Hormone Content and Movement of Neurosecretory Granules in the Rat Neural Lobe during and after Dehydration

Nordmann, J

doi:10.1159/000124047

Cited by 34 publications

(18 citation statements)

References 25 publications

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“…Using a radioimmunoassay for ET-1 and ET-2 (27) we have found the isolated nerve endings to contain immunoreactive ET, although quantitatively ET is present at concentrations %5 x 104-fold less than AVP (Table 1). To examine if AVP and ET were colocalized in neurosecretory granules and coreleased from the nerve endings, animals were subjected to dehydration, which leads to a timedependent depletion of AVP (31) in the nerve endings. Following 3 days of dehydration AVP and ET had decreased by about 50%, (Table 1), whereas after 5 days of dehydration no further decrease in the ET content was observed, although the amount of AVP in the nerve endings had dropped by =93% (Table 1).…”

Section: Resultsmentioning

confidence: 99%

Endothelin regulation of neuropeptide release from nerve endings of the posterior pituitary.

Ritz

Stuenkel

Dayanithi

et al. 1992

Proc. Natl. Acad. Sci. U.S.A.

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We have investigated the role of endothelin (ET) in the stimulus-secretion coupling mechanism in the posterior pituitary. We report that isolated nerve endings contain immunoreactive endothelin, the level of which is regulated by homeostatic mechanisms involved in control of water balance. ET-1 and ET-3 potentiate vasopressin release induced by depolarization through interaction with specific receptors of the ETA subtype and this response is antagonized by sarafotoxin S6b. The second messenger for this effect, however, remains unknown since the potentiation of depolarizationinduced vasopressin release occurs in the absence of an increase in cellular calcium.The widespread distribution of receptors for the endothelin (ET) family of vasoconstrictor peptides outside the vasculature (1-4) suggests that these molecules may have physiological functions beyond the regulation of vascular tone (5). Two distinct receptors for the ETs (6-11) have been cloned, with both receptors belonging to the superfamily of G-protein-coupled receptors homologous with mammalian rhodopsin and bacterial opsin (12). One receptor subtype (ETA) shows differential affinities for the isopeptides ET-1, ET-2, and ET-3 and for the peptide sarafotoxin S6b (Sxb), but its second messenger remains to be determined. The second receptor subtype (ETB) does not discriminate between the isopeptides and is coupled, upon activation, via a G protein to phospholipase C (13) to stimulate a common cell-signaling pathway leading to the generation of diacylglycerol and inositol 1,4,5-trisphosphate (IP3) and a subsequent IP3-induced mobilization of intracellular calcium. In some cell types the Ca2+ response is predominated by activation of considerable Ca2+ influx through either receptor-operated channels (14) MATERIALS AND METHODSPreparation and Perfusion of Nerve Endings. The nerve endings were prepared according to ref. 22 with slight modifications. Briefly, rat neurohypophyses were separated from the pars intermedia and homogenized in a solution containing 270 mM sucrose, 10 mM Hepes-KOH (pH 7.0), and 2 mM EGTA. The homogenate was centrifuged at 100 x g for 1 min and the supernatant was further centrifuged at 2400 x g for 4 min. Compared to the original protocol this gives a larger yield of nerve endings. The resulting pellet contains highly purified nerve endings from arginine-8-vasopressin (AVP) and oxytocin neurons (23). The nerve endings were loaded on filters (0.22-,.um Acro disk, Gellman) and perfused at 370C (50 pl/min) with physiological saline (see ref. 22). The perfusate was collected (4-min periods) and evoked release was triggered by a 6-min pulse of a depolarizing concentration of potassium. AVP radioimmunoassay was performed as described (24). The medium before and after the depolarizing period contained 40 mM NaCl, 5 mM KHCO3, 100 mM N-methyl-D-glucamine (NMG), 1 mM MgCl2, 2.2 mM CaCl2, 10 mM glucose, 10 mM Hepes-Tris (pH 7.1-7.2), and 0.01% bovine serum albumin (25). Depolarization was achieved by increasing the external K+ concentratio...

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Section: Resultsmentioning

confidence: 99%

Endothelin regulation of neuropeptide release from nerve endings of the posterior pituitary.

Ritz

Stuenkel

Dayanithi

et al. 1992

Proc. Natl. Acad. Sci. U.S.A.

