Localization and osmotic regulation of vesicular glutamate transporter-2 in magnocellular neurons of the rat hypothalamus

In this report we present immunocytochemical and in situ hybridization evidence that magnocellular vasopressin and oxytocin neurons in the hypothalamic supraoptic and paraventricular nuclei express type-2 vesicular glutamate transporter, a marker for their glutamatergic neuronal phenotype. To address the issue of whether an increase in magnocellular neuron activity coincides with the altered synthesis of the endogenous glutamate marker, we have introduced a new dual-label in situ hybridization method which combines fluorescent and autoradiographic signal detection components for vasopressin and vesicular glutamate transporter-2 mRNAs, respectively. Application of this technique provided evidence that 2% sodium chloride in the drinking water for 7 days produced a robust and significant increase of vesicular glutamate transporter-2 mRNA in vasopressin neurons of the supraoptic nucleus. The immunocytochemical labeling of pituitary sections, followed by the densitometric analysis of vesicular glutamate transporter-2 immunoreactivity in the posterior pituitary, revealed a concomitant increase in vesicular glutamate transporter-2 protein levels at the major termination site of the magnocellular axons. These data demonstrate that magnocellular oxytocin as well as vasopressin cells contain the glutamatergic marker vesicular glutamate transporter-2, similarly to most of the parvicellular neurosecretory neurons examined so far. The robust increase in vesicular glutamate transporter-2 mRNA and immunoreactivity after salt loading suggests that the cellular levels of vesicular glutamate transporter-2 in vasopressin neurons are regulated by alterations in water–electrolyte balance. In addition to the known synaptic actions of excitatory amino acids in magnocellular nuclei, the new observations suggest novel mechanisms whereby glutamate of endogenous sources can regulate magnocellular neuronal functions.     

Neuroendocrine gene expression in the hypothalamus:In situ hybridization histochemical studies

1. We have reviewed recent studies in which in situ hybridization histochemistry (ISHH) was used to investigate the regulation of expression of neurohypophysial peptides and hypothalamic releasing hormones. 2. ISHH is a technique in which the presence and quantity of a specific mRNA can be determined in tissue sections with a high degree of resolution and sensitivity. 3. ISHH has been used to measure changes in cellular levels of mRNAs encoding vasopressin, oxytocin, corticotropin-releasing factor, gonadotropin-releasing hormone, thyrotropin-releasing hormone and somatostatin in response to various physiological challenges. 4. A theme emerging from these studies is that changes in levels of mRNA encoding neuroendocrine peptides reflect changes in biosynthesis and secretion.     

Transitory coexistence of oxytocin and vasopressin in the hypothalamo neurohypophysial system of parturient rats.

We used in situ hybridization and immunocytochemistry to investigate a possible coexistence of vasopressin and oxytocin in hypothalamic neurons of parturient rats. We found that a fraction of magnocellular neurons in the paraventricular and supraoptic nuclei contained immunostaining for both peptides as well as oxytocin and vasopressin mRNA hybridization. Colocalization of immunoreactive vasopressin and oxytocin could be observed in some of the Herring bodies in the median eminence and the posterior lobe. No coexistence of vasopressin and oxytocin was found in pregnant or in lactating animals, indicating that the observed coexistence is transitory, perhaps mediated through changing hormonal conditions peri partum.     

In situ hybridization of oxytocin messenger RNA: macroscopic distribution and quantitation in rat hypothalamic cell groups

Oxytocin mRNA was detected in the rat hypothalamus by in situ hybridization to a single stranded 35S-labelled DNA probe and the distribution of oxytocin mRNA-containing cell groups was studied at the macroscopic level. Specificity of hybridization was confirmed by comparison to vasopressin mRNA hybridization in parallel tissue sections. Cell groups containing oxytocin mRNA were confined to a set of hypothalamic cell groups, i.c. the supraoptic, paraventricular, anterior commissural nuclei, nucleus circularis and scattered hypothalamic islets. These cell groups displayed similar densities of autoradiographic signals indicating that the oxytocin gene is expressed at approximately the same average level at these various sites.     

