Localization of vasopressin mRNA and immunoreactivity in pituicytes of pituitary stalk-transected rats after osmotic stimulation

Classification of Large Cellular Populations and Discovery of Rare Cells Using Single Cell Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Cell-to-cell variability and functional heterogeneity are integral features of multicellular organisms. Chemical classification of cells into cell type is important for understanding cellular specialization as well as organismal function and organization. Assays to elucidate these chemical variations are best performed with single cell samples because tissue homogenates average the biochemical composition of many different cells and oftentimes include extracellular components. Several single cell microanalysis techniques have been developed but tend to be low throughput or require preselection of molecular probes that limit the information obtained. Mass spectrometry (MS) is an untargeted, multiplexed, and sensitive analytical method that is well-suited for studying chemically complex individual cells that have low analyte content. In this work, populations of cells from the rat pituitary, the rat pancreatic islets of Langerhans, and from the Aplysia californica nervous system, are classified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI) MS by their peptide content. Cells were dispersed onto a microscope slide to generate a sample where hundreds to thousands of cells were separately located. Optical imaging was used to determine the cell coordinates on the slide, and these locations were used to automate the MS measurements to targeted cells. Principal component analysis was used to classify cellular subpopulations. The method was modified to focus on the signals described by the lower principal components to explore rare cells having a unique peptide content. This approach efficiently uncovers and classifies cellular subtypes as well as discovers rare cells from large cellular populations.

Application of NeuroTrace staining in the fresh frozen brain samples to laser microdissection combined with quantitative RT-PCR analysis

Background

The heterogeneity of the brain requires appropriate molecular biological approaches to account for its morphological complexity. Laser-assisted microdissection followed by transcript profiling by quantitative determination has been reported to be an optimal methodology. Nevertheless, not all brain regions can be identified easily without staining, restricting the accuracy and efficiency in sampling. The aim of the present study was to validate whether fixation and staining treatments are suitable for quantitative transcript expression analysis in laser microdissection (LMD) samples. Quantitative RT-PCR was used to determine the absolute transcript expression levels and profiles of samples obtained from the hippocampal dentate gyrus from fresh frozen mice brain sections that had been fixed with ethanol and stained with NeuroTrace. The results were compared with those obtained from unfixed and unstained samples.

Results

We found that the quantitative relationship of transcript expression levels between various housekeeping genes and immediate early genes was preserved, although the preparation compromised the yield of the transcripts. In addition, histological and molecular integrities of the fixed and stained specimens were preserved for at least a week at room temperature. Based on the lobe specific profiles of transcripts in the anterior and posterior lobes of the pituitary, we confirmed that no cross-contamination on transcription expressions occurred as a result of the fixation and staining.

Conclusions

We have provided detailed information of the procedures on ethanol fixation followed by NeuroTrace staining on the absolute quantitative RT-PCR analysis using microdissected fresh frozen mouse brain tissues. The present study demonstrated that quantitative transcript expression analysis can be conducted reliably on stained tissues. This method is suitable for applications in basic and clinical studies on particular transcript expressions in various regions of the brain.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1222-9) contains supplementary material, which is available to authorized users.

Effects of galanin-monoaminergic interactions on vasopressin secretion in rat neurohypophyseal cell cultures

The effects of dopamine (DA), serotonin (5-HT), histamine (HA), adrenaline (ADR), noradrenaline (NADR) and K(+) administration on vasopressin (VP) secretion were studied in 13-14-day cultures of rat neurohypophyseal (NH) cells, and it was examined whether galanin (GAL) can modify the VP release enhancement induced by these monoaminergic compounds. An enzymatic dissociation technique was used to make the rat NH cell cultures. The VP contents of the supernatants of 14-day cultures were determined by radioimmunoassay. Following the administration of 10(-6) M GAL, the VP secretion into the supernatant media decreased. DA, 5-HT, ADR or NADR treatment increased the VP level substantially, while the enhancing effect of HA was more moderate. GAL administration before DA, ADR and NADR treatment prevented the VP concentration increase induced by DA, ADR or NADR. Preincubation with GAL reduced the 5-HT- or HA-induced VP level increases; the VP concentrations of the supernatant media remained above the control level. The GAL blocking effect was prevented by previous treatment with the GAL receptor antagonist galantid (M15). GAL had no effect on the VP level increase induced by K(+), which causes a non-specific hormone secretion. The results indicate that the changes in VP secretion induced by the monoaminergic system can be directly influenced by the GAL-ergic system. The interactions between the monoaminergic and GAL-ergic systems regarding VP secretion occur at the level of the posterior pituitary.

