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At least 73 records · Page 4Linked to original sources
PubMed1991

Ca(2+)-dependent phosphorylation of synapsin I as a possible regulatory mechanism of neurosecretion.

Phosphorylation of homogeneous synapsin I isolated from human brain by Ca2+, phospholipid-dependent protein kinase (protein kinase C) from the same source was studied. The inhibitory effect of calmodulin on this process was demonstrated. The kinetics of activation of synapsin I phosphorylation by acidic phospholipids, phosphatidylserine and phosphatidylinositol, in the absence and presence of phosphatidylinositol-4,5-bisphosphate and diacylglycerol was compared. The proteolytic effect of degradation of the synapsin I molecule phosphorylated by Ca2+, calmodulin-dependent protein kinase II was revealed. No proteolysis of synapsin phosphorylated under similar conditions either by protein kinase C or cAMP-dependent protein kinase was detected. In view of the process specificity, the physiological significance of the observed effect is suggested. The inter-relationship between two ways of neurosecretion regulation is discussed: an earlier known, conventional way, mediated by synapsin I phosphorylation by Ca2+, calmodulin-dependent protein kinase II, and another one, mediated by synapsin I phosphorylation by protein kinase C. The modulating role of polyphosphoinositides in the PK C-dependent way of regulation is considered.

Brain↗
PubMedDate not supplied

A review of the role of neurosecretion in the control of juvenile hormone synthesis: a tribute to Berta Scharrer.

In the 1950s, Berta Scharrer predicted that neurosecretions from the brain regulated corpus allatum activity based upon the observation of the change in localization of neurosecretory material in the brain and change in gland activity after severance of nerves between the brain and corpus allatum. Isolation and characterization of neuropeptide regulators of juvenile hormone production by the corpora allata in the late 1980s has confirmed this prediction. Both a stimulatory allatotropin and an inhibitory allatostatin have been isolated from moth brains. Two families of allatostatins, both quite different from each other and that of moths, have been isolated from cockroaches and crickets. The wide distribution of these peptides in the nervous system, in nerves to visceral muscle, in endocrine cells of the midgut and in blood cells, indicate multifunctions in the insects in which they are allatoregulatory. Some of these other functions have been demonstrated in these insects and in insects in which these neuropeptides occur but do not act as corpus allatum regulators. For the latter group, the neuropeptide regulators of the corpora allata have yet to be isolated. The families of neurosecretory regulators will continue to grow.

Amino Acid Sequence↗
PubMed1998

Molecular diversity in neurosecretion: reflections on the hypothalamo-neurohypophysial system.

1. The diversity of molecules involved in various aspects of neurosecretion, such as proprotein processing, axonal transport of large dense core vesicles (LDCVs), and regulated secretion, is discussed in the context of the hypothalamo-neurohypophysial system (HNS). 2. Recent studies have uncovered a family of at least seven processing enzymes known as proprotein convertases (PCs) which are involved in proteolytically cleaving protein precursors at paired basic amino acid motifs to yield biologically active peptides. Three of these, PC1(3), 2, and 5, are found in neurons and are involved in producing regulated secretory peptide products. 3. The axonal transport of LDCVs occurs on microtubule tracks by still unknown mechanisms. There are over 11 distinct kinesin-related molecules that have now been identified as possible microtubule motor candidates. 4. Calcium channels in the nervous system are known to be derived from at least five alpha-subunit and four beta-subunit genes with multiple alternatively spliced isoforms in each case. These could account, in part, for the varied calcium currents found in the HNS. 5. The large number of proteins and isoforms now demonstrated to be involved in regulated secretion are discussed, with a focus on LDCV compositions and the synaptotagmin gene family.

Animals↗
PubMed1998

Neuronal Ca2+ sensor 1, the mammalian homologue of frequenin, is expressed in chromaffin and PC12 cells and regulates neurosecretion from dense-core granules.

Neuronal Ca2+ sensor 1 (NCS-1) is the mammalian homologue of the Ca2+-binding protein frequenin previously implicated in regulation of neurotransmission in Drosophila (Pongs, O., Lindemeier, J., Zhu, X. R., Theil, T., Endelkamp, D., Krah-Jentgens, I., Lambrecht, H.-G., Koch, K. W., Schwemer, J., Rivosecchi, R., Mallart, A., Galceran, J. , Canal, I., Barbas, J. A., and Ferrus, A. (1993) Neuron 11, 15-28). NCS-1 has been considered to be expressed only in neurons, but we show that NCS-1 expression can be detected in bovine adrenal chromaffin and PC12 cells, two widely studied model neuroendocrine cells. NCS-1 was present in both cytosolic and membrane fractions including purified chromaffin granules, and in immunofluorescence, its distribution overlapped with peripheral punctate staining seen with the synaptic-like microvesicle marker synaptophysin in PC12 cells. The possible functional role of NCS-1 in exocytosis of dense-core granules was tested using transient transfection in PC12 cells and assay of co-transfected growth hormone (GH) release. Overexpression of NCS-1 increased evoked GH release in intact cells in response to ATP. No effect of overexpression was seen on GH release because of Ca2+ in permeabilized cells suggesting that NCS-1 may have a regulatory but not direct role in neurosecretion.

