Effects of estradiol, phytoestrogens, and Ginkgo biloba extracts against 1-methyl-4-phenyl-pyridine-induced oxidative stress

Oxidative stress has been recently considered as a mediator of nerve cell death in several neurodegenerative diseases. We studied the effect of the parkinsonism-inducing toxine 1-methyl-4-phenyl-pyridine (MPP+) on several parameters of cell distress using native and neuronal PC12 cells. Then, since estrogens have been reported to prevent neuronal degeneration caused by oxidative damage, we investigated the ability of 17beta- estradiol (E2); two Ginkgo biloba extracts, EGb 761 and Cp 202; as well as two flavonoids, quercetin and kaempferol, to rescue PC12 cells submitted to MPP+- induced oxidative stress. Our results consistently show that both Ginkgo biloba extracts could prevent cell death in native and neuronal PC12 cells, while in neuronal PC12 cells also quercetin and E2 could reverse MPP+ neurotoxic effet. Western blot analysis demonstrated that MPP+ injuries might modulate dopamine transporter (DAT) protein expression but not estrogen receptor beta (ERbeta) protein expression. EGb 761 and Cp 202 also modulate DAT and ERbeta protein expression in neuronal cells. From these studies, we outline the importance of testing estrogen-like plant-derived molecules as potent antioxidants and examine their effect on protein expression.

Neuroprotective effect of estradiol and phytoestrogens on MPP+-induced cytotoxicity in neuronal PC12 cells

A large body of experimental evidence supports a role for oxidative stress as a mediator of nerve cell death in Parkinson's disease. To better understand the cellular insult of oxidative stress on dopaminergic neurons, we studied the cytotoxic effect of the 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) metabolite, 1-methyl-4-phenyl pyridium (MPP(+)), on several parameters of cell distress using neuronal PC12 cells. We also measured the level of protein expression for the dopamine transporter and the estrogen receptors alpha and beta. Since estrogens have been reported to prevent neuronal degeneration caused by increased oxidative burden, we investigated the ability of 17beta-estradiol, the stereoisomer 17alpha-estradiol, and several phytoestrogens to rescue neuronal PC12 cells submitted to MPP(+)-induced cytotoxicity. Our results consistently show a protective effect of 17alpha-estradiol, 17beta-estradiol and certain phytoestrogens such as quercetin and resveratrol, in neuronal PC12 cells treated with MPP(+). In our cellular paradigm, phytoestrogens coumestrol, genistein, and kaempferol did not revert MPP(+)-induced cellular death. By Western blot, we demonstrated that administration of MPP(+) alone decrease dopamine transporter expression, while treatments with MPP(+) together with 17alpha-estradiol, 17beta-estradiol, quercetin, or resveratrol could restore dopamine transporter protein expression to control levels. Moreover, the same treatments did not modulate alpha estrogen receptor or beta estrogen receptor expression. By these studies, we aim to provide more evidence for the involvement of phytoestrogens in the process of neuroprotection and to test our hypothesis that some of these compounds may act as neuroprotective molecules and have a lesser hormonal effect than estrogens.

Combined effect of xenoestrogens and growth factors in two estrogen-responsive cell lines

It is now well recognized that estrogenic signaling mechanisms are far more complex than once thought. Several crosstalks between the estrogen receptor and other signaling pathways may influence the estrogenic stimulation of cell growth. Thus, the estrogenic effects of several environmental contaminants, now suspected to act as endocrine disrupters, may be influenced by a simultaneous stimulation of other signaling pathways. The aim of this study was to investigate whether the growth response of two estrogen-responsive cell lines, MCF-7 and GH3, treated with xenoestrogens might be affected by the addition of growth factors to their culture medium. Cells were treated with two known xenoestrogens, endosulfan and chlordane, alone or in the presence of insulin-like growth factor-1 and epidermal growth factor, respectively, and their growth was measured using the 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxyanilide proliferation assay. Our results show that treatment with endosulfan or chlordane as well as treatment with growth factors increased cell growth, while the administration of xenoestrogens together with growth factors triggered a partly additive response with no antagonist or synergistic effect. These results sustain a role for xenoestrogens in cellular growth.

