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At least 811 records · Page 45Linked to original sources
PubMed1984

Calcium uptake and calcium-dependent phosphorylation during development of rat brain neurons in culture.

The emergence of the capacities for calcium uptake and calcium-regulated protein phosphorylation during the development of embryonic brain neurons in tissue culture was examined. In the maturing cells, the enhancement in 45Ca2+-uptake upon stimulation with high K+ increased by 3-4 fold during the second week in vitro, in parallel to an increase in the capacity for high K+-induced Ca2+-dependent release of prelabeled [3H]dopamine. The pattern of incorporation of [32Pi]phosphate into the major phosphoproteins in maturing cells under nonstimulating conditions also changed during cell development: the incorporation of 32Pi into two proteins of apparent molecular weights--55,000 and 43,000 dalton--increased, but decreased in a 45,000 dalton protein. Stimulation of mature cells (after 10-11 days in vitro) resulted in a Ca2+-dependent increase in the amount of 32Pi incorporated into the 43,000 dalton protein and a decrease in the amount incorporated into the 55,000 dalton protein. This calcium-regulated phosphorylation pattern was not observed until 6 days in vitro. Introduction of Ca2+ into the immature cells by means of the Ca2+ ionophore A23187 did not alter the phosphorylation pattern and did not cause neurotransmitter release. The amount of [35S]methionine incorporated into a 43,000 dalton protein which comigrated with the 43,000 dalton phosphoprotein also increased upon cell maturation. The results suggest that this phosphoprotein (which does not comigrate with nonphosphorylated actin on two-dimensional polyacrylamide gels) develops in the cells in parallel to the emerging processes of the stimulation-induced calcium entry and calcium-dependent neurosecretion.

Animals↗
PubMed1991

Do calcium channel classifications account for neuronal calcium channel diversity?

Calcium (Ca2+) ions are involved in the development and control of a variety of neuronal properties and functions such as channel expression, synaptic transmission and neurosecretion. The main pathway by which Ca2+ enters the intracellular space is through voltage-activated Ca2+ channels that can be classified according to their different biophysical and pharmacological properties. Identification and characterization of these channel types are prerequisites for understanding the mechanisms that underlie Ca2(+)-controlled processes. In this article we summarize the efforts made to identify neuronal Ca2+ channel types, and we attempt to evaluate how useful existing classifications are in assigning specific properties and functions to distinct channel types in neurons.

Animals↗
PubMed1992

Oxygen and acid chemoreception in the carotid body chemoreceptors.

The carotid bodies are arterial chemoreceptors that are sensitive to blood PO2, PCO2 and pH. They are the origin of reflexes that are crucial for maintaining PCO2 and pH in the internal milieu and for adjusting the O2 supply according to the metabolic needs of the organism in situations of increased demand, such as exercise and while breathing at decreased O2 partial pressures during ascent or when living at high altitude. Chemoreceptor cells of the carotid body transduce the blood-borne stimuli into a neurosecretory response that is dependent on external Ca2+. These cells have an O2-sensitive K+ current that is reversibly inhibited by low PO2. It is proposed that the depolarization produced by inhibition of this K+ current activates Ca2+ channels; Ca2+ influx and neurosecretion follow. The cells have also a potent Na(+)-Ca2+ antiporter that could be responsible for the intracellular Ca2+ rise required to trigger the release of neurotransmitters during high PCO2 or low pH stimulation.

Acids↗
PubMed1983

Chromogranin: widespread immunoreactivity in polypeptide hormone producing tissues and in serum.