Dehydration-induced proteome changes in the rat hypothalamo-neurohypophyseal system

The hypothalamo-neurohypophyseal system (HNS) mediates neuroendocrine responses to dehydration through the action of the antidiuretic hormone vasopressin (VP). VP is synthesized as part of a prepropeptide in magnocellular neurons of the hypothalamic supraoptic nucleus (SON) and paraventricular nucleus. This precursor is processed during transport to axon terminals in the posterior pituitary gland, in which biologically active VP is stored until mobilized for secretion by electrical activity evoked by osmotic cues. During release, VP travels through the blood stream to specific receptor targets located in the kidney in which it increases the permeability of the collecting ducts to water, reducing the renal excretion of water, thus promoting water conservation. The HNS undergoes a dramatic function-related plasticity during dehydration. We hypothesize that alterations in steady-state protein levels might be partially responsible for this remodeling. We investigated dehydration-induced changes in the SON and pituitary neurointermediate lobe (NIL) proteomes using two-dimensional fluorescence difference gel electrophoresis. Seventy proteins were altered by dehydration, including 45 in the NIL and 25 in the SON. Using matrix-assisted laser desorption/ionization mass spectrometry, we identified six proteins in the NIL (four down, two up) and nine proteins in the SON (four up, five down) that are regulated as a consequence of chronic dehydration. Results for five of these proteins, namely Hsp1alpha (heat shock protein 1alpha), NAP22 (neuronal axonal membrane protein 22), GRP58 (58 kDa glucose regulated protein), calretinin, and ProSAAS (proprotein convertase subtilisin/kexin type 1 inhibitor), have been confirmed using independent methods such as semiquantitative Western blotting, two-dimensional Western blotting, enzyme-linked immunoassay, and immunohistochemistry. These proteins may have roles in regulating and effecting HNS remodeling.

Galanin-like peptide mRNA alterations in arcuate nucleus and neural lobe of streptozotocin-diabetic and obese zucker rats. Further evidence for leptin-dependent and independent regulation

Galanin-like peptide (GALP) is a 60-amino-acid peptide with structural similarities to galanin and a high affinity for galanin receptors. GALP is expressed by a discrete population of neurons in the arcuate nucleus (ARC) and median eminence of the hypothalamus of several species, including the rat. GALP neurons express leptin receptors and GALP mRNA levels are decreased slightly in fasted rats and stimulated significantly by acute leptin treatment in combination with fasting. In studies to further explore the leptin dependence of GALP expression, we examined GALP mRNA levels in the hypothalamus of obese Zucker and streptozotocin-induced diabetic (STZ-DM) rats. In leptin receptor-deficient obese Zucker rats, with 75% higher body weight than lean littermates, GALP mRNA levels in the ARC were decreased by 75%, while neuropeptide Y (NPY) mRNA levels were increased 7-fold (n = 5, p < 0.001), consistent with earlier reports. In hypoleptinemic diabetic rats with 4.5-fold higher blood glucose and 15% lower body weight than controls, GALP mRNA levels in the ARC were decreased by 90%, while NPY mRNA levels were increased 9-fold (n = 5, p < 0.001). GALP is also expressed by pituicytes in the neural lobe of the rat pituitary gland and GALP expression is increased by osmotic stimulation such as dehydration and salt loading. Thus, in STZ-DM rats that are in a hyperosmotic state with elevated plasma vasopressin levels, GALP mRNA levels were increased by approximately 20-fold in the neural lobe relative to control (n = 4, p < 0.001). The current findings are consistent with a strong tonic influence of leptin receptor signalling on hypothalamic GALP expression under normal conditions, and possible abnormalities in GALP neuronal signalling and their putative targets, thyrotropin-releasing hormone and gonadotropin hormone-releasing hormone neurons, under pathophysiological conditions such as diabetes and obesity. Our data in STZ-DM rats also clearly demonstrate that GALP gene expression is differentially regulated in neurons and pituicytes.