Modulation of prolactin expression by xenoestrogens

Xenoestrogens are widely used environmental chemicals that have recently been under scrutiny because of their possible role as endocrine disrupters. Among them are endosulfan and chlordane, two persistent insecticides suspected to act as estrogens in living organisms. To test and better understand the potential estrogenic activity of these chemicals, we used a pituitary cell line (GH(3)) known to respond to estrogens by increasing its secretion of prolactin (PRL), a hormone that is well known for its many physiological functions, especially in fetal growth, development, and reproduction. We measured the levels of PRL secretion and PRL mRNA transcription using immunometric tests, Northern blots, and relative quantitative RT-PCR. We also employed the XTT proliferation assay to compare the growth of GH(3) cells stimulated with 17-beta estradiol and endosulfan or chlordane. Our results show that endosulfan and chlordane are able to induce a substantial increase of PRL expression while these two chemicals do not increase cell growth. Together, our results suggest that endosulfan and chlordane could indeed modulate an estrogen-inducible gene such as PRL, possibly acting via second messenger-mediated cellular mechanisms instead of solely competing with estrogens for the nuclear estrogen receptor sites.

Effect of oxidative stress on stability and structure of neurofilament proteins

Neurofilament proteins are highly phosphorylated molecules in the axonal compartment of the adult nervous system. We report the structural analysis of neurofilament proteins after oxidative damage. SDS-PAGE, immunoblotting, circular dichroism, and Fourier transform infrared spectroscopy were used to investigate the relative sensitivity of neurofilaments to oxidative stress and to identify changes in their molecular organization. An ascorbate-Fe+3-O2 buffer system as well as catechols were used to generate free radicals on a substrate of phosphorylated and dephosphorylated neurofilaments. By Fourier Transform Infrared spectroscopy and circular dichroism, we established that the neurofilament secondary structure is mainly composed of alpha-helices and that after free radical damage of the peptide backbone of neurofilaments, those helices are partly modified into beta-sheet and random coil structures. These characteristic reorganizations of the neurofilament structure after oxidative exposure suggest that free radical activity might play an important role in the biogenesis of the cytoplasmic inclusions found in several neurodegenerative diseases.

Effect of oxidative stress on stability and structure of neurofilament proteins

Neurofilament proteins are highly phosphorylated molecules in the axonal compartment of the adult nervous system. We report the structural analysis of neurofilament proteins after oxidative damage. SDS-PAGE, immunoblotting, circular dichroism, and Fourier transform infrared spectroscopy were used to investigate the relative sensitivity of neurofilaments to oxidative stress and to identify changes in their molecular organization. An ascorbate-Fe+3-O2 buffer system as well as catechols were used to generate free radicals on a substrate of phosphorylated and dephosphorylated neurofilaments. By Fourier Transform Infrared spectroscopy and circular dichroism, we established that the neurofilament secondary structure is mainly composed of α-helices and that after free radical damage of the peptide backbone of neurofilaments, those helices are partly modified into β-sheet and random coil structures. These characteristic reorganizations of the neurofilament structure after oxidative exposure suggest that free radical activity might play an important role in the biogenesis of the cytoplasmic inclusions found in several neurodegenerative diseases.Key words: neurofilaments, oxidative stress, neurodegeneration, phosphorylation, infrared spectroscopy, circular dichroism.

AMPA receptor properties in adult rat hippocampus following environmental enrichment

In adult rats, environmental enrichment has been shown to selectively increase -AMPA binding in the hippocampus but the molecular mechanisms underlying this effect remain unknown. We used in situ hybridization with antisense oligonucleotides to determine possible changes in the hippocampal expression of messenger RNAs for different subunits of AMPA receptors in adult rats following exposure to an enriched environment. Quantitative analysis revealed that mRNA levels for three subtypes of AMPA glutamate receptors (GluR1-3; Flip and Flop variants) were not modified in any hippocampal region after environmental enrichment. In addition, no differences were detected in the levels of GluR1 and GluR2/3 proteins in Western blots of hippocampal membranes from enriched rats. Nevertheless, quantitative ligand binding autoradiography indicated that environmental enrichment evoked a significant and uniform decrease in the capacity of calcium or phosphatidylserine (PS) to up-regulate -AMPA binding in various hippocampal regions but not in the cerebral cortex. These findings support previous observations suggesting that post-translational changes in AMPA receptor properties, as a result of the activation of calcium-dependent processes, may represent an important mechanism underlying long-term modifications of synaptic efficacy in the rat hippocampus.

