ISOLATED NERVE ENDINGS (NEUROSECRETOSOMES) FROM THE POSTERIOR PITUITARY : Partial Separation of Vasopressin and Oxytocin and the Isolation of Microvesicles

Subcellular fractions of the bovine posterior pituitary, including one composed almost exclusively of pinched-off nerve endings (neurosecretosomes), were characterized electron microscopically, hormonally, and enzymically. 15% of the nerve terminals in the gland were isolated as neurosecretosomes, as estimated from determinations of lactic dehydrogenase, a soluble, cytoplasmic enzyme. Neurosecretosomes were subdivided into three fractions by density-gradient centrifugation. The three subfractions, each shown to be nearly homogeneous populations of neurosecretosomes by means of electron microscopic and enzymic criteria, differed from each other in their vasopressin/oxytocin (VP/OT) ratios. The VP/OT ratio increased from the lightest to the densest fraction, indicating that VP is localized to denser and OT to lighter neurosecretosomes; similar results have been obtained previously for subfractions of neurosecretory granules (NSG). No morphological differences were apparent in neurosecretosomes among the three subfractions. Although complete separation of VP and OT was not achieved, the findings suggest that VP and OT are each stored in a different species of nerve ending and support the hypothesis that a given neurosecretory cell synthesizes, stores, and secretes only one of the peptide hormones. Microvesicles, 40–80 mµ diameter and contained in typical neurosecretory cell terminals, are believed to be degradation products of membrane ghosts of depleted NSG; electron micrographs indicative of this transformation are presented. A fraction rich in microvesicles, but containing some NSG membranes, was prepared by density-gradient centrifugation of an osmolysate of neurosecretosomes. Smaller, apparently nonneurosecretory nerve endings, lacking NSG but filled with small vesicles, are occasionally seen in sections from whole gland. The vesicles in these atypical posterior pituitary nerve endings may be true neurohumor-containing, "synaptic" vesicles.     

Effects of adrenalectomy and hypercorticism on the ACTH content of the anterior and posterior pituitary in rats with inherited diabetes insipidus (Brattleboro strain).

The effects of adrenalectomy (Adx) and hypercorticism on the ACTH content in the anterior (AH) and the neurointermediate lobe (NIL) of the pituitary in Long Evans (+/+), heterozygous (+/DI) and homozygous (DI/DI) Brattleboro rats were determined using dispersed adrenal cells bioassay. Adx decreased the NIL-ACTH content in +/DI and DI/DI rats and left it unchanged in the +/+ rats. Adx increased the AH-ACTH content in the three groups. Hypercorticism had a delayed decreasing effect both in the AH and in the NIL in all rats, with one exception for the NIL in DI/DI rats. Conversely to what appeared in Wistar rats, in Long Evans and Brattleboro rats the corticosterone administered in drinking water was unable to reduce the increase in AH-ACTH activity. These data suggest that Brattleboro, and, to a lesser extent, Long Evans rats from which the former are derived present some particularities in the regulation of their corticotropic function at the AH and the NIL level. We also observed that NaCl (0.9%) added to drinking water and hypercorticism are two factors able to increase diabetes insipidus in homozygous rats without modifying the water intake in Long Evans and heterozygous rats.     

Ultrastructural localization of acid phosphatase in the posterior pituitary of the dehydrated rat

Summary Acid phosphatase (AcPase) was localized by means of electron-microscopic histochemistry and estimated biochemically in the posterior pituitary of rats deprived of water, given 2% NaCl ad libitum, or given tap water ad libitum over 6 days. Autophagic vacuoles, some of which gave a positive AcPase reaction, often contained neurosecretory granules (NSG) in nerve endings of control animals on tap water. Nerve endings of water-deprived or salt-treated rats were depleted of NSG, but frequently contained dense membranous residual bodies, some of which appeared to enclose microvesicles. Smooth endoplasmic reticulum located in axons and terminals appears to be a source of hydrolytic enzymes for neurohypophysial lysosomes. The total amount of AcPase per posterior lobe increased progressively to 40% above control levels after 6 days of water deprivation or salt administration, and this increase may reflect accelerated production of neuronal components in neurohypophysial cells whose secretory rate has been stimulated by elevated body osmolarity.Supported by the Medical Research Council of Canada.Medical Research Associate of the Medical Research Council of Canada.     