Gene expression in the rat supraoptic nucleus induced by chronic hyperosmolality versus hyposmolality

Magnocellular neurons of the hypothalamo-neurohypophysial system play a fundamental role in the maintenance of body homeostasis by secreting vasopressin and oxytocin in response to systemic osmotic perturbations. During chronic hyperosmolality, vasopressin and oxytocin mRNA levels increase twofold, whereas, during chronic hyposmolality, these mRNA levels decrease to 10-20% of that of normoosmolar control animals. To determine what other genes respond to these osmotic perturbations, we have analyzed gene expression during chronic hyper- versus hyponatremia. Thirty-seven cDNA clones were isolated by differentially screening cDNA libraries that were generated from supraoptic nucleus tissue punches from hyper- or hyponatremic rats. Further analysis of 12 of these cDNAs by in situ hybridization histochemistry confirmed that they are osmotically regulated. These cDNAs represent a variety of functional classes and include cytochrome oxidase, tubulin, Na(+)-K(+)-ATPase, spectrin, PEP-19, calmodulin, GTPase, DnaJ-like, clathrin-associated, synaptic glycoprotein, regulator of GTPase stimulation, and gene for oligodendrocyte lineage-myelin basic proteins. This analysis therefore suggests that adaptation to chronic osmotic stress results in global changes in gene expression in the magnocellular neurons of the supraoptic nucleus.     

Primer extension studies on α-amylase mRNAs in barley aleurone. I. Characterization and quantification of the transcripts

Primer extension was used to characterize alpha-amylase mRNAs from aleurone tissue of barley (Hordeum vulgare L. cv. Himalaya) grains. Two synthetic oligonucleotides, specific for the low-pI and high-pI alpha-amylase groups, were used as primers for synthesis of cDNA from total RNA preparations. Between them, these two oligonucleotides appear to account for all major alpha-amylase mRNAs as judged by hybrid-arrested translation of alpha-amylase mRNAs in a cell-free system. Reconstruction experiments indicated that the levels of extended primers (determined by scintillation counting) were directly proportional to the level of input mRNA over a wide range. This indicates that the technique is suitable for quantification of relative levels of individual alpha-amylase from approximately 2% to 100% of maximal levels. The nucleotide sequences of extended primers defined two different alpha-amylase mRNAs in each of the low-pI and high-pI groups, and possibly a third mRNA in the high-pI group.     

The use ofin situ hybridization histochemistry for the study of neuropeptide gene expression in the human brain

1. The application of in situ hybridization histochemistry to the study of neuropeptide gene expression in human brain postmortem tissues is reviewed. We focus on neuropeptides preferentially expressed in hypothalamus and basal ganglia. 32P-labeled oligonucleotides were used as hybridization probes. 2. Autoradiography combined with computerized image analysis was used to visualize and quantify the hybridization signal. 3. Several criteria were considered in order to ascertain the specificity of the signal, including Northern analysis, use of heterologous probes, competition assays, and thermal stability of the hybrids. 4. In control human striatum high levels of hybridization signal were observed for somatostatin, neuropeptide Y, and preproenkephalin A mRNAs. In contrast, no detectable signal was observed with the cholecystokinin, arginine-vasopressin, and oxytocin probes in this area. In the hypothalamus high levels of oxytocin and arginine-vasopressin mRNAs were visualized in several nuclei. Preproenkephalin A and somatostatin mRNAs were also observed in this region, while cholecystokinin mRNA was not detected. 5. No significant correlations were found between the density of the hybridization signal and parameters such as postmortem delay, age, and gender in the population studied. 6. Finally, alterations of mRNA levels for some of these peptides were found in Parkinson's disease and Huntington's chorea striatal tissues. 7. These results show that in situ hybridization histochemistry can be used to examine at the microscopic level neuropeptide gene expression in postmortem materials.     

