Preliminary studies on space charge compensation by analyzing residual argon gas ion signals

An experimental method is related to research the space charge compensation (SCC) effect in low energy intense proton beams by analyzing residual gas (RG) ion signals. The signal curves were measured with an energy spectrometer under the RG pressure from 1.2x10(-3) to 1.6x10(-2) Pa. Most of the data showed a similar trend with our theoretical predicts. From the RG ion energy spectra the potential distribution in the beam was calculated both with and without the SCC effect. Moreover, as a preliminary result, a best compensating point is achieved for the low energy beam transport transmission of 40 KeV, 60 mA H(+) beam in Peking University.

[On molecular identification and taxonomic status of Anopheles lesteri and Anopheles anthropophagus in China (Diptera: Culicidae)]

OBJECTIVE

To clarify the taxonomic status of Anopheles lesteri and An. anthropophagus in China.

METHODS

Using molecular identification (PCR assay and rDNA-ITS2 sequencing) to examine the field anopheline mosquito specimens from Liaoning and Shandong. According to the ITS2 sequences, molecular phylogenetic tree was made.

RESULTS

According to the molecular identification, An. lesteri and An. anthropophagus were distributed both in Liaoning Province and Shandong Province. The length and GC content of rDNA-ITS2 sequence were 451 bp, 46.2% in An. lesteri (n = 6), and 448 bp, 46.0% in An. anthropophagus (n = 10), respectively. The ITS2 sequences from presentation sites were same in An. lesteri, while the intraspecies difference in An. anthropophagus was 0.88%. The specific difference between An. lesteri and An. anthropophagus was 25.7%. By analyzing molecular phylogenetic tree, the relationship between An. lesteri and An. sinensis, An. anthropophagus and An. liangshanensis was found to be closer.

CONCLUSION

According to the molecular identification, it was defined that An. lesteri and An. anthropophagus were sympatric independent species in China.

Protective effect of a prosaposin-derived, 18-mer peptide on slowly progressive neuronal degeneration after brief ischemia

Slowly progressive degeneration of the hippocampal CA1 neurons was induced by 3-minute transient global ischemia in gerbils. Sustained degeneration of hippocampal CA1 neurons was evident 1 month after ischemia. To investigate the effects of an 18-mer peptide comprising the hydrophilic sequence of the rat saposin C domain (18MP) on this sustained neuronal degeneration, an intracerebroventricular 18MP infusion was initiated 3 days after ischemia. Histopathologic and behavior evaluations were conducted 1 week and 1 month after induction of ischemia. When compared with the vehicle infusion, 18MP treatment significantly increased the response latency time in a passive avoidance task. Increased neuronal density was also evident, as was the number of intact synapses in the hippocampal CA1 region at 1 week and 1 month after ischemia. 18MP treatment also significantly decreased the number of TUNEL-positive CA1 neurons 1 week after ischemia. Subsequent in vitro experiments using cultured neurons demonstrated that the 18MP at optimal extracellular concentrations of 1 to 100 fg/mL prevented nitric oxide-induced neuronal damage as expected and significantly up-regulated the expressions of bcl-x(L) mRNA and its translated protein. These results suggest that the gerbil model of 3-minute ischemia is useful in studying the pathogenesis of slowly progressive neuronal degeneration after stroke and in evaluating effects of novel therapeutic agents. It is likely that the 18MP at low extracellular concentrations prevents neuronal apoptosis possibly through up-regulation of the mitochondrial antiapoptotic factor Bcl-x(L).

[Effects of vitamin K on bone metabolism in tail-suspended rats]

Objective. To study the effects of vitamin K on bone metabolize in simulated weightlessness rats. Method. Male SD rats were divided into three groups (n = 9): the free active control (FAC), the tail-suspended control (SC), and the tail-suspended group treated with vitamin K (SVK) (50 mg/kg weight/d). The experiment lasted for 3 weeks. Bone biomechanical properties, bone mineral contents (BMC) and bone biochemical markers of bone metabolism were determined. Result. Compared with SC, total and bound bone gla protein (BGP) of serum, BMC of the femur and tibia, femoral mechanical properties, ALP activity of tibia all increased significantly; while NO content of femoral trunk decreased significantly. Conclusion. Vitamin K improved the bone metabolism and bone structure, decreased bone loss, increased bone biomechanical properties, decreased catagmatic fatalness. It proved that vitamin K prevented bone loss of simulated weightlessness rats.