Binding properties of glutamate receptors in streptozotocin-induced diabetes in rats

The biochemical mechanisms by which diabetes modulates cognitive function are not well established. Here, we determined the effects of streptozotocin (STZ) administration on the binding properties of alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) subtypes of glutamate receptors in rats, using quantitative autoradiographic analysis of (3)H-AMPA and [(3)H]glutamate binding on brain tissue sections. The STZ injection (70 mg/kg intraperitoneally) produced a reduction of (3)H-AMPA binding in various brain regions, an effect that is due to a decrease in receptor affinity. The STZ-induced reduction of (3)H-AMPA binding varied in different brain structures, being more pronounced in the striatum, cerebral cortex, and hippocampus and almost absent in the cerebellum. Western blots performed on hippocampal membranes revealed that the decrease in (3)H-AMPA binding is possibly associated with changes in immunologic properties for one glutamate receptor subunit (GluR1). Finally, the effect of STZ-induced diabetes appeared to be specific to the AMPA subtype of glutamate receptors, as the same treatment did not modify [(3)H]glutamate binding to NMDA receptors. These changes in AMPA receptor properties may have important implications for understanding the biochemical mechanisms underlying cognitive impairment in diabetes.

Apolipoprotein E genotype in schizophrenia: frequency, age of onset, and neuropathologic features

Apolipoprotein E (ApoE) genotype has been found to affect the expression of a variety of neuropsychiatric disorders. We determined ApoE genotype frequencies and their relationship to clinical and pathological features in a diverse cohort of individuals with schizophrenia. There were no differences in ApoE genotype frequencies between schizophrenics and controls. However, the ApoE epsilon 4 genotype was associated with a younger age of onset of schizophrenia, and in an elderly subsample, individuals with the epsilon 4 allele more frequently exhibited co-existent dementia and had more neurofibrillary pathology (although none of the cases met criteria for Alzheimer's disease). This examination of ApoE in relation to clinical and neurobiological features of schizophrenia suggests that it modifies the phenotypic expression of the disease.

Melatonin receptors are present in non-optic regions of the brain of a deep-sea fish living in the absence of solar light

Pineal melatonin hormonally transduces photoperiod to influence daily and seasonal cycles in most vertebrates (1, 2). Evidence of melatonin receptors throughout the brain of several fish species (3-5), particularly in retinorecipient structures, also indicates a role in visual processing. Despite the absence of solar light many deepsea organisms show seasonality (6-8). The presence of central melatonin receptors was investigated by quantitative in vitro autoradiography in the deep-sea fish Coryphaenoides (Nematonurus) armatus. Specific, time-dependent, saturable, high affinity and guanine nucleotide sensitive, 2-[125I]iodomelatonin binding was found over the mid-brain tegmentum and hindbrain. Competing ligand potency was iodomelatonin > melatonin >> 5-HT. Although C.(N.) armatus has well developed eyes no 2-[125I]iodomelatonin binding occurred in optic tectum, cerebellum or hypothalamus. Thus melatonin involvement in processing of visual information and control of seasonal physiology via hypothalamic areas appears to be absent in this species. The presence of central G-protein coupled receptors indicates a function for melatonin unrelated to solar light.

