Neurosecretion by Exocytosis

A Dual Functional Electroactive and Fluorescent Probe for Coupled Measurements of Vesicular Exocytosis with High Spatial and Temporal Resolution

In this work, Fluorescent False Neurotransmitter 102 (FFN102), a synthesized analogue of biogenic neurotransmitters, was demonstrated to show both pH-dependent fluorescence and electroactivity. To study secretory behaviors at the single-vesicle level, FFN102 was employed as a new fluorescent/electroactive dual probe in a coupled technique (amperometry and total internal reflection fluorescence microscopy (TIRFM)). We used N13 cells, a stable clone of BON cells, to specifically accumulate FFN102 into their secretory vesicles, and then optical and electrochemical measurements of vesicular exocytosis were experimentally achieved by using indium tin oxide (ITO) transparent electrodes. Upon stimulation, FFN102 started to diffuse out from the acidic intravesicular microenvironment to the neutral extracellular space, leading to fluorescent emissions and to the electrochemical oxidation signals that were simultaneously collected from the ITO electrode surface. The correlation of fluorescence and amperometric signals resulting from the FFN102 probe allows real-time monitoring of single exocytotic events with both high spatial and temporal resolution. This work opens new possibilities in the investigation of exocytotic mechanisms.

The chemopreventive agent development research program in the Division of Cancer Prevention of the US National Cancer Institute: an overview

Chemoprevention is an innovative area of cancer research that focuses on the development of pharmacological, biological, and nutritional interventions to prevent, reverse, or delay carcinogenesis. Over the past two decades the Division of Cancer Prevention of the US National Cancer Institute has organized a research and development program to provide resources and infrastructure to the research community for the clinical evaluation of potential cancer preventive agents. This program now encompasses preclinical agent and molecular target identification, in vitro and in vivo screening, efficacy and intermediate endpoint testing, pharmacology and toxicology assessments, and finally chemical synthesis and manufacturing leading to Investigational New Drug applications and clinical studies. In this review, examples of agents currently in development, preclinical testing models, and phase 1 and 2 clinical studies are described. Continued commitment to cancer prevention will significantly reduce the economic and medical burden of cancer.

The anterior cardiac plexus: an intrinsic neurosecretory site within the stomatogastric nervous system of the crab Cancer productus

The stomatogastric nervous system (STNS) of decapod crustaceans is modulated by both locally released and circulating substances. In some species, including chelate lobsters and freshwater crayfish, the release zones for hormones are located both intrinsically to and at some distance from the STNS. In other crustaceans, including Brachyuran crabs, the existence of extrinsic sites is well documented. Little, however, is known about the presence of intrinsic neuroendocrine structures in these animals. Putative intrinsic sites have been identified within the STNS of several crab species, though ultrastructural confirmation that these structures are in fact neuroendocrine in nature remains lacking. Using a combination of anatomical techniques, we demonstrate the existence of a pair of neurosecretory sites within the STNS of the crab Cancer productus. These structures, which we have named the anterior cardiac plexi (ACPs), are located on the anterior cardiac nerves (acns), which overlie the cardiac sac region of the foregut. Each ACP starts several hundred micro m from the origin of the acn and extends distally for up to several mm. Transmission electron microscopy done on these structures shows that nerve terminals are present in the peripheral portion of each acn, just below a well defined epineurium. These terminals contain dense-core and, occasionally, electron-lucent vesicles. In many terminals, morphological correlates of hormone secretion are evident. Immunocytochemistry shows that the ACPs are immunopositive for FLRFamide-related peptide. All FLRFamide labeling in the ACPs originates from four axons, which descend to these sites through the superior oesophageal and stomatogastric nerves. Moreover, these FLRFamide-immunopositive axons are the sole source of innervation to the ACPs. Collectively, our results suggest that the STNS of C. productus is not only a potential target site for circulating hormones, but also serves as a neuroendocrine release center itself.