Glia-to-neuron signaling and the neuroendocrine control of female puberty

It is becoming increasingly clear that astroglial cells are active participants in the process by which information is generated and disseminated within the central nervous system (CNS). In the hypothalamus, astrocytes regulate the secretory activity of neuroendocrine neurons. They contribute to facilitating sexual development by stimulating the release of luteinizing hormone-releasing hormone (LHRH), the neuropeptide that controls sexual development, from LHRH neurons. Astrocytes secrete several growth factors able to stimulate LHRH secretion. Two members of the epidermal growth factor (EGF) family--transforming growth factor alpha (TGFalpha) and the neuregulins (NRGs)-are produced in hypothalamic astrocytes and elicit LHRH secretion indirectly, via activation of receptor complexes formed by three members of the EGF receptor family, also located on astrocytes. Activation of these receptors results in the production of at least one neuroactive substance, prostaglandin E2 (PGE2), which stimulates LHRH secretion upon binding to specific receptors on LHRH neurons. Overexpression of TGFalpha in the hypothalamus accelerates puberty, whereas blockade of either TGFalpha or NRG actions delays the process, indicating that both peptides are physiological components of the neuroendocrine mechanism that controls sexual maturation. An increase in hypothalamic expression of at least two of the erbB receptors is initiated before the pubertal augmentation of gonadal steroid secretion and is completed on the day of the first preovulatory surge of gonadotropins. This secondary increase is brought about by gonadal steroids. Estrogen and progesterone facilitate erbB-mediated glia-to-LHRH neuron communication by enhancing astrocytic gene expression of at least one of the EGF-related ligands (TGFalpha) and two of the receptors (erbB-2 and erbB-4). They also facilitate the LHRH response to PGE2 via induction of PGE2 receptors in LHRH neurons. A search for genes that may act as upstream regulators of the pubertal process resulted in the identification of two potential candidates: Oct-2, a POU domain gene originally described in cells of the immune system, and TTF-1, a member of the Nkx family of homeodomain transcriptional regulators required for diencephalic morphogenesis. The hypothalamic expression of both genes increases during juvenile development before the first hormonal manifestations of puberty take place. Their mRNA transcripts are localized to specific hypothalamic cellular subsets, where they appear to regulate different, but interactive, components of the neuronal-glial complex controlling LHRH secretion. While Oct-2 transactivates the TGFalpha promoter, TTF-1 does so to the erbB-2 and LHRH genes but inhibits preproenkephalin promoter activity, suggesting that both transcriptional regulators may act coordinately in the normal hypothalamus to activate genes involved in facilitating the advent of puberty and repress those restraining sexual development. Altogether, these observations indicate that the central activation of the pubertal process involves the participation of both neuronal and astroglial networks and the contribution of upstream transcriptional regulators acting on both the neuronal and glial components of the system.

Efficient utilization of starch by a recombinant strain of Saccharomyces cerevisiae producing glucoamylase and isoamylase

Two plasmids, designated pRTI and pTI, were constructed to allow the integration of a bacterial isoamylase gene (iso) into Saccharomyces cerevisiae G23-8 chromosome. The integrative plasmid pRTI comprises the iso gene from Pseudomonas amyloderamosa, a portion of S. cerevisiae ribosomal DNA (rDNA), S. cerevisiae trp1 gene deficient in promoter and the bacterial vector pSP72. The structure of plasmid pTI is similar to that of pRTI, except that it lacks an rDNA segment. The Aspergillus awamori glucoamylase and P. amyloderamosa isoamylase genes were expressed in the recombinant strain of S. cerevisiae under the control of the yeast alcohol dehydrogenase gene (adh1) promoter. Southern-blot analysis showed that these plasmids were integrated into the yeast chromosome in tandem repeat and dispersion copies. The recombinant strains could assimilate starch more efficiently than the recipient strain with a conversion rate of greater than 95%.

[Comparison of rDNA-ITS2 sequences and morphological characters of Anopheles kunmingensis and Anopheles langshanensis in China, with discussion on taxonomic status]

OBJECTIVE

To determine the taxonomic status of Anopheles kunmingensis (AK) and An. liangshanensis(AL) from China.

METHODS

Sequence differences of rDNA-ITS2 and main morphological characters variability between different sources of AK and AL were compared.

RESULTS

The level of rDNA-ITS2 sequence differences among eight samples was under 2.9%. The total occurrence rates of main morphological characters examined in the female mosquitoes with pale fringe spot on V5.2, white basal band (or spot) on hind tarsomere IV, and larvae with bifurcated head hair 2-C were 43%(9/21), 89%(17/19), 40(4/10) in AK, and 79%(34/43), 44%(17/39), 20%(4/20) in AL, respectively. These rates calculated from separate colonies fluctuated within a wide range and overlapped, suggesting that there was no definite, stable morphological difference between AK and AL.

CONCLUSION

The morphological and molecular variations between AK and AL were small and belong to intraspecific level. The AK and AL may be considered as the same species, and that the An. kunmingensis may be recognized as the synonym of An. liangshanensis.

Some hypothalamic hamartomas contain transforming growth factor alpha, a puberty-inducing growth factor, but not luteinizing hormone-releasing hormone neurons

Activation of LH-releasing hormone (LHRH) secretion, essential for the initiation of puberty, is brought about by the interaction of neurotransmitters and astroglia-derived substances. One of these substances, transforming growth factor alpha (TGFalpha), has been implicated as a facilitatory component of the glia-to-neuron signaling process controlling the onset of female puberty in rodents and nonhuman primates. Hypothalamic hamartomas (HH) are tumors frequently associated with precocious puberty in humans. The detection of LHRH-containing neurons in some hamartomas has led to the concept that hamartomas advance puberty because they contain an ectopic LHRH pulse generator. Examination of two HH associated with female sexual precocity revealed that neither tumor had LHRH neurons, but both contained astroglial cells expressing TGFalpha and its receptor. Thus, some HH may induce precocious puberty, not by secreting LHRH, but via the production of trophic factors--such as TGFalpha--able to activate the normal LHRH neuronal network in the patient's hypothalamus.