Vasopressin-induced taurine efflux from rat pituicytes: a potential negative feedback for hormone secretion

Previous work on the whole neurohypophysis has shown that hypotonic conditions increase release of taurine from neurohypophysial astrocytes (pituicytes). The present work confirms that taurine is present in cultured pituicytes, and that its specific release increases in response to a hypotonic shock. We next show that vasopressin (VP) and oxytocin (OT) also specifically release taurine from pituicytes. With an EC(50) of approximately 2 nm, VP is much more potent than OT, and the effects of both hormones are blocked by SR 49059, a V(1a) receptor antagonist. This pharmacological profile matches the one for VP- and OT-evoked calcium signals in pituicytes, consistent with the fact that VP-induced taurine efflux is blocked by BAPTA-AM. However, BAPTA-AM also blocks the taurine efflux induced by a 270 mosmol l(-1) challenge, which per se does not evoke any calcium signal, suggesting a permissive role for calcium in this case. Nevertheless, the fact that structurally unrelated calcium-mobilizing agents and ionomycin are able to induce taurine efflux suggests that calcium may also play a signalling role in this event. It is widely accepted that in hypotonic conditions taurine exits cells through anionic channels. Antagonism by the chloride channel inhibitors 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) suggests the same pathway for VP-induced taurine efflux, which is also blocked in hypertonic conditions (330 mosmol l(-1)). Moreover, it is likely that the osmosensitivity of the taurine channel is up-regulated by calcium. These results, together with our in situ experiments showing stimulation of taurine release by endogenous VP, strengthen the concept of a glial control of neurohormone output.

In vivo gene transfer studies on the regulation and function of the vasopressin and oxytocin genes

Novel genes can be introduced into the germline of rats and mice by microinjecting fertilized one-cell eggs with fragments of cloned DNA. A gene sequence can thus be studied within the physiological integrity of the resulting transgenic animals, without any prior knowledge of its regulation and function. These technologies have been used to elucidate the mechanisms by which the expression of the two genes in the locus that codes for the neuropeptides vasopressin and oxytocin is confined to, and regulated physiologically within, specific groups of neurones in the hypothalamus. A number of groups have described transgenes, derived from racine, murine and bovine sources, in both rat and mouse hosts, that mimic the appropriate expression of the endogenous vasopressin and genes in magnocellular neurones (MCNs) of the supraoptic and paraventricular nuclei. However, despite considerable effort, a full description of the cis-acting sequences mediating the regulation of the vasopressin-oxytocin locus remains elusive. Two general conclusions have nonetheless been reached. First, that the proximal promoters of both genes are unable to confer any cell-specific regulatory controls. Second, that sequences downstream of the promoter, within the structural gene and/or the intergenic region that separates the two genes, are crucial for appropriate expression. Despite these limitations, sufficient knowledge has been garnered to specifically direct the expression of reporter genes to vasopressin and oxytocin MCNs. Further, it has been shown that reporter proteins can be directed to the regulated secretory pathway, from where they are subject to appropriate physiological release. The use of MCN expression vectors will thus enable the study of the physiology of these neurones through the targeted expression of biologically active molecules. However, the germline transgenic approach has a number of limitations involving the interpretation of phenotypes, as well as the large cost, labour and time demands. High-throughput somatic gene transfer techniques, principally involving the stereotaxic injection of hypothalamic neuronal groups with replication-deficient adenoviral vectors, are now being developed that obviate these difficulties, and which enable the robust, long-lasting expression of biologically active proteins in vasopressin and oxytocin MCNs.

