IGSF1 Deficiency Results in Human and Murine Somatotrope Neurosecretory Hyperfunction

CONTEXT

The X-linked immunoglobulin superfamily, member 1 (IGSF1), gene is highly expressed in the hypothalamus and in pituitary cells of the POU1F1 lineage. Human loss-of-function mutations in IGSF1 cause central hypothyroidism, hypoprolactinemia, and macroorchidism. Additionally, most affected adults exhibit higher than average IGF-1 levels and anecdotal reports describe acromegaloid features in older subjects. However, somatotrope function has not yet been formally evaluated in this condition.

OBJECTIVE

We aimed to evaluate the role of IGSF1 in human and murine somatotrope function.

PATIENTS, DESIGN, AND SETTING

We evaluated 21 adult males harboring hemizygous IGSF1 loss-of-function mutations for features of GH excess, in an academic clinical setting.

MAIN OUTCOME MEASURES

We compared biochemical and tissue markers of GH excess in patients and controls, including 24-hour GH profile studies in 7 patients. Parallel studies were undertaken in male Igsf1-deficient mice and wild-type littermates.

RESULTS

IGSF1-deficient adult male patients demonstrated acromegaloid facial features with increased head circumference as well as increased finger soft-tissue thickness. Median serum IGF-1 concentrations were elevated, and 24-hour GH profile studies confirmed 2- to 3-fold increased median basal, pulsatile, and total GH secretion. Male Igsf1-deficient mice also demonstrated features of GH excess with increased lean mass, organ size, and skeletal dimensions and elevated mean circulating IGF-1 and pituitary GH levels.

CONCLUSIONS

We demonstrate somatotrope neurosecretory hyperfunction in IGSF1-deficient humans and mice. These observations define a hitherto uncharacterized role for IGSF1 in somatotropes and indicate that patients with IGSF1 mutations should be evaluated for long-term consequences of increased GH exposure.

An electrostatic and probabilistic simulation model to describe neurosecretion at the synaptic scale

A hybrid simulation model (macro-molecular dynamics and Monte Carlo method) is proposed to reproduce neurosecretion and exocytosis. A theory has been developed for vesicular dynamics based on quasi-static electric interactions and a simple transition-state model for the vesicular fusion. Under the non-equilibrium electric conditions in an electrolytic fluid, it is considered that the motion of each synaptic vesicle is influenced by electrostatic forces exerted by the membranes of the synaptic bouton, other vesicles, the intracellular and intravesicular fluids, and external elements to the neuron. In addition, friction between each vesicle and its surrounding intracellular fluid is included in the theory, resulting in a drift type movement. To validate the vesicle equations of motion, a molecular dynamics method has been implemented, where the synaptic pool was replaced by a straight angle parallelepiped, the vesicles were represented by spheres and the fusion between each vesicle and the presynaptic membrane was simulated by a Monte Carlo type probabilistic change of state. Density profiles showing clusters of preferential activity as well as fusion distributions similar to the Poisson distributions associated with miniature end-plate potentials were obtained in the simulations.

Influence of abiraterone acetate on neuroendocrine differentiation in chemotherapy-naive metastatic castration-resistant prostate cancer

BACKGROUND

To determine the influence of abiraterone Acetate (AA) on neuroendocrine differentiation (NED) in patients with chemotherapy-naive metastatic castration-resistant prostate cancer (mCRPC).

METHODS

We conducted an analysis in 115 chemotherapy-naïve mCRPC patients who would be treated with chemotherapy. The serum levels of chromogranin A (CgA), neurone-specific enolase (NSE) were measured in 67 mCRPC patients without AA treatment and 48 patients after the failure of AA treatment, in which these markers were also measured in 34 patients before and after 6 months of AA treatment. Comparative t-test was used to evaluate the serial changes of serum NED markers during AA treatment and univariate and multivariate analyses were performed to test the influence of AA treatment on NED.

RESULTS

Serum CgA were NSE were evaluated to be above the upper limit of normal (ULN) in 56 (48.7%) and 29 (25.2%) patients before chemotherapy. In 34 patients with serial evaluation, serum CgA level of 14 patients and NSE of 14 patients increased after the failure of AA treatment. There was no significant difference of NED markers (CgA or NSE variation (P = 0.243) between at baseline and after the failure of AA treatment. Compared with the CgA elevation group in the first 6 months of AA treatment and baseline supranormal CgA group, the CgA decline group, and baseline normal CgA group has a much longer median PSA PFS (14.34 vs 10.00 months, P < 0.001, and 14.23 vs 10.30 months, P = 0.02) and rPFS, respectively (18.33 vs 11.37 months, P < 0.001, and 17.10 vs 12.07 months, P = 0.03). In logistic univariate analysis, AA treatment and its duration were not independent factors influencing NED.

CONCLUSIONS

We hypothesized that AA might not significantly lead to progression of NED of mCRPC in general. Furthermore, we found there was heterogeneity in changes of NED markers in different mCRPC patients during AA treatment. Serial CgA and NSE evaluation might help clinicians guide clinical treatment of mCRPC patients.

Novel cell types, neurosecretory cells, and body plan of the early-diverging metazoan Trichoplax adhaerens

BACKGROUND

Trichoplax adhaerens is the best-known member of the phylum Placozoa, one of the earliest-diverging metazoan phyla. It is a small disk-shaped animal that glides on surfaces in warm oceans to feed on algae. Prior anatomical studies of Trichoplax revealed that it has a simple three-layered organization with four somatic cell types.

RESULTS

We reinvestigate the cellular organization of Trichoplax using advanced freezing and microscopy techniques to identify localize and count cells. Six somatic cell types are deployed in stereotyped positions. A thick ventral plate, comprising the majority of the cells, includes ciliated epithelial cells, newly identified lipophil cells packed with large lipid granules, and gland cells. Lipophils project deep into the interior, where they alternate with regularly spaced fiber cells whose branches contact all other cell types, including cells of the dorsal and ventral epithelium. Crystal cells, each containing a birefringent crystal, are arrayed around the rim. Gland cells express several proteins typical of neurosecretory cells, and a subset of them, around the rim, also expresses an FMRFamide-like neuropeptide.

CONCLUSIONS

Structural analysis of Trichoplax with significantly improved techniques provides an advance in understanding its cell types and their distributions. We find two previously undetected cell types, lipohil and crystal cells, and an organized body plan in which different cell types are arranged in distinct patterns. The composition of gland cells suggests that they are neurosecretory cells and could control locomotor and feeding behavior.

[Age-associated reproductive cycle hypothalamic regulation impairment and its correction]

This review covers present-day ideas of the female organism reproductive system neuroendocrine regulation in aging. The literature data on the key role of the hypothalamus in formation, organization and age-related decline of the reproductive function in both mammals and humans are considered in detail. Special focus is on catecholamines, peptides and other biologically active compounds acting in these processes. The authors discuss data showing interaction between the suprachiasmatic nuclei of the hypothalamus and the pineal gland synchronizing circadian and diurnal rhythms of gonadotropine-releasing hormone being normally synthesised and secreted during the reproductive period, but failing in aging or under the influence of neurotoxic compounds. Molecular mechanisms of ovarian cycle hypothalamic regulation impairment and possible ways of its correction by means of melatonin and peptide preparations from the pineal gland are described. The data presented may be of utility to prevent premature aging of reproductive function.

[Morphological basis of the effect of hypothalamic neurosecretion on structural and functional homeostasis of pro- and eukaryotes]

Experimental histological aspects of neuroendocrinology are examined together with the emphasis on the regulatory and adaptogenic role of hypothalamic nonapeptidergic neurosecretory system in provision of structural-functional homeostasis in animal organism, including the conditions of its interaction with the microorganisms. Some new facts are presented demonstrating the positive effect of oxytocin on the realization of histo- and organotypical potencies by the tissues with different cambial characteristics during the necrotic suppurative processes. The priority directions are indicated for the further development of the fundamental and applied aspects of neuroendocrinology for optimization of the reparative histogeneses and inactivation of bacterial persistence potential.