Neuregulins signaling via a glial erbB-2-erbB-4 receptor complex contribute to the neuroendocrine control of mammalian sexual development

Activation of erbB-1 receptors by glial TGFalpha has been shown to be a component of the developmental program by which the neuroendocrine brain controls mammalian sexual development. The participation of other members of the erbB family may be required, however, for full signaling capacity. Here, we show that activation of astrocytic erbB-2/erbB-4 receptors plays a significant role in the process by which the hypothalamus controls the advent of mammalian sexual maturation. Hypothalamic astrocytes express both the erbB-2 and erbB-4 genes, but no erbB-3, and respond to neuregulins (NRGs) by releasing prostaglandin E(2) (PGE(2)), which acts on neurosecretory neurons to stimulate secretion of luteinizing hormone-releasing hormone (LHRH), the neuropeptide controlling sexual development. The actions of TGFalpha and NRGs in glia are synergistic and involve recruitment of erbB-2 as a coreceptor, via erbB-1 and erbB-4, respectively. Hypothalamic expression of both erbB-2 and erbB-4 increases first in a gonad-independent manner before the onset of puberty, and then, at the time of puberty, in a sex steroid-dependent manner. Disruption of erbB-2 synthesis in hypothalamic astrocytes by treatment with an antisense oligodeoxynucleotide inhibited the astrocytic response to NRGs and, to a lesser extent, that to TGFalpha and blocked the erbB-dependent, glia-mediated, stimulation of LHRH release. Intracerebral administration of the oligodeoxynucleotide to developing animals delayed the initiation of puberty. Thus, activation of the erbB-2-erbB-4 receptor complex appears to be a critical component of the signaling process by which astrocytes facilitate the acquisition of female reproductive capacity in mammals.

Glial-neuronal interactions in the neuroendocrine control of mammalian puberty: facilitatory effects of gonadal steroids

It is now clear that astroglial cells actively contribute to both the generation and flow of information within the central nervous system. In the hypothalamus, astrocytes regulate the secretory activity of neuroendocrine neurons. A small subset of these neurons secrete luteinizing hormone-releasing hormone (LHRH), a neuropeptide essential for sexual development and adult reproductive function. Astrocytes stimulate LHRH secretion via cell-cell signaling mechanisms involving growth factors recognized by receptors with either serine/threonine or tyrosine kinase activity. Two members of the epidermal growth factor (EGF) family and their respective tyrosine kinase receptors appear to play key roles in this regulatory process. Transforming growth factor-alpha (TGFalpha) and its distant congeners, the neuregulins (NRGs), are produced in hypothalamic astrocytes. They stimulate LHRH secretion indirectly, via activation of erbB-1/erbB-2 and erbB-4/erbB-2 receptor complexes also located on astrocytes. Activation of these receptors leads to release of prostaglandin E(2) (PGE(2)), which then binds to specific receptors on LHRH neurons to elicit LHRH secretion. Gonadal steroids facilitate this glia-to-neuron communication process by acting at three different steps along the signaling pathway. They (a) increase astrocytic gene expression of at least one of the EGF-related ligands (TGFalpha), (b) increase expression of at least two of the receptors (erbB-4 and erbB-2), and (c) enhance the LHRH response to PGE(2) by up-regulating in LHRH neurons the expression of specific PGE(2) receptor isoforms. Focal overexpression of TGFalpha in either the median eminence or preoptic area of the hypothalamus accelerates puberty. Conversely, blockade of either TGFalpha or NRG hypothalamic actions delays the process. Thus, both TGFalpha and NRGs appear to be physiological components of the central neuroendocrine mechanism controlling the initiation of female puberty. By facilitating growth factor signaling pathways in the hypothalamus, ovarian steroids accelerate the pace and progression of the pubertal process.

The Oct-2 POU domain gene in the neuroendocrine brain: a transcriptional regulator of mammalian puberty

POU homeodomain genes are transcriptional regulators that control development of the mammalian forebrain. Although they are mostly active during embryonic life, some of them remain expressed in the postnatal hypothalamus, suggesting their involvement in regulating differentiated functions of the neuroendocrine brain. We show here that Oct-2, a POU domain gene originally described in cells of the immune system, is one of the controlling components of the cell-cell signaling process underlying the hypothalamic regulation of female puberty. Lesions of the anterior hypothalamus cause sexual precocity and recapitulate some of the events leading to the normal initiation of puberty. Prominent among these events is an increased astrocytic expression of the gene encoding transforming growth factor-alpha (TGF alpha), a tropic polypeptide involved in the stimulatory control of LHRH secretion. The present study shows that such lesions result in the rapid and selective increase in Oct-2 transcripts in TGF alpha-containing astrocytes surrounding the lesion site. In both lesion-induced and normal puberty, there is a preferential increase in hypothalamic expression of the Oct-2a and Oct-2c alternatively spliced messenger RNA forms of the Oct-2 gene, with an increase in 2a messenger RNA levels preceding that in 2c and antedating the peripubertal activation of gonadal steroid secretion. Both Oct-2a and 2c trans-activate the TGF alpha gene via recognition motifs contained in the TGF alpha gene promoter. Inhibition of Oct-2 synthesis reduces TGF alpha expression in astroglial cells and delays the initiation of puberty. These results suggest that the Oct-2 gene is one of the upstream components of the glia to neuron signaling process that controls the onset of female puberty in mammals.