Association of apolipoprotein epsilon 4 allele and neuropathologic findings in patients with dementia

Apolipoprotein E (APOE) is a lipoprotein expressed in liver and brain as one of three isoforms (APOE 2, APOE 3 and APOE 4). Recent findings suggest that the presence of APOE 4 is associated with an increased risk for both familial Alzheimer's disease and late-onset Alzheimer's disease. We extended these observations by determining the frequency of APOE alleles in patients with pathologically confirmed Alzheimer's Disease (AD), Parkinson's disease (PD), diffuse Lewy Body disease (DLBD), AD with concomitant PD pathology, demented PD patients without or with concomitant AD pathology and in schizophrenics with a progressive dementia (SCHIZ+DEM). The APOE genotype was determined by restriction digestion of polymerase chain reaction-amplified DNA isolated from frozen brain samples. The frequency of the APOE epsilon 4 allele was highest among sporadic AD and DLBD patients (0.30 and 0.38, respectively) and lowest in the SCHIZ+DEM and non-demented PD patients (0.06 and 0.1, respectively). Thus, the APOE epsilon 4 allele is over-represented selectively in patients with dementias associated with plaques and tangles and/or cortical Lewy bodies, but not in demented schizophrenics or non-demented PD patients.

Alterations of intermediate filaments in various histopathological conditions

Intermediate filament proteins belong to a multigene family and constitute an important cytoskeletal component of most vertebrate cells. Their pattern of expression is tissue specific and is highly controlled during embryonic development. Numerous pathologies are known to be associated with modifications of intermediate filament organisation, although their precise role has not yet been elucidated. The present review focuses on the most recent data concerning the possible causes of intermediate filaments disorganization in specific pathologic conditions affecting the epidermis, the liver, and the nervous system. We discuss the formation of abnormal intermediate filament networks that arise as a consequence of mutations that directly affect intermediate filament structure or are induced by multifactorial causes such as modifications of post-translational processes and changes in the levels of expression.

Variants of the heavy neurofilament subunit are associated with the development of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder primarily affecting motor neurons. The etiology of the majority of cases remains unknown. Recent findings from several laboratories suggest a role for neurofilaments in the development of motor neuron disorders. The C-terminal region of the human neurofilament heavy subunit (NEFH) contains a unique functional domain consisting of 43 repeat motifs of the amino acids Lys-Ser-Pro (KSP). This C-terminal region of NEFH forms the sidearm projections which cross-link the neurofilaments. Previously, we have demonstrated polymorphism in the C-terminal region of the human NEFH: an allelic variant of a slightly larger molecular size, containing an additional KSP phosphorylation motif. Novel mutations in this region were found in five ALS patients. We propose that changes in the KSP-repeat domain may affect the cross-linking properties of the heavy neurofilament subunit and perhaps contribute to the development of neurofilamentous swellings in motor neurons, a hallmark of ALS.

A new orphan member of the nuclear hormone receptor superfamily that interacts with a subset of retinoic acid response elements

We have identified and characterized a new orphan member of the nuclear hormone receptor superfamily, called MB67, which is predominantly expressed in liver. MB67 binds and transactivates the retinoic acid response elements that control expression of the retinoic acid receptor beta 2 and alcohol dehydrogenase 3 genes, both of which consist of a direct repeat hexamers related to the consensus AGGTCA, separated by 5 bp. MB67 binds these elements as a heterodimer with the 9-cis-retinoic acid receptor, RXR. However, MB67 does not bind or activate other retinoic acid response elements with alternative hexamer arrangements or any of several other wild-type and synthetic hormone response elements examined. The transactivation of retinoic acid response elements by MB67 is weaker than that conferred by the retinoic acid receptors but does not require the presence of all-trans retinoic acid, 9-cis-retinoic acid, or any exogenously added ligand. We propose that MB67 plays an important role in the complex network of proteins that govern response to retinoic acid and its metabolites.