Colocalization of FM1-43, Bassoon, and GnRH-1: GnRH-1 release from cell bodies and their neuroprocesses

Pulsatile release of GnRH-1 is critical for reproductive function. However, the cellular mechanism of GnRH-1 neurosecretion is still elusive. In this study, we examined the neurosecretory process of GnRH-1 neurons using time-lapse image acquisition followed by immunocytochemistry with confocal microscopy. To monitor exocytotic processes, cultured GnRH-1 neurons derived from monkey embryos were labeled with the lipophilic dye, FM1-43, or its fixable form FM1-43Fx, in the presence or absence of depolarization signals, and changes in vesicles labeled with FM1-43 were analyzed. The results show FM1-43 was taken up into the cell and labeled puncta in the soma and neuroprocesses in the absence of depolarization signals, indicating that GnRH-1 neurons were spontaneously active. Depolarization of GnRH-1 neurons with high K+ or veratridine challenge increased the intensity and size of puncta in both soma and neuroprocesses, and the veratridine-induced changes in puncta were blocked by tetrodotoxin, indicating that changes in the puncta intensity and size reflect neurosecretory activity. Subsequent double immunocytochemistry for GnRH-1 and the synaptic vesicle marker, vesicle-associated membrane protein, demonstrated that the FM1-43Fx-labeled puncta were synaptic vesicles with the GnRH-1 peptide. Additional double immunocytochemistry for GnRH-1 and the marker of the neurosecretory active zone, Bassoon, indicated that the FM1-43Fx-labeled puncta were located at the sites of neurosecretory active zones in GnRH-1 neurons. These results suggest that GnRH-1 neurons have the capacity to release the peptide from the soma and dendrites. Collectively, we hypothesize that soma-dendritic release of the peptide may be a mechanism of synchronized activity among GnRH-1 neurons.

Metabolic stress responses in Drosophila are modulated by brain neurosecretory cells that produce multiple neuropeptides

In Drosophila, neurosecretory cells that release peptide hormones play a prominent role in the regulation of development, growth, metabolism, and reproduction. Several types of peptidergic neurosecretory cells have been identified in the brain of Drosophila with release sites in the corpora cardiaca and anterior aorta. We show here that in adult flies the products of three neuropeptide precursors are colocalized in five pairs of large protocerebral neurosecretory cells in two clusters (designated ipc-1 and ipc-2a): Drosophila tachykinin (DTK), short neuropeptide F (sNPF) and ion transport peptide (ITP). These peptides were detected by immunocytochemistry in combination with GFP expression driven by the enhancer trap Gal4 lines c929 and Kurs-6, both of which are expressed in ipc-1 and 2a cells. This mix of colocalized peptides with seemingly unrelated functions is intriguing and prompted us to initiate analysis of the function of the ten neurosecretory cells. We investigated the role of peptide signaling from large ipc-1 and 2a cells in stress responses by monitoring the effect of starvation and desiccation in flies with levels of DTK or sNPF diminished by RNA interference. Using the Gal4-UAS system we targeted the peptide knockdown specifically to ipc-1 and 2a cells with the c929 and Kurs-6 drivers. Flies with reduced DTK or sNPF levels in these cells displayed decreased survival time at desiccation and starvation, as well as increased water loss at desiccation. Our data suggest that homeostasis during metabolic stress requires intact peptide signaling by ipc-1 and 2a neurosecretory cells.

Endocannabinoids and the regulation of bone metabolism

In mammals, including humans, bone metabolism is manifested as an ongoing modelling/remodelling process whereby the bone mineralised matrix is being continuously renewed. Recently, the main components of the endocannabinoid system have been reported in the skeleton. Osteoblasts, the bone forming cells, and other cells of the osteoblastic lineage, as well as osteoclasts, the bone resorbing cells, and their precursors, synthesise the endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG). CB(1) cannabinoid receptors are present in sympathetic nerve terminals in close proximity to osteoblasts. Activation of these CB(1) receptors by elevated bone 2-AG levels communicates brain-to-bone signals as exemplified by traumatic brain injury-induced stimulation of bone formation. In this process, the retrograde CB(1) signalling inhibits noradrenaline release and alleviates the tonic sympathetic restrain of bone formation. CB(2) receptors are expressed by osteoblasts and osteoclasts. Their activation stimulates bone formation and suppresses bone resorption. CB(2)-deficient mice display a markedly accelerated age-related bone loss. Ovariectomy-induced bone loss can be both prevented and rescued by a CB(2) specific agonist. Hence, synthetic CB(2) ligands, which are stable and orally available, provide a basis for developing novel anti-osteoporotic therapies, free of psychotropic effects. The CNR2 gene (encoding CB(2)) in women is associated with low bone mineral density, offering an assay for identifying females at risk of developing osteoporosis.

The PC12 cell as model for neurosecretion

This review attempts to touch on the history and application of amperometry at PC12 cells for fundamental investigation into the exocytosis process. PC12 cells have been widely used as a model for neural differentiation and as such they have been used to examine the effects of differentiation on exocytotic release and specifically release at varicosities. In addition, dexamethasone-differentiated cells have been shown to have an increased number of releasable vesicles with increased quantal size, thereby allowing for an even broader range of applications including neuropharmacological and neurotoxicological studies. PC12 cells exhibiting large numbers of events have two distinct pools of vesicles, one about twice the quantal size of the other and each about half the total releasable vesicles. As will be outlined in this review, these cells have served as an extremely useful model of exocytosis in the study of the latency of stimulation-release coupling, the role of exocytotic proteins in regulation of release, effect of drugs on quantal size, autoreceptors, fusion pore biophysics, environmental factors, health and disease. As PC12 cells have some advantages over other models for neurosecretion, including chromaffin cells, it is more than likely that in the following decade PC12 cells will continue to serve as a model to study exocytosis.

Secrets of the secretory pathway in dendrite growth

Dendrites and axons exhibit different morphologies and patterns of growth. This difference in neuronal structure is controlled by evolutionarily conserved directed trafficking through the secretory pathway.

Synergistic activation of astrocytes by ATP and norepinephrine in the rat supraoptic nucleus

Supraoptic nucleus (SON) neurons receive a dense innervation from noradrenergic fibers, the activity of which stimulates vasopressin (VP) and oxytocin (OT) release, notably during homeostatic regulation of blood pressure and volume. This regulation is known to involve the co-release of norepinephrine (NE) and ATP, which act in synergy to stimulate Ca(2+) increase in SON neurons and to enhance release of VP and OT from hypothalamo-neurohypophysial explants. We here demonstrate that both ATP and NE also trigger transient intracellular Ca(2+) rise in rat SON astrocytes, the two agonists showing a synergistic action similarly to what has been reported in SON neurons. The responses to both agonists are not or are only moderately affected after blockade of neuronal activity by tetrodotoxin, or of neurotransmitter release by removal of extracellular Ca(2+), suggesting that the receptors involved are located on the astrocytes themselves. ATP acts via P2Y(1) receptors, as indicated by the pharmacological profile of Ca(2+) responses and the strong immunolabeling for this receptor in SON astrocytes. Responses to NE involve both alpha and beta adrenergic receptors, the latter showing a permissive role on the former. These results point to further implication of SON astrocytes in the regulation of VP and OT secretion, and suggest that they are potentially important elements participating in all regulatory processes of hypothalamo-neurohypophysial function that involve activation of noradrenergic pathways.