Epidermal growth factor tyrosine kinase receptors and the neuroendocrine control of mammalian puberty

In recent years evidence has begun to accumulate indicating that the central control of mammalian puberty requires not only changes in transsynaptic communication, but also the participation of glial cells. Neurons and astrocytes control the pubertal process by regulating the secretory activity of those neurons that produce luteinizing hormone-releasing hormone (LHRH), the neuropeptide that governs sexual development. LHRH, in turn, directs sexual development by stimulating the secretion of pituitary gonadotropins. Astrocytes affect LHRH neuronal function via cell-cell signaling mechanisms involving several growth factors acting via receptors endowed with tyrosine kinase activity. We have identified two members of the epidermal growth factor/transforming growth factor alpha (EGF/TGFalpha) family and their respective receptors as key players in the glial-neuronal interactive process that regulates LHRH secretion. Our results indicate that TGFalpha and its distant congener neuregulin (NRG) are produced in hypothalamic astrocytes and stimulate LHRH release indirectly via activation of their respective receptors, located--surprisingly--not on LHRH neurons, but on astrocytes. Activation of EGF receptors by TGFalpha, and/or the erbB2/erbB4 receptor complex by NRG, leads to glial release of prostaglandin (PG) E2, which then acts directly on LHRH neurons to stimulate LHRH release. That a central blockade of TGFalpha or NRG action delays puberty, and focal overexpression of TGFalpha advances it, leads to the conclusion that both TGFalpha and NRG are physiological components of the central mechanism controlling the initiation of female puberty.

Estradiol enhances prostaglandin E2 receptor gene expression in luteinizing hormone-releasing hormone (LHRH) neurons and facilitates the LHRH response to PGE2 by activating a glia-to-neuron signaling pathway

Prostaglandin E2 (PGE2) mediates the stimulatory effect of norepinephrine (NE) on the secretion of luteinizing hormone-releasing hormone (LHRH), the neuropeptide controlling reproductive function. In rodents, this facilitatory effect requires previous exposure to estradiol, suggesting that the steroid affects downstream components in the cascade that leads to PGE2-induced LHRH release. Because astroglia are the predominant cell type contacting LHRH-secreting nerve terminals, we investigated the involvement of hypothalamic astrocytes in the estradiol facilitation of PGE2-induced LHRH release. A subpopulation of LHRH neurons was found to express the mRNA encoding the PGE2 receptor subtype EP1-R, which is coupled to calcium mobilization. The LHRH-producing cell line GT1-1 also contains EP1-R mRNA and, to a lesser extent, the three alternatively spliced forms of EP3-R mRNA (alpha, beta, and gamma) that encode receptors linked to inhibition and stimulation of cAMP formation. Hypothalamic astrocytes treated with estradiol produced a conditioned medium that when applied to GT1-1 cells resulted in a selective upregulation of EP1-R and EP3gamma-R mRNAs. The conditioned medium also enhanced the LHRH response to EP1-R and EP3-R agonists and the cAMP response to EP3-R activation. Thus, one mechanism by which estradiol facilitates the effect of neurotransmitters acting via PGE2 to stimulate LHRH release is by enhancing the glial production of substances that upregulate PGE2 receptors on LHRH neurons. The existence of such a mechanism underscores the emerging importance of glial-neuronal communication in the control of brain neurosecretory activity.

Topographic comparison of the expression of norepinephrine transporter, tyrosine hydroxylase and neuropeptide Y mRNA in association with dopamine beta-hydroxylase neurons in the rabbit brainstem

In mammalian species, ovulation occurs following a massive release of hypothalamic gonadotropin-releasing hormone (GnRH). Several chemicals, including norepinephrine (NE) and neuropeptide Y (NPY), are responsible for the initiation and/or magnitude and duration of this pre-ovulatory GnRH surge. In the central nervous system, NE neural cell bodies are located in the brainstem; some are co-localized with NPY neurons and/or co-express the NE transporter (NET) gene which dictates NET protein production. The activity of NET at NE terminals is critical for synaptic NE function. In the rabbit, coitus induces a hypothalamic NE release which precedes the GnRH surge. We hypothesize that the coital stimulus is transmitted to the brainstem and transformed and integrated into GnRH-stimulating signals via NE, NET and/or NPY. However, very little is known about the distribution of cells expressing NET, NPY and tyrosine hydroxylase (TH, the rate-limiting enzyme of NE synthesis) in this species. Therefore, we utilized the sensitive in situ hybridization technique to identify the presence of these messages in conjunction with the location of NE cells, the latter being marked by dopamine beta-hydroxylase (DBH), the specific enzyme for NE synthesis. Three non-mated New Zealand White does were perfused with 4% paraformaldehyde and their brainstems were sectioned at 20-micron thick between 2 mm caudal to the obex and the rostral pons. Serial sections were immunohistochemically stained for DBH and hybridized with rabbit-specific TH and NET cRNAs and a human NPY probe. The data suggest that several DBH-positive areas in the medulla expressed one or more messages, i.e. the lateral tegmentum (A1) and the nucleus of the solitary tract (A2) expressed all three mRNAs, the area postrema (AP) contained NET and TH mRNAs but not NPY cells. In the pons, the locus coeruleus (LC), subnucleus of coeruleus (LCs) and lateral tegmental nuclei (A5) expressed NET and TH mRNAs but contained little or no NPY message. The distribution patterns of TH and NET appeared to be similar in the LC, LCs, A2 and AP.