Adrenal Medulla↗
PubMed2004

Altered interaction and expression of proteins involved in neurosecretion in scrapie-infected GT1-1 cells.

Prions cause transmissible and fatal diseases that are associated with spongiform degeneration, astrogliosis, and loss of axon terminals in the brains. To determine the expression of proteins involved in neurosecretion and synaptic functions after prion infection, gonadotropin-releasing hormone neuronal cell line subclone (GT1-1) was infected with the RML scrapie strain and analyzed by Western blotting, real time PCR, and immunohistochemistry. As revealed by Western blotting of lysates exposed to different temperatures, the levels of complexed SNAP-25, syntaxin 1A, and synaptophysin were decreased in scrapie-infected GT1-1 cells (ScGT1-1), whereas the level of monomeric forms of these proteins was increased and correlated to the level of scrapie prion protein (PrPSc). However, when complex formation was prevented by prolonged heating of samples in SDS, the levels of monomeric SNAP-25, syntaxin 1A and synaptophysin in ScGT1-1 cells were decreased in comparison to GT1-1 cells. The reduced level of SNAP-25 was observed as early as 32 days postinfection. Increased mRNA levels of both splice variants SNAP-25a and -b in ScGT1-1 cells were seen. No difference in the morphology, neuritic outgrowth or distribution of SNAP-25, syntaxin 1A, or synaptophysin could be observed in ScGT1-1 cells. Treatment with quinacrine or pentosan polysulfate cleared the PrPSc from the ScGT1-1 cell cultures, and the increase in levels of monomeric SNAP-25 and synaptophysin was reversible. These results indicate that a scrapie infection can cause changes in the expression of proteins involved in neuronal secretion, which may be of pathogenetic relevance for the axon terminal changes seen in prion-infected brains.

1-Methyl-3-isobutylxanthine↗
PubMed2007

The hop cassette of the PAC1 receptor confers coupling to Ca2+ elevation required for pituitary adenylate cyclase-activating polypeptide-evoked neurosecretion.

We have identified the single PAC1 receptor variant responsible for Ca2+ mobilization from intracellular stores and influx through voltage-gated Ca2+ channels in bovine chromaffin cells and the domain of this receptor variant that confers coupling to [Ca2+]i elevation. This receptor (bPAC1hop) contains a 28-amino acid "hop" insertion in the third intracellular loop, with a full-length 171-amino acid N terminus. Expression of the bPAC1hop receptor in NG108-15 cells, which lack endogenous PAC1 receptors, reconstituted high affinity PACAP binding and PACAP-dependent elevation of both cAMP and intracellular Ca2+ concentrations ([Ca2+]i). Removal of the hop domain and expression of this receptor (bPAC1null) in NG108-15 cells reconstituted high affinity PACAP binding and PACAP-dependent cAMP generation but without a corresponding [Ca2+]i elevation. PC12-G cells express sufficient levels of PAC1 receptors to provide PACAP-saturable coupling to adenylate cyclase and to drive PACAP-dependent differentiation but do not express PAC1 receptors at levels found in postmitotic neuronal and endocrine cells and do not support PACAP-mediated neurosecretion. Expression of bPAC1hop, but not bPAC1(null), at levels comparable with those of bPAC1hop in bovine chromaffin cells resulted in acquisition by PC12-G cells of PACAP-dependent [Ca2+]i increase and extracellular Ca2+ influx. In addition, PC12-G cells expressing bPAC1hop acquired the ability to release [3H]norepinephrine in a Ca2+ influx-dependent manner in response to PACAP. Expression of PACAP receptors in neuroendocrine rather than nonneuroendocrine cells reveals key differences between PAC1hop and PAC1null coupling, indicating an important and previously unrecognized role of the hop cassette in PAC1-mediated Ca2+ signaling in neuroendocrine cells.

Animals↗
PubMed1974

The nature of hypthalamo-neurohypophyseal neurosecretion in the rat. A study by light- and electron microscope autoradiography.

The nature of hypothalamo-neurohypophyseal neurosecretion was examined in the rat by means of intraventricular injections of tritiated amino acids. Quantitation of autoradiographs was used at the light microscope level to study the sites of synthesis of proteins and their time of arrival in the neural lobe. Electron microscope autoradiographs were used to study the labeling of neural lobe tissue. It was concluded that the great majority of the labeled material was translocated inside dense-cored granules and was probably composed mostly of neurophysins. The effect of ether anesthesia was also examined. It was found to remove the dense cores from about 20% of the granules in the neural lobe tissue, a process accompanied by the loss of most of their labeled material. The mechanism of the ether effect is discussed and compared to the normal secretion process.

Animals↗
PubMed1990

Tetrahydroaminoacridine (tacrine) stimulates neurosecretion at mammalian motor endplates.