Physiological control of Xunc18 expression in neuroendocrine melanotrope cells of Xenopus laevis

In mammals, the brain-specific protein munc18-1 regulates synaptic vesicle exocytosis at the synaptic junction, in a step before vesicle fusion. We hypothesize that the rate of biosynthesis of munc18-1 messenger RNA (mRNA) and the amount of munc18-1 present in neurons and neuroendocrine cells are related to the physiologically controlled state of activity. To test this hypothesis, the homolog of munc18-1 in the clawed toad Xenopus laevis, xunc18, was studied in the brain and in the neuroendocrine melanotrope cells in the intermediate lobe of the pituitary gland, at both the mRNA and the protein level. In toads adapted to a black background, the melanotropes release the peptide alpha-melanophore-stimulating hormone (alpha-MSH), which induces darkening of the skin, whereas in animals adapted to a white background the cells hardly release but store alpha-MSH, making the animal's skin look pale. The intermediate pituitary lobe of black-adapted animals revealed a strong hybridization reaction with the xunc18 mRNA probe, whereas a much weaker hybridization was observed in the intermediate lobe of white-adapted animals (optical density black: 3.4 +/- 0.2 vs. white: 0.8 +/- 0.1; P < 0.02). Immunocytochemically, Xenopus munc18-like protein has been detected throughout the brain, in identified neuronal perikarya as well as in axon tracts. Western blot analysis and immunocytochemistry further demonstrated the presence of xunc18 in the neural, intermediate and distal lobe of the pituitary gland. Xunc18 protein was furthermore determined in immunoblots of homogenates of melanotropes dissociated from the pituitary gland. In melanotropes of toads adapted to a black background, the integrated optical density of the xunc18 immunosignal was 2.7 +/- 0.5 times higher than in cells of white-adapted toads (P < 0.0001). It is concluded that, in Xenopus melanotrope cells, the amounts of both xunc18 mRNA and xunc18 protein are up-regulated in conjunction with the induction of exocytosis of alpha-MSH as a result of a physiological stimulation (environmental light condition). We propose that xunc18 is involved in physiologically controlled exocytotic secretion of neuroendocrine messengers.

Neuropeptide release by efficient recruitment of diffusing cytoplasmic secretory vesicles

Neuropeptides are slowly released from a limited pool of secretory vesicles. Despite decades of research, the composition of this pool has remained unknown. Endocrine cell studies support the hypothesis that a population of docked vesicles supports the first minutes of hormone release. However, it has been proposed that mobile cytoplasmic vesicles dominate the releasable neuropeptide pool. Here, to determine the cellular basis of the releasable pool, single green fluorescent protein-labeled secretory vesicles were visualized in neuronal growth cones with the use of an inducible construct or total internal reflection fluorescence microscopy. We report that vesicle movement follows the diffusion equation. Furthermore, rapidly moving secretory vesicles are used more efficiently than stationary vesicles near the plasma membrane to support stimulated release. Thus, randomly moving cytoplasmic vesicles participate in the first minutes of neuropeptide release. Importantly, the preferential recruitment of diffusing cytoplasmic secretory vesicles contributes to the characteristic slow kinetics and limited extent of sustained neuropeptide release.

Preclinical drug development paradigms for chemopreventives

Preclinical screening studies and animal efficacy testing models currently are used by the National Cancer Institute's chemoprevention drug discovery program to assess and identify chemical agents and natural products that may have the potential to prevent human cancer. Identification of potential cancer preventing agents begins by subjecting each compound to a sequential series of short-term, in vitro prescreens of mechanistic, biochemical assays to provide quantitative data to help establish an early indication of chemopreventive efficacy and to assist in prioritizing agents for further evaluation in longer-term, in vitro transformation bioassays and whole animal models. Promising chemical agents or combinations of agents that work through different inhibitory mechanisms subsequently are tested in well-established, chemically induced, animal tumor models, which include models of the lung, bladder, mammaries, prostate, and skin. These preclinical bioassays afford a strategic framework for evaluating agents according to defined criteria, and not only provide evidence of agent efficacy, but also serve to generate valuable dose-response, toxicity, and pharmacokinetic data required prior to phase I clinical safety testing. Based on preclinical efficacy and toxicity screening studies, only the most successful agents considered to have potential as human chemopreventives progress into clinical chemoprevention trials.