Increased atrial natriuretic peptide (6-33) binding sites in the subfornical organ of water deprived and Brattleboro rats

Binding sites for rat atrial natriuretic peptide (6-33) (ANP) were quantitated in the subfornical organ of chronically dehydrated homozygous Brattleboro rats unable to synthesize vasopressin; heterozygous Brattleboro rats, their controls, Long Evans rats and Long Evans rats after 4 days of water deprivation. Brain sections were incubated in the presence of 125I-ANP and the results analyzed by autoradiography coupled to computerized microdensitometry and comparison to 125I-standards. Brattleboro rats and water deprived Long Evans rats presented a higher number of ANP binding sites than their normally hydrated controls. Our results suggest a role of ANP binding sites in the subfornical organ in the central regulation of fluid balance and vasopressin secretion.     

Phospholipid and glycolipid synthesis in brain structures of Brattleboro rats

The incorporation of labeled precursors in phospholipids and glycolipids was studied in discrete brain areas of rats with innate vasopressin deficiency (Brattleboro, DI) and intact Long Evans animals (LE). Tracer incorporation was found to be reduced in septal, hypothalamic and hippocampal phospholipids, but enhanced in the glycolipid fraction isolated from the hypothalamus and hippocampus of Brattleboro rats. The results indicate that inherited vasopressin deficit seems to be associated with altered lipid synthesis in some brain areas of the Brattleboro rat, suggesting a probability for impaired translation of chemical signals.     

Visualization of the interaction of native and modified low density lipoproteins with isolated rat liver cells

Morphological characteristics of the interaction of low density lipoproteins (LDL) and acetylated low density lipoproteins (AcLDL) with rat liver cells are described. These liver cell types are mainly responsible for the catabolism of these lipoproteins in vivo. Isolated rat liver Kupffer, endothelial, and parenchymal cells were incubated with LDL or AcLDL conjugated to 20 nm colloidal gold. LDL was mainly internalized by Kupffer cells, whereas AcLDL was predominantly found in endothelial cells. Kupffer and endothelial cells displayed different morphological characteristics in the processing of these lipoproteins. Kupffer cells bound LDL at uncoated regions of the plasma membrane often at the base of pseudopodia, and internalized the particles via small smooth vesicles. These uptake characteristics differ from the classical LDL uptake pathway, as described for other cell types, and may be related to the unique recognition properties of the receptor of Kupffer cells as observed in biochemical studies. Liver endothelial cells bound AcLDL in coated pits, followed by rapid uptake. Uptake proceeded through small coated vesicles, and after 5 min of incubation large (600-1200 nm) electron-lucent vacuoles (endosomes) with AcLDL-gold particles arranged along the membrane region were present. The endosomes were often associated closely with the cell membrane which might enable direct recycling of AcLDL receptors. These observations might explain the high efficiency of these cells in the processing of modified LDL in vivo.     

Granule populations in oxytocin and abnormal perikarya of the supraoptic nucleus of homozygous Brattleboro rats: Effects of colchicine administration

Summary Magnocellular neurones in the supraoptic nucleus of the homozygous Brattleboro rat, which are unable to produce vasopressin, were investigated by immunocytochemistry to identify both the oxytocin cells and the abnormal neurones, which in normal animals would produce vasopressin. The abnormal cell profiles were significantly more rounded than those of the oxytocin cells. Both cell types showed evidence of hyperactivity, but the Golgi apparatus was more extensive in the oxytocin cells, probably as a result of the failure of the abnormal cells to produce vasopressin and its neurophysin and the resultant reduction in hormone packaging. Neurosecretory granules (NSG) 160 nm in diameter were found in the oxytocin perikarya but were absent from the abnormal cell bodies. In addition, a population of small dense granules (SDG) 100 nm in diameter was observed in both types of neurone, in numbers equal to the NSG in oxytocin cells.Injection of a low, non-lethal dose of the axonal transport inhibitor colchicine resulted in a rapid and equal accumulation of both NSG and SDG in oxytocin perikarya and of SDG in the abnormal perikarya after one day. The effects of colchicine were reversed 2–3 days after administration. The SDG, which may contain a co-transmitter or co-hormone substance, are thus produced at a similar rate to NSG, and appear to be transported from the perikarya for subsequent release at the nerve endings.     