Chromogranin A is the major soluble protein, co-stored and co-released with catecholamines from storage vesicles of adrenal medulla and sympathetic nerve, and has been used as an index of exocytotic sympathoadrenal neurosecretion. Since some neuropeptides have a rather wide distribution in nerve, gut, and endocrine glands, we used a sensitive chromogranin A radioimmunoassay to probe the occurrence of chromogranin in several polypeptide hormone producing tissues. Immunoreactive chromogranin was ubiquitous in such tissues, in rank order of concentration (microgram/g wet weight): adrenal medulla greater than pituitary gland (anterior greater than intermediate greater than posterior) greater than pancreas greater than small intestine greater than thyroid greater than hypothalamus. In each case, the tissue homogenate displaced 125I-labelled chromogranin A from antibody in parallel with displacement generated by pure unlabeled chromogranin A, and the immunoreactivity was not abolished by boiling or by several protease inhibitors. Quantitatively, the endocrine tissues other than adrenal medulla possessed 0.1-2.8% of the immunoreactivity found in the adrenal medulla. Immunoreactive chromogranin was also present in serum and sympathetic nerve, but contamination of the endocrine tissues by chromogranin from serum or sympathetic innervation could not account for the observed immunoreactivity. Immunoreactive chromogranin was undetectable in platelets. Tissues with predominant exocrine function (salivary glands) had very little chromogranin (0.004-0.005% of that found in the adrenal medulla). Within the cell, differential centrifugation localized the immunoreactive chromogranin to a hormone storage granule fraction in the anterior pituitary gland (60 +/- 6% of total, with 2.0 +/- 0.3-fold enrichment in the granule) and the adrenal medulla (74 +/- 13% of total, with 1.7 +/- 0.2-fold enrichment in granules). Gel filtration suggested a lower effective molecular radius for pituitary and pancreatic immunoreactive chromogranin than for purified 125I-labelled chromogranin A. Thus, chromogranin in the other endocrine glands differed from adrenal medullary chromogranin both quantitatively (less microgram/g tissue) and qualitatively (lower molecular weight). The results suggest a widespread, though as yet undefined, role for chromogranin in the neurosecretory process, and raise the possibility that chromogranin may be co-stored and secreted with a variety of polypeptide hormones.

Adrenal Medulla↗
PubMed1996

Nematode neuropeptides: Localization, isolation and functions.

Historically, peptidergic substances (in the form of neurosecretions) were linked to moulting in nematodes. More recently, there has been a renewal of interest in nematode neurobiology, initially triggered by studies demonstrating the localization of peptide immunoreactivities to the nervous system. Here, David Brownlee, Ian Fairweather, Lindy Holden-Dye and Robert Walker will review progress on the isolation of nematode neuropeptides and efforts to unravel their physiological actions and inactivation mechanisms. Future avenues for research are suggested and the potential exploitation of peptidergic pathways in future therapeutic strategies highlighted.

Journal Article↗
PubMed1985

Stimulated secretion of pro-opiomelanocortin-related peptides in hypothalamic cells.

UNLABELLED: Although it has been suggested pro-opiomelanocortin (POMC) related peptides in brain may be neurotransmitters or neuromodulators, little is known about their secretion from neurons because it is difficult to study neurosecretion with an in vivo model. To demonstrate the possibility that POMC peptides may be neuroregulators which can be secreted in response to specific stimuli, we studied the secretion of immunoreactive (IR-) adrenocorticotropin (ACTH) and IR-beta-endorphin from dissociated hypothalamic cells during potassium-induced depolarization. Significant increments (p less than 0.025) in secretion of IR-ACTH (267%) and IR-beta-endorphin (88-172%) over basal secretion were stimulated by 60 mM KCl in the presence of calcium. CONCLUSION: Stimulated secretion of POMC peptides from hypothalamic cells by potassium and calcium follows classical neurosecretory mechanisms and suggests these neuropeptides could be neuroregulators in brain.

Adrenocorticotropic Hormone↗
PubMed1987

On the status of the study of invertebrate neurons in tissue culture--phyla Mollusca and Annelida.

The utilization of tissue culture in neurobiological studies is discussed for all phyla phylogenetically preceding Phylum Arthropoda. Only two phyla, Mollusca and Annelida, are represented in such studies. The members of Phylum Mollusca which have been so investigated are Aplysia, Helisoma and Lymnaea. The mollusc Aplysia has been used to investigate several processes, including neurosecretion, synaptic transmission and synaptogenesis. Helisoma was employed to study factors regulating neurite growth and the specificity of synapse formation; mechanisms of neurite growth were investigated in the snail Lymnaea. The only member of Phylum Annelida involved in appropriate studies has been the leech Hirudo. This organism was used to investigate axonal regeneration and synaptic mechanisms.

Animals↗
PubMed1994

Arginine vasopressin (AVP) causes the reversible phosphorylation of the myristoylated alanine-rich C kinase substrate (MARCKS) protein in the ovine anterior pituitary: evidence that MARCKS phosphorylation is associated with adrenocorticotropin (ACTH) secretion.