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“…An acute stimulation leads to granule depletion in nerve fiber endings and, if prolonged, depletion occurs also in the nerve fiber swellings [14]. So, these light bodies observed in the SG might be depleted nerve fiber swellings caused by a chronic stimulation with a large mobilization and progressive depletion of NSG to neurosecretory sites.…”

Section: Discussionmentioning

confidence: 98%

“…They are secreted into the blood circulation under appropriate stimuli, such as acute or chronic dehydration, parturition, or saline solution beverage [12]. Whereas standard experimental studies have assumed a rodent NL structural remodeling caused by different laboratory conditions [12][13][14][15], our approach allows for an explanatory relationship between true living conditions and NL adaptation.…”

Section: Introductionmentioning

confidence: 99%

Adaptation of <i>Camelus dromedarius</i> pars nervosa of the hypophysis to winter and summer living conditions

Alim

Rodrı́guez

Andrade

et al. 2012

Folia Histochem Cytobiol.

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Abstract:The aim of this work is to study the characteristics of the dromedary nervous lobe and determine how the seasons condition its organization. To this end, electron microscopy was performed and examined quantitatively on animals from winter and summer periods. The results show a higher number of cells in the nervous lobe in summer than in winter. The most abundant glial elements in winter are light pituicytes engulfing neurosecretory nerve fibers making neuroglial contact, and dark pituicytes containing numerous heterogeneous light bodies. In summer, the most distinctive glial cells may be pituicytes in a phagocytic state making contact with characteristic large light bodies that could represent a degenerative process of large neuropeptide storage. Granular pituicytes were also observed in contact with glial and neuronal components. However, lipid droplets, described in pituicytes of other mammals, were not observed in our samples. Quantitative analysis of neurovascular contacts revealed that the number of nerve terminals contacting the basal lamina did not differ between summer and winter, but the mean number of glial processes increased in winter. Our data provides evidence that the storage of neuropeptides is very marked in summer and that, associated with an autophagic and phagocytic phenomenon, this suggests an adaptation to anticipate any situation that would cause dehydration of the dromedary. Thus, in its tough environment, the animal remains permanently prepared to avoid any large water loss.

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“…Cells increase their VP mRNA content within 12 h, long before any significant deple tion of VP stores from the neural lobe of the pituitary' [22,23]. This finding and the observation that Brattleboro rats, which transcribe a mutant nontranslatable VP gene [24,25], have low levels of VP mRNA [26][27][28][29] in spite of low plasma VP and chronic diuresis suggest that depletion of pituitary VP is un likely to be the source of regulatory feedback which triggers in creased VP mRNA production.…”

Section: Discussionmentioning

confidence: 99%

Vasopressin mRNA Expression in Individual Magnocellular Neuroendocrine Cells of the Supraoptic and Paraventricular Nucleus in Response to Water Deprivation

Meeker

Greenwood

Hayward³

1991

Neuroendocrinology

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Vasopressin neuroendocrine function involves the regulation of both secretion and synthesis from magnocellular neuroendocrine cells but the coordination of these two processes is poorly understood. To explore the temporal relationship between physiological stimulation and vasopressin mRNA levels we measured vasopressin mRNA content within individual magnocellular neurons of the supraoptic and paraventricular nucleus during the course of water deprivation. Analysis of autora-diographic silver grain densities from in situ hybridization of an [¹²⁵I]dCTP-labeled oligonucleotide specific for vasopressin mRNA revealed a wide variety of resting vasopressin mRNA levels and differential responses to water deprivation in the magnocellular neuroendocrine cells. During water deprivation, the vasopressin mRNA content of the paraventricular nucleus increases rapidly and with shorter latency and greater incremental response than the supraoptic nucleus. Double-labeling experiments with combined in situ hybridization and immunocytochemistry identified a population of vasopressin immunoreactive cells which maintain very low basal levels of vasopressin mRNA. The location of these cells correlates with the location of increased silver grain densities during water deprivation. One subset of vasopressin magnocellular neurons failed to show high levels of vasopressin mRNA, indicating that all cells are not equally responsive to water deprivation. These patterns of vasopressin mRNA expression suggest the presence of functional subpopulations of vasopressin neuroendocrine cells which may reflect stimulus-specific patterns of afferent input to the supraoptic and paraventricular nucleus.

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Hormone Content and Movement of Neurosecretory Granules in the Rat Neural Lobe during and after Dehydration

Cited by 34 publications

References 25 publications

Endothelin regulation of neuropeptide release from nerve endings of the posterior pituitary.

Endothelin regulation of neuropeptide release from nerve endings of the posterior pituitary.

Adaptation of <i>Camelus dromedarius</i> pars nervosa of the hypophysis to winter and summer living conditions

Vasopressin mRNA Expression in Individual Magnocellular Neuroendocrine Cells of the Supraoptic and Paraventricular Nucleus in Response to Water Deprivation

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