Isolation of IFAPa-400 cDNAs: evidence for a transient cytostructural gene activity common to the precursor cells of the myogenic and the neurogenic cell lineages

Differentiation of neural and muscle cells is characterized by a switch in the expression of the type of intermediate filament protein subunit. In these lineages, vimentin is transiently expressed in the initial stages of development and is gradually replaced by a tissue specific protein. We have identified a giant developmentally regulated antigen (IFAPa-400) which colocalizes with vimentin in the precursor cells of the neurogenic and myogenic lineages of the chick embryo [Chabot and Vincent (1990) Dev. Brain Res. 54, 195-204; Cossette and Vincent (1991) J. Cell Sci. 98, 251-260]. Based on the expression of this protein during neurogenesis and myogenesis, we hypothesize that IFAPa-400 and vimentin define a special intermediate filament network, common to the non-differentiated cells derived from the neuroectoderm and those of the myogenic tissues. We report here the isolation and sequence of partial cDNAs encoding more than 400 amino acids of the carboxy-terminus of this protein. RNA blot analysis and in situ hybridization indicate that IFAPa-400 represents a bona fide developmentally regulated gene product. These results further confirm that IFAPa-400 mRNA transcripts are limited to the early precursor cells of both neurogenic and myogenic lineages.

Ontogeny of Ha-ras and c-myc mRNA levels in rabbit embryo and extraembryonic tissues by quantitative in situ hybridization

A large variety of proto-oncogenes are known to be of key importance in cellular growth and differentiation during embryonic development. Using quantitative in situ hybridization, we studied in detail the levels of the proto-oncogenes Ha-ras and c-myc mRNA in embryos and extraembryonic tissues (maternal and embryonic placentas, trophoblast, and endometrial epithelium) during prenatal life of rabbit. cDNA probes encoding for Ha-ras (fragment Kpn 1-BstE II of 883 bp) and c-myc (fragment Pst 1-Pst 1 of 490 bp) were used to detect specific transcripts in fixed cryostat sections. High levels of Ha-ras and c-myc mRNA were detected in the rabbit embryo as well as in the decidua and in the trophoblast as early as day 9 of gestation. At 12 and 15 days of gestation, Ha-ras and c-myc mRNA levels decreased in both embryonic and maternal placenta while in the embryo a significant increase of Ha-ras and c-myc expression was detected with particular evidence in the central nervous system. Finally, at 25 days of gestation the expression of the two proto-oncogenes, Ha-ras and c-myc, was greatly decreased in both the embryo and extraembryonic tissues, and was undetectable by 30 days of gestation. These results show that in rabbit the expression of the two proto-oncogenes Ha-ras and c-myc is localized in the same tissues with similar intensity and follows an unparallel temporal modulation in the embryo and in the extraembryonic tissues during prenatal development.

Growth hormone and somatostatin gene expression in adult and aging rats as measured by quantitative in situ hybridization

We have investigated the variations in growth hormone (GH) and somatostatin (SOM) mRNAs in adult, middle-aged and aging rats of both sexes using quantitative in situ hybridization. cDNA probes complementary to GH mRNA and SOM mRNA were used on fixed pituitary and hypothalamic sections, respectively. A clear sexual dimorphism in GH gene expression was observed in all age groups examined, mRNA levels always being higher in males than in females. In male rats, GH mRNA levels reached a maximum at 7 months of age and then dramatically decreased in middle-aged and aging animals. In female animals, the highest expression of GH was observed at 9 months of age followed by a gradual and constant decline during the aging period. SOM mRNA levels in the periventricular nucleus of the hypothalamus also showed a sexual dimorphism in adult rats, being higher in males than females. A gradual decline in SOM mRNA was observed in middle-aged and aging rats of both sexes. These results suggest that middle age and aging are critical periods for the control of GH and SOM gene expression and that the decrease in GH mRNA levels observed during aging is probably not a consequence of an increase of SOM activity.

Dihydrotestosterone (DHT) regulation of insulin-like growth factor II mRNA in neonatal rats