Prolactin and epidermal growth factor regulation of the proliferation, morphogenesis, and functional differentiation of normal rat mammary epithelial cells in three dimensional primary culture

The epithelial cell-specific effects of prolactin and epidermal growth factor (EGF) on the development of normal rat mammary epithelial cells (MEC) were evaluated using a three dimensional primary culture model developed in our laboratory. Non-milk-producing MEC were isolated as spherical end bud-like mammary epithelial organoids (MEO) from pubescent virgin female rats. The cultured MEO developed into elaborate multilobular and lobuloductal alveolar organoids composed of cytologically and functionally differentiated MEC. Prolactin (0.01-10 micrograms/ml) and EGF (1-100 ng/ml) were each required for induction of cell growth, extensive alveolar, as well as multilobular branching morphogenesis, and casein accumulation. MEO cultured without prolactin for 14 days remained sensitive to the mitogenic, morphogenic, and lactogenic effects of prolactin upon subsequent exposure. Similarly, cells cultured in the absence of EGF remained sensitive to the mitogenic and lactogenic effects of EGF, but were less responsive to its morphogenic effects when it was added on day 14 of a 21-day culture period. If exposure to prolactin was terminated after the first week, the magnitude of the mitogenic and lactogenic effects, but not the morphogenic response was decreased. Removal of EGF on day 7 also reduced the mitogenic response, but did not have any effect on the magnitude of the lactogenic or morphogenic responses. These studies demonstrate that physiologically relevant development of normal MEC can be induced in culture and that this model system can be used to study the mechanisms by which prolactin and EGF regulate the complex developmental pathways operative in the mammary gland.

Ultrastructural visualization of exocytosis in the pig pineal gland

The pinealocytes of the pig contain conspicuous dense bodies, the nature and role of which are not yet fully elucidated. The aim of this study was to demonstrate whether or not these structures are involved in the secretion process. The tannic acid-Ringer incubation (TARI)-method, which allows a clear-cut ultrastructural study of secretory discharge by exocytosis, has been used. The results indicate that pig pinealocytes release the content of the dense bodies with an amorphous inner structure into the extracellular space via exocytosis and that this secretion is quantitatively important. The secreted material is proteinaceous in nature; this indicates that polypeptides are released by the pineal.

Secretory activity and postembryonic development of the tentacle sensory system controlling growth hormone-producing neurons in Lymnaea stagnalis

The cerebral neuroendocrine peptidergic light green cells (LGC) of the freshwater snail Lymnaea stagnalis regulate body growth. The LGC are controlled by a tentacle sensory system that consists of two types (S1 and S2) of primary sensory neuron located at the base of each tentacle. Sensory (S2) axons make synaptic contacts (type A synapse-like structures) with the somata and axons of the LGC, where they release the contents of secretory granules, by exocytosis (demonstrated with the ultrastructural tannic acid-Ringer incubation method). Ultracytochemistry indicates that the granule contents are glycoproteinaceous. Furthermore, the S2 axons release secretory material in a nonsynaptic fashion into the interneuronal space of the central nervous system (CNS), at the level of the neuropiles of the cerebral ganglia and of the cerebral commissure. This release occurs by exocytosis from nonsynaptic release sites. It is proposed that the tentacle sensory system not only (synaptically) controls LGC activity but also influences other, remote neuronal targets in the CNS in a nonsynaptic ("at long distance," "paracrine," "hormone-like") fashion. Already in newly hatched snails (with a shell height of 1 mm) S2 axons show a fair rate of exocytotic activity, in both synaptic and nonsynaptic respects. During postembryonic development the secretory capacity of the S2 sensory neurons increases markedly, by increases in (1) the number of axons, (2) the size of the secretory granules, and (3) exocytosis activity. This increased capacity may meet a growing demand of the developing CNS, including the LGC, for neurochemical input from the tentacle sensory system.

Developmental and comparative aspects of nonsynaptic release by the egg-laying controlling caudodorsal cells of basommatophoran snails