Influence of steroid aerosol treatments on the clearance of inhaled gold particles

Female Long Evans rats were used to test the hypothesis that inhaled triamcinolone acetonide accelerates the rate of clearance of particles from the lung. Three groups of animals inhaled a radioactive gold aerosol, which functioned as a tracer of respiratory tract clearance, and then were subjected to various inhalation treatments. The group treated with triamcinolone acetonide aerosol showed a significant acceleration in the rate of early clearance, but the total amount of tracer particles cleared in the first day was not significantly increased. Inhaled triamcinolone acetonide appears to accelerate the translocation of foriegn particles from small airways to larger ones, but stimulation of clearance does not appear to be a large effect.     

Internalization of surface anionic sites and phagosome-lysosome fusion during interaction of Toxoplasma gondii with macrophages

The participation of cell surface anionic sites on the interaction between tachyzoites of Toxoplasma gondii and macrophages and the process of phagosome-lysosome fusion were analyzed using cationized ferritin as a marker of cell surface anionic sites and albumin-colloidal gold as a marker for secondary lysosomes. Incubation of either the macrophages or the parasites with cationized ferritin before the interaction increased the ingestion of parasites by macrophages. Anionic sites of the macrophage's surface, labeled with cationized ferritin before the interaction, were internalized together with untreated parasites. However, after interaction with glutaraldehyde-fixed or specific antibody-coated parasites, the cationized ferritin particles were observed in endocytic vacuoles which did not contain parasites. Macrophages previously labeled with albumin-gold at 37 degrees C, were incubated in the presence of cationized ferritin at 4 degrees C and then incubated with untreated or specific antibody-coated parasites. After interaction with opsonized parasites, the colloidal gold particles were observed in the parasitophorous vacuoles while the cationized ferritin particles were observed in cytoplasmic vesicles. However, when the interaction was carried out with untreated parasites, the parasitophorous vacuoles exhibited ferritin particles while the colloidal gold particles were observed in cytoplasmic vesicles. These observations, in association with studies previously reported, suggest that the state of the parasite surface determines the mechanism of parasite entry into the macrophage, the composition of the membrane lining the parasitophorous vacuole and the ability of lysosomes to fuse with the vacuoles.     

STUDIES ON THE INTRACELLULAR DIGESTIVE PROCESS IN MAMMALIAN TISSUE CULTURE CELLS

DNA-protein coacervates containing colloidal gold particles were readily phagocytized by strain L fibroblasts. During the subsequent digestion process, the gold particles served as markers which permitted the demonstration of the evolution of digestive vacuoles to multivesicular bodies and finally to dense bodies. Acid phosphatase and esterolytic activity was present in these structures. The hydrolytic enzymes were apparently brought to the phagocytotic vacuoles in small vesicles originating in the Golgi region. These vesicles entered the vacuoles prior to the digestion of the coacervates and the appearance of positive cytochemical reactions. The cytoplasmic dense bodies frequently merged with the phagocytotic vacuoles. This was demonstrated by prelabeling the dense bodies with colloidal iron prior to phagocytosis of the coacervates. In addition, evidence is presented for the interrelationship of the phagocytotic and autophagic pathways.     

