References of "Alvarez Gonzalez, Maria-Luz"
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See detailGonadotropin Releasing Hormone Inhibitory Autofeedback by Subproducts Antagonist at N-Methyl-D-Aspartate Receptors: A Model of Autocrine Regulation of Peptide Secretion
Bourguignon, Jean-Pierre ULg; Alvarez Gonzalez, Maria-Luz ULg; Gerard, Arlette ULg et al

in Endocrinology (1994), 134(3), 1589-92

The secretion of Gonadotropin-releasing Hormone (GnRH) involves activation of N-methyl-D-aspartate (NMDA) receptors. Here, we show that pulsatile GnRH secretion from hypothalamic explants is suppressed by ... [more ▼]

The secretion of Gonadotropin-releasing Hormone (GnRH) involves activation of N-methyl-D-aspartate (NMDA) receptors. Here, we show that pulsatile GnRH secretion from hypothalamic explants is suppressed by 1-5GnRH, an endogenous breakdown product of GnRH, while 2-10GnRH has no effect. GnRH secretion evoked by NMDA is selectively inhibited by 1-5GnRH and this effect is similar to that of AP-5, a competitive antagonist at NMDA receptors. In addition, 1-5GnRH accounts for a dose-related inhibition of tritiated glutamate binding to hypothalamic membrane preparations. Using GnRH secretion as a model of NMDA-receptor controlled system, the effect of different peptides has been studied. Growth Hormone Releasing Factor (GRF), Insulin-like Growth Factor-I (IGF-I) and Proinsulin result in inhibition of GnRH secretion. Bioactive subproducts of those peptides (1-29GRF, 4-701GF-I and insulin) do not show any effect, suggesting that their classical receptors are not involved. In contrast, GnRH secretion is inhibited by other subproducts (1-37GRF, 1-31GF-I and C-peptide) all terminating in a glutamate residue. These subproducts selectively suppress the NMDA-evoked secretion of GnRH. Protease inhibitors prevent the inhibitory effects of IGF-I on GnRH secretion. This, breakdown products of different peptide hormones are possible endogenous antagonists at NMDA receptors. This effect could account for an autocrine or paracrine limitation of NMDA-receptor-mediated secretion of peptides. [less ▲]

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See detailControl of Pulsatile Secretion of Gonadotrophin Releasing Hormone from Hypothalamic Explants
Bourguignon, Jean-Pierre ULg; Gerard, Arlette ULg; Alvarez Gonzalez, Maria-Luz ULg et al

in Human Reproduction (1993), 8 Suppl 2(NULL), 18-22

We have studied the secretion of gonadotrophin releasing hormone (GnRH) from hypothalamic explants of male rats at different ages in an attempt to delineate the neuroendocrine mechanism of the onset of ... [more ▼]

We have studied the secretion of gonadotrophin releasing hormone (GnRH) from hypothalamic explants of male rats at different ages in an attempt to delineate the neuroendocrine mechanism of the onset of puberty. In this paper, we review some of our recent studies and we provide evidence of a dual control played by receptors to neuroexcitatory amino acids. We showed previously that isolated explants of rat hypothalamus could secrete GnRH in a pulsatile manner. The onset of puberty was characterized by a 2-fold increase in frequency of GnRH secretory pulses. This reduction of the interval between GnRH pulses involved an inhibitory autofeedback effect of GnRH on the pulse generator which was shut off following a secretory episode. This period of refractoriness was longer before puberty than after the onset of puberty. Activation of receptors to neuroexcitatory amino acids (N-methyl-D-aspartate; NMDA-type) was involved in the mechanism of pulsatile GnRH secretion. Striking developmental changes in NMDA-receptor-mediated GnRH secretion were demonstrated with a maximal activity around the time of the onset of puberty. Similar changes occurred in orchidectomized animals, indicating that this maturational process was gonad-independent. While evidence accumulated that NMDA receptors were involved in a stimulatory control of GnRH secretion, we found that NMDA receptors mediated an inhibitory effect on GnRH secretion. This inhibitory effect was very potent in the immature hypothalamus and it showed a marked reduction in potency before onset of puberty.(ABSTRACT TRUNCATED AT 250 WORDS) [less ▲]

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See detailAcute Suppression of Gonadotropin-Releasing Hormone Secretion by Insulin-Like Growth Factor I and Subproducts: An Age-Dependent Endocrine Effect
Bourguignon, Jean-Pierre ULg; Gerard, Arlette ULg; Alvarez Gonzalez, Maria-Luz ULg et al

in Neuroendocrinology (1993), 58(5), 525-30

Using rat hypothalamic explants, we showed previously that activation of N-methyl-D-aspartate (NMDA) receptors was involved in the mechanism of gonadotropin-releasing hormone (GnRH) secretion. (1-3 ... [more ▼]