In an immunoelectron microscope study the postembryonic development of the cerebral caudodorsal cells (CDC) in the freshwater snail Lymnaea stagnalis was studied as well as the development of similar neurons in other basommatophoran families. The CDC of adult L. stagnalis control egg-laying and associated behaviors by releasing various peptides, including the ovulation hormone CDCH. The CDC release peptides from neurohemal axon terminals and from nonsynaptic release sites of axon collaterals. During postembryonic development the collateral system develops synchronously with the neurohemal area. The first collaterals appear in the cerebral commissure of juvenile snails (10 mm shell height; S = 10). Up to S = 30 they gradually increase in size and length and eventually run through the entire inner compartment. Secretory granules in both collaterals and neurohemal axon terminals increase in size as well. Immunoelectron microscopy combined with the TARI-method for the demonstration of exocytosis indicates that CDCH-release from collaterals and neurohemal terminals occurs already in S = 10; exocytosis of immunoreactive granule contents takes place from nonsynaptic release sites, unspecialized areas of the axolemma of the collaterals. Release activity in the collaterals gradually increases up to S greater than or equal to 20. Neurohemal release activity shows a similar picture except for a steep increase in adult snails. A distinct glial sheath, separating the neurohemal area from the collateral system, appears around S = 15. Representatives of three families of Basommatophora, viz. the lymnaeid L. ovata, the planorbid Planorbis planorbis, and the bulinid Bulinus truncatus possess a well-developed collateral system showing many signs of exocytosis. A glial sheath separates the collaterals from the neurohemal area. Secretory granules of the CDC in L. ovata stain weakly positive with the anti-CDCH antiserum. Since the other Basommatophora did not show immunoreactivity, the chemical structure of egg laying peptides in Basommatophora seems to be genus specific. Apparently the secretory activity of both the neurohemal area and the collateral system is not only important in the sexually mature animal, being involved in the control of egg laying and egg-laying behavior, but also in the juvenile snail. The finding of a collateral system in representatives of three basommatophoran families strongly indicates the importance of the system for the control of reproduction in basommatophoran snails in general.

Release of neuropeptides does not only occur at nerve terminals

Neurohypophysial hormones are packed in secretory granules which are stored in nerve endings and in dilatations called nerve swellings. Although it was originally believed that the nerve swellings were storage compartments and that release occurred solely from the nerve terminals, the present paper demonstrates that secretion can occur to the same extent from both nerve endings and nerve swellings.

Secretory activity in the floor plate neuroepithelium of the developing human spinal cord: morphological evidence

The developing spinal cord at the cervical and thoracic levels in 14 human embryos ranging from Carnegie stages 14 to 20 were examined with the electron microscope. The floor plate-forming cells contained numerous cytoplasmic organelles, such as rough endoplasmic reticulum (ER), Golgi apparatus, and well-developed junctional complexes between the adjacent cells. Microvilli and cilia were numerous at the apical surface of neuroepithelial cells in the floor plate, but few were found in the lateral walls. Periodic acid-Schiff-positive substances were predominantly present in the neuroepithelial cells of the floor plate. In all specimens examined, multivesicular structures were observed in the floor plate neuroepithelium, but not in other regions of the spinal cord. The number of multivesicular structures appeared to increase with embryonic age. These structures contained numerous small and translucent vesicles within an electron-dense matrix; most vesicles were 40-70 nm in diameter. It appeared that the envelope of the multivesicular structures was first formed by the fusion of smooth ER-like cisterns, followed by invagination of the envelope by the vesicular contents. Presumably, the mature multivesicular structures were subsequently translocated to peduncular processes and their contents released into the central canal lumen in an exocytotic manner. This morphological evidence suggests that the floor plate cells of the spinal cord may have secretory activity during embryonic development.

Structural aspects, potassium stimulation and calcium dependence of nonsynaptic neuropeptide release by the egg laying controlling caudodorsal cells of Lymnaea stagnalis

The cerebral peptidergic caudodorsal cells of the freshwater snail Lymnaea stagnalis control egg laying and egg-laying behaviour by releasing peptides into (1) the haemolymph, from neurohaemal axon terminals in the periphery of the cerebral commissure and (2) the intercellular space of the central nervous system, from collaterals in the inner compartment of this commissure. Recently, it was shown that collateral release occurs from nonsynaptic release sites, which lack the morphological specializations that are characteristic of classical synapses. Probably, these sites enable the caudodorsal cells to communicate with central neurons in a nonsynaptic ("paracrine", "diffuse", "hormone-like") fashion. The structural and ionic bases of nonsynaptic release were studied using the tannic acid-Ringer incubation-method for the detection of exocytotic release of secretory granule contents in vitro. Elevation of the extracellular potassium concentration strongly stimulates exocytotic activity in the collaterals. No stimulation was found in the absence of extracellular calcium ions. Similar results have been obtained for the neurohaemal axon terminals. Electron-dense material occurs apposed at the cytoplasmic side of the axolemma of collaterals (ethanolic phosphotungstic acid method). This material appears homologous with the presynaptic dense projections forming the "vesicular grid" in classical synapses. Such projections are also present in the neurohaemal axon terminals. It is concluded that secretion from nonsynaptic release sites in caudodorsal cell collaterals shares fundamental characteristics with secretion from conventional neuronal release sites (neurohaemal axon terminals and classical synapses); release occurs by exocytosis of secretory granules, is associated with a vesicular grid, is stimulated by membrane depolarization, and depends on the presence of extracellular calcium ions.(ABSTRACT TRUNCATED AT 250 WORDS)