1. Tacrine (20 microM) induced, like 4-aminoquinoline (4-AQ, 200 microM), the appearance of a population of miniature endplate potentials (m.e.p.ps) with more than twice the normal amplitude or time-to-peak. The times-to-peak of nerve impulse-evoked endplate potentials were not similarly affected. 2. Cholinesterase inhibition by edrophonium (25 microM) did not prevent tacrine or 4-AQ from inducing this population of m.e.p.ps. 3. Nerve-muscle preparations in which the normal calcium-sensitive quantal release of acetylcholine had been blocked by botulinum neurotoxin type A also responded to tacrine by an increase in the frequency of giant or slow m.e.p.ps. 4. Reduction of the temperature from 30 degrees to 14 degrees C reduced the frequency of giant or slow m.e.p.ps induced either by tacrine or by 4-AQ. A similar effect was obtained by colchicine (5 mM). This supports the idea that proximo-distal axonal transport is required for the secretory activity. 5. The neurosecretion evoked by tacrine could explain the therapeutic effects of the drug claimed in the treatment of Alzheimer's type of dementia.

Acetylcholine↗
PubMed2002

Centrally administered neuromedin U activates neurosecretion and induction of c-fos messenger ribonucleic acid in the paraventricular and supraoptic nuclei of rat.

We examined the effects of intracerebroventricular (icv) administration of neuromedin U (NMU) on plasma arginine vasopressin (AVP), oxytocin (OXT), and ACTH in rats, using RIA. The induction of c-fos protein (Fos) was examined by immunohistochemical study, and in situ hybridization histochemistry was used to detect c-fos gene expression in the paraventricular (PVN) and supraoptic nuclei (SON). Plasma AVP, OXT, and ACTH were increased in a dose-related manner 15 min after icv administration of NMU. The icv administration of NMU caused a marked induction of Fos-like immunoreactivity (LI) in the SON and the magnocellular and parvocellular divisions of the PVN. In the SON and the magnocellular divisions of the PVN, OXT-LI cells predominantly exhibited nuclear Fos-LI in comparison with AVP-LI cells. The marked induction of the expression of c-fos gene in the PVN and SON was observed 15, 30, and 60 min after icv administration of NMU. Neurosecretion and induction of c-fos gene expression after centrally administered NMU were significantly reduced by pretreatment with anti-NMU IgG. These results suggest that centrally administered NMU activates OXTergic cells in the PVN and SON predominantly as well as hypothalamo-pituitary adrenal axis.

Adrenocorticotropic Hormone↗
PubMed1988

Cholinergic inhibition of adrenergic neurosecretion in the rabbit iris-ciliary body.

The prejunctional effects of cholinergic agents on release of norepinephrine from sympathetic nerve endings were investigated in the isolated, superfused rabbit iris-ciliary body. Stimulation-evoked release of 3H-norepinephrine was inhibited by the cholinergic agonists methacholine, oxotremorine, muscarine, carbamylcholine and acetylcholine (plus eserine), but was unmodified by pilocarpine or nicotine. Agonist-induced inhibition was antagonized selectively by atropine, indicating a muscarinic response. Atropine alone markedly enhanced norepinephrine release, revealing considerable tonic activation of prejunctional cholinergic receptors in this system. Prejunctional inhibition by carbamylcholine was found to completely override the facilitative action of forskolin or 8-bromo-cyclic AMP on neurotransmitter release. Cholinergic and alpha 2-adrenergic effects on neurosecretion were non-additive, suggesting that the underlying receptors coexist at neurotransmitter release sites.

Animals↗
PubMed1982

Enhancement of depolarization-dependent neurosecretion from PC12 cells by forskolin-induced elevation of cyclic AMP.

The effects of elevated intracellular cyclic AMP on the release of neurotransmitters was studied using the clonal pheochromocytoma cell line, PC12, and forskolin, a direct activator of adenylate cyclase. Intracellular cyclic AMP concentrations ranging from 8 to 400 times basal levels were achieved with 0.1 to 100 uM forskolin. Unstimulated release of neurotransmitters was unchanged by any concentration of forskolin. However, K+-stimulated release of both norepinephrine (NE) and acetylcholine was enhanced by 0.1 to 10 uM forskolin. Release of NE elicited by depolarization with carbachol and veratridine also was enhanced by 1 uM forskolin. Enhancement of release was reversed by higher concentrations of forskolin, especially in the presence of a phosphodiesterase inhibitor (RO 20-1724) which caused very large increases in cyclic AMP content. The enhancement of transmitter release from the PC12 cells occurred without concomitant changes in agonist-stimulated ion flux through the acetylcholine receptor ion channel, or in depolarization-dependent uptake of 45Ca++. Thus, increasing the cyclic AMP content of PC12 cells fails to initiate neurosecretion but appears to facilitate some element in the secretion process subsequent to Ca++ influx.

Adrenal Gland Neoplasms↗
PubMed1982

[Aminergic neurosecretions in invertebrates].

This minireview of aminergic neurosecretions of invertebrates deals with technics of detection and localization of these substances and considers their mode of action at cellular or organ level. A comparison with vertebrates is given. Some examples are analyzed as models. It is concluded that besides a phylogenetic interest, the studies done on invertebrates constitute an important contribution to the understanding of neurobiological mechanisms.

Acetylcholine↗