The transforming growth factor alpha gene family is involved in the neuroendocrine control of mammalian puberty

The concept is proposed that the central control of mammalian female puberty requires the interactive participation of neuronal networks and glial cells of the astrocytic lineage. According to this concept neurons and astrocytes control the pubertal process by regulating the secretory activity of those neurons that secrete luteinizing hormone-releasing hormone (LHRH). LHRH, in turn, governs sexual development by stimulating the secretion of pituitary gonadotropins. Astrocytes affect LHRH neuronal function via a cell-cell signaling mechanism involving several growth factors and their corresponding receptors. Our laboratory has identified two members of the epidermal growth factor/transforming growth factor (EGF/TGF alpha) family as components of the glial-neuronal interactive process that regulates LHRH secretion. Transforming growth factor alpha (TGF alpha) and its distant congener neu-differentiation factor, NDF, are produced in hypothalamic astrocytes and stimulate LHRH release via a glial intermediacy. The actions of TGF alpha and NDF on hypothalamic astrocytes involve the interactive activation of their cognate receptors and the synergistic effect of both ligands in stimulating the glial release of prostaglandin E2 (PGE2). In turn, PGE2 acts directly on LHRH neurons to stimulate LHRH release. A variety of experimental approaches has led to the conclusion that both TGF alpha and NDF are physiological components of the central mechanism controlling the initiation of female puberty.

Neuroendocrine control of female puberty: glial and neuronal interactions

Emerging evidence suggests that, in addition to neuronal inputs, growth factors of glial origin are also important in the control of mammalian puberty via a cell-cell interaction that ultimately affects the neurons that release gonadotropin-releasing hormone (GnRH), a neurohormone controlling sexual development. Among these growth factors, transforming growth factor-alpha (TGF alpha) appears to be one of the physiologic components that controls the onset of female puberty by affecting GnRH neuronal activity in a glia-mediated autocrine/paracrine manner. Specifically, TGF alpha induces glia to produce bioactive substances, such as prostaglandin E2 (PGE2). In turn, PGE2 directly acts on GnRH neurons to stimulate the release of GnRH. Furthermore, the neuroregulin of glial origin neu differentiation factor (NDF) was found to facilitate the action of TGF alpha, suggesting that other growth factors may exert their biologic effects on GnRH neuronal function via a glia/neuron interaction. Another indication that glial cells may be involved in the regulation of neuroendocrine function is the presence of estrogen receptors on hypothalamic astrocytes. Thus, region-specific glial cells appear to play an integral role in the regulation of neuroendocrine function.

Hypothalamic astrocytes respond to transforming growth factor-alpha with the secretion of neuroactive substances that stimulate the release of luteinizing hormone-releasing hormone

Previous studies demonstrated the involvement of transforming growth factor-alpha (TGF alpha), a member of the epidermal growth factor (EGF) family, in the developmental regulation of hypothalamic LHRH release. Although both TGF alpha and EGF stimulate LHRH release, they do not appear to act directly on LHRH neurons, as no EGF/TGF alpha receptors are detected on these cells in vivo. Instead, the stimulatory effect of TGF alpha on LHRH release seems to require a glial intermediacy. The present study identifies one of the glial molecules involved in this process. In vitro exposure of purified hypothalamic astrocytes to TGF alpha or EGF in a defined medium led to activation of the cyclooxygenase-mediated pathway of arachidonic acid metabolism, as indicated by an increase in PGE2 release, but failed to affect lipooxygenase-mediated metabolism, as assessed by the lack of increase in leukotriene C4 production; addition of TGF alpha- (T-CM) or EGF-conditioned medium to cultures of LHRH-producing GT1-1 cells stimulated LHRH release. In contrast, direct exposure of GT1-1 cells to the growth factors was ineffective. Incubation of the cells in medium conditioned by untreated astrocytes (CM) was also ineffective. Blockade of either EGF receptor signal transduction or cyclooxygenase activity in the astrocytic cultures prevented both TGF alpha-induced PGE2 formation in astrocytes and the stimulatory effect of T-CM on LHRH release. Immunoneutralization of PGE2 actions or selective removal of the PG from T-CM also prevented T-CM-induced LHRH release. Addition of exogenous PGE2 restored the effect. Thus, PGE2 is one of the glial molecules involved in mediating the stimulatory effect of TGF alpha on LHRH release. The effectiveness of PGE2 in eliciting LHRH release was, however, greatly reduced when PG was delivered to GT1-1 cells in astrocyte-defined medium instead of CM. Thus, astrocytes appear to produce a yet to be identified substance(s) that facilitates the stimulatory effect of PGE2 on LHRH output. We postulate that the ability of TGF alpha to enhance LHRH release depends on the potentiating interaction of PGE2 with these additional glial-derived molecules.