Visualization of non-synaptic release sites in the myenteric plexus of the snail Helix pomatia

Following conventional glutaraldehyde-osmium tetroxide fixation, a rich myenteric plexus was detected in the gastrointestinal tract of the snail Helix pomatia. Although hundreds of nerve processes were observed in the extensive myoneural neuropil, true synaptic specializations were not recognized in them. In the absence of synaptic specializations, tannic acid-Ringer incubation was applied to visualize the non-synaptic release sites in the enteric nerve plexus. After incubation for 1 h, a great number of exocytosis profiles were recorded at nerve-muscle contacts, at axoglial connections and in the myoneural neuropil. The frequency of occurrence of exocytosis profiles was the same for adrenergic and peptidergic fibres. In some gut wall areas, a dense staining of both basal lamina and collagen fibres was observed. Invagination of dense basal lamina into the omega-shaped profiles of the axolemma led to "false exocytosis" profiles. A detailed morphological analysis is needed to distinguish false exocytosis profiles from the true transmitter-releasing loci.

Neurosecretory cells with 'synaptoid perikarya' in Helix. A definitive description of secretory release from the somata of endocrine neurones

Neurosecretory cells in the mollusc Helix have perikarya that show clear signs of adaptation for both the synthesis and the discharge of secretory material. They are characterized morphologically by juxtaposition with the neural lamella. Passage of hormone into the haemocoel is apparently facilitated in many cases by the extreme attenuation of areas of the lamella and perineurium adjacent to the perikarya and by other forms of histological differentiation. Presumptive sites of release are characterized by prominent aggregations of synaptoid vesicles and the discharge of the contents of secretory granules by exocytosis.

'Neurosecretion' by aminergic synaptic terminals in vivo--a study of secretory granule exocytosis in the corpus cardiacum of the flying locust

Most nerve terminals forming typical synaptic junctions contain both synaptic vesicles and larger 'secretory granules' with electron-dense contents. Visualization of granule exocytosis from within terminals in the corpus cardiacum is facilitated by injection of tannic acid which immobilizes granule cores as they are discharged. The process of discharge is stimulated by flight-induced activation of the neurones and there is a correlated response by the innervated cells. In contrast to synapses with their vesicle clusters, granule discharge is not targeted upon the postsynaptic cells. These findings have general implications for mechanisms of discharge of neuropeptides and other transmitters from synaptic terminals.

Dopamine beta-hydroxylase: biochemistry and molecular biology

Dopamine beta-hydroxylase (DBH) catalyzes the conversion of dopamine to norepinephrine (NE), and is known to exist in two forms: soluble and membrane-bound. It has been reported that the two forms are similar in their immunoreactivity, carbohydrate content, and binding affinities for various substrates, and are apparently dissimilar in subunit structures and hydrophilicity. Furthermore, added structural complexity is observed within sDBH itself. Our results indicate that purified sDBH, which runs a single band on a nondenaturing gel, exhibits three protein bands of 75 kDa, 72 kDa, and 69 kDa on SDS polyacrylamide gel. The majority of sDBH exists as a 72-kDa protein. The NH2-terminal amino acid sequence of this 72-kDa protein indicates that it consists of two polypeptides of equimolar concentrations, where one differs from the other by three extra amino acids at its NH2 terminus. Whether they are different proteolytic cleavage products is not known. Thus, the structure of DBH appears to be more complex than originally considered. In vitro translation of total mRNA of bovine adrenal medulla followed by immunoprecipitation of DBH produces a single 72-kDa band on SDS polyacrylamide gel. This suggests either that there is only one in vitro mRNA translation product, which is modified to become different forms of DBH, or that multiple translation products are present but are indistinguishable by molecular weight. These subjects have been discussed in detail in this paper.