Histological detection of messenger RNAs with biotinylated synthetic oligonucleotide probes

We achieved histological detection of the messenger RNAs coding for vasopressin, calcitonin, or calcitonin gene-related peptide by using biotinylated synthetic oligonucleotides, and defined the technical parameters enabling optimal detection of these mRNAs. Oligonucleotides labeled by fixation of one biotin at their 5' end or by addition of a biotin-11-dUTP tail at their 3' end can be used to detect mRNAs, although the latter are more sensitive. Streptavidin-alkaline phosphatase revealed with nitroblue tetrazolium-bromo-chloro-indolyl phosphate as substrate makes possible detection of the biotinylated oligonucleotides. Increasing formaldehyde concentration in the fixative decreases the signal intensity; 1% formaldehyde fixation provides the most intense signal. Several controls, including those with addition of unlabeled oligonucleotides to the hybridization buffer, confirm the specificity of mRNA detection. The sensitivity of the biotinylated probes is identical or lower as compared to the corresponding radiolabeled oligonucleotides. Histological and subcellular resolution is greatly enhanced with biotinylated probes. The rat vasopressin probes stain magnocellular neurons in the supraoptic and paraventricular nuclei and, under optimal conditions, parvocellular neurons in the suprachiasmatic nucleus. Vasopressin mRNA is present in the cytoplasm of the cell bodies and in the roots of certain processes. Calcitonin and calcitonin gene-related peptide mRNA are found co-localized in the cytoplasm of the same tumor cells in human medullary thyroid carcinoma.     

Quantitation of Vasopressin mRNA and Oxytocin mRNA in Hypothalamic Nuclei by Solution Hybridization Assays

Concentrations of vasopressin (VP) precursor and oxytocin (OT) precursor mRNA were measured in magnocellular cell groups of the rat hypothalamus by newly developed solution hybridization assays. The assays employed single-stranded 35S-labeled VP-specific and OT-specific DNA probes that were prepared by primer extension on recombinant M13 DNA templates. Solution hybridization assays were standardized by known amounts of cloned DNA. The detection limit was less than 1 pg DNA equivalent of the respective mRNA. In total RNA preparations of microdissected supraoptic nucleus (SON) mean (+/- SEM) basal levels of 1.37 +/- 0.18 pg VP mRNA and 1.95 +/- 0.14 pg OT mRNA were measured. RNA of the microdissected paraventricular nucleus (PVN) contained 0.35 +/- 0.02 pg VP mRNA and 1.77 +/- 0.15 pg OT mRNA. Elevation of plasma osmolality induced by drinking of 2% saline for 25 days resulted in a 1.85-fold increase in VP mRNA levels of the SON and a 1.6-fold increase in VP mRNA levels of the PVN. The solution hybridization assays are suitable tools to study the regulation of VP and OT mRNAs in magnocellular neurons of the brain.     

The vasopressin mRNA poly(A) tract is unusually long and increases during stimulation of vasopressin gene expression in vivo.

We developed a method, termed an H-blot, by which the poly(A) tract of any specific mRNA may be detected by RNA filter hybridization after its removal from the body of the mRNA by a RNase H-catalyzed endonucleolytic cleavage in the 3' untranslated region. Using this method, we studied the modulation of the length of the poly(A) tract of rat vasopressin mRNA in vivo during changes in the levels of this mRNA resulting from a physiologic stimulus, osmotic stress. The poly(A) tract of hypothalamic vasopressin mRNA in hydrated rats was, quite remarkably, approximately 250 nucleotides in length, in contrast to that of somatostatin mRNA, which was approximately 30 nucleotides long. Vasopressin mRNA poly(A) tail length increased progressively from approximately 250 to approximately 400 nucleotides with the application of the hyperosmotic stimulus and declined to base line after its removal; somatostatin mRNA poly(A) tail length did not change during osmotic stress. The poly(A) tract length of total hypothalamic mRNA was between 35 and 140 nucleotides and also did not change with osmotic stress. Modulation of poly(A) tract length of specific mRNAs during stimulation of gene expression may provide an additional level of genetic regulation.     