Endocytosis by African trypanosomes. II. Occurrence in different life-cycle stages and intracellular sorting

Horseradish peroxidase (HRP) and colloidal gold-labeled proteins enter many of the endocytic organelles of bloodstream forms of Trypanosoma brucei and T. congolense. However, the colloidal gold markers were excluded from substantial parts of the pathway that contained HRP. Morphometric studies revealed that HRP entered organelles that accounted for approximately 5% of the total cell volume while transferrin-gold entered organelles that comprised approximately 2% of the total cell volume. In addition, large colloidal gold particles were excluded from organelles that contained smaller gold particles. Antibodies, raised against the variable surface glycoprotein, when applied to thawed cryosections were found to label structures from which endocytosed colloidal gold coupled to bovine serum albumin (BSA) was excluded. Endocytosis was shown to occur in two in vitro propagated forms of trypanosomes, similar to those found in the insect vector (Glossina spp.). The mammal-infective metacyclic forms were similar to bloodstream forms in that they endocytosed HRP and colloidal gold markers but excluded colloidal gold from approximately 3% of the endocytic organelles. Estimation of the flagellar pocket volumes of bloodstream form T. brucei showed that this organelle occupied 0.5% to 1.4% of the total cell volume. The flagellar pocket volume of T. congolense varied between life-cycle stages, with a fractional volume of 4.4% for bloodstream forms, 2.3% for metacyclic forms and 1.4% for procyclic forms. Endocytosis of HRP, but not of protein-gold markers, occurred in procyclic (uncoated) forms. Endocytosis by procyclic forms has heretofore not been reported.(ABSTRACT TRUNCATED AT 250 WORDS)     

A morphological study of ferritin synthesis in macrophages with ingested ferric hydroxide-potassium polyvinyl sulfate complexes

A ferric hydroxide-polyvinyl sulfate colloidal solution (Fe-PVS), prepared by mixing potassium polyvinyl sulfate (PVSK) and ferric hydroxide colloidal solution was used to study ferritin synthesis in rat peritoneal macrophages. The colloidal particles had spherical electron opaque ferric hydroxide cores with diameters of about 250 nm surrounded by radially arranged fibrous PVS molecules. They also had strong negative electric charges. Fe-PVS particles injected into the peritoneal cavity were taken up by the macrophages then disintegrated rapidly. In the phagolysosomes the electron opaque ferric hydroxide cores of Fe-PVS were denuded of their PVS frames then decomposed into small 5-6 nm granules 24 to 48 h after injection. These small granules were released from the lysosomes into the hyaloplasm and the myelin figures were found in the lysosomal vacuoles. No reaccumulation of granules in lysosomes was found even 3 months later. The intracellular distribution of ferritin in macrophages demonstrated by the immunocytochemical method showed a pattern similar to that of the small granules formed by the disintegration of Fe-PVS. This means that in rat peritoneal macrophages that contain ingested Fe-PVS particles ferritin first is synthesized in phagolysosomes by the ferric hydroxide cores that conjugate with apoferritin or protein subunits then they are dispersed into the cytoplasm. Two possible pathways for the biosynthesis of ferritin are discussed.     

Biosynthesis of isorenin in cell cultures from pineal glands of adult and newborn rats

Renin-like activity (RA) was detected by bioassay and radioimmunoassay in culture media of pineal glands of male rats. The monolayer tissue culture of pineal cells from adult and newborn male white rats produced in 30 days, an amount of RA that was 20-fold greater than the RA in nonincubated pineal glands from rats of the same age. The cultured intact pineal glands from Long Evans and Brattleboro adult male rats produced in 7 days an amount of RA (radioimmunoassay) that was about 3 times greater than that found in nonincubated pineal glands from the same rat. These results suggest that cultured cells of rat pineal glands synthesize renin-like enzymes.     

ELECTRON MICROSCOPY OF HELA CELLS AFTER THE INGESTION OF COLLOIDAL GOLD

Tissue cultures of HeLa cells were grown in media containing colloidal gold, and after various intervals, the cells were fixed, embedded, and sectioned for electron microscopy. Uncoated grids with small holes were used in many of the experiments. Intracellular particles of gold were identified in areas surrounded by single membranes, in moderately dense granules, in globoid bodies, and in the cytoplasmic matrix. Gold particles were not found in typical mitochondria, Golgi complex, ergastoplasm (granular forms of endoplasmic reticulum), or nuclei. The phenomenon of pinocytosis was considered to be the most likely means by which the gold particles were ingested, and the locations of gold particles appeared to have significance concerning theories that membranous organelles of the cytoplasm may be derived from the cell membrane.     

