Ultrastructural localization of oxytocin mRNA in the rat hypothalamus by in situ hybridization using a synthetic oligonucleotide

Three-dimensional Imaging of the Intracellular Localization of Growth Hormone and Prolactin and Their mRNA Using Nanocrystal (Quantum Dot) and Confocal Laser Scanning Microscopy Techniques

Semiconductor nanocrystals (Quantum dots, Qdots) have recently been used in biological research, because they do not fade on exposure to light, and they enable us to obtain multicolor imaging because of a narrow emission peak that can be excited via a single wavelength of light. There have been no reports of simultaneous localization of mRNA and protein using Qdots. We successfully applied these advantages of Qdot and confocal laser scanning microscopy (CLSM) to three-dimensional images of the intracellular localization of growth hormone and prolactin and to their mRNA. In situ hybridization and immunohistochemistry using Qdots combined with CLSM can optimally illustrate the relationship between protein and mRNA simultaneously in three dimensions. Such an approach enables us to visualize functional images of proteins in relation with mRNA synthesis and localization.

Molecular morphology of pituitary cells, from conventional immunohistochemistry to fluorescein imaging

In situ hybridization (ISH) at the electron microscopic (EM) level is essential for elucidating the intracellular distribution and role of mRNA in protein synthesis. EM-ISH is considered to be an important tool for clarifying the intracellular localization of mRNA and the exact site of pituitary hormone synthesis on the rough endoplasmic reticulum. A combined ISH and immunohistochemistry (IHC) under EM (EM-ISH&IHC) approach has sufficient ultrastructural resolution, and provides two-dimensional images of the subcellular localization of pituitary hormone and its mRNA in a pituitary cell. The advantages of semiconductor nanocrystals (quantum dots, Qdots) and confocal laser scanning microscopy (CLSM) enable us to obtain three-dimensional images of the subcellular localization of pituitary hormone and its mRNA. Both EM-ISH&IHC and ISH & IHC using Qdots and CLSM are useful for understanding the relationships between protein and mRNA simultaneously in two or three dimensions. CLSM observation of rab3B and SNARE proteins such as SNAP-25 and syntaxin has revealed that both rab3B and SNARE system proteins play important roles and work together as the exocytotic machinery in anterior pituitary cells. Another important issue is the intracellular transport and secretion of pituitary hormone. We have developed an experimental pituitary cell line, GH3 cell, which has growth hormone (GH) linked to enhanced yellow fluorescein protein (EYFP). This stable GH3 cell secretes GH linked to EYFP upon stimulation by Ca²⁺ influx or Ca²⁺ release from storage. This GH3 cell line is useful for the real-time visualization of the intracellular transport and secretion of GH. These three methods from conventional immunohistochemistry and fluorescein imaging allow us to consecutively visualize the process of transcription, translation, transport and secretion of anterior pituitary hormone.

[André Calas, the original path of a neuroendocrinologist]

This talk, given as an introduction to a symposium organised to honor André Calas, calls forth his personality, recalls the major events in his career and summarizes the evolution of his research.

Expression of tyrosine hydroxylase and vasopressin in magnocellular neurons of salt-loaded aged rats

Tyrosine hydroxylase (TH) is expressed in catecholaminergic neurons. However, under certain conditions it is also ectopically expressed in magnocellular neurons of the hypothalamus. To test the hypothesis that this expression of TH is related to the cellular activation of these neurons and/or to the vasopressin (VP) expression, we studied the expression of both TH and VP in control and salt-loaded aged rats. Our results demonstrate that aged rats show a marked TH expression in VP cells which is further increased by osmotic stimulation in the absence of increase in VP synthesis in the supraoptic nucleus. The presence of TH-immunopositive dendritic swellings in the ventral part of this nucleus reveals the high state of plasticity of these neurons. Furthermore, the lack of several actors of catecholamine biosynthesis in these neurons suggests a different role for TH. This study further demonstrates an ectopic expression of TH in hypothalamic neurons of aged rats and a TH expression linked to the activation of VP neurons but unrelated to VP synthesis.