Structural sequences are conserved in the genes coding for the alpha, alpha' and beta-subunits of the soybean 7S seed storage protein.

Cloned DNAs encoding four different proteins have been isolated from recombinant cDNA libraries constructed with Glycine max seed mRNAs. Two cloned DNAs code for the alpha and alpha'-subunits of the 7S seed storage protein (conglycinin). The other cloned cDNAs code for proteins which are synthesized in vitro as 68,000 d., 60,000 d. or 53,000 d. polypeptides. Hybrid selection experiments indicate that, under low stringency hybridization conditions, all four cDNAs hybridize with mRNAs for the alpha and alpha'-subunits and the 68,000 d., 60,000 d. and 53,000 d. in vitro translation products. Within three of the mRNA, there is a conserved sequence of 155 nucleotides which is responsible for this hybridization. The conserved nucleotides in the alpha and alpha'-subunit cDNAs and the 68,000 d. polypeptide cDNAs span both coding and noncoding sequences. The differences in the coding nucleotides outside the conserved region are extensive. This suggests that selective pressure to maintain the 155 conserved nucleotides has been influenced by the structure of the seed mRNA. RNA blot hybridizations demonstrate that mRNA encoding the other major subunit (beta) of the 7S seed storage protein also shares sequence homology with the conserved 155 nucleotide sequence of the alpha and alpha'-subunit mRNAs, but not with other coding sequences.     

Vasopressin and oxytocin excite MCH neurons, but not other lateral hypothalamic GABA neurons

Neurons that synthesize melanin-concentrating hormone (MCH) colocalize GABA, regulate energy homeostasis, modulate water intake, and influence anxiety, stress, and social interaction. Similarly, vasopressin and oxytocin can influence the same behaviors and states, suggesting that these neuropeptides may exert part of their effect by modulating MCH neurons. Using whole cell recording in MCH-green fluorescent protein (GFP) transgenic mouse hypothalamic brain slices, we found that both vasopressin and oxytocin evoked a substantial excitatory effect. Both peptides reversibly increased spike frequency and depolarized the membrane potential in a concentration-dependent and tetrodotoxin-resistant manner, indicating a direct effect. Substitution of lithium for extracellular sodium, Na(+)/Ca(2+) exchanger blockers KB-R7943 and SN-6, and intracellular calcium chelator BAPTA, all substantially reduced the vasopressin-mediated depolarization, suggesting activation of the Na(+)/Ca(2+) exchanger. Vasopressin reduced input resistance, and the vasopressin-mediated depolarization was attenuated by SKF-96265, suggesting a second mechanism based on opening nonselective cation channels. Neither vasopressin nor oxytocin showed substantial excitatory actions on lateral hypothalamic inhibitory neurons identified in a glutamate decarboxylase 67 (GAD67)-GFP mouse. The primary vasopressin receptor was vasopressin receptor 1a (V1aR), as suggested by the excitation by V1aR agonist [Arg(8)]vasotocin, the selective V1aR agonist [Phe(2)]OVT and by the presence of V1aR mRNA in MCH cells, but not in other nearby GABA cells, as detected with single-cell RT-PCR. Oxytocin receptor mRNA was also detected in MCH neurons. Together, these data suggest that vasopressin or oxytocin exert a minimal effect on most GABA neurons in the lateral hypothalamus but exert a robust excitatory effect on presumptive GABA cells that contain MCH. Thus, some of the central actions of vasopressin and oxytocin may be mediated through MCH cells.     