The Ingestion of Proteins and Colloidal Materials by Columnar Absorptive Cells of the Small Intestine in Suckling Rats and Mice

Proteins and colloidal materials, administered orally to suckling rats and mice, were ingested by columnar absorptive cells of the jejunum and ileum, but not of the duodenum. Bovine gamma globulin and ovalbumin were identified in the apical cytoplasm by staining with fluorescent antibody; trypan blue, Evans blue, saccharated iron oxide, and colloidal gold were detected intracellularly by their color, specific staining, and appearance in the electron microscope. Each substance was segregated in membrane-enclosed vacuoles, apparently part of a system of potentially interconnecting vacuoles and tubules in the apical cytoplasm which is continuous in places with the apical cell membrane. We postulate that ingestion of foreign materials was accomplished by pinocytosis, that is, by invagination of the apical cell membrane to form vacuoles containing material from the intestinal lumen. Approximately 18 days after birth columnar absorptive cells lost the ability to ingest proteins and colloids, and no longer contained large vacuoles and numerous tubules. At this age rats and mice lose the ability to absorb antibodies from the intestine in an immunologically intact form, and we conclude that cellular ingestion is part of the mechanism of absorption of intact proteins in suckling animals. Particulate fat apparently is absorbed in both newborn and adult animals by micropinocytosis. Thus adult animals may not have lost the capacity for pinocytosis, but rather have become selective as to what substances provoke it. Cortisone acetate, administered subcutaneously to rats 8 to 10 days old alters the columnar absorptive cells within 72 hours so that they resemble the cells in adult animals and no longer ingest proteins.     

Distribution of insulin binding sites on Leydig cells of rat testes using insulin-coated gold particles

Summary The distribution of insulin binding sites in Leydig cells dispersed with collagenase from rat testes was studied using insulin-coated gold particles as an electron opaque ligand. Using electron microscope is convenient to distinguish Leydig cells among a variety of cells in crude preparations by their ultrastructural characteristics. Leydig cells were shown to possess insulin-binding sites on their plasma membranes. Initial binding sites of insulin were located to the microvillous surfaces. Following binding, receptor-ligand complexes seemed to move to the intermicrovillous plasma membrane, then to be internalized. Two modes of the internalization were confirmed. Most of the receptor-ligand complexes on Leydig cells appeared to be internalized via large, uncoated plasma membrane invaginations, while the remainder became internalized via small pits into vesicles. The receptor-ligand complexes were subsequently transferred to large subsurface vacuoles with electron-lucent lumens believed to correspond to endosomes. The reason why IGCs on the postendosomal pathway moving toward lysosomes was also discussed.     

Distribution of insulin binding sites on Leydig cells of rat testes using insulin-coated gold particles.

The distribution of insulin binding sites in Leydig cells dispersed with collagenase from rat testes was studied using insulin-coated gold particles as an electron opaque ligand. Using electron microscope is convenient to distinguish Leydig cells among a variety of cells in crude preparations by their ultrastructural characteristics. Leydig cells were shown to possess insulin-binding sites on their plasma membranes. Initial binding sites of insulin were located to the microvillous surfaces. Following binding, receptor-ligand complexes seemed to move to the intermicrovillous plasma membrane, then to be internalized. Two modes of the internalization were confirmed. Most of the receptor-ligand complexes on Leydig cells appeared to be internalized via large, uncoated plasma membrane invaginations, while the remainder became internalized via small pits into vesicles. The receptor-ligand complexes were subsequently transferred to large subsurface vacuoles with electron-lucent lumens believed to correspond to endosomes. The reason why IGCs on the postendosomal pathway moving toward lysosomes was also discussed.     