Conserved sensory-neurosecretory cell types in annelid and fish forebrain: insights into hypothalamus evolution

Neurosecretory control centers form part of the forebrain in many animal phyla, including vertebrates, insects, and annelids. The evolutionary origin of these centers is largely unknown. To identify conserved, and thus phylogenetically ancient, components of neurosecretory brain centers, we characterize and compare neurons that express the prohormone vasotocin (vasopressin/oxytocin)-neurophysin in the developing forebrain of the annelid Platynereis dumerilii and of the zebrafish. These neurons express the same tissue-restricted microRNA, miR-7, and conserved, cell-type-specific combinations of transcription factors (nk2.1, rx, and otp) that specify their identity, as evidenced by the specific requirement of zebrafish rx3 for vasotocin-neurophysin expression. MiR-7 also labels another shared population of neurons containing RFamides. Since the vasotocinergic and RFamidergic neurons appear to be directly sensory in annelid and fish, we propose that cell types with dual sensory-neurosecretory properties were the starting point for the evolution of neurosecretory brain centers in Bilateria.

Fish caudal neurosecretory system: a model for the study of neuroendocrine secretion

The caudal neurosecretory system (CNSS) is unique to fish and has suggested homeostatic roles in osmoregulation and reproduction. Magnocellular neuroendocrine Dahlgren cells, located in the terminal segments of the spinal cord, project to a neurohaemal organ, the urophysis, from which neuropeptides are released. In the euryhaline flounder Platichthys flesus Dahlgren cells synthesise at least four peptides, including urotensins I and II and CRF. These peptides are differentially expressed with co-localisation of up to three in a single cell. Dahlgren cells display a range of electrical firing patterns, including characteristic bursting activity, which is dependent on L-type Ca(2+) and Ca-activated K(+)channels. Activity is modulated by a range of extrinsic and intrinsic neuromodulators. This includes autoregulation by the secreted peptides themselves, leading to enhanced bursting. Electrophysiological and mRNA expression studies have examined changes in response to altered physiological demands. Bursting activity is more robust and more Dahlgren cells are recruited in seawater compared to freshwater adapted fish and this is mirrored by a reduction in mRNA expression for L-type Ca(2+) and Ca-activated K(+) channels. Acute seawater/freshwater transfer experiments support a role for UII in adaptation to hyperosmotic conditions. Responses to stress suggest a shared role for CRF and UI, released from the CNSS. We hypothesise that the Dahlgren cell population is reprogrammed, both in anticipation of and in response to changed physiological demands, and this is seen as changes in gene expression profile and electrical activity. The CNSS shows striking parallels with the hypothalamic-neurohypophysial system, providing a highly accessible system for studies of neuroendocrine mechanisms. Furthermore, the presence of homologues of urotensins throughout the vertebrates has sparked new interest in these peptides and their functional evolution.

New insights on Saccus vasculosus evolution: a developmental and immunohistochemical study in elasmobranchs

The saccus vasculosus (SV) is a circumventricular organ of the hypothalamus of many jawed fishes whose functions have not yet been clarified. It is a vascularized neuroepithelium that consists of coronet cells, cerebrospinal fluid-contacting (CSF-c) neurons and supporting cells. To assess the organization, development and evolution of the SV, the expression of glial fibrillary acidic protein (GFAP) and the neuronal markers gamma-aminobutyric acid (GABA), glutamic acid decarboxylase (GAD; the GABA synthesizing enzyme), neuropeptide Y (NPY), neurophysin II (NPH), tyrosine hydroxylase (TH; the rate-limiting catecholamine-synthesizing enzyme) and serotonin (5-HT), were investigated by immunohistochemistry in developing and adult sharks. Coronet cells showed GFAP immunoreactivity from embryos at stage 31 to adults, indicating a glial nature. GABAergic CSF-c neurons were evidenced just when the primordium of the SV becomes detectable (at stage 29). Double immunolabeling revealed colocalization of NPY and GAD in these cells. Some CSF-c cells showed TH immunoreactivity in postembryonic stages. Saccofugal GABAergic fibers formed a defined SV tract from the stage 30 and scattered neurosecretory (NPH-immunoreactive) and monoaminergic (5-HT- and TH-immunoreactive) saccopetal fibers were first detected at stages 31 and 32, respectively. The early differentiation of GABAergic neurons and the presence of a conspicuous GABAergic saccofugal system are shared by elasmobranch and teleosts (trout), suggesting that GABA plays a key function in the SV circuitry. Monoaminergic structures have not been reported in the SV of bony fishes, and were probably acquired secondarily in sharks. The existence of saccopetal monoaminergic and neurosecretory fibers reveals reciprocal connections between the SV and hypothalamic structures which have not been previously detected in teleosts.

Regulation of growth hormone action by gonadal steroids

Sex steroids modulate growth hormone (GH) secretion and action. Estrogen attenuates GH action in a dose- and route-dependent manner by inhibiting GH-regulated endocrine function of the liver. Testosterone amplifies the metabolic action of GH while exhibiting similar but independent effects of its own. The strong modulatory effect of gonadal steroids on GH responsiveness provides insights into the biologic basis of sexual dimorphism in growth, development, and body composition and practical information for the clinical endocrinologist in the treatment of hypopituitary patients.

The polybasic sequence in the C2B domain of rabphilin is required for the vesicle docking step in PC12 cells

Rabphilin is generally thought to be involved in the regulation of secretory vesicle exocytosis in neurons and neuroendocrine cells, and it has recently been hypothesized that the C2B domain of rabphilin promotes the docking of dense-core vesicles to the plasma membrane through simultaneous interaction with a vesicle protein, Rab3A/27A, and a plasma membrane protein, SNAP-25 (synaptosome-associated protein of 25 kDa). However, the physiological significance of the rabphilin-SNAP-25 interaction in the vesicle-docking step has never been elucidated. In this study we demonstrated by a mutation analysis that the polybasic sequence (587 KKAKHKTQIKKK 598) in the C2B domain of rabphilin is required for SNAP-25 binding, and that the Asp residues in the Ca(2+)-binding loop 3 (D628 and D630) of the C2B domain are not required. We also investigated the effect of Lys-->Gln (KQ) mutations in the polybasic sequence of the C2B domain on vesicle dynamics by total internal reflection fluorescence microscopy in individual PC12 cells. A rabphilin(KQ) mutant that completely lacks SNAP-25-binding activity significantly decreased the number of plasma-membrane-docked vesicles and strongly inhibited high-KCl-induced dense-core vesicle exocytosis. These results indicate that the polybasic sequence in the C2B domain functions as an effector domain for SNAP-25 and controls the number of 'releasable' vesicles docked to the plasma membrane.

Localization of synaptic proteins involved in neurosecretion in different membrane microdomains

A number of proteins and signalling molecules modulate voltage-gated calcium channel activity and neurosecretion. As recent findings have indicated the presence of Ca(v)2.1 (P/Q-type) channels and soluble N-ethyl-maleimide-sensitive fusion protein attachment protein receptors (SNAREs) in the cholesterol-enriched microdomains of neuroendocrine and neuronal cells, we investigated whether molecules known to modulate neurosecretion, such as the heterotrimeric G proteins and neuronal calcium sensor-1 (NCS-1), are also localized in these microdomains. After immuno-isolation, flotation gradients from Triton X-100-treated synaptosomal membranes revealed the presence of different detergent-resistant membranes (DRMs) containing proteins of the exocytic machinery (Ca(v)2.1 channels and SNAREs) or NCS-1; both DRM subtypes contained aliquots of heterotrimeric G protein subunits and phosphatidylinositol-4,5-bisphosphate. In line with the biochemical data, confocal imaging of immunolabelled membrane sheets revealed the localization of SNARE proteins and NCS-1 in different dot-like structures. This distribution was largely impaired by treatment with methyl-beta-cyclodextrin, thus suggesting the localization of all three proteins in cholesterol-dependent domains. Finally, bradykinin (which is known to activate the NCS-1 pathway) caused a significant increase in NCS-1 in the DRMs. These findings suggest that different membrane microdomains are involved in the spatial organization of the complex molecular network that converges on calcium channels and the secretory machinery.