Inhibitory effect of galanin on dopamine-induced enhanced vasopressin secretion in rat neurohypophyseal tissue cultures

The effect of galanin (GAL) on vasopressin (VP) secretion was studied in 13-14-day cultures of isolated rat neurohypophyseal (NH) tissue. The VP content of the supernatant was determined by radioimmunoassay (RIA) after a 1- or 2-h incubation. A significantly decreased content of VP was detected following the administration of 10(-6)-10(-9) M doses of GAL. Dopamine (DA) and the DA-active drugs apomorphine (APM) and Pro-Lys-Gly (PLG) (10(-6) M in each medium) increased the VP level of NH tissue cultures. This VP concentration elevation could be blocked by the administration of GAL together with DA, APM or PLG. The DA-blocking effect of GAL was prevented by previous treatment with the GAL receptor antagonist galantid (M15). The results indicate that VP release is directly influenced by the GAL-ergic system. The GAL-ergic control of VP secretion from NH tissue in rats can occur independently of the hypothalamus, at the level of the posterior pituitary.

Mechanism of AVP release and synthesis in chronic salt-loaded rats

Arginine vasopressin (AVP) is involved in osmotic regulation in the brain and peripheral tissues. To elucidate the regulatory mechanism that involves AVP release in hyperosmolality, we investigated the regulation of the synthesis and release of AVP in chronic salt-loaded rats. In chronic salt-loaded rats, which were generated by free access to water containing 2% NaCl for 7 days, plasma osmolality was significantly increased compared with control value. When tested, the AVP content was significantly higher in plasma but lower in the pituitary and whole brain (hypothalamus, cortex and striatum) than in control rats. The expression of AVP mRNA in the brain was significantly up-regulated compared with that in control rats. These data lead to the suggestion that hyperosmolality stimulates AVP release from the brain and subsequently induces AVP synthesis in the brain. On the other hand, mRNA levels of vasopressin V1a receptor (V1aR), whose down-regulation is known to be a counteraction to the V1aR activation, was not changed in the brain, suggesting that the AVP seems not to interact with the V1aR in the brain. These results suggest that hyperosmosis promotes the release of AVP into plasma, the subsequent induction of AVP mRNA in the brain and its action on the peripheral tissues.

Hypothalamic pituitary adrenal axis and hypothalamic-neurohypophyseal responsiveness in water-deprived rats

The differential effects of osmotic stimulation on magnocellular and parvocellular hypothalamic neurons were studied by analysis of corticotropin-releasing hormone (CRH) and vasopressin (VP) expression in controls and 48-h water-deprived rats subjected to either restraint for 1 h or a single lipopolysaccharide injection (250 microg/100 g). Water deprivation reduced basal CRH mRNA levels but the increments following 4 h of restraint or 6 h lipopolysaccharide (LPS) injection were similar to those in controls. In contrast, water deprivation had no effect on basal VP heteronuclear RNA (hnRNA) and mRNA levels in parvocellular neurons, but responses to restraint or LPS injection were reduced. VP expression in magnocellular paraventricular and supraoptic nuclei, and plasma sodium and vasopressin were higher in water-deprived rats, changes which were unaffected by restraint. LPS injection reduced VP mRNA but not hnRNA levels in magnocellular neurons and increased plasma vasopressin levels only in water-deprived rats independently of changes in plasma sodium. This was accompanied by an increase in vasopressin mRNA content in the posterior pituitary. The data show that the blunted ACTH responses to acute stress during chronic osmotic stimulation are correlated with the inability of parvocellular neurons to increase VP rather than CRH expression. In addition, LPS-induced endotoxemia causes disturbances of the magnocellular vasopressinergic system with an unexpected potentiation of osmotic simulated VP secretion. The lack of increase in VP transcription after LPS and changes in VP mRNA distribution suggest that endotoxemia affect the secretory process at the levels of the neurohypophyseal axon terminal.