Ultrastructural demonstration of exocytosis in the pineal gland

Granular vesicles are present in pinealocytes and in rudimentary photoreceptor cells of many vertebrates, sometimes in large amounts. Their dense cores have been shown to store proteinaceous compounds, but the way they are released remains speculative. The aim of this study was to demonstrate whether or not exocytosis is the mechanism by which secretory products stored within granular vesicles are released. Therefore, a method has been used allowing a clear ultrastructural study of secretory products by exocytosis, even in tissues in which this process of secretion is quite rare and/or very slow. Exocytotic figures have been clearly demonstrated in the three species studied: golden hamster, snake, and parakeet. Nevertheless, they were never commonly observed as it was the case in neurohypophysis, even in such animals as the parakeet and snake, in which granular vesicles are very numerous. The possible reasons of this observation are discussed.

Ultrastructural demonstration of nonsynaptic release sites in the central nervous system of the snail Lymnaea stagnalis, the insect Periplaneta americana, and the rat

Release of neuronal secretory products by exocytosis was studied ultrastructurally in the central nervous systems of three different species (the snail Lymnaea stagnalis, the cockroach Periplaneta americana and the rat). Tissues were fixed with: (1) a mixture of glutaraldehyde and osmium tetroxide, (2) the tannic acid-glutaraldehyde-osmium tetroxide (TAGO) method, and (3) the tannic acid-Ringer incubation (TARI) method. Especially after TARI-treatment, release of the contents of the secretory vesicles by exocytosis could be clearly demonstrated in: (1) synapses, (2) neurohaemal axon terminals (L. stagnalis), and (3) neuronal processes without morphological synaptic specializations (nonsynaptic release sites). Release from nonsynaptic release sites occurs in most cases over a large area of the plasma membrane of a neuronal process facing several neural elements. On the basis of the differences in morphology of the secretory vesicles at nonsynaptic release sites, it is proposed that various types of (peptidic) messenger are released from such sites. In some neurones of L. stagnalis nonsynaptic release sites have been found together with synapses, or with neurohaemal axon terminals (caudodorsal cells, light green cells and light yellow cells). The possibility that nonsynaptic release sites represent the morphological correlates of nonsynaptic communication in the central nervous system has been discussed.

A monoclonal antibody to dopamine beta-monooxygenase: detection of biosynthetic intermediates

A monoclonal antibody to dopamine beta-monooxygenase (DBH) has been produced by an in vitro immunization technique. This antibody has been found to react with an epitope common to both soluble DBH (SDBH) and membrane-bound DBH (MDBH). A single CNBr fragment contains this antigenic site. Examination of electrophoretograms of chromaffin granule membrane and lysate by the immunoblot procedure revealed additional complexity. A 58-KDa polypeptide in low abundance was stained which could not be detected with the polyclonal antiserum. Chemical deglycosylation of SDBH produces two new polypeptides of 67 and 58 KDa. The entirety of this data suggests that the 58-KDa band is an unglycosylated form of DBH, proteolytically cleaved after biosynthesis.

Direct effects of the hyperglycemic factor of the freshwater snail Lymnaea stagnalis on isolated glycogen cells

In the freshwater pulmonate snail Lymnaea stagnalis special cells, the glycogen cells (GC) are present for the storage of glycogen reserves. These cells occur in large numbers in the anterior mantle region. In a previous paper in vitro experiments with intact anterior mantle tissue indicated that a hyperglycemic factor is released from the central nervous system (CNS) which stimulates glycogen mobilization in mantle tissue (M. A. Hemminga, J. J. Maaskant, W. Koomen, and J. Joosse (1985). Neuroendocrine control of glycogen mobilization in the freshwater snail Lymnaea stagnalis. Gen. Comp. Endocrinol. 57, 117-123). In the present study the question of whether this factor affects glycogen metabolism of GC isolated from mantle tissue was investigated. It is reported that in high-K+ Ringers the CNS is stimulated to release a factor which, in a dose-dependent way, inhibits glycogen synthesis in isolated GC (measured as a decreased incorporation of [14C]glucose into glycogen). Simultaneous with this glycogen synthesis-inhibiting effect, stimulation of glycogen degradation is found (measured as a decreased retention of prelabeled glycogen). It is concluded that (1) the factor released by the CNS having these effects on isolated GC is the same as the hyperglycemic factor which was reported to stimulate glycogen mobilization in intact mantle tissue, and (2) GC after isolation from mantle tissue have retained their ability to respond to this factor.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative ultrastructural analysis of differences in exocytosis number in adrenomedullary adrenaline cells of golden hamsters related to time of day, pinealectomy, and intracellular region