RNase Protection Assay

The RNase protection assay is a highly sensitive technique developed to detect and measure the abundance of specific mRNAs in samples of total cellular RNA. The assay utilizes in vitro transcribed 32P-labeled antisense RNA probes that are hybridized in solution to their complementary cellular mRNAs. This is followed by digestion of nonhybridizing (single-stranded) RNA species with RNases, removal of the RNases by treatment with proteinase K, phenol extraction of the cRNA:mRNA complexes, and electrophoretic isolation of the hybridizing cRNA fragments. Since one can synthesize "sense" mRNAs having the same sequence as the target cellular mRNA, appropriate standard curves can be generated and used to quantitate the changes in tissue mRNA levels. Because the assay requires perfect sequence complementarity for full protection, it not only serves as a quantitative tool but also provides conclusive evidence for the existence of a specific mRNA in a given tissue. The procedure described here is a modification of that originally described by M. Gilman [1993, in Current Protocols in Molecular Biology (Ausubel, F. M., Brent, R., Kingston, R. E., Moore, D. D., Seidman, J. G., Smith, J. A., and Struhl, K., Eds.), Vol. 1, pp. 4.7.1-4.7.6, Greene and Wiley-Interscience, New York].

Neural and glial-mediated effects of growth factors acting via tyrosine kinase receptors on luteinizing hormone-releasing hormone neurons

It is becoming increasingly evident that the secretory activity of LHRH neurons is regulated not only by transsynaptic inputs but also by trophic molecules of glial and neuronal origin. The present experiments were undertaken to gain insights into the potential cell-cell mechanisms by which basic fibroblast growth factor (bFGF) and transforming growth factor-alpha (TGF alpha), two growth factors produced in the hypothalamus, may affect LHRH neuronal function. Northern blot analysis showed that the LHRH-producing cell line GT1-7 contains the messenger RNA (mRNA) encoding the type 1 fibroblast growth factor receptor (FGFR-1) but not that encoding the epidermal growth factor (EGF) receptors, which mediates the biological actions of both TGF alpha and EGF. Ligand-induced receptor phosphorylation experiments demonstrated that GT1-7 cells possess biologically active FGFR-1s but not EGF receptors. Exposure of the cells to bFGF resulted not only in FGFR-1 tyrosine phosphorylation, but also in tyrosine phosphorylation of phospholipase C gamma, one of the initial enzymes in the intracellular signaling cascade initiated by FGFR activation. GT1-7 cells proliferated in response to this activation. Despite the presence of biologically active receptors, bFGF did not significantly stimulate release of the mature LHRH decapeptide. Instead, bFGF increased the steady-state levels of the mRNA encoding the LHRH precursor processing endoprotease PC2, with a time course comparable to that of phorbol esters, suggesting that, as shown in the companion paper, the actions of the growth factor on LHRH neurons involve facilitation of the initial step in LHRH prohormone processing. The increase in PC2 gene expression was not accompanied by changes in LHRH mRNA levels. Unlike these direct actions of bFGF on GT-1 cells, TGF alpha appears to act indirectly via astroglial intermediacy. Exposure of GT1-7 cells to TGF alpha or EGF failed to affect several parameters of cellular activity including LHRH release, LHRH and PC2 mRNA levels, and cell proliferation. In contrast, astrocyte culture medium conditioned by treatment with TGF alpha led to sustained stimulation of LHRH release with no changes in LHRH gene expression and a transient increase in PC2 mRNA levels. Although no definitive evidence for the presence of FGFR-1 in normal LHRH neurons could be obtained by either double immunohistochemistry or double in situ hybridization procedures, fetal LHRH neurons in primary culture responded to bFGF with neurite outgrowth. Thus, normal LHRH neurons may have an FGFR-1 content too low for detection by regular histochemical procedures, and/or detectable expression of the receptor may be confined to a much earlier developmental stage. The mitogenic effect of bFGF on GT1-7 cells supports this possibility and suggests a role for FGF in the cell proliferation events that precede acquisition of the LHRH neuronal phenotype. It appears that once this phenotype is established, bFGF may promote the differentiation of LHRH neurons. The results also suggest that the secretory capacity of LHRH neurons develops under a dual trophic influence, one on peptide processing exerted directly by bFGF on early neurons, and another on LHRH release, exerted by TGF alpha via the intermediacy of astroglial cells.