Using rat hypothalamic explants, we showed previously that activation of N-methyl-D-aspartate (NMDA) receptors was involved in the mechanism of gonadotropin-releasing hormone (GnRH) secretion. (1-3)Insulin-like growth factor I (IGF-I), the N-terminal tripeptide of IGF-I, was suggested to be a possible antagonist at NMDA receptors. Here, we study the effects of IGF-I and its subproducts, (1-3)IGF-I and (4-70)IGF-I, either given in vivo as a single subcutaneous injection or used in vitro, on the secretion of GnRH by hypothalamic explants. At the three ages studied (15, 25 and 50 days), (4-70)IGF-I does not show any effect. At 50 days, the in vivo administration or the in vitro use of IGF-I results in a dose-related inhibition of the GnRH secretion induced by veratridine, a depolarizing agent. In addition, the spontaneous pulsatile secretion of GnRH in vitro is transiently suppressed after the in vivo administration of IGF-I. (1-3)IGF-I results in an inhibitory effect similar to that of IGF-I. At 25 days, IGF-I and (1-3)IGF-I show the same effects as at 50 days though higher concentrations are required. At 15 days, IGF-I does not show any effect whereas a potent inhibition of GnRH secretion is observed using (1-3)IGF-I either in vivo or in vitro. At all ages, the effects of (1-3)IGF-I parallel those of AP-5, a competitive antagonist at NMDA receptors.(ABSTRACT TRUNCATED AT 250 WORDS) [less ▲]

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See detailNeuroendocrine Mechanism of Onset of Puberty. Sequential Reduction in Activity of Inhibitory and Facilitatory N-Methyl-D-Aspartate Receptors
Bourguignon, Jean-Pierre ULg; Gerard, Arlette ULg; Alvarez Gonzalez, Maria-Luz ULg et al

in Journal of Clinical Investigation (1992), 90(5), 1736-44

In humans and in several animal species, puberty results from changes in pulsatile gonadotropin-releasing hormone (GnRH) secretion in the hypothalamus. In particular, the frequency of pulsatile GnRH ... [more ▼]

In humans and in several animal species, puberty results from changes in pulsatile gonadotropin-releasing hormone (GnRH) secretion in the hypothalamus. In particular, the frequency of pulsatile GnRH secretion increases at the onset of puberty, as can be shown by using hypothalamic explants of male rats of 15 and 25 d. Previous observations from us and others suggested that the initiation of puberty could involve a facilitatory effect of excitatory amino acids mediated through N-methyl-D-aspartate (NMDA) receptors. We found that GnRH secretion could be activated through NMDA receptors only around the time of onset of puberty (25 d). The aim of this study was to clarify why this activation did not occur earlier (at 15 d) and could no longer be observed by the end of puberty (at 50 d). We studied GnRH secretion in the presence of MK-801, a noncompetitive antagonist of NMDA receptors or AP-5, a competitive antagonist. We showed that, in the hypothalamus of immature male rats (15 d), a highly potent inhibitory control of pulsatile GnRH secretion in vitro was mediated through NMDA receptors. These data were confirmed in vivo because administration of the antagonist MK-801 (0.001 mg/kg) to immature male rats resulted in early pubertal development. Onset of puberty (25 d) was characterized by the disappearance of that NMDA receptor-mediated inhibition, thus unmasking a facilitatory effect also mediated through NMDA receptors. During puberty, there was a reduction in activity of this facilitatory control which was no longer opposed by its inhibitory counterpart. We conclude that a sequential reduction in activity of inhibitory and facilitatory NMDA receptors provides a developmental basis for the neuroendocrine mechanism of onset of puberty. [less ▲]

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See detailGonadal-Independent Developmental Changes in Activation of N-Methyl-D-Aspartate Receptors Involved in Gonadotropin-Releasing Hormone Secretion
Bourguignon, Jean-Pierre ULg; Gerard, Arlette ULg; Alvarez Gonzalez, Maria-Luz ULg et al

in Neuroendocrinology (1992), 55(6), 634-41

Using hypothalamic explants of male rats, we have shown that the N-methyl-D-aspartate (NMDA) receptors involved in a stimulatory control of gonadotropin-releasing hormone (GnRH) secretion were transiently ... [more ▼]