Kiss-and-run and full-collapse fusion as modes of exo-endocytosis in neurosecretion

Neurotransmitters and hormones are released from neurosecretory cells by exocytosis (fusion) of synaptic vesicles, large dense-core vesicles and other types of vesicles or granules. The exocytosis is terminated and followed by endocytosis (retrieval). More than fifty years of research have established full-collapse fusion and clathrin-mediated endocytosis as essential modes of exo-endocytosis. Kiss-and-run and vesicle reuse represent alternative modes, but their prevalence and importance have yet to be elucidated, especially in neurons of the mammalian CNS. Here we examine various modes of exo-endocytosis across a wide range of neurosecretory systems. Full-collapse fusion and kiss-and-run coexist in many systems and play active roles in exocytotic events. In small nerve terminals of CNS, kiss-and-run has an additional role of enabling nerve terminals to conserve scarce vesicular resources and respond to high-frequency inputs. Full-collapse fusion and kiss-and-run will each contribute to maintaining cellular communication over a wide range of frequencies.

Changes in FAD and NADH fluorescence in neurosecretory terminals are triggered by calcium entry and by ADP production

We measured changes in the intrinsic fluorescence (IF) of the neurosecretory terminals of the mouse neurohypophysis during brief (1-2 s) trains of stimuli. With fluorescence excitation at either 350 +/- 20 or 450 +/- 50 nm, and with emission measured, respectively, at 450 +/- 50 or > or = 520 nm, DeltaF/F(o) was approximately 5-8 % for a 2 s train of 30 action potentials. The IF changes lagged the onset of stimulation by approximately 100 ms and were eliminated by 1 microM tetrodotoxin (TTX). The signals were partially inhibited by 500 microM Cd(2+), by substitution of Mg(2+) for Ca(2+), by Ca(2+)-free Ringer's with 0.5 mM EGTA, and by 50 microM ouabain. The IF signals were also sensitive to the mitochondrial metabolic inhibitors CCCP (0.3 microM), FCCP (0.3 microM), and NaN(3) (0.3 mM), and their amplitude reflected the partial pressure of oxygen (pO(2)) in the bath. Resting fluorescence at both 350 nm and 450 nm exhibited significant bleaching. Flavin adenine dinucleotide (FAD) is fluorescent, while its reduced form FADH(2) is relatively non-fluorescent; conversely, NADH is fluorescent, while its oxidized form NAD is non-fluorescent. Thus, our experiments suggest that the stimulus-coupled rise in [Ca(2+)](i) triggers an increase in FAD and NAD as FADH(2) and NADH are oxidized, but that elevation of [Ca(2+)](i), alone cannot account for the totality of changes in intrinsic fluorescence.

How neurosecretory vesicles release their cargo

Neurons and related cell types often contain two major classes of neurosecretory vesicles, synaptic vesicles (SVs) and dense-core granules (DCGs), which store and release distinct cargo. SVs store and release classic neurotransmitters, which facilitate propagation of action potentials across the synaptic cleft, whereas DCGs transport, store, and release hormones, proteins, and neuropeptides, which facilitate neuronal survival, synaptic transmission, and learning. Over the past few years, there has been a major surge in our understanding of many of the key molecular mechanisms underlying cargo release from SVs and DCGs. This surge has been driven largely by the use of fluorescence microscopy (especially total internal reflection fluorescence microscopy) to visualize SVs or DCGs in living cells. This review highlights some of the recent insights into cargo release from neurosecretory vesicles provided by fluorescence microscopy, with emphasis on DCGs.

Plasticity of nonapeptidergic neurosecretory cells in fish hypothalamus and neurohypophysis

The structure and function of nonapeptidergic neurosecretory cells (NP-NSC) are considered in terms of comparative morphology. Among NSC of different ergicity for NP-NSC the most characteristic involve massive accumulation and storage of neurohormonal products. Only in NP-NSC are the secretory cycles of functioning clearly expressed. Their highest reactivity is established during experimental and physiological stresses. In contrast, liberinergic, statinergic, and monoaminergic NSC, unlike NP-NSC, are characterized even in the "norm" by a constantly high level of extrusion processes. As signs of maximum NP-NSC plasticity, we consider the largest size of elementary neurosecretory granules, the diversity of secretion forms, and the maximum development of Herring bodies-clear manifestations of secretory cycles of functioning. In particular, phases of massive storage of neurosecretory granules in the extrusion cycle of NP-NSC neurosecretory terminals express accumulation of neurosecretory products. It is concluded that a particularly high degree of plasticity of NP-NSC is provided by their capability for functional reversion. This reversion is manifested first in the form of the restoration of the initial moderate level of functioning and especially in the accumulation of neurosecretory products. The reversion is considered an important mechanism providing a high degree of NSC plasticity. This degree turns out to be sufficient for participation of NP-NSC in the integration of fish reproduction. It is shown that NP-NSC are organized by the principle of a triad of the balanced system. This system consists of two alternative states: accumulation and release of neurosecretory products and the center of control of dynamics of their interrelations, the self-regulating center. In the latter, the key role is probably played by the Golgi complex.

The role of Snapin in neurosecretion: snapin knock-out mice exhibit impaired calcium-dependent exocytosis of large dense-core vesicles in chromaffin cells

Identification of the molecules that regulate the priming of synaptic vesicles for fusion and the structural coupling of the calcium sensor with the soluble N-ethyl maleimide sensitive factor adaptor protein receptor (SNARE)-based fusion machinery is critical for understanding the mechanisms underlying calcium-dependent neurosecretion. Snapin binds to synaptosomal-associated protein 25 kDa (SNAP-25) and enhances the association of the SNARE complex with synaptotagmin. In the present study, we abolished snapin expression in mice and functionally evaluated the role of Snapin in neuroexocytosis. We found that the association of synaptotagmin-1 with SNAP-25 in brain homogenates of snapin mutant mice is impaired. Consequently, the absence of Snapin in embryonic chromaffin cells leads to a significant reduction of calcium-dependent exocytosis resulting from a decreased number of vesicles in releasable pools. Overexpression of Snapin fully rescued this inhibitory effect in the mutant cells. Furthermore, Snapin is relatively enriched in the purified large dense-core vesicles of chromaffin cells and associated with synaptotagmin-1. Thus, our biochemical and electrophysiological studies using snapin knock-out mice demonstrate that Snapin plays a critical role in modulating neurosecretion by stabilizing the release-ready vesicles.

Role of a novel maintained low-voltage-activated inward current permeable to sodium and calcium in pacemaking of insect neurosecretory neurons

Among ionic currents underlying neuronal pacemaker activity, low-threshold-activated calcium currents contribute to setting the threshold for spike firing. In the insect central nervous system, dorsal unpaired median (DUM) neurons are capable of generating spontaneous electrical activity. It has previously been shown that two distinct (transient and maintained) low-voltage-activated (LVA) calcium currents are responsible for the generation of the pacemaker potential. Whole-cell recordings in voltage- and current-clamp mode were obtained from short-term cultured DUM neurons. Using 100 mM sodium and 2 mM calcium as charge carrier in the external solution as well as conditions that eliminate calcium currents (0.5 mM CdCl2), voltage-clamp experiments showed that a hitherto unanticipated LVA maintained inward current, activated at around -60 mV, was present. The current amplitude was strongly dependent on internal ATP concentration. Sodium-free solution reduced by 80% the current amplitude. Increasing (5 mM) or decreasing (calcium-free) external calcium concentrations enhanced or reduced, respectively, the maximum conductance without any effect on the voltage dependence. This novel ion channel was permeable to barium but manipulating internal or external magnesium concentrations was without effect on current amplitude or reversal potential. Based on IC50 values, the maintained current was 50-fold less sensitive to TTX than the classical transient voltage-dependent sodium current. Furthermore, it was insensitive to ethosuximide and halothane. Voltage-dependent inactivation analysis revealed an unexpected calcium-sensitive process that involved calcineurin. From these results it appears that, besides the two LVA calcium currents previously described, another LVA maintained inward current permeable to both sodium and calcium was also involved in the generation of the predepolarization. Based on these findings, we propose that a novel calcium-dependent mechanism is involved in the regulation of the pacemaker activity.