Overexpression of a human transforming growth factor-alpha (TGF alpha) transgene reveals a dual antagonistic role of TGF alpha in female sexual development

The importance of transforming growth factor-alpha (TGF alpha) in female reproductive development was assessed using transgenic mice bearing a human TGF alpha complementary DNA under the control of a mouse metallothionein-1 promoter (MT1-hTGF alpha). Examination of the brain and ovaries 5 h after a single sc injection of zinc chloride, administered to activate the MT1-hTGF alpha transgene, revealed that prominent sites of human TGF alpha messenger RNA expression within these tissues were the hypothalamus and ovarian follicles, respectively. In vitro experiments showed that acute transgene activation increased hypothalamic release of LH-releasing hormone. In contrast, the ovarian steroidal response to gonadotropins, examined in vitro, was markedly attenuated. Chronic activation of transgene expression by daily administration of zinc chloride delayed the time of first estrus (an index of peripubertal estrogen secretion), but shortened the interval between first estrus and the onset of estrous cyclicity (an index of reproductive competence). Accumulation of small antral follicles, accompanied by thecal hypertrophy and enhanced androgen production, preceded the acquisition of ovulatory capacity. These changes were accompanied by reduced serum LH levels, suggesting that the relative inability of small antral follicles to develop further in TGF alpha-overexpressing mice is at least in part due to inappropriate gonadotropin support. Serum LH levels in these animals may be reduced by an augmented androgen negative feedback signal. Nontransgenic mouse ovaries, placed under the control of a transgenic hypothalamus by heterologous grafting, rapidly ovulated and initiated estrous cyclicity. In contrast, acquisition of reproductive capacity was severely delayed in nontransgenic mice bearing transgenic ovarian grafts. The results indicate that TGF alpha regulates female reproductive development through two opposing mechanisms: within the brain, it facilitates the neuroendocrine activation of the process; at the ovarian level, modulates the stimulatory effect of gonadotropin hormones on follicular growth and steroidogenesis.

Developmental expression of the genes encoding transforming growth factor alpha and its receptor in the hypothalamus of female rhesus macaques

Studies in female rats have shown that transforming growth factor alpha (TGF alpha) stimulates release of luteinizing hormone-releasing hormone (LHRH), the neuropeptide controlling sexual maturation, and that expression of the TGF alpha gene in the hypothalamus increases during both the initiation of normal puberty and after hypothalamic lesions that induce sexual precocity. Since blockade of epidermal growth factor receptors (EGFR), which mediate TGF alpha actions, delayed the normal timing of puberty, it was postulated that TGF alpha/EGFR contributes to the neuroendocrine process that underlies the initiation of normal female puberty. The present study was undertaken to examine the hypothesis that hypothalamic expression of the TGF alpha gene and its receptor changes in relation to the stage of sexual development in nonhuman primates, and to determine whether these changes are accompanied by corresponding alterations in LHRH gene expression. DNA fragments complementary to the coding regions of the rhesus monkey TGF alpha, EGFR and LHRH genes were cloned by reverse transcription-polymerase chain reaction (RT-PCR), sequenced and used to prepare monkey-specific antisense RNA probes. A quantitative RT-PCR was developed in which the cloned sequences were utilized to prepare RNA standards for the quantitation of tissue mRNA levels. Both TGF alpha and EGFR mRNA levels in the medial basal hypothalamus and preoptic area of female monkeys were elevated during neonatal life (1 week to 6 months of age), when FSH secretion is also high, decreased during juvenile development (8-18 months of age), when secretion of both FSH and LH is low, and markedly increased during the expected time of puberty (30-36 months of age). No such changes were observed in either the cerebellum or the cerebral cortex, two brain regions irrelevant to neuroendocrine reproductive control. In contrast to the pronounced alterations in hypothalamic TGF alpha/EGFR gene expression observed during sexual development, LHRH mRNA levels did not vary significantly during this time. Hybridization histochemistry revealed the presence of both TGF alpha and EGFR mRNAs in cells scattered throughout the hypothalamus, but more predominantly in the median eminence, suprachiasmatic nuclei, optic chiasm and cells along the wall of the third ventricle. These results demonstrate that increases in TGF alpha and EGFR gene expression, specific to the neuroendocrine brain, occur during developmental phases in which gonadotropin output is also elevated--most noticeably at the time of puberty.(ABSTRACT TRUNCATED AT 400 WORDS)

Region-specific regulation of transforming growth factor alpha (TGF alpha) gene expression in astrocytes of the neuroendocrine brain

Certain glial cells of the hypothalamus have been implicated in the neuroendocrine control of reproductive development. Hypothalamic astrocytes appear to exert this function via a cell-cell interactive mechanism that involves the production of transforming growth factor alpha (TGF alpha), a polypeptide able to affect both glial and neuronal functions in the CNS. In the hypothalamus, TGF alpha stimulates neuronal secretion of luteinizing hormone-releasing hormone (LHRH), the neuropeptide controlling sexual development, via activation of epidermal growth factor receptors (EGFR). Since astrocytes but not LHRH neurons express EGFR, it has been postulated that the stimulatory effect of TGF alpha on LHRH release is not exerted directly on LHRH neurons, but rather via glial intermediacy. The present experiments were undertaken to define whether TGF alpha is able to exert paracrine/autocrine effects on isolated hypothalamic astrocytes, and to determine if estradiol-previously shown to increase TGF alpha mRNA levels in the hypothalamus of immature animals--can act directly on hypothalamic astrocytes to upregulate TGF alpha gene expression. Treatment with either TGF alpha or its structural homolog, epidermal growth factor (EGF), increased TGF alpha mRNA levels within 8 hr of exposure; the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA) was similarly effective. Blockade of EGFR with either tyrphostin RG-50864, an inhibitor of tyrosine kinase activity, or a monoclonal antibody that prevents ligand binding abolished the upregulatory effect of TGF alpha on TGF alpha mRNA levels. In contrast to hypothalamic astrocytes, cerebellar astrocytes did not respond to either TGF alpha or EGF with changes in TGF alpha mRNA abundance.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of epidermal growth factor receptor changes in the hypothalamus during the onset of female puberty