Quantitativein situ hybridization to measure single-cell changes in vasopressin and oxytocin mRNA levels after osmotic stimulation

1. The measurement of cellular mRNA content by quantitative in situ hybridization is a valuable approach to the study of gene expression in brain since this tissue exhibits a high degree of phenotypic heterogeneity. 2. The cellular content of vasopressin and oxytocin mRNA in hypothalamo-neurohypophysial system neurons was altered by maintaining rats for 24 hr on 2% sodium chloride water. 3. Statistical and graphical techniques were then used to analyze cell by cell how mRNA levels were altered as a result of osmotic stimulation. We propose that the negative binomial probability distribution is a suitable model to describe how mRNA content varies across a defined cell population. For both measures of oxytocin and vasopressin mRNA levels, maximum-likelihood estimation indicated that this model adequately described empirical findings obtained from rats drinking tap water or salt water. 4. Both graphical and statistical analyses suggested how the defined neural system responds to osmotic stimulation: mRNA content was altered as a multiplicative function of "initial state." The utility and limitations of the quantitative approach are discussed.     

Sequence complexity and tissue distribution of chick lens crystallin mRNAs

Using hybridization reactions with a cDNA copy, the complexity of polysomal polyadenylated mRNA from the day-old chick lens was found to correspond to 5800–7200 sequences of average size, arranged in three abundance classes. Experiments with heterologous cDNAs suggest on a qualitative basis that many of the sequences expressed in 8-day embryonic neural retina and pigmented epithelium mRNAs are also present in lens mRNA. A cDNA fraction complementary to the most abundant lens mRNAs, representing an approximate minimum of four sequences, was used to assay the dosage of putative crystallin sequences in these and other embryonic tissues. Neural retina and pigmented epithelium cytoplasmic mRNAs have low concentrations of these sequences, which appear to be absent from mRNA prepared from headless bodies and muscle.     

Nucleotide sequence of mouse prolactin and growth hormone mRNAs and expression of these mRNAs during pregnancy

The mRNAs for mouse prolactin and growth hormone have been isolated from anterior pituitary glands and cloned as cDNAs. The nucleotide sequences of these mRNAs have been determined, and these sequences, along with the predicted amino acid sequences, are compared to those of other mammalian prolactin and growth hormone mRNAs. Levels of prolactin and growth hormone mRNAs during pregnancy have been monitored by hybridization to the cloned cDNA probes. We find the levels of these mRNAs to remain nearly constant during mid-to-late gestation.     

Antisense oligodeoxynucleotide effects on the hypothalamic-neurohypophysial system and the hypothalamic-pituitary-adrenal axis

The possibility of sequence-dependent, transient, and local inhibition of neuropeptide or neuropeptide receptor expression within the brain makes antisense targeting an attractive approach for those interested in the involvement of brain neuropeptide systems in behavioral and neuroendocrine regulation. Here, I describe our attempts to manipulate the synthetic activity of peptidergic systems of the hypothalamic-neurohypophysial system, i.e. , oxytocin and vasopressin, and the hypothalamic-pituitary-adrenal (HPA) axis by antisense oligodeoxynucleotides. Detailed experimental protocols including different approaches for intracerebral antisense application in anesthetized or conscious rats are provided. As a consequence of local oxytocin or vasopressin antisense treatment within the hypothalamic supraoptic nucleus, various aspects of the neuronal activity are already altered after a few hours. Thus, we monitored electrophysiological parameters of oxytocinergic and vasopressinergic neurons, stimulus-induced expression of the Fos protein in oxytocin neurons, and stimulated release of oxytocin or vasopressin into blood as well as within the hypothalamus by dendrites and cell bodies as measured by simultaneous microdialysis in blood and brain, shortly after a single acute antisense infusion. We also employed chronic antisense infusion via osmotic minipumps or by repeated local infusion into the targeted brain region; for example, septal vasopressin receptor downregulation impairs the ability of male rats to discriminate between juvenile rats. Further, reduction of the amount of available CRH, vasopressin, and oxytocin within the hypothalamic paraventricular nuclei alters the neuroendocrine stress response of the HPA axis.