Using hypothalamic explants of male rats, we have shown that the N-methyl-D-aspartate (NMDA) receptors involved in a stimulatory control of gonadotropin-releasing hormone (GnRH) secretion were transiently activated at 25 days around the time of onset of puberty. This was evidenced by studying the dose-related inhibition of veratridine-induced GnRH secretion by MK-801, a use dependent antagonist of NMDA receptors. An increase in sensitivity of GnRH secretion to the inhibitory effect of MK-801 was used as a marker of increased activation of NMDA receptors involved in stimulation of GnRH secretion. Here, we report on data obtained in intact and castrated rats at different ages. The aim was to determine whether the absence of gonads would affect the developmental changes in activation of NMDA receptors that we described recently. In pubertal (50-day-old) rats, orchidectomy resulted in an activation of NMDA receptors which was nonsignificant after 4 days but significant after 13 days. In prepubertal rats orchidectomized at 5 or 10 days and studied 10 days later, the NMDA receptors involved in GnRH secretion were also more activated than in intact animals. Using explants of intact and castrated animals, a similar increase in activation of NMDA receptors was observed between 15 and 25 days of age, a period preceding onset of puberty. Subsequently, between 25 and 50 days, a reduction in NMDA receptor activation was seen. This decrease was observed in intact rats showing normal sexual development and in castrated rats as well.(ABSTRACT TRUNCATED AT 250 WORDS) [less ▲]

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See detailCytogenetic Changes in Hepatocarcinomas from Rats Treated with Chronic Exposure to Diethylnitrosamine
Herens, Christian ULg; Alvarez Gonzalez, Maria-Luz ULg; Barbason, Hervé ULg

in Cancer Genetics & Cytogenetics (1992), 60(1), 45-52

Cytogenetic analysis of rat hepatocarcinomas obtained after diethylnitrosamine (DEN) exposure showed a wide variety of numerical and structural chromosomal changes: 53 of 86 hepatocellular carcinomas ... [more ▼]

Cytogenetic analysis of rat hepatocarcinomas obtained after diethylnitrosamine (DEN) exposure showed a wide variety of numerical and structural chromosomal changes: 53 of 86 hepatocellular carcinomas showed at least one recurrent chromosomal aberration. Some of these recurrent changes occurred in several tumors. Chromosomes 1, 3, 11, and 12 were abnormal in more than 30% of the carcinomas; chromosomes 2, 4, 5, and 10 were abnormal in 10%. Moreover, chromosomes 1 and 10 were generally lost or deleted and chromosome 3, 4, and 11 were very often gained. The most frequent anomaly was loss of chromosome 1 which was observed in 35% of the tetraploid cell populations. The occurrence in several tumors of recurrent chromosomal rearrangements as well as various repeated aneuploidies strongly suggests that these anomalies are implicated in the process of rat hepatocarcinogenesis induced by DEN treatment. [less ▲]

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See detailEffects of Changes in Nutritional Conditions on Timing of Puberty: Clinical Evidence from Adopted Children and Experimental Studies in the Male Rat
Bourguignon, Jean-Pierre ULg; Gerard, Arlette ULg; Alvarez Gonzalez, Maria-Luz ULg et al

in Hormone Research (1992), 38 Suppl 1(NULL), 97-105

Among 32 patients with idiopathic central precocious puberty seen during a 3-year period, 1/4 were adopted children from developing countries who showed early sexual maturation during the catch-up process ... [more ▼]

Among 32 patients with idiopathic central precocious puberty seen during a 3-year period, 1/4 were adopted children from developing countries who showed early sexual maturation during the catch-up process following their arrival in Belgium. To study the possible mechanism accounting for such clinical observations, we used the male rat as a model, and evaluated the effect of variations in early nutritional conditions, by manipulating litter size, on hypothalamic and testicular maturation. We had shown previously that, in the male rat, onset of puberty was preceded, between 15 and 25 days of age, by a transiently increased activation of N-methyl-D-aspartate receptors involved in a facilitatory control of pulsatile secretion of gonadotropin-releasing hormone. We also showed that the proportion of elongated spermatids in testicular cell homogenates increased between 25 and 45 days of age. When compared to pups of a small litter (6/dam), those of a large litter (14/dam) showed a reduced growth rate (1.9 vs. 3.5 g/day) before weaning (21 days), whereas they grew at a similar rate (5.6 vs. 4.7 g/day) after weaning. At 35 days of age, the animals raised in the large litter showed evidence of delayed hypothalamic and testicular maturation when compared to animals from the small litter. Reduction of litter size at 17 days allowed food-restricted pups of a large litter to resume a normal growth rate before weaning.(ABSTRACT TRUNCATED AT 250 WORDS) [less ▲]

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See detailNeuroendocrine Control of the Onset of Puberty: Secretion of Gonadotrophin-Releasing Hormone from Rat Hypothalamic Explants
Bourguignon, Jean-Pierre ULg; Gerard, Arlette ULg; Fawe, L. et al

in Acta Paediatrica Scandinavica. Supplement (1991), 372

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