A neuroendocrine mechanism for sustaining fear

Fear is an adaptive response to recognition of a potentially dangerous event. Glucocorticoids are essential for maintaining a wide variety of behavioral events by their regulation of numerous genes; one such gene encodes corticotrophin-releasing hormone (CRH). CRH is involved in diverse behavioral responses to changing environmental demands. In this review, we focus on one aspect of glucocorticoid regulation of CRH--namely, fear-related responses to diverse classes of adverse events, such as those represented by contextual and cue-specific stimuli. Three extra-hypothalamic forebrain sites appear crucial for fear-related behavioral responses: the amygdala and the bed nucleus of the stria terminalis for sustaining adaptive fear-related behaviors, and the medial prefrontal cortex for modulating fear-related behaviors. Central regulation of CRH by glucocorticoids is important for adaptive and sustained fear-related behaviors, and its aberration is associated with anxiety and depressive disorders.

Phosphatidylinositol 3-kinase C2alpha is essential for ATP-dependent priming of neurosecretory granule exocytosis

Neurotransmitter release and hormonal secretion are highly regulated processes culminating in the calcium-dependent fusion of secretory vesicles with the plasma membrane. Here, we have identified a role for phosphatidylinositol 3-kinase C2alpha (PI3K-C2alpha) and its main catalytic product, PtdIns3P, in regulated exocytosis. In neuroendocrine cells, PI3K-C2alpha is present on a subpopulation of mature secretory granules. Impairment of PI3K-C2alpha function specifically inhibits the ATP-dependent priming phase of exocytosis. Overexpression of wild-type PI3K-C2alpha enhanced secretion, whereas transfection of PC12 cells with a catalytically inactive PI3K-C2alpha mutant or a 2xFYVE domain sequestering PtdIns3P abolished secretion. Based on these results, we propose that production of PtdIns3P by PI3K-C2alpha is required for acquisition of fusion competence in neurosecretion.

Serotonin (5-HT) receptor subtypes mediate specific modes of 5-HT-induced signaling and regulation of neurosecretion in gonadotropin-releasing hormone neurons

Serotonin (5-HT), the endogenous nonselective 5-HT receptor agonist, activates the inositol 1,4,5-triphosphate/calcium (InsP3/Ca2+) signaling pathway and exerts both stimulatory and inhibitory actions on cAMP production and GnRH release in immortalized GnRH neurons. The high degree of similarity between the signaling and secretory responses elicited by GnRH and 5-HT prompted us to target specific 5-HT receptor subtypes to deconvolute the complex actions of these agonists on signal transduction and GnRH release. Specific mRNA transcripts for 5-HT1A, 5-HT2C, 5-HT4, and 5-HT7 were identified in immortalized GnRH neurons (GT1-7). The rate of firing of spontaneous action potentials (APs) by hypothalamic GnRH neurons and cAMP production and pulsatile GnRH release in GT17 cells were profoundly inhibited during activation of the Gi-coupled 5-HT1A receptor. Treatment with a selective agonist to activate the Gq-coupled 5-HT2C receptor increased the rate of firing of spontaneous APs, stimulated InsP3 production and caused a delayed increase in GnRH release. Selective activation of the Gs-coupled 5-HT4 receptor also increased the rate of firing of APs, stimulated cAMP production, and caused a sustained and robust increase in GnRH release. The ability of 5-HT receptor subtypes expressed in GnRH neurons to activate single or multiple G proteins in a time- and dose-dependent manner differentially regulates the phospholipase C/InsP3/Ca2+, and adenylyl cyclase/cAMP signaling pathways, and thereby regulates the frequency and amplitude of pulsatile GnRH release. This process, in conjunction with the modulation of spontaneous electrical activity of the GnRH neuron, contributes to the control of the pulsatile mode of neuropeptide secretion that is characteristic of GnRH neuronal function in vivo and in vitro.

Is hyperosmotic neurosecretion from motor nerve endings a calcium-dependent process?

Spontaneous liberation of neurotransmitter quanta is strongly affected by the osmotic pressure of the extracellular fluid. Elevation of the osmolarity by 20-30% increases the rate of release from motor nerve endings by more than one order of magnitude. In this respect the neuromuscular junction resembles some other secretory systems. The mechanism of this hyperosmotic neurosecretion is not yet understood; extracellular calcium ions are not directly responsible, since this effect can be produced in their absence. Recently, it has been suggested that the liberation of neurotransmitter is regulated by the intracellular concentration of free calcium ions. We have therefore examined the hypothesis that hyperosmotic neurosecretion originates from an increase in internal calcium concentration ([Ca]in). At the frog neuromuscular synapse however, it is impossible at present to estimate directly free [Ca]in; hence we used an indirect technique, which is based on two assumptions; first, the frequency of the miniature endplate potentials (m.e.p.p.s.) reflects free [Ca]in. Second, the movement of calcium ions across the presynaptic membrane is governed by the electrochemical gradient, and by the calcium conductance (g(Ca)). If hyperosmotic neurosecretion is caused by an increase in [Ca]in, then increasing g(Ca), under reversed electrochemical gradient for the calcium should cause a reduction in the effect of hyperosmotic stress on transmitter release. We report that hyperosmotic neurosecretion is dependent on [Ca]in.

Molecular regulation of gonadotropin secretion by gonadotropin-releasing hormone in salmonid fishes

Gonadotropin-releasing hormone (GnRH) plays a central role in the control of reproductive function in vertebrates. In salmonids, salmon GnRH (sGnRH) secreted by preoptic GnRH neurons regulates gonadal maturation through stimulation of synthesis and release of pituitary gonadotropins (GTHs). In addition, several lines of our evidence indicate that sGnRH is involved in spawning behavior, and serves to integrate the gonadal maturation with the reproductive behavior. A growing number of studies show that the effects of GnRH are mediated by multiple subtypes of GnRH receptors, successive multiple signaling pathways, and finally multiple transcription factors which act cooperatively to stimulate transcription of GTH subunit genes. This complex regulatory system of the action of GnRH may serve as a molecular basis of divergent physiological strategies of reproductive success in various vertebrate species. In this article, recent data on the molecular mechanisms of action of GnRH are reviewed with special reference to the regulation of synthesis and release of GTHs in the pituitary of salmonids to elucidate the multifunctional action of GnRH.

Estrogen receptor (ER)-mediated transcriptional regulation of the human corticotropin-releasing hormone-binding protein promoter: differential effects of ERalpha and ERbeta

CRH-binding protein (CRH-BP) regulates activation of the hypothalamic-pituitary-adrenal (HPA) axis by binding and inhibiting CRH. We investigated for the first time transcriptional regulation of the human CRH-BP promoter using transient transfections. Estrogen receptors (ERs) contributed to ligand-independent constitutive activation of the promoter, whereas in the presence of estradiol ERalpha induced and ERbeta repressed promoter activity in a dose-dependent manner. TNFalpha inhibited promoter induction by ERalpha in the absence and presence of estradiol. Three ERE half-sites in the CRH-BP promoter bound ERalpha and ERbeta in an EMSA, and disruption of ERE half-sites by site-directed mutagenesis abolished ligand-independent induction by ERalpha and ERbeta and promoter enhancement by estradiol-activated ERalpha. Repression by estradiol/ERbeta was unaffected by disruption of ERE half-sites, activating protein 1, cAMP response element, GATA, or nuclear factor kappaB sites, and reversed to promoter induction by estrogen antagonists, tamoxifen and ICI 182,780, suggesting corepressor involvement. In hypothalamic GT1-7 cells, Western blotting demonstrated rapid induction of endogenous CRH-BP expression by estradiol-bound ER, which was inhibited by TNFalpha. We propose a model in which ERs maintain basal CRH-BP expression in pituitary and neurosecretory cells, whereas in the presence of ERalpha estrogen enhances CRH-BP transcription, causing down-regulation of the HPA axis, and nuclear factor kappaB-activating cytokines activate the HPA axis by inhibiting ERalpha.