This research analyzed differences mainly in the incidence of exocytotic figures in adrenaline cells (A-cells) in pinealectomized (PX), sham-operated (SPX), and non-operated (NO) adult male golden hamsters, with the aim of determining whether these parameters change with the time of day and following pinealectomy, and whether intracellular regional differences exist in such changes. Animals acclimated to a standardized light:dark (LD) 12:12 photoperiod were sacrificed at 11 h after the onset of light (L-11h) and 1 h after the onset of darkness (D-1h) (8 animals/group/time) at 28 days postoperation. The adrenal medullas were examined and analyzed morphometrically by electron microscopy. The number of exocytoses per unit length (NEL) and the exocytosis index (a rough index of the number of exocytoses per cell) were measured in PF (perivascular-space-facing) and non-PF plasma membranes. NEL increased from L-11h (NO: 0.040 +/- 0.010, mean +/- SE) to D-1h (0.078 +/- 0.012) in all three experimental groups (ANOVA: P less than 0.005), showing over fourfold higher levels in PF than in non-PF membranes. NEL in PF membranes in PX animals showed higher levels than those in NO and SPX animals (P less than 0.025), but in non-PF membranes, no differences owing to time of day or surgery were seen. Exocytosis indices were (1) higher at D-1h than at L-11h in all three experimental groups (P less than 0.005), (2) similar in PF and non-PF membranes in control groups, and (3) higher in PF membranes in the PX group than in either non-PF membranes or PF membranes in control groups. In conclusion, the exocytosis number in A cells changes in relation to time of day, rising in early dark phase, and its rise following pinealectomy can be seen only in PF membranes.

Neuroendocrine control of glycogen mobilization in the freshwater snail Lymnaea stagnalis

In the freshwater snail Lymnaea stagnalis the anterior mantle region, which mainly consists of large numbers of special glycogen-storing cells, is an important depot for the energy reserves of this snail. In organ culture experiments the central nervous system (CNS), in contrast to other tissues, both inhibits glycogen synthesis (measured as incorporation of [14C]glucose into glycogen) and stimulates glycogen breakdown in anterior mantle tissue (measured as a decreased retention of prelabeled glycogen). These effects are dose dependent, with saturation at the highest doses tested. High-potassium Ringer solution stimulates the secretion of a CNS factor which induces glucose release by anterior mantle tissue. This glucose-release-stimulating effect of the CNS is also dose dependent, but saturation of the response was not achieved. It is concluded that inhibition of glycogen synthesis and stimulation of glycogen breakdown and glucose release are probably effects of a single neurohormone which controls glycogen mobilization from the storage cells in the mantle. Like similar factors in other animal phyla, this putative neurohormone is referred to as a hyperglycemic factor.

On mechanical aspects of vesicular transport

From the chain of events leading to secretion we have identified and isolated stages in which mechanical and physical mechanics may play important roles. These include the vesicle motion towards the cell wall, drainage of the cytoplasmic fluid from the gap between the membranes, reorganization of the membrane constituents, failure of the membrane structure and coalescence into a new configuration. We suggest a unified mechanism, relevant to the neural, secretory and vascular systems, based on physical factors as flow, pressure and stress distributions, and membranes properties. The simulation of several stages of secretion is coupled with experimental observations. By use of the proposed hypothesis it is possible to explain some observed phenomena, such as spontaneous and induced secretion, membrane failure, protein lateral dislocation and the omega-shapes in electron microscopic exposures of fusion sites.

Ultrastructural demonstration of exocytosis of neural, neuroendocrine and endocrine secretions with an in vitro tannic acid (TARI-) method

The release of neural, neuroendocrine, and endocrine secretory products by exocytosis was ultrastructurally studied by means of tissue incubation in Ringer containing tannic acid (Tannic Acid Ringer Incubation-method; TARI -method), followed by conventional fixation. Tannic acid strongly enhances the electron density of extracellular (secretory) substances. During TARI -treatment of tissues exocytosis proceeds, but the exteriorized contents of the secretory granules are immediately fixed by tannic acid and do not diffuse away into the extracellular space. In this way detection of exocytosis is markedly facilitated since the number of exocytosis phenomena visible at the ultrastructural level considerably increases with progressing incubation time. Studies of the central nervous system of the mollusc Lymnaea stagnalis show that the occurrence of exocytosis during TARI -treatment is calcium-dependent. With the TARI -method exocytosis has been clearly demonstrated in a variety of structures (endocrine cells, neurohaemal axon terminals, synapses) of L. stagnalis, the insect Locusta migratoria, and the rat, including cell types where exocytotic release had not been shown before.