We have recently shown that AVP causes a protein kinase C (PKC)-dependent increase in ACTH release and biosynthesis in ovine anterior pituitary cells. In these cells, AVP also causes the translocation of PKC from the cytosol to the cell membrane which is maximal at 5 min, but the intracellular events distal to protein kinase C activation that underlie ACTH secretion have not been well characterized to date. Since the MARCKS protein has been implicated in neurosecretion and is phosphorylated by PKC in synaptosomes, studies were carried out to determine whether AVP might cause MARCKS phosphorylation in the ovine anterior pituitary, and to determine whether this phenomenon might be temporally correlated with PKC translocation and the release of ACTH. When cytosolic fractions of rat brain, ovine anterior pituitary, and cultured ovine anterior pituitary cells were incubated with purified PKC, several proteins were phosphorylated including those in the region of 83-85 kDa. After precipitation of the proteins with 40% acetic acid, the 83-85 kDa phosphoproteins were selectively recovered in the acid soluble phase. Phosphopeptide maps of either the 83 or 85 kDa proteins were generated with Staphylococcus aureus V8 protease and revealed 13 and 9 kDa phosphopeptides, which are characteristic of the authentic MARCKS protein. An identical phosphopeptide map was also obtained when the MARCKS protein was selectively extracted from intact 32P-labeled anterior pituitary cells. MARCKS phosphorylation was markedly increased when ovine anterior pituitary cells were exposed to 1 microM phorbol 12-myristate 13-acetate (PMA). When the cells were exposed to 1 microM AVP, MARCKS phosphorylation increased at 15 s and reached the maximal plateau value at 30 s. MARCKS phosphorylation then started to diminish at 2 min, and baseline levels were attained by 10 min. In the same cells, AVP stimulated ACTH release in a biphasic manner-during the first 30 s, there resulted a rapid burst of ACTH secretion that was followed by a slower, but sustained rate of secretion. We conclude that: (1) AVP causes a rapid, and reversible, phosphorylation of the MARCKS protein in the ovine anterior pituitary; (2) since the AVP-induced increase in MARCKS phosphorylation occurs much earlier in these cells than does PKC trans-location, MARCKS phosphorylation may provide a more sensitive index of the onset of PKC activation than the translocation assay; (3) the close temporal association between MARCKS phosphorylation and the rapid early release of ACTH suggests that MARCKS phosphorylation may be involved in the initial intracellular events that underly exocytosis of the hormone.

Adrenocorticotropic Hormone↗
PubMed1994

Arginine vasopressin (AVP) causes the reversible phosphorylation of the myristoylated alanine-rich C kinase substrate (MARCKS) protein in the ovine anterior pituitary: evidence that MARCKS phosphorylation is associated with adrenocorticotropin (ACTH) secretion.

We have recently shown that AVP causes a protein kinase C (PKC)-dependent increase in ACTH release and biosynthesis in ovine anterior pituitary cells. In these cells, AVP also causes the translocation of PKC from the cytosol to the cell membrane which is maximal at 5 min, but the intracellular events distal to protein kinase C activation that underlie ACTH secretion have not been well characterized to date. Since the MARCKS protein has been implicated in neurosecretion and is phosphorylated by PKC in synaptosomes, studies were carried out to determine whether AVP might cause MARCKS phosphorylation in the ovine anterior pituitary, and to determine whether this phenomenon might be temporally correlated with PKC translocation and the release of ACTH. When cytosolic fractions of rat brain, ovine anterior pituitary, and cultured ovine anterior pituitary cells were incubated with purified PKC, several proteins were phosphorylated including those in the region of 83-85 kDa. After precipitation of the proteins with 40% acetic acid, the 83-85 kDa phosphoproteins were selectively recovered in the acid soluble phase. Phosphopeptide maps of either the 83 or 85 kDa proteins were generated with Staphylococcus aureus V8 protease and revealed 13 and 9 kDa phosphopeptides, which are characteristic of the authentic MARCKS protein. An identical phosphopeptide map was also obtained when the MARCKS protein was selectively extracted from intact 32P-labeled anterior pituitary cells. MARCKS phosphorylation was markedly increased when ovine anterior pituitary cells were exposed to 1 microM phorbol 12-myristate 13-acetate (PMA). When the cells were exposed to 1 microM AVP, MARCKS phosphorylation increased at 15 s and reached the maximal plateau value at 30 s. MARCKS phosphorylation then started to diminish at 2 min, and baseline levels were attained by 10 min. In the same cells, AVP stimulated ACTH release in a biphasic manner - during the first 30 s, there resulted a rapid burst of ACTH secretion that was followed by a slower, but sustained rate of secretion. We conclude that: (1) AVP causes a rapid, and reversible, phosphorylation of the MARCKS protein in the ovine anterior pituitary; (2) since the AVP-induced increase in MARCKS phosphorylation occurs much earlier in these cells than does PKC trans-location, MARCKS phosphorylation may provide a more sensitive index of the onset of PKC activation than the translocation assay; (3) the close temporal association between MARCKS phosphorylation and the rapid early release of ACTH suggests that MARCKS phosphorylation may be involved in the initial intracellular events that underly exocytosis of the hormone.