Gonadotropin-Releasing Hormone (GnRH) Receptor Expression and Membrane Signaling in Early Embryonic GnRH Neurons: Role in Pulsatile Neurosecretion

The characteristic pulsatile secretion of GnRH from hypothalamic neurons is dependent on an autocrine interaction between GnRH and its receptors expressed in GnRH-producing neurons. The ontogeny and function of this autoregulatory process were investigated in studies on the properties of GnRH neurons derived from the olfactory placode of the fetal rat. An analysis of immunocytochemically identified, laser-captured fetal rat hypothalamic GnRH neurons, and olfactory placode-derived GnRH neurons identified by differential interference contrast microscopy, demonstrated coexpression of mRNAs encoding GnRH and its type I receptor. Both placode-derived and immortalized GnRH neurons (GT1-7 cells) exhibited spontaneous electrical activity that was stimulated by GnRH agonist treatment. This evoked response, as well as basal neuronal firing, was abolished by treatment with a GnRH antagonist. GnRH stimulation elicited biphasic intracellular calcium ([Ca2+]i) responses, and both basal and GnRH-stimulated [Ca2+]i levels were reduced by antagonist treatment. Perifused cultures released GnRH in a pulsatile manner that was highly dependent on extracellular Ca2+. The amplitude of GnRH pulses was increased by GnRH agonist stimulation and was diminished during GnRH antagonist treatment. These findings demonstrate that expression of GnRH receptor, GnRH-dependent activation of Ca2+ signaling, and autocrine regulation of GnRH release are characteristics of early fetal GnRH neurons and could provide a mechanism for gene expression and regulated GnRH secretion during embryonic migration.

Insulinoma-Associated Protein IA-2, a Vesicle Transmembrane Protein, Genetically Interacts with UNC-31/CAPS and Affects Neurosecretion in Caenorhabditis elegans

IA-2 (insulinoma-associated protein 2), a major autoantigen in type 1 diabetes, is a receptor-tyrosine phosphatase-like protein associated with the membrane of secretory granules of neural and endocrine-specific cells. Loss of IA-2 activity in the mouse results in reduced insulin release and additional phenotypes, consistent with a general effect on neurosecretion and hormone release. To gain further insight into the cellular mechanisms of IA-2 function, we have studied the Caenorhabditis elegans homolog, CeIA-2 encoded by the ida-1 gene. Using two independent putative null alleles of ida-1, we demonstrate that animals lacking CeIA-2 activity are viable and exhibit subtle defects. Genetic studies of mutants in ida-1 and several genes involved in neurosecretory vesicle cargo release and signaling highlight two roles for CeIA-2. First, CeIA-2 has a specific and novel genetic interaction with UNC-31/CAPS, a protein that has been shown in other systems to regulate dense-core vesicle cargo release. Second, loss of CeIA-2 activity enhances weak alleles in the insulin-like signaling pathway. These results suggest that CeIA-2 may be an important factor in dense-core vesicle cargo release with parallels to insulin signaling in mammals.

Mechanism of alpha-latrotoxin action at nerve endings of neurohypophysis

The neurotoxin alpha-latrotoxin elicits spontaneous exocytosis of neurotransmitter from neurons and peptide hormones from endocrine cells. While the mechanism of action is not fully understood, both Ca(2+)-dependent and Ca(2+)-independent pathways participate in the facilitation of release, with the relative contribution of the pathways differing among neuronal and endocrine cell types. Here, we investigate the actions of alpha-latrotoxin on neuroendocrine nerve endings that emanate from central nervous system neurons and, therefore, are unique in that they possess properties of central nerve endings and endocrine cells. Using intracellular [Ca(2+)] measurements both calcium-independent receptors for latrotoxin (CIRL or latrophilin) and neurexin 1 alpha receptors were found to be functionally present. Interaction of alpha-latrotoxin with these receptors stimulated secretion of vasopressin and oxytocin neuropeptide. The secretory response was entirely dependent upon toxin-mediated extracellular Ca(2+) influx, although alpha-latrotoxin also consistently triggered mobilization of Ca(2+) from an intracellular store. The mobilization of intracellular Ca(2+) relied on alpha-latrotoxin-mediated Na(+) influx and was blocked by the protonophore FCCP, thereby implicating mitochondria as the Ca(2+) store being mobilized. Using the whole cell recording configuration of the patch clamp, we report that alpha-latrotoxin interaction with the CIRL receptor on these nerve endings resulted in ionic pore formation, generating unitary inward current steps of 20 pA and a channel conductance of approximately 220 pS in Ca(2+)-free saline. Thus, alpha-latrotoxin stimulates Ca(2+)-dependent exocytosis in neurohypophysial nerve endings through receptor interaction and insertion of Ca(2+) permeable membrane pores. While alpha-latrotoxin mobilizes intracellular Ca(2+) stores the elevation in [Ca(2+)] reached is insufficient to trigger measurable exocytosis.

Secretory Granule Biogenesis and Neuropeptide Sorting to the Regulated Secretory Pathway in Neuroendocrine Cells

Neuropeptide precursors synthesized at the rough endoplasmic reticulum are transported and sorted at the trans-Golgi network (TGN) to the granules of the regulated secretory pathway (RSP) of neuroendocrine cells. They are then processed into active peptides and stored in large dense-core granules (LDCGs) until secreted upon stimulation. We have studied the regulation of biogenesis of the LDCGs and the mechanism by which neuropeptide precursors, such as pro-opiomelanocortin (POMC), are sorted into these LDCGs of the RSP in neuroendocrine and endocrine cells. We provide evidence that chromogranin A (CgA), one of the most abundant acidic glycoproteins ubiquitously present in neuroendocrine/endocrine cells, plays an important role in the regulation of LDCG biogenesis. Specific depletion of CgA expression by antisense RNAs in PC12 cells led to a profound loss of secretory granule formation. Exogenously expressed POMC was neither stored nor secreted in a regulated manner in these CgA-deficient PC12 cells. Overexpression of CgA in a CgA- and LDCG-deficient endocrine cell line, 6T3, restored regulated secretion of transfected POMC and the presence of immunoreactive CgA at the tips of the processes of these cells. Unlike CgA, CgB, another granin protein, could not substitute for the role of CgA in regulating LDCG biogenesis. Thus, we conclude that CgA is a key player in the regulation of the biogenesis of LDCGs in neuroendocrine cells. To examine the mechanism of sorting POMC to the LDCGs, we carried out site-directed mutagenesis, transfected the POMC mutants into PC12 cells, and assayed for regulated secretion. Our previous molecular modeling studies predicted a three-dimensional sorting motif in POMC that can bind to a sorting receptor, membrane carboxypeptidase E (CPE). The sorting signal consists of four conserved residues at the N-terminal loop structure of POMC: two acidic residues and two hydrophobic residues. The two acidic residues were predicted to bind to a domain on CPE (CPE254-273) containing two basic residues (R255 and K260) to effect sorting into immature secretory granules. Site-directed mutagenesis of the motif on POMC resulted in accumulation of the mutant in the Golgi, as well as high basal secretion, indicating that the mutant POMC was inefficiently sorted to the RSP. These results support the model that POMC is actively sorted to the RSP granules for processing and secretion by a sorting signal-mediated mechanism.