Ectopic expression of non-catecholaminergic tyrosine hydroxylase in rat hypothalamic magnocellular neurons

Hypothalamic magnocellular neurons constitute a good model of neurochemical plasticity, because a single neuron can express various combinations of neuropeptides and enzymes under different physiological conditions. Tyrosine hydroxylase has been shown to occur ectopically in various non-catecholaminergic neurons. We investigated the expression of tyrosine hydroxylase and its possible role in the magnocellular neurons of the supraoptic and paraventricular nuclei in salt-loaded and lactating rats, using in situ hybridization and immunohistochemistry, alone or combined, in light and electron microscopy. Our results demonstrated that almost 25% of the magnocellular neurons in the supraoptic nucleus and 15% in the paraventricular nucleus expressed tyrosine hydroxylase in salt-loaded rats, and 10% in the supraoptic nucleus of two-day lactating rats. Double labelling showed that this tyrosine hydroxylase was essentially synthesized in magnocellular neurons expressing vasopressin. The ultrastructural localization of tyrosine hydroxylase was less homogeneous in the cytoplasm of magnocellular neurons than in periventricular neurons. In lactating and salt-loaded rats, magnocellular neurons were devoid of the catecholamine biosynthesis markers aromatic L-amino acid decarboxylase, L-3,4 dihydroxyphenylalanine, dopamine and GTP-cyclohydrolase I. Tyrosine hydroxylase expression did not increase after rats were injected with reserpine. Our results indicate that the phenotype of the magnocellular neurons expressing tyrosine hydroxylase in lactating and salt-loaded rats is non-catecholaminergic, and suggest that this tyrosine hydroxylase might be involved in osmoregulation.

Combination of immunohistochemical and in situ hybridization methods to reveal tyrosine hydroxylase and oxytocin and vasopressin mRNAs in magnocellular neurons of obese Zucker rats

Co-localization of chemical messengers in the same neuron is linked to neurochemical plasticity and has been studied extensively [B. Meister, M.J. Villar, S. Ceccatelli, T. Hökfelt, Localization of chemical messengers in magnocellular neurons of the hypothalamic supraoptic and paraventricular nuclei: an immunohistochemical study using experimental manipulation, Neuroscience 37 (1990) 603-633; B. Meister, R. Cortés, M.J. Villar, M. Schalling, T. Hökfelt, Peptides and transmitter enzymes in hypothalamic magnocellular neurons after administration of hyperosmotic stimuli: comparison between messenger RNA and peptide/protein levels, Cell Tissue Res. 260 (1990) 279-297]. Obese Zucker rats display an example of such a phenomenon expressing an enzyme of catecholamine synthesis-tyrosine hydroxylase (TH)-in magnocellular neurons (MCN) of supraoptic and paraventricular nuclei of hypothalamus [S. Fetissov, F. Marsais, S. Nicolaïdis, A. Calas, Expression of tyrosine hydroxylase in magnocellular hypothalamic neurons of obese (fa/fa) and lean heterozygous (Fa/fa) Zucker rats, Mol. Brain Res. 50 (1997) 314-318]. To understand the biological role of TH in MCN of obese Zucker rat, we studied TH expression in relation to the vasopressinergic and oxytocinergic neurons. We present a protocol of double labelling including immunohistochemical for TH and in situ hybridization for OT and VP mRNA. The described protocol can be applied for detection of co-localized expressions of a broad range of chemical brain messengers and proteins.

Electron Microscopic and Confocal Laser Scanning Microscopic Observation of Subcellular Organelles and Pituitary Hormone mRNA: Application of Ultrastructural In Situ Hybridization and Immunohistochemistry to the Pathophysiological Studies of Pituitary Cells

Nonradioisotopic electron microscopic (EM) in situ hybridization (ISH) (EM-SH) with biotinylated oligonucleotide probes is utilized for the ultrastructural visualization of pituitary hormone mRNA in rat pituitary cells. EMISH is an important tool for clarifying the intracellular localization of mRNA and the exact site of specific hormone synthesis on the rough endoplasmic reticulum. The simultaneous visualization of mRNA and encoded protein in the same cell using preembedding EM-ISH and subsequent postembedding immunoreaction with protein A colloidal gold complex can provide an important clue for elucidating the intracellular correlation of mRNA translation and secretion of translated protein. Another focus of this review is the utilization of a recently developed imaging system of confocal laser scanning microscopy (CLSM). The combination of CLSM and image analysis system (lAS) enables us to visualize an individual dimensional image of the intracellular distribution of