interstitial cells of the rat ovary.

The insulin receptor-related receptor (IRR) is a member of the insulin receptor family that, on its own, recognizes neither insulin nor any of the identified insulin-related peptides. In both the nervous system and peripheral tissues, IRR mRNA is detected in cells that also express trkA, the nerve growth factor tyrosine kinase receptor. In the ovary, the trkA gene is transiently activated in thecal-interstitial cells of large antral follicles at the time of the preovulatory surge of gonadotropins. The present study shows that the IRR gene is expressed in the same ovarian compartment, that IRR mRNA content increases strikingly in these cells in the afternoon of the first proestrus, and that--as in the case of trkA mRNA--the increase is caused by gonadotropins. The IRR mRNA species primarily affected is that encoding the full-length receptor; its increased abundance was accompanied by a corresponding change in IRR protein content. An extensive molecular search using several approaches, including the screening of cDNA libraries and PCR amplification with degenerate primers, did not yield an IRR ligand. Phylogenetic analysis of 20 insulin-related sequences and 15 relaxin family peptides from selected vertebrates indicated that the mammalian genome is unlikely to contain an additional ligand expressed from a distinct gene that is closely related to the insulin family. Although the functional nature of the relationship between IRR and trkA receptors is unknown, the remarkable temporal and spatial specificities of their coordinated expression in the ovary before ovulation suggests that they target a functionally related set of downstream events associated with the ovulatory process.

Alternative Splicing↗

PubMed2005

Loss of synaptonemal complex protein-1, a synaptonemal complex protein, contributes to the initiation of follicular assembly in the developing rat ovary.

In the rat ovary, germ and somatic cells become organized into primordial follicles 48-72 h after birth. Although several genes have been implicated in the control of early follicular growth, less is known about the factors involved in the formation of primordial follicles. Using the method of differential display of mRNAs, we found several genes differentially expressed at the time of follicular assembly. One of them encodes synaptonemal complex protein-1 (SCP1), a core component of the protein complex that maintains recombining chromosomes together during prophase I of the first meiotic division in germ cells. This association, evident during the pachytene stage, ends when chromosomal desynapsis begins in the diplotene stage at the end of prophase I. Oocytes become arrested in the diplotene/dictate stage before becoming enclosed into primordial follicles, suggesting that oocytes must complete meiotic prophase I before becoming competent to direct follicle assembly. We now show that attainment of the diplotene stage results in follicular formation. In developing rat ovaries, SCP1 mRNA expression is confined to oocytes and decreases precipitously within 24 h after birth, preceding the organization of primordial follicles. The premature loss of SCP1, achieved via treatment with an antisense oligodeoxynucleotide targeting SCP1 mRNA, resulted in more oocytes reaching the diplotene stage, as evidenced by a decrease in the number of oocytes containing germ cell nuclear antigen-1 (a nuclear protein whose expression ceases in diplotene) and an increase in the number of oocytes expressing MSY2 (a cytoplasmic Y box protein expressed in oocytes that have become arrested in diplotene). SCP1-deficient ovaries exhibited an increased number of newly formed follicles, suggesting that completion of meiotic prophase I endows oocytes with the ability to orchestrate follicular assembly.

Animals↗

PubMed2005

Increased hypothalamic GPR54 signaling: a potential mechanism for initiation of puberty in primates.

To further study the role of GPR54 signaling in the onset of primate puberty, we used the monkey to examine the ability of kisspeptin-10 to elicit the release of gonadotropin-releasing hormone (GnRH) precociously, and we describe the expression of GPR54 and KiSS-1 in the hypothalamus during the peripubertal period. Agonadal juvenile male monkeys were implanted with a lateral cerebroventricular cannula and a jugular vein catheter. The responsiveness of the juvenile pituitary to endogenous GnRH release was heightened with a chronic pulsatile i.v. infusion of synthetic GnRH before kisspeptin-10 (112-121) injection. Intracerebroventricular (30 microg or 100 microg) or i.v. (100 microg) bolus injections of kisspeptin-10 elicited a robust GnRH discharge, as reflected by luteinizing hormone secretion, which was abolished by pretreatment with a GnRH-receptor antagonist. RNA was isolated from the hypothalamus of agonadal males before (juvenile) and after (pubertal) the pubertal resurgence of pulsatile GnRH release and from juvenile, early pubertal, and midpubertal ovary-intact females. KiSS-1 mRNA levels detected by real-time PCR increased with puberty in both male and female monkeys. In intact females, but not in agonadal males, GPR54 mRNA levels in the hypothalamus increased approximately 3-fold from the juvenile to midpubertal stage. Hybridization histochemistry indicated robust KiSS-1 and GPR54 mRNA expression in the region of the arcuate nucleus. These findings are consistent with the hypothesis that GPR54 signaling by its cognate ligand in the primate hypothalamus may be activated at the end of the juvenile phase of development and may contribute to the pubertal resurgence of pulsatile GnRH release, the central drive for puberty.