Gene regulation in the magnocellular hypothalamo-neurohypophysial system

The hypothalamo-neurohypophysial system (HNS) is the major peptidergic neurosecretory system through which the brain controls peripheral physiology. The hormones vasopressin and oxytocin released from the HNS at the neurohypophysis serve homeostatic functions of water balance and reproduction. From a physiological viewpoint, the core question on the HNS has always been, "How is the rate of hormone production controlled?" Despite a clear description of the physiology, anatomy, cell biology, and biochemistry of the HNS gained over the last 100 years, this question has remained largely unanswered. However, recently, significant progress has been made through studies of gene identity and gene expression in the magnocellular neurons (MCNs) that constitute the HNS. These are keys to mechanisms and events that exist in the HNS. This review is an inventory of what we know about genes expressed in the HNS, about the regulation of their expression in response to physiological stimuli, and about their function. Genes relevant to the central question include receptors and signal transduction components that receive and process the message that the organism is in demand of a neurohypophysial hormone. The key players in gene regulatory events, the transcription factors, deserve special attention. They do not only control rates of hormone production at the level of the gene, but also determine the molecular make-up of the cell essential for appropriate development and physiological functioning. Finally, the HNS neurons are equipped with a machinery to produce and secrete hormones in a regulated manner. With the availability of several gene transfer approaches applicable to the HNS, it is anticipated that new insights will be obtained on how the HNS is able to respond to the physiological demands for its hormones.

Effects of dopamine and dopamine-active compounds on oxytocin and vasopressin production in rat neurohypophyseal tissue cultures

The effects of dopamine (DA) or DA-active drugs on the synthesis of neurohypophyseal (NH) hormones were studied in 13-14 day cultures of isolated NH tissue from rats. The following DA-active compounds were used (10(-6) M in each medium): DA, apomorphine (APM), Pro-Lys-Gly (PLG), butaclamol (B), haloperidol (HP), chlorpromazine (CPZ) and sulpiride (SP). The oxytocin (OT) and vasopressin (VP) contents of the condensed media were determined by RIA after a 1 or 2 h incubation. Significantly increased contents of OT and VP were detected in the tissue culture media following DA, APM or PLG administration. This elevation of NH hormone production could be blocked by previous administration of B or the DA receptor antagonists HP, CPZ or SP. The application of B after DA agonists proved ineffective. The results indicate that NH hormone production can be directly influenced by the DA-ergic system. The DA-ergic control of NH hormone secretion in rats can occur independently of the hypothalamus, at the level of the posterior pituitary.

Transgenic studies in rats and mice on the osmotic regulation of vasopressin gene expression

Over the past 10-15 years, profoundly important transgenic techniques have been developed that enable new genes to be introduced into whole mammalian organisms. This review describes the ways in which transgenic animals, both rats and mice, have been used to study the mechanisms by which the expression of the vasopressin gene is confined to specific neurones in the hypothalamus, and how the pattern of that expression is altered following an osmotic challenge to the organism.

Astroglial modulation of neurotransmitter/peptide release from the neurohypophysis: present status

Reviewed in this article are those studies that have contributed heavily to our current conceptualizations of glial participation in the functioning of the magnocellular hypothalamo-neurohypophysial system. This system undergoes remarkable morphological and functional reorganization induced by increased demand for peptide synthesis and release, and this reorganization involves the astrocytic elements in primary roles. Under basal conditions, these glia appear to be vested with the responsibility of controlling the neuronal microenvironment in ways that reduce neuronal excitability, restrict access to neuronal membranes by neuroactive substances and deter neuron neuron interactions within the system. With physiological activation, the glial elements, via receptor-mediated mechanisms, take up new positions. This permissively facilitates neuron neuron interactions such as the exposure of neuronal membranes to released peptides and the formation of gap junctions and new synapses, enhances and prolongs the actions of those excitatory neurotransmitters for which there are glial uptake mechanisms, and facilitates the entry of peptides into the blood. In addition, subpopulations of these glia either newly synthesize or increase synthesis of neuroactive peptides for which their neuronal neighbors have receptors. Release of these peptides by the glia or their functional roles in the system have not yet been demonstrated.