Regulation of cyclic adenosine 3',5'-monophosphate signaling and pulsatile neurosecretion by Gi-coupled plasma membrane estrogen receptors in immortalized gonadotropin-releasing hormone neurons

Immortalized GnRH neurons (GT1-7) express receptors for estrogen [estrogen receptor-alpha and -beta(ERalpha and ERbeta)] and progesterone (progesterone receptor A) and exhibit positive immunostaining for both intracellular and plasma membrane ERs. Exposure of GT1-7 cells to picomolar estradiol concentrations for 5-60 min caused rapid, sustained, and dose-dependent inhibition of cAMP production. In contrast, treatment with nanomolar estradiol concentrations for 60 min increased cAMP production. The inhibitory and stimulatory actions of estradiol on cAMP formation were abolished by the ER antagonist, ICI 182,780. The estradiol-induced inhibition of cAMP production was prevented by treatment with pertussis toxin, consistent with coupling of the plasma membrane ER to an inhibitory G protein. Coimmunoprecipitation studies demonstrated an estradiol-regulated stimulatory interaction between ERalpha and Galphai3 that was prevented by the ER antagonist, ICI 182,780. Exposure of perifused GT1-7 cells and hypothalamic neurons to picomolar estradiol levels increased the GnRH peak interval, shortened peak duration, and increased peak amplitude. These findings indicate that occupancy of the plasma membrane-associated ERs expressed in GT1-7 neurons by physiological estradiol levels causes activation of a Gi protein and modulates cAMP signaling and neuropeptide secretion.

Ral-GTPases: approaching their 15 minutes of fame

Andy Warhol, the famous pop artist, once claimed that "in the future everyone will be famous for 15 minutes". The same, it seems, can be said of proteins, because at any given time some proteins become more "fashionable" to study than others. But most proteins have been highly conserved throughout millions of years of evolution, which implies that they all have essential roles in cell biology. Thus, each one will no doubt enter the limelight if the right experiment in the right cell type is done. A good example of this is the Ras-like GTPases (Ral-GTPases), which until recently existed in the shadow of their close cousins--the Ras proto-oncogenes. Recent studies have yielded insights into previously unappreciated roles for Ral-GTPases in intensively investigated disciplines such as vesicle trafficking, cell morphology, transcription and possibly even human oncogenesis.

Contributions of insect research toward our understanding of neurosecretion

The process of neurosecretion is an important and widespread method of biological communication among animals. Although insects and vertebrates appear to be very different, neurosecretory mechanisms and the neuropeptides themselves are often the same. The gradual acceptance of neurosecretion as a biological phenomenon, largely as a result of research done with insects, is discussed.

Neuroendocrine facets of human puberty

The unfolding of pubertal growth and maturation entails multisystem collaboration. Most notably, the outflow of gonadotropins and growth hormone (GH) proceeds both independently and jointly. The current update highlights this unique dependency in the human.

Neuroendocrine stress response in patients undergoing benign ovarian cyst surgery by laparoscopy, minilaparotomy, and laparotomy

STUDY OBJECTIVE

To quantify and compare neuroendocrine stress responses during and immediately after surgery by laparoscopy, minilaparotomy, and laparotomy for benign ovarian cysts.

DESIGN

Prospective study (Canadian Task Force classification II-1).

SETTING

Tertiary care university hospital.

PATIENTS

Thirty healthy women with no major diseases and without endocrine disorders.

INTERVENTIONS

Surgery for benign ovarian cysts performed by laparoscopy (10), minilaparotomy (10), or laparotomy (10).

MEASUREMENTS AND MAIN RESULTS

Venous blood samples were collected at fixed times as follows: at 8 A.M. in the ward before transferring the patient to the operating room (time 0), 30 minutes after the beginning of surgery (time 1), at the end of surgery after extubation with the patient awake (time 2), and 2 and 4 hours after the end of surgery (times 3 and 4). We evaluated intraoperative and postoperative variations of the following stress-related markers: norepinephrine (NE), epinephrine (E), adrenocorticotropic hormone (ACTH), human growth hormone (hGH), prolactin (PRL), and cortisol, and postoperative pain. No differences were present in demographic characteristics and operating times in the three groups. No anesthesiologic or surgical complications occurred. Postoperative pain was similar in the laparoscopy and minilaparotomy group but significantly higher in the laparotomy group (p <0.001). Serum levels of markers were not significantly different among the groups at baseline. In the laparoscopy group the increase of hGH was limited to intraoperative time (p <0.05); increases in NE, E, ACTH, and PRL were limited to intraoperative and early postoperative time after extubation (p <0.01), with only PRL persisting with significantly higher levels after the end of surgery (p <0.05). In the minilaparotomy group no increase was detected for hGH, a significant intraoperative increase in cortisol was present (p <0.05), and NE, E, ACTH, and PRL were significantly higher even after the end of surgery (p <0.01). In this group levels of NE, E, and hGH were significantly higher than in the laparoscopy group 2 and 4 hours after the end of surgery (p <0.05). In the laparotomy group significant intraoperative increases were present for all stress markers and persisted until after extubation for ACTH (p <0.01) and to the postoperative period for NE (p <0.01), E (p <0.01), cortisol (p <0.01), PRL (p <0.05), and hGH (p <0.01). In this group levels of NE, E, ACTH, and hGH were significantly higher than those in the laparoscopy group from the beginning (NE p <0.05, E p <0.01, ACTH p <0.05, hGH p <0.01) until after the end of surgery. Comparison of laparotomy and minilaparotomy groups showed the former to have significantly higher plasma levels of E, cortisol, and hGH in intraoperative and postoperative times (p <0.001); significantly higher NE at sampling times 1 and 2 (p <0.001) and time 4 (p <0.01), and no difference at sampling time 3; and ACTH significantly higher only during surgery (p <0.01).

CONCLUSION

Laparoscopic surgery causes minimal activation of stress hormones, which in some instances is confined to the intraoperative period. Minilaparotomy may be a valid alternative to laparoscopy in high-risk patients who cannot tolerate abdominal distention.

Calcium requirements for exocytosis do not delimit the releasable neuropeptide pool

Recently, it was proposed that secretory vesicles have widely varying Ca(2+) thresholds for exocytosis. This model can explain adaptation of secretory responses and predicts that incomplete release is a consequence of insufficient Ca(2+). However, membrane capacitance-based measurements have not supported varying Ca(2+) thresholds. Here, Green Fluorescent Protein (GFP) imaging is used to test whether a Ca(2+) limitation determines the size of the releasable neuropeptide pool in differentiated PC12 cells. We show that depolarization-evoked release correlates with failure to sustain fully elevated [Ca(2+)](i). However, this is coincidental because release remains incomplete when [Ca(2+)](i) is maintained at a relatively high level by application of an ionophore or by dialysis with a buffered Ca(2+) solution. Furthermore, in contradiction with the existence of high threshold vesicles, stimulating maximal release with moderate [Ca(2+)](i) prevents secretory responses to large increases in [Ca(2+)](i) induced by photolysis of the caged dimethoxynitrophenyl-EGTA-4 (DMNPE-4). Thus, optical measurements show that limited capacity for neuropeptide release in response to depolarization is not caused by an insufficient duration of [Ca(2+)](i) elevation or by variation among vesicles in Ca(2+) sensitivity for exocytosis.