Animals↗

PubMed2005

Hypothalamic hamartoma: a paradigm/model for studying the onset of puberty.

This article discusses the potential mechanisms by which hypothalamic hamartomas (HHs) are formed and cause precocious puberty. The hypothesis is presented suggesting that HHs accelerate sexual development by producing bioactive substances that mimic - in an accelerated time-course - the cascade of events underlying the normal initiation of puberty. It is also proposed that because HHs contain key transcriptional and signaling networks required to initiate and sustain a pubertal mode of gonadotropin-releasing hormone (GnRH) release, they are able to trigger the pubertal process at an earlier age. The cellular components of this activating complex may include: (a) neurons able to produce GnRH within the HH: (b) controlling neurons synaptically connected to GnRH neurons in the HH itself and/or to neuronal networks (including GnRH neurons) in the patient's hypothalamus, and (c) signaling-competent astrocytic and ependymoglial cells. It is also possible that the developmental abnormalities leading to the formation of HHs result from sporadic defects affecting the same genes and hence the same morphogenic pathways involved in the embryonic development of the ventral hypothalamus and the floor of the third ventricle.

Child↗

PubMed2005

Early onset of puberty: tracking genetic and environmental factors.

Under physiological conditions, factors affecting the genetic control of hypothalamic functions are predominant in determining the individual variations in timing of pubertal onset. In pathological conditions, however, these variations can involve different genetic susceptibility and the interaction of environmental factors. The high incidence of precocious puberty in foreign children migrating to Belgium and the detection in their plasma of a long-lasting 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane (DDT) residue suggest the potential role of environmental endocrine disrupting chemicals in the early onset of puberty. This hypothesis was confirmed by experimental data showing that temporary exposure of immature female rats to DDT in vivo results in early onset of puberty. We compared the gene expression profile of hypothalamic hamartoma associated or not with precocious puberty in order to identify gene networks responsible for both hamartoma-dependent sexual precocity and the onset of normal human puberty. In conclusion, pathological variations in the timing of puberty may provide unique information about the interactions of either environmental conditions or genetic susceptibility with the hypothalamic mechanism controlling the onset of sexual maturation, as shown by examples of precocious puberty following exposure to endocrine disrupters or due to hypothalamic hamartoma.

Adolescent↗

PubMed2005

Genes involved in the neuroendocrine control of normal puberty and abnormal puberty of central origin.

There is now compelling evidence that both normal puberty and disturbed pubertal development of central origin are, to a significant extent, determined by genetic factors. Although delayed sexual development can result from a deficient pituitary responsiveness to GnRH caused by mutations in the GnRH receptor gene, until recently the only genetically determined hypothalamic defects known to affect puberty were those caused by mutations in genes required for the migration of gonadotropin releasing hormone (GnRH) neurons, such as KAL1, FGFR1, and NELF. Recently, mutations in a gene termed GPR54 were identified as causing isolated hypogonadotrophic hypogonadism (IHH), due to a functional, instead of a structural hypothalamic defect. Studies in nonhuman primates and rodent models suggest that the functional integrity of the hypothalamic mechanism controlling puberty requires a gene network that includes GPR54. Altogether, these findings indicate that the genetic underpinnings of disturbed pubertal development of central origin are polygenic, rather than specified by a single gene.

Animals↗

PubMed2004

erbB-1 and erbB-4 receptors act in concert to facilitate female sexual development and mature reproductive function.

Glial erbB-1 and erbB-4 receptors are key components of the process by which neuroendocrine glial cells control LHRH secretion and the onset of female puberty. We now provide evidence that these two signaling systems work in a coordinated fashion to control reproductive function. To generate animals carrying functionally impaired erbB-1 and erbB-4 receptors, we crossed Waved 2 (Wa-2+/+) mice harboring a point mutation of the erbB-1 receptor with mice expressing a dominant-negative erbB-4 receptor in astrocytes. In comparison to single-deficient mice, double-mutant animals exhibited a further delay in the onset of puberty and a strikingly diminished adult reproductive capacity. Ligand-dependent erbB receptor phosphorylation and erbB-mediated MAPK (ERK 1/2) phosphorylation were impaired in mutant astrocytes. Wa-2+/+ or double-mutant astrocytes failed to respond to TGF alpha with production of prostaglandin E2, one of the factors mediating the stimulatory effect of astroglial erbB receptor activation on LHRH release. Medium conditioned by Wa-2+/+ or double-mutant astrocytes treated with TGF alpha failed to stimulate LHRH release from GT1-7 cells. The LH response to ovariectomy was significantly attenuated in mutant mice in comparison with wild-type controls. Although the Wa-2 mutation affects all cells bearing erbB-1 receptors, these results suggest that a major defect underlying the reproductive defects of animals with impaired erbB signaling is a decreased ability of glial cells to stimulate LHRH release. Thus, a coordinated involvement of erbB-1 and erbB-4 signaling systems is required for the normalcy of sexual development and the maintenance of mature female reproductive function.