Vasopressin gene expression in rat choroid plexus

Vasopressin (VP) levels in cerebrospinal fluid (CSF) change in response to physiological stimuli and under various pathological conditions. The sources of CSF VP have yet to be clarified, however. In the present study, we provide evidence indicating that VP is synthesized in the choroid plexus, the primary site of CSF formation. All experiments were performed on adult male Sprague-Dawley rats. The presence of VP mRNA in choroid plexus epithelium was demonstrated by in situ hybridization histochemistry using the 35S-labeled riboprobe that was complementary to cDNA fragment of rat VP encoding the C-terminus part of proVP. In situ hybridization findings were confirmed by reverse transcriptase-polymerase chain reaction analysis. Immunohistochemistry for VP-associated neurophysin (VP-NP), a polypeptide component of proVP, revealed subapical accumulation of VP-NP-immunopositive product in choroidal epithelial cells. Immunoprecipitation and immunoblotting of choroidal protein extracts with anti-VP-NP antibody demonstrated the presence of a approximately 10-kD polypeptide that was also detected in hypothalamus. We hypothesize that the choroid plexus-derived VP exerts autocrine and/or paracrine effects on tissues near the CSF system.

Hyperosmolarity-induced gene stimulation is mediated by the negative calcium responsive element

The negative calcium responsive elements of the parathyroid hormone gene bind to a specific set of nuclear proteins in an extracellular calcium (Ca2+e)-dependent manner. We have found that one of the negative calcium responsive elements, named oligo B, is found in the 5'-flanking region of such vasoactive genes as the vasopressin and atrial natriuretic polypeptide genes. Furthermore, the oligo B-like sequence in the former gene is conserved throughout evolution. Because expression of some of these vasoactive genes is altered by external stimuli which change cell volume, we examined whether oligo B is involved in gene regulation by hyperosmolarity. Here, we demonstrate that the binding between oligo B and its binding nuclear proteins including a redox factor 1 was reduced by hyperosmolarity generated by sodium chloride but not by urea. Such attenuated binding was reversed by dephosphorylating nuclear proteins by a potato acid phosphatase, suggesting that NaCl treatment elicited phosphorylation of these nuclear proteins to weaken their binding activity to oligo B. Furthermore, these nuclear events led to hyperosmolarity-mediated transcriptional stimulation of the genes bearing this DNA element in the cultured cells.

The presence of arginine vasopressin and its mRNA in rat choroid plexus epithelium

Arginine vasopressin (AVP) plays an important role in the regulation of secretory function and hemodynamics of choroid plexus, the primary site of cerebrospinal fluid (CSF) production. In the present study, localization of AVP and its transcripts in choroid plexus of adult male Sprague-Dawley rats was studied by immunohistochemistry and in situ hybridization histochemistry, respectively. For immunohistochemical analysis, AVP-specific polyclonal rabbit antibody was employed. Plasmid, pGrVP, containing a 232-bp fragment of rat AVP cDNA encoding the C-terminus of proAVP, was used as a probe to detect AVP mRNA. AVP-immunoreactive product was predominantly localized close to the apical (CSF-facing) membrane of choroidal epithelium while AVP transcripts were distributed throughout the cytoplasm of the cells. Our findings indicate that AVP is synthesized in choroid plexus epithelium, which suggests autocrine and/or paracrine actions of this peptide in choroidal tissue.

RNAs encoded by a 3.5-kb bovine vasopressin gene construct are targeted to the neurohypophysis of transgenic mice

Recent studies have established that the RNA coding for the neuropeptide arginine-vasopressin (AVP) is expressed in the neurohypophyseal compartment of the hypothalamo-neurohypophyseal system. In order to determine the molecular mechanisms that direct this novel expression pattern we have now investigated whether an AVP transgene is similarly regulated. Using a reverse transcriptase-polymerase chain reaction (RT-PCR) approach that permits simultaneous analysis of both endogenous and transgene RNA levels, we have demonstrated that RNA derived from a 3.5-kb bovine vasopressin transgene is expressed in the neurohypophysis of transgenic mice, and is up-regulated by a physiological stimulus (salt-loading) in a similar manner to mouse AVP RNA. Sequences conserved between this region of the murine and bovine AVP genes are therefore sufficient to mediate neurohypophyseal expression. These lines of transgenic mice will serve as a model for the delineation of sequences that target expression beyond the neuronal perikaryon.