Isolation of neurosecretory granules from the neurohaemal areas of peptidergic systems of Lymnaea stagnalis, with special reference to the ovulation hormone-producing caudodorsal cells

Neurosecretory granules (NSG) were isolated by density-gradient centrifugation from homogenates of the intercerebral commissure (COM) and the median lip nerves (LN) of the freshwater snail Lymnaea stagnalis. COM and LN are rich in axon terminals of the ovulation hormone-producing caudodorsal cells (CDC) and of the growth hormone-producing light green cells (LGC), respectively. Electron microscopy of COM isolates showed that a single fraction contained large numbers of NSG, which were identical to NSG of CDC axon terminals of the intact COM. High ovulation hormone activity was associated with this fraction. LN NSG were also isolated in large numbers in a single fraction. The isolated LN NSG were identical to NSG of intact LGC axon terminals. They appeared to have a higher specific gravity than CDC NSG.

Ultrastructural comparison of the perisympathetic organs in three Coleoptera: Chrysocarabus auronitens F., Oryctes rhinoceros L. and Tenebrio molitor L

Ultrastructural comparison of different types of perisympathetic organs (POs) in three species of Coleoptera (Chrysocarabus auronitens, Oryctes rhinoceros, and Tenebrio molitor) showed that the structure of these organs was not related to their morphological types but to their topography. Two kinds of PO structure may be distinguished: compact median and diffuse lateral. They were similar in that both were surrounded by thin neural lamellae and exhibited numerous glial cells originating in the perineurium (type I perineurial cells) as well as abundant neurosecretory endings. They were different in as much as in median POs, the neurosecretory endings were generally surrounded by perineurial processes but in transverse POs, these endings were sheathless. Only one type of neurosecretory axon was distinguished in the median organs but three or four in the transverse. The nature of the processes by which neurosecretory granules are released may depend on the type of neurosecretory axon. For instance, exocytosis always occurred for dense spherical granules, and granule fragmentation was visualized for granules of smaller size.

Pre- and post-synaptic structures in insect CNS: intramembranous features and sites of alpha-bungarotoxin binding

The central neuropile of thoracic ganglia in the central nervous system (CNS) of the cockroach Periplaneta americana contains synapses with characteristic pre- and post-synaptic membrane specializations and associated structures. These include dense pre-synaptic T-bars surrounded by synaptic vesicles, together with post-synaptic densities of varying electron opacity. Exocytotic release of synaptic vesicles is observed only rarely near presynaptic densities, but coated pits are seen at variable distances from them, and may be involved in membrane retrieval. After freeze-fracture, paralinear arrays of intramembranous articles (IMPs) are detected on the P face of many presynaptic terminals, with associated dimples indicative of vesicular release. The E face of these membranes exhibits protuberances complementary to the P face dimples, as well as scattered larger IMPs. Post-synaptic membranes possess dense IMP aggregates on the P face, some of which may represent receptor molecules. Electrophysiological studies with biotinylated alpha-bungarotoxin reveal that biotinylation does not inhibit the pharmacological effectiveness of the toxin in blocking acetylcholine receptors on an identified motoneurone in the metathoracic ganglion. Preliminary thin section ultrastructural analysis of this tissue post-treated with avidin-HRP or avidin-ferritin indicates that alpha-bungarotoxin-binding sites are localized at certain synapses in these insect thoracic ganglia.

Presence of T-bars, intramembranous particle arrays and exocytotic profiles in neuroendocrine terminals of an insect

Definitive evidence is presented to show that arthropod neurohaemal terminals contain electron-dense T-bar structures with clustered microvesicles similar to those present in neuropilar and neuromuscular terminals. In terminal membranes of the locus corpus cardiacum, studied by freeze-fracture, intramembranous particle arrays, considered to correlate with the dense bars, are seen. However, there does not appear to be a spatial association between the arrays and the exocytotic profiles seen following exposure to stimulants for hormone release. The presence of the densities in both neuroendocrine and conventional terminals is discussed in the light of current theories for mechanisms of release of neurotransmitters and neurohormones in arthropods and vertebrates.