Recent findings have led to the concept that transforming growth factor alpha (TGF alpha) contributes to the neuroendocrine regulation of female puberty by stimulating the release of luteinizing hormone-releasing hormone (LHRH), the neurohormone controlling sexual development. It was postulated that this effect is mediated by epidermal growth factor receptors (EGFR) and that EGFR may not be located on LHRH neurons, so that TGF alpha-induced LHRH release would require an intermediate cell-to-cell interaction, presumably of glial-neuronal nature. The present study was undertaken to characterize the presence of EGFR in rat hypothalamus and to determine if changes in EGFR gene expression and EGFR protein occur at the time of puberty. RNA blot hybridization demonstrated that the hypothalamus expresses all mRNA species known to encode EGFR. RNase protection assays revealed that alternative splicing of the EGFR primary mRNA transcript occurs in the hypothalamus and produces a predominant transcript encoding the full-length EGFR and a much less abundant, shorter mRNA encoding a truncated, and presumably secreted form of EGFR. EGFR-like immunoreactive material was found in several hypothalamic regions including the organum vasculosum of the lamina terminalis, supraoptic, suprachiasmatic, and paraventricular nuclei, ependymal cells lining the third ventricle, some astrocytes associated with blood vessels, astrocytes of the pial surface, and tanycytes and glial cells of the median eminence (ME). Low levels of EGFR mRNA were detected by hybridization histochemistry in cells of the same areas containing EGFR-like immunoreactivity. Double-immunohistochemistry revealed that even though LHRH neurons are in close proximity to EGFR-positive cells, they do not contain EGFR. In the ME, EGFR-immunonegative LHRH nerve terminals tightly coexist with EGFR-positive cells, presumably tanycytes and glial astrocytes. EGFR mRNA levels measured by quantitative reverse transcription-polymerase chain reaction assay (RT-PCR) in the ME-arcuate nucleus region at the time of puberty decreased in the morning of the first proestrus, i.e., preceding the first preovulatory surge of gonadotropins, and rebounded at the time of the surge. Functional EGFR protein levels, detected by the ability of the receptor to autophosphorylate in response to ligand or divalent antibody-induced activation, changed in a similar manner at the time of puberty. No such changes were observed in the cerebellum, a brain region irrelevant to neuroendocrine reproductive control. These results demonstrate the existence of EGF receptors in the prepubertal female rat hypothalamus and suggest that changes in EGFR gene expression and biologically active EGFR protein contributes to the neuroendocrine process underlying the first preovulatory surge of gonadotropins.(ABSTRACT TRUNCATED AT 250 WORDS)

[A clinical analysis of 117 cases of acute arsenic poisoning]

117 cases of acute arsenic poisoning, caused by ingestion of food contaminated by As2O2, presented with abdominal pain, vomiting, nausea and diarrhea. The average level of urinary arsenic was 3.926 mg/L. The incidence of neuritis, poisoning hepatopathy and abdominal ECG was respectively 7.7%, 32.54%, 35.9%. All the cases recovered after oral or parenteral administration of dimecapto succinate (DMS) in six weeks. DMS is the drug of choice in the treatment of arsenic poisoning.

[Effect of glycerol-induced acute renal failure in rabbit with Ligusticum wallichii on thromboxane B2, 6-keto-prostaglandin F1 alpha/thromboxane B2]

The effect in preventing and treating glycerol-induced acute renal failure (ARF) in rabbit with Ligusticum wallichii (LW) has been studied. 33 male and female rabbits weighing 2.0-3.0 Kg were divided into three groups randomly: (1) LW treated group. (2) pathological control group and (3) normal control group. The measurement of plasma 6-keto-PGF1 alpha, TXB2 concentration and 6-keto-PGF1 alpha/TXB2 ratio were carried out with radioimmunoassay after 24 hr, 48 hr and 72 hr of ARF. The results showed that plasma TXB2 concentration obviously increased (P < 0.01), 6-keto-PGF1 alpha concentration had no obvious changes (P > 0.05), 6-keto-PGF1 alpha/TXB2 ratio markedly decreased and LW could reduce plasma TXB2 concentration, slightly increase the plasma 6-keto-PGF1 alpha concentration, keep 6-keto-PGF1 alpha/TXB2 ratio in normal level after ARF. It showed that LW could inhibit effectively platelet activation, correct 6-keto-PGF1 alpha/TXB2 imbalance and have a preventing and treating effect for ARF.