Animals↗

PubMed2004

Vascular endothelial cells promote acute plasticity in ependymoglial cells of the neuroendocrine brain.

Glial and endothelial cells interact throughout the brain to define specific functional domains. Whether endothelial cells convey signals to glia in the mature brain is unknown but is amenable to examination in circumventricular organs. Here we report that purified endothelial cells of one of these organs, the median eminence of the hypothalamus, induce acute actin cytoskeleton remodeling in isolated ependymoglial cells and show that this plasticity is mediated by nitric oxide (NO), a diffusible factor. We found that both soluble guanylyl cyclase and cyclooxygenase products are involved in this endothelial-mediated control of ependymoglia cytoarchitecture. We also demonstrate by electron microscopy that activation of endogenous NO release in the median eminence induces rapid structural changes, allowing a direct access of neurosecretory axons containing gonadotropin-releasing hormone (GnRH) (the neuropeptide controlling reproductive function) to the portal vasculature. Local in vivo inhibition of NO synthesis disrupts reproductive cyclicity, a process that requires a pulsatile, coordinated delivery of GnRH into the hypothalamic-adenohypophyseal portal system. Our results identify a previously unknown function for endothelial cells in inducing neuroglial plasticity and raise the intriguing possibility that endothelial cells throughout the brain may use a similar signaling mechanism to regulate glial-neuronal interactions.

Actins↗

PubMed2004

Alcohol alters luteinizing hormone secretion in immature female rhesus monkeys by a hypothalamic action.

We determined whether the effect of alcohol (ALC) to suppress LH secretion in immature female monkeys is due to a hypothalamic or pituitary site of action. Beginning at 20 months of age, four monkeys received a single intragastric dose of ALC (2.4 g/kg), and four monkeys received an equal volume of a saline/sucrose solution daily until they were 36 months old. For the hypothalamic response test, two basal samples (3.5 ml) were collected at 15-min intervals via the saphenous vein, and then N-methyl-D-L-aspartic acid (NMA; 20 mg/kg) was given iv and four more blood samples collected. Three weeks later, this protocol was repeated except LH-releasing hormone (LHRH) (5 microg/kg) was used to test pituitary responsiveness. NMA or LHRH was administered 3 h after the ALC. After the pituitary challenge, each monkey was ovariectomized and 6 wk later, implanted with an indwelling subclavian vein catheter. Blood samples were drawn every 10 min for 8 h to assess effects of ALC on post-ovariectomy LH levels and the profile of LH pulsatile secretion. The hypothalamic challenge showed NMA stimulated LH release in control monkeys, an action that was blocked by ALC. The pituitary challenge revealed that LHRH stimulated LH release equally well in control and ALC-treated monkeys. A post-ovariectomy rise in LH was observed in both groups, but levels were 45% lower in ALC-treated monkeys. This reduction was attributed to an ALC-induced suppression of both baseline and amplitude of pulses. Results demonstrate that the ALC-induced suppression of LH in immature female rhesus monkeys is due to an inhibitory action of the drug at the hypothalamic level.

Animals↗

PubMed2004

TrkB receptors are required for follicular growth and oocyte survival in the mammalian ovary.

Although it is well established that both follicular assembly and the initiation of follicle growth in the mammalian ovary occur independently of pituitary hormone support, the factors controlling these processes remain poorly understood. We now report that neurotrophins (NTs) signaling via TrkB receptors are required for the growth of newly formed follicles. Both neurotrophin-4/5 (NT-4) and brain-derived neurotrophic factor (BDNF), the preferred TrkB ligands, are expressed in the infantile mouse ovary. Initially, they are present in oocytes, but this site of expression switches to granulosa cells after the newly assembled primordial follicles develop into growing primary follicles. Full-length kinase domain-containing TrkB receptors are expressed at low and seemingly unchanging levels in the oocytes and granulosa cells of both primordial and growing follicles. In contrast, a truncated TrkB isoform lacking the intracellular domain of the receptor is selectively expressed in oocytes, where it is targeted to the cell membrane as primary follicles initiate growth. Using gene-targeted mice lacking all TrkB isoforms, we show that the ovaries of these mice or those lacking both NT-4 and BDNF suffer a stage-selective deficiency in early follicular development that compromises the ability of follicles to grow beyond the primary stage. Proliferation of granulosa cells-required for this transition-and expression of FSH receptors (FSHR), which reflects the degree of biochemical differentiation of growing follicles, are reduced in trkB-null mice. Ovaries from these animals grafted under the kidney capsule of wild-type mice fail to sustain follicular growth and show a striking loss of follicular organization, preceded by massive oocyte death. These results indicate that TrkB receptors are required for the early growth of ovarian follicles and that they exert this function by primarily supporting oocyte development as well as providing granulosa cells with a proliferative signal that requires oocyte-somatic cell bidirectional communication. The predominance of truncated TrkB receptors in oocytes and their developmental pattern of subcellular expression suggest that a significant number of NT-4/BDNF actions in the developing mammalian ovary are mediated by these receptors.

Animals↗