Insulin-like growth factors (IGFs) are well known as peptide mitogens and important growth factors in fetal as well as in early postnatal development. In particular, IGF II is strongly expressed during fetal life and in neonatal animals. Very little is known about the regulation of IGF II gene expression. In order to study in detail the regulation of IGF II mRNA levels in the liver by the potent nonaromatizable androgen dihydrotestosterone (DHT), we have used quantitative in situ hybridization to detect the mRNA encoding for this growth factor. Pups were separated into 4 groups and injected twice a day immediately after birth with 3 different doses of DHT: 0.1 mg DHT/day, 0.25 mg DHT/day, 0.5 mg DHT/day for 4 and 7 days, and the control groups were injected with the vehicle alone. Animals were perfused with 4% paraformaldehyde and sections from the liver, heart, kidneys and brain were cut with a cryostat. A [35S]-labeled cDNA probe was used to detect IGF II mRNA levels. After hybridization, sections were autoradiographed with X-ray films and then coated with liquid photographic emulsion. Densitometric measurement revealed that, at 4 days of age, IGF II mRNA levels were lower in DHT-treated rats than in control animals. No statistically significant differences in IGF II mRNA levels were observed among the three groups treated with the different doses of DHT, thus revealing that even the lowest dose of DHT (0.1 mg/day) used was sufficient to inhibit IGF II gene expression in neonatal rats. Moreover, at 7 days of age, DHT-treated rats showed the same levels of IGF II mRNA as those observed in rats treated with DHT for 4 days. These results suggest that DHT may play an important role in the regulation of IGF II gene expression in the rat liver during the neonatal period.

Regional changes of striatal dopamine receptors following denervation by 6-hydroxydopamine and fetal mesencephalic grafts in the rat

Young adult female rats received a 6-hydroxydopamine lesion in the left substantia nigra and, 3 weeks later, some of them were grafted with a cell suspension from the ventral mesencephalon of rat embryos (14-15 days old). Six months after transplantation, some grafted rats, following injection of amphetamine, had switched to turning only toward the intact side (type 1), whereas others turned toward the intact side only during the first half of the test (type 2). Levels of dopamine, dihydroxyphenylacetic acid and homovanillic acid were, respectively, 2%, 15% and 35% of the intact side in the denervated striatum of 6-hydroxydopamine rats. Dopamine concentrations were restored to 13% and 10% of the intact side in the grafted striatum of type 1 and type 2 animals, respectively. Levels of homovanillic acid were unchanged following grafts whereas those of dihydroxyphenylacetic acid increased by 209% and 247% in the grafted striatum of type 1 and type 2 animals, respectively. The ratios of dihydroxyphenylacetic acid/dopamine as well as homovanillic acid/dopamine were low in the intact striatum whereas they increased in the denervated striatum with or without graft. The tyrosine hydroxylase immunoreactivity decreased by about 80% in the denervated striatum of 6-hydroxydopamine rats. In type 1 rats, tyrosine hydroxylase immunoreactivity revealed that the graft was localized in the dorsomedial part of the denervated striatum, whereas in type 2 animals, it was also in the medial striatum but it overlapped the dorsal and ventral parts of it equally. D1 as well as D2 dopamine receptors were measured throughout the striatum (9.0-7.6 rostral-caudal coordinates), by autoradiography, using [3H]SCH 23390 (D1 antagonist) and [3H]spiperone (D2 antagonist) binding. Supersensitive D2 receptors were normalized in the dorso- and ventromedial parts of the grafted striatum. D2 receptor density was higher in type 2 than in type 1 rats, more specifically at 8.6-8.2 rostral-caudal coordinates, where the graft was. D1 receptor supersensitivity was modest compared to D2 receptors in the striatum of 6-hydroxydopamine rats and decreased following grafts. DA receptors changes in the striatum, following fetal mesencephalic grafts, may explain the behavioral recovery seen in grafted rats.

The ontogeny of central melatonin binding sites in the rat

The maternal transfer of circadian rhythmicity and photoperiodic information to the fetus has been clearly demonstrated in several species, as has the importance of the pineal hormone, melatonin, in conveying this information. Maternal melatonin is known to readily cross the placenta and be taken up by the fetal brain. Specific melatonin receptors have been demonstrated in the rodent brain and pituitary from the 21st day of gestation. To better understand the mechanisms by which melatonin brings about the transfer of information to the fetus and to define the receptivity of the fetus to the melatonin signal, we have followed the ontogeny of central melatonin binding sites in the rat from the 13th day of gestation to 5 days after birth. The use of in vitro autoradiography allows for the precise localization of binding sites as well as their quantification. In the present study melatonin binding sites were first found on the 15th day of gestation, at which time specific binding was limited to the pituitary. At birth it was possible to identify a strong label in the pars tuberalis of the pituitary, whereas the pars distalis appeared to be less intensely and more unevenly labeled. Neuronal melatonin binding sites became apparent from day 17 of gestation in an area of the dorsal brain that in older fetuses and in neonatal rats appeared to be the paraventricular nucleus of the thalamus. Moreover, melatonin binding sites are identifiable over the suprachiasmatic nuclei from day 18 of gestation. These data show that the fetal pituitary may have the potential to respond to the maternal melatonin signal as early as the 15th day of gestation, and that the brain may attain that potential at the 17th or 18th day of gestation.