Cystic fibrosis transmembrane conductance regulator modulates neurosecretory function in pulmonary neuroendocrine cell-related tumor cell line models

The pulmonary neuroendocrine cell (PNEC) system consists of solitary cells and distinctive cell clusters termed neuroepithelial bodies (NEB) localized in the airway epithelium. PNEC/NEB express a variety of bioactive substances, including amine (serotonin, 5HT) and neuropeptides. We have previously shown that NEB cells are O(2) sensors expressing nicotinamide adenine diphosphate oxidase complex and O(2) sensitive K(+) channel. Recently, we demonstrated expression of functional cystic fibrosis transmembrane conductance regulator (CFTR) and Cl(-) conductances in NEB cells of rabbit neonatal lung. Because PNEC/NEB are sparsely distributed and difficult to study in native lung, we investigated small-cell lung carcinoma (SCLC) and carcinoid tumor cell lines (tumor counterparts of normal PNEC/NEB) as models for PNEC/NEB. SCLC (H146, H345) and carcinoid (H727) cell lines express neuroendocrine cell markers, including chromogranin A, neural cell adhesion molecule (N-CAM), 5HT, and tryptophan hydroxylase. We report that H146, H345, and H727 express CFTR messenger RNA (reverse transcription polymerase chain reaction) and protein (immunoblotting) and possess functional CFTR Cl(-) conductance, demonstrated by an iodide efflux assay inhibitable by transfection with antisense CFTR. Using an immunoassay to quantitate 5HT secretion, we also show that downregulation of CFTR abolishes hypoxia-induced 5HT release, and reduces secretory response to high potassium. Our findings suggest that CFTR may modulate neurosecretory activity of PNEC/NEB possessing O(2) sensor function. We propose that these tumor cell lines may be useful models for investigating the role of CFTR in PNEC/NEB functions in health and disease.

Calmodulin increases transmitter release by mobilizing quanta at the frog motor nerve terminal

The role of calmodulin (CaM) in transmitter release was investigated using liposomes to deliver CaM and monoclonal antibodies against CaM (antiCaM) directly into the frog motor nerve terminal. Miniature endplate potentials (MEPPs) were recorded in a high K+ solution, and effects on transmitter release were monitored using estimates of the quantal release parameters m (number of quanta released), n (number of functional transmitter release sites), p (mean probability of release), and var(s) p (spatial variance in p). Administration of CaM, but not heat-inactivated CaM, encapsulated in liposomes (1000 units ml(-1)) produced an increase in m (25%) that was due to an increase in n. MEPP amplitude was not altered by CaM. Administration of antiCaM, but not heat-inactivated antiCaM, in liposomes (50 microl ml(-1)) produced a progressive decrease in m (40%) that was associated with decreases in n and p. MEPP amplitude was decreased (15%) after a 25 min lag time, suggesting a separation in time between the decreases in quantal release and quantal size. Bath application of the membrane-permeable CaM antagonist W7 (28 microM) produced a gradual decrease in m (25%) that was associated with a decrease in n. W7 also produced a decrease in MEPP amplitude that paralleled the decrease in m. The decreases in MEPP size and m produced by W7 were both reversed by addition of CaM. Our results suggest that CaM increases transmitter release by mobilizing synaptic vesicles at the frog motor nerve terminal.

Naturally occurring free D-aspartate is a nuclear component of cells in the mammalian hypothalamo-neurohypophyseal system

It is generally believed that only L-amino acids have a physiological role in species other than bacteria. Recently, the existence of some D-amino acids, particularly D-aspartate, in various organs of several higher animals has been reported. Here we demonstrate that naturally occurring free D-aspartate is localized subcellularly to the heterochromatin in the nucleoli (but not in either the dendrites or axonal terminals) of magnocellular neurosecretory neurons in the rat hypothalamus, and also of microglia and pericytes in the posterior pituitary. Our results imply that naturally occurring free D-aspartate might have a physiological role in nuclear function in mammals. The findings provide new insight for the biological function of D-stereoisomers of amino acids as well as the organization of the nucleus of at least some eukaryotic cells.

Beacon-like immunoreactivity in the hypothalamus of Sprague-Dawley rats

Distribution of the novel peptide beacon in the hypothalamus of Sprague-Dawley rats was examined by immunohistochemical methods. Beacon-immunoreactive (irBC) neurons were found in the paraventricular, supraoptic, and accessory neurosecretory nuclei, and intensely labeled fibers in the median eminence and infundibulo-pituitary stalk. Scattered cells and/or fibers were noted in the suprachiasmatic nucleus, arcuate nucleus, retrochiasmatic area, lateral and medial preoptic area, as well as anterior and lateral hypothalamic area. The wide distribution of irBC in the hypothalamus of Sprague-Dawley rats suggests that the peptide may influence, in addition to a proposed role in feeding, a multitude of biological activities associated with the hypothalamic-pituitary axis.

Effects of radiation damage on intestinal morphology

The current flow of papers on intestinal structure, radiation science, and intestinal radiation response is reflected in the contents of this review. Multiparameter findings and changes in compartments, cells, or subcellular structure all contribute to the overall profile of the response. The well-recognized changes in proliferation, vessels, and fibrogenesis are accompanied by alterations in other compartments, such as neuroendocrine or immune components of the intestinal wall. The responses at the molecular level, such as in levels of hormones, cytokines, or neurotransmitters, are of fundamental importance. The intestine responds to localized radiation, or to changes in other organs that influence its structure or function: some structural parameters respond differently to different radiation schedules. Apart from radiation conditions, factors affecting the outcome include the pathophysiology of the irradiated subject and accompanying treatment or intervention. More progress in understanding the overall responses is expected in the next few years.

Oxytocin mediates the inhibitory action of acute lithium on the morphine dependence in rats

The role of central oxytocin in inhibitory action of lithium on the development of morphine dependence was behavioral investigated in rats. Acute lithium could enhance the morphine-induced analgesia in rats with or without chronic morphine treatment; this effect could be inhibited by intraventricular injection of oxytocin antagonist d (CH(2))(5)-Tyr (Me)-[Orn(8)]-Vasotocin (OVT). Lithium could attenuate naloxone-precipitated withdrawal signs in morphine dependent rats. The reduction of the expression of naloxone-precipitated withdrawal signs by lithium was reversed by ICV of OVT. The lithium significantly inhibited the conditioned place preference (CPP) induced by morphine, which inhibitory action of lithium could also reverse by ICV injection of OVT. These results suggested that lithium might inhibit the physical dependence on morphine as well as psychological dependence in rats, and that this inhibitory effect of lithium on the development of morphine dependence might be associated with oxytocin systems in the central nervous system.

Postnatal development of catecholamine inputs to the paraventricular nucleus of the hypothalamus in rats

Adrenergic and noradrenergic neural projections to the paraventricular nucleus of the hypothalamus (PVN) contribute importantly to viscerosensory modulation of pituitary hormone secretion. Immaturity of ascending catecholamine pathways may partially underlie the documented hyporesponsiveness of PVN neurosecretory cells to certain interoceptive stimuli in rats during the first few weeks of postnatal development. To explore this possibility, the present study compared the distribution and number of dopamine-beta-hydroxylase (DBH)- and phenylethanolamine-N-methyltransferase (PNMT)-positive neurons projecting to the PVN in newborn and adult rats. In addition, a quantitative analysis of DBH- and PNMT-immunoreactive fibers in the medial parvocellular subnucleus, dorsal division (PVNmpd) and posterior magnocellular subnucleus, lateral division (PVNpml) was performed in adult rats and in developing rats on postnatal day (P)1, P7, P14, and P21. The numbers of PVN-projecting neurons in the A1, C1, A2/C2, C3, or A6 catecholamine cell groups were similar in newborn and adult rats, as were the proportions of PVN-projecting neurons in each region that were PNMT-positive. However, fewer PVN-projecting neurons in the C1 and C3 regions expressed DBH immunolabeling in newborn rats compared to adults. DBH immunolabeling increased progressively in the PVNmpd and PVNpml between postnatal days P1 and P21, when adult-like levels were achieved. Conversely, PNMT immunolabeling in the same PVN subdivisions was most dense at P1, gradually decreasing to adult-like levels by P21. These dynamic developmental changes in catecholamine synthetic enzyme immunolabeling densities in the PVN may reflect functional changes in noradrenergic and adrenergic signaling capacity in rats during the first few weeks of postnatal development.