Adrenocorticotropic Hormone↗
PubMed1995

Real-time detection of mitochondrial inhibition at frog motor nerve terminals using increases in the spatial variance in probability of transmitter release.

The effects of Hg2+, methyl mercury, and flufenamic acid, all of which inhibit mitochondria, were examined at frog motor nerve terminals. Unbiased estimates of m (no. of transmitter quanta released), n (no. of functional release sites), p (probability of release), and vars p (spatial variance in p) were obtained using K(+)-induced asynchronous neurosecretion (m, n and p not having the same definitions as with nerve-evoked release). Transient but significant increases in m, n, p and vars p were found with all three agents. These findings indicate that mitochondrial inhibition and release of sequestered Ca2+ can be detected as a real-time increase in vars p. The results also suggest that changes in vars p might be used to differentiate between cellular (membrane) and subcellular (organellar) actions of drugs at the nerve terminal.

Animals↗
PubMed1984

Axon collaterals of supraoptic neurones: anatomical and electrophysiological evidence for their existence in the lateral hypothalamus.

The magnocellular neurones of the supraoptic nucleus which synthesize and secrete vasopressin and oxytocin have been commonly regarded as simple "output" neurones in that they receive an input, generate an action potential and in turn release hormone from their terminals in the posterior pituitary. Three lines of evidence are presented which suggest that rat supraoptic nucleus neurons also have axon collaterals which terminate in the hypothalamus close to the nucleus. Small injections of horseradish peroxidase were made directly into the nucleus in hypothalamic slices, allowing visualization of the axons of supraoptic neurones. Collaterals of these axons could be observed in regions both dorsal and dorsolateral to the supraoptic nucleus. In a separate series of experiments, sections of perfusion-fixed hypothalamus were stained for vasopressin and oxytocin using specific antisera. Peptide-containing collaterals of both types were observed near the supraoptic nucleus, in a region similar to that seen after horseradish peroxidase injections. Finally, electrophysiological studies were carried out on hypothalamic slices containing the supraoptic nucleus. A small concentric bipolar stimulating electrode was placed directly into the nucleus and activity of lateral hypothalamic neurones within 0.1-1 mm of the nucleus was recorded. Of 68 neurones studied, 52 were excited by supraoptic stimulation via a synaptic pathway that could be blocked by Ca2+ -free solutions containing 18 mM Mg2+. These studies suggest that supraoptic neurones communicate via axon collaterals with other neurones in the lateral hypothalamus, in addition to their previously well characterised functional role in neurosecretion.

Animals↗
PubMed1987

Evidence for the coexistence and co-release of [Met]enkephalin and noradrenaline from sympathetic nerves of the bovine vas deferens.

The localization and neurosecretion of methionine-enkephalin was studied in sympathetic nerves of the bovine vas deferens. Immunostaining showed methionine-enkephalin-like immunoreactivity in a network of varicose nerve fibres in the smooth muscle layers of the vas deferens. When vas deferens homogenates were subjected to differential and sucrose density gradient centrifugation, methionine-enkephalin was found to parallel the distribution of noradrenaline in the more dense region of the gradient, where "heavy" or large dense-cored vesicles are present. Electron microscopic immunochemistry confirmed this finding and showed methionine-enkephalin-like immunoreactivity in large dense-cored vesicles. The release of methionine-enkephalin upon electrical stimulation was studied in superfusion experiments. The methionine-enkephalin secretion was shown to be Ca2+-dependent and was inhibited by adding the adrenergic neuron blocking drug guanethidine to the superfusion medium. We conclude that in the bovine vas deferens methionine-enkephalin is only present in large dense-cored vesicles of adrenergic neurons and that the peptide is released from these vesicles together with noradrenaline by a Ca2+-dependent mechanism.

Adrenergic Fibers↗
PubMedDate not supplied

The role of protocerebrum in the modulation of circadian rhythmicity in the crayfish visual system.

Dark-adapted crayfishes with protocerebrum only, were submitted to continuous recordings of electroretinogram (ERG) and of eye glow area (EGA) during several days. Circadian variations of ERG amplitude similar to that of intact animals, were revealed by means of restrained test light stimuli (0.2 Cd/ft2) bilaterally applied to each eyestalk. The period (24.6-38 hr) and range (40-80%) value of ERG oscillations always resulted quite similar to one another side. As in intact animals retinal shielding pigments (RSP) position as measured as EGA size showed a clear circadian rhythm, and also a clear consensual reflex in these preparations. We found a loss of both: circadian and consensual mobilization of distal RSP in animals with complete removal of cerebral ganglion. Our proposition is that the crayfish protocerebrum plays a major role in the modulation of circadian retinal sensitivity, probably through the control-release of hormonal neurosecretions from the sinus gland along the day.

