Somatostatin neuronal systems in the hypothalamus of peripubertal female lambs

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Prepubertal changes in the hypothalamo-gonadotrophic and hypothalamo-somatotrophic axes of the female lamb

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Prepubertal changes in the synthesis, storage and release of the somatostatin in the hypothalamus of female lambs. A morphofunctional study

International audienceIt is assumed that hypothalamic somatostatin plays a role in the preovulatory phase of the oestrous cycle in sheep. The aim of the study was to investigate the processes of synthesis, storage and release of somatostatin in hypothalamic neurons, in immature female lambs, in the period approaching to puberty. Experiments were carried out on 10 prepubertal (17 weeks old) and 10 peripubertal (32 weeks old) ovary-intact lambs. Morphofunctional changes in the somatostatin neurons were assayed with immunohistochemistry and hybridisation in situ. Computer image analysis was used to determine the density of both reactions and the percentage of the area exhibiting immunohistochemical staining. These parameters express the content of immunoreactive (ir) somatostatin and expression of mRNA for prepro-somatostatin (PPS). Two populations of ir somatostatin perikarya were localized in the hypothalamus: a very large number of perikarya in the periventricular (PEV) nucleus, and single cell bodies in the arcuate (ARC) nucleus. Only it somatostatin fibres, but no perikarya were seen in the ventromedial (VM) nucleus and preoptic area. The analysis of mRNA PPS showed perikarya filled with silver grains localized in the PEV, ARC and VM, There were differences in the content of ir somatostatin and the intensity of the PPS mRNA signal between the two periods investigated. In the median eminence, the content of ir somatostatin in the terminals decreased in the peripubertal compared to the prepubertal group (P < 0.001). In the PEV, the content of it somatostatin in the perikarya and the expression of PPS mRNA decreased in the peripubertal compared to the prepubertal group (P < 0.001). In the ARC, the content of ir somatostatin in the perikarya increased (P < 0.001), but expression of PPS mRNA decreased (P < 0.001) in the peripubertal compared to the prepubertal group. There were no differences in the expression of PPS mRNA in the VM. We concluded, that the different secretory activity of the two hypothalamic populations of somatostatin neurons can be related to their different physiological functions in the prepubertal period of female lambs. (c) 2008 Elsevier B.V. All rights reserved

Implication des neurones à neuropeptide Y du noyau arqué dans le contrôle des neurones à somatostatine du noyau périventriculaire au moment de la puberté. Etude morphofonctionnelle chez la brebis

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Hypothalamic arcuate neuropeptide Y-neurons modulate periventricular somatostatin-neurons around puberty in the sheep: morphological arguments

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The secretory activity of somatostatin neuronal system in the hypothalamus of prepubertal female lambs

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Prepubertal changes in the synthesis, storage and release of growth hormone and luteinising hormone and in the immunoreactivity of oestrogen receptor-alpha in lamb pituitary cells. A morphofunctional study

International audienceThe present study was designed to determine the changes in the synthesis, storage and release of luteinising hormone (LH) and growth hormone (GH) in the hypophyseal cells by investigating the presence of oestrogen receptor-a (ER(x) in developing prepubertal female lambs. The experiment was carried out on 14 prepubertal (17-week-old) and 14 peripubertal (32-week-old) ovary-intact lambs. Morphofunctional changes in the cells of the adenohypophyseal population were assayed with immunohistochemistry (M), in situ hybridisation (ISH), Real-time PCR and radioimmunoassay (RIA). Blood samples (n = 14) were taken every 2 weeks from 17 to 32 weeks of age for estimation of GH and LH by RIA. Computer image analysis was used to determine the percent of cells exhibiting IH and/or ISH reaction. The percentage of cells stained for LH beta and GH increased for both LH- and GH-producing cells and were higher (P < 0.001) in the peripubertal than prepubertal group. The percentage of mRNA LHP-expressing cells decreased and were lower for the peripubertal (P < 0.001) than prepubertal group. The GH mRNA in pituitaries of prepubertal lambs was higher in comparison to peripubertal ones (P < 0.001). The percentage of ER alpha positive cells increased significantly (P < 0.001) in peripubertal compared to prepubertal lambs and this increase was significant (P < 0.001) in both LH- and GH-producing cells. Plasma LH concentrations increased from 27 weeks of age, while GH concentrations gradually decreased from 17 weeks of age (P < 0.05). The histomorphological changes in the LH- and GH-producing cells reflect the increasing pattern of the regulation of secretory processes of these hormones and an escalating regulatory role of oestrogen in the physiology of these cells during the prepubertal period. These results support the involvement of both hormones in the events leading up to puberty. (C) 2008 Elsevier B.V. All rights reserved

Les neurones à NPY impliqués dans la mise en place de la puberté chez la brebis : interaction avec les neurones à somatostatine et les neurones à kisspeptine

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