Intragranular colocalization of immunoreactive methionine-enkephalin and oxytocin within the nerve terminals in the posterior pituitary

To determine differential tissue antigens in the same section immunocytochemically using the electron microscope, the neurohypophysis was examined following the application of a freeze-drying tissue preparation and staining with the protein A-colloidal gold-antibody complex method (Hisano S, Adachi T, Daikoku S: J Histochem Cytochem 32:705, 1984). At the light microscopic level, colocalized immunostaining for methionine-enkephalin (ENK) and oxytocin (OXT) was found in the rat neurohypophysis under different physiological states. Small pieces of the neurohypophysial tissue were frozen and dried. The dried tissue was fixed with paraformaldehyde vapor and embedded. The ultrathin sections were stained with the antibody for ENK coupled with protein A-small colloidal gold, and antibody for OXT or vasopressin (VP) conjugated with protein A-large colloidal gold. The ultrastructures of the nerve terminals were well preserved and showed many membrane-limited secretory granules. It was possible to identify both OXT- and VP-containing nerve terminals as their secretory granules were differentially labeled with protein A-colloidal gold anti-OXT or anti-VP complex, respectively. The secretory granules, which were labeled with large gold particles for OXT, also carry small gold particles. It is evident that ENK coexists with OXT in the same granules.     

Electron microscope observations of the melanocyte of the human epidermis

Proteins and colloidal materials, administered orally to suckling rats and mice, were ingested by columnar absorptive cells of the jejunum and ileum, but not of the duodenum. Bovine gamma globulin and ovalbumin were identified in the apical cytoplasm by staining with fluorescent antibody; trypan blue, Evans blue, saccharated iron oxide, and colloidal gold were detected intracellularly by their color, specific staining, and appearance in the electron microscope. Each substance was segregated in membrane-enclosed vacuoles, apparently part of a system of potentially interconnecting vacuoles and tubules in the apical cytoplasm which is continuous in places with the apical cell membrane. We postulate that ingestion of foreign materials was accomplished by pinocytosis, that is, by invagination of the apical cell membrane to form vacuoles containing material from the intestinal lumen. Approximately 18 days after birth columnar absorptive cells lost the ability to ingest proteins and colloids, and no longer contained large vacuoles and numerous tubules. At this age rats and mice lose the ability to absorb antibodies from the intestine in an immunologically intact form, and we conclude that cellular ingestion is part of the mechanism of absorption of intact proteins in suckling animals. Particulate fat apparently is absorbed in both newborn and adult animals by micropinocytosis. Thus adult animals may not have lost the capacity for pinocytosis, but rather have become selective as to what substances provoke it. Cortisone acetate, administered subcutaneously to rats 8 to 10 days old alters the columnar absorptive cells within 72 hours so that they resemble the cells in adult animals and no longer ingest proteins.     

AUTOPHAGIC VACUOLES PRODUCED IN VITRO : II. Studies on the Mechanism of Formation of Autophagic Vacuoles Produced by Chloroquine

Continuous phase-contrast observations have been made on macrophages following exposure to chloroquine. The initial abnormality is the appearance in the Golgi region of small vacuoles with an intermediate density between that of pinosomes and granules. Over the course of 1–2 hr these vacuoles grow larger and accumulate amorphous material or lipid. Pinosomes or granules frequently fuse with the toxic vacuoles. Chloroquine derivatives can be seen by fluorescence microscopy; the drug is rapidly taken up by macrophages and localized in small foci in the Golgi region. Chloroquine continues to produce vacuoles when pinocytosis is suppressed. Electron microscopic studies of chloroquine effects on macrophages preincubated with colloidal gold to label predominately pinosomes or granules suggest that toxic vacuoles can arise from unlabeled organelles. Later vacuoles regularly acquire gold label, apparently by fusion, from both granules and pinosomes. L cells also develop autophagic vacuoles after exposure to chloroquine. Smooth endoplasmic reticulum apparently is involved early in the autophagic process in these cells. Information now available suggests an initial action of chloroquine on Golgi or smooth endoplasmic reticulum vesicles, and on granules, with alterations in their membranes leading to fusion with one another and with pinosomes.