Animals↗
PubMedDate not supplied

Slow bursting thermal sensitive neurons in the preoptic area of the rabbit.

Recent data have shown the presence of some hypothalamic neurons with a slow bursting activity. This study reports the interactions of slow bursting neurons with thermoregulatory control in the preoptic/anterior hypothalamus (POAH). Ninety-seven single units studied with direct thermal stimulation and with central injections of norepinephrine (NE) or serotonin (5-HT) were assessed for slow bursting activity. Twenty-one percent of the neurons had slow bursting activity patterns with frequencies ranging from 0.02-0.10 Hz. Intraventricular or direct POAH injected monoamines frequently inhibited bursting activity during normothermia and/or POAH thermal stimulation. Slow bursting neurons may elicit rhythmic thermoregulatory motor outputs, neurosecretion, and infraslow DC potentials in the central nervous system.

Animals↗
PubMed1983

Stimulation of neutral, magnesium-stimulated sphingomyelinase activity in the neurohypophysis of the rat by hypertonic saline ingestion.

Neutral, magnesium-stimulated sphingomyelinase and acid sphingomyelinase activities in the neurohypophysis, adenohypophysis and cerebrum of rats given 2.25% NaCl drinking water for 7 or 14 days were compared with the same enzyme activities in the tissues of control animals allowed free access to distilled drinking water. Neutral sphingomyelinase activity in the neurohypophysis was significantly increased in both experimental groups (7-day, 85.2 +/- 8.4 units/mg protein; 14-day, 110.1 +/- 14.8 units/mg; control, 61.4 +/- 5.5 units/mg). Acid sphingomyelinase activity was significantly but only transiently increased in the tissue (7-day, 73.2 +/- 3.4 units/mg; 14-day, 66.3 +/- 7.5 units/mg; control, 54.3 +/- 2.8 units). Enzyme activities in adenohypophysis and cerebrum of the experimental animals were not significantly different from those of controls. The results suggest a specific role for neutral, Mg2+-stimulated sphinomyelinase in neurosecretion.

Animals↗
PubMedDate not supplied

Changes in tissue responsiveness to hormones and neurotransmitters during aging.

Responsiveness to many hormones and neurotransmitters by target tissues is altered during aging. Three model systems that are representative of these changes are reviewed. These are (1) striatal dopaminergic regulation of motor function, (2) IP3 and calcium-mediated electrolyte and neurosecretion by the alpha1-adrenergic and muscarinic cholinergic systems in parotid and corpus striatum, and (3) beta adrenergic and epidermal growth factor (EGF) stimulated DNA synthesis in hepatocytes.

Aging↗
PubMed1988

John Henry Welsh: his years, works and flock.

John H. Welsh came down from Boothbay, Maine in the late twenties and landed at Harvard. There he launched his academic career, raised a family, raised an additional family of graduate students and postdoctoral associates, and (with them all) shaped and cultivated diurnal rhythmicity, the biology of neurosecretion, and comparative neuropharmacology. After about 45 yr in the vineyards of Cambridge, he returned to Boothbay and his garden, tree-farm, grandchildren, writings and other good works.

Animals↗
PubMed1995

Transmitter-mediated inhibition of N-type calcium channels in sensory neurons involves multiple GTP-binding proteins and subunits.

The modulation of voltage-activated Ca2+ channels by neurotransmitters and peptides is very likely a primary means of regulating Ca(2+)-dependent physiological functions such as neurosecretion, muscle contraction, and membrane excitability. In neurons, N-type Ca2+ channels (defined as omega-conotoxin GVIA-sensitive) are one prominent target for transmitter-mediated inhibition. This inhibition is widely thought to result from a shift in the voltage independence of channel gating. Recently, however, voltage-independent inhibition has also been described for N channels. As embryonic chick dorsal root ganglion neurons express both of these biophysically distinct modulatory pathways, we have utilized these cells to test the hypothesis that the voltage-dependent and -independent actions of transmitters are mediated by separate biochemical pathways. We have confirmed this hypothesis by demonstrating that the two modulatory mechanisms activated by a single transmitter involve not only different classes of G protein but also different G protein subunits.

Animals↗