Effects of triiodothyronine, dexamethasone and estradiol-17 beta on GH mRNA in rat pituitary cells in culture as revealed by in situ hybridization

The GH lines of rat pituitary tumour cells have been largely used to study the regulation of GH mRNA. In order to investigate the role of T3, dexamethasone and estradiol-17 beta on GH expression in non-tumoural pituitary cells, we have used in situ hybridization techniques performed on rat anterior pituitary cells in monolayer culture. The amounts of mRNA encoding for GH, as evaluated by counting the number of grains per somatotrope, were markedly reduced after 4 days of culture in a steroid-free medium supplemented with an hypothyroid calf serum. Addition of T3 or dexamethasone for 3 days increased GH mRNA levels. The concomitant administration of the two hormones produced a synergistic effect on GH mRNA levels which became higher than those observed after T3 or dexamethasone administration alone. However, this effect did not restore GH mRNA levels to those measured in monolayer pituitary cells grown in medium containing 10% fetal calf serum. Moreover GH mRNA levels appeared higher in male than in female pituitary cells. The administration of E2 to pituitary cell cultures from both male and female rats produced an increase by 15, and 12.8% in GH mRNA levels in male and female, respectively. This stimulatory effect of E2 in cell culture was competitively blocked by simultaneous incubation with the antiestrogen LY156758 (Keoxifene). These results demonstrate that T3, dexamethasone as well as E2 act directly on somatotropic cells to regulate GH gene expression.

Ontogenesis and Sexual Dimorphism of Rat Growth Hormone Messenger Ribonucleic Acid as Studied by in situ Hybridization

Abstract We have investigated the ontogeny of growth hormone (GH) mRNA in the developing rat foetus and also from birth to adulthood. Using quantitative in situ hybridization, we studied the variations in the levels of GH mRNA during foetal and postnatal life in the pituitary of both male and female rats. A cDNA probe to GH mRNA was used to detect GH transcripts on fixed pituitary sections at different stages of development. Few labelled cells were observed in the lateral wings of the anterior pituitary from the 17th to 19th day of gestation in both sexes. The amounts of GH mRNA significantly increased in both male and female rats from neonatal to adult life, reaching the highest levels after puberty. A clear sexual dimorphism was observed at the 20th day of foetal life, GH mRNA levels being higher in male than in female rats. After birth, no significant differences of GH mRNA levels could be observed between male and female rats until 30 days of age (prepubertal period) when male rats exhibited GH mRNA levels higher than females. This sexual difference in GH mRNA levels remained constant throughout adult life. Moreover, gonadectomy performed at neonatal, prepubertal and adult periods in both male and female rats did not modify GH mRNA levels in either sex. These results indicate that an early synthesis of GH mRNA occurs in foetal pituitary and that the sexual dimorphism of GH mRNA observed from 30 days of age is not related to sex steroids.

Thyroid and glucocorticoid hormone regulation of rat pituitary growth hormone messenger ribonucleic acid as revealed by in situ hybridization

The effect of thyroid and glucocorticoid hormones on mRNA have been largely studied using tumor cell lines. To investigate the role of these hormones in vivo, we have used in situ hybridization techniques to study GH mRNA regulation in the rat pituitary. The amount of mRNA encoding for GH was dramatically reduced after 1 month of treatment with 6-N-propyl-2-tiouracil. However, daily injections of L-T4 for 10 days restored GH mRNA to control levels. Similarly, adrenalectomy decreased GH mRNA levels, and subsequent daily injections of dexamethasone for 1 and 5 days restored the levels of GH mRNA to those before adrenalectomy. Moreover, 6-N-propyl-2-tiouracil treatment in combination with adrenalectomy dramatically reduced pituitary levels of GH mRNA, which were increased by administration of both thyroid hormones and glucocorticoids. These results show that the effects of thyroid and glucocorticoid hormones on GH synthesis are largely mediated by the hypothalamus. Our results obtained in implanted pituitaries under the kidney capsula demonstrated that these two hormones also exert a smaller effect of GH mRNA directly at the pituitary level.

Effects of sex steroids on regulation of the levels of C1 peptide of rat prostatic steroid-binding protein mRNA evaluated by in-situ hybridization

Prostatic steroid-binding protein (PBP) is the most abundant protein synthesized in the rat ventral prostate. The protein is under strict androgenic control and is made of two subunits containing the polypeptides C1, C2 and C3. Using an 35S-labelled cDNA probe, we have used quantitative in-situ hybridization to assess the regulation of polypeptide C1 mRNA levels by sex steroids in the adult male rat. Densitometric quantification of autoradiographic hybridization signals revealed that a significant decrease in C1 mRNA levels could be detected 5 h after castration. Levels of C1 mRNA decreased by 50% 2.5 days after castration, while undetectable levels were reached within 7 days. Administration of the potent androgen 5 alpha-dihydrotestosterone to castrated rats caused a progressive increase in C1 mRNA levels which became significant 5 h after the first injection, while prolonged treatment, for 3 and 7 days, caused 50 and 100% reversals respectively of the effect of castration on C1 mRNA levels. Similar results were obtained by dot-blot hybridization using the same 32P-labelled cDNA probe, thus confirming the specificity and quantification achieved by in-situ hybridization. Administration of oestradiol-17 beta to orchiectomized adult rats for 14 days had no effect on steady-state C1 mRNA levels. Progesterone, on the other hand, at the dose used (2 mg twice daily) caused a marked increase in C1 mRNA levels, measured by in-situ hybridization, which was completely reversed by concomitant administration of the pure antiandrogen flutamide. The present data clearly demonstrate that the expression of PBP C1 peptide mRNA is under strict androgenic control and is a very sensitive and specific parameter of androgenic activity. They also indicate that quantitative in-situ hybridization is a powerful, sensitive and most efficient tool to study the regulation of gene expression while, in addition, providing precise information about the site of mRNA localization as well as information about the histology of the tissue, particularly the heterogeneous nature of the acinar response to androgenic stimulation and deprivation.

Central GABAergic innervation of the pituitary in goldfish: a radioautographic and immunocytochemical study at the electron microscope level

The GABAergic innervation of the goldfish pituitary was studied at the light and electron microscope levels by means of radioautography after in vitro incubation in tritiated gamma-aminobutyric acid (GABA) and immunocytochemistry using antibodies against GABA. Following incubation of pituitary fragments in a medium containing tritiated GABA, a selective uptake of the tracer was observed within the digitations of the neurohypophysis. Silver grain clusters were also observed in the adenohypophyseal tissue. At the electron microscope level, this uptake was found to correspond to nerve endings containing small clear and dense-core vesicles. These labeled profiles were located mainly in neurohypophyseal digitations in close apposition with the basement membrane separating the neurohypophysis from the adenohypophysis. However, they were also encountered in direct contact with most adenohypophyseal cell types in the different lobes. These results were confirmed by immunocytochemical data demonstrating the presence of numerous GABA immunoreactive fibers in both anterior and neurointermediate lobes. They were found either in the digitations of the neurohypophysis or in the adenohypophysis in direct contact with the glandular cells with a distribution and an ultrastructural aspect similar to those observed by radioautography. These data demonstrate that the pituitary of teleosts receives a massive GABAergic innervation. Although physiological data providing a functional significance for such an innervation are lacking, the present study suggests that, as already documented in mammals, GABA may be involved in the neuroendocrine regulation of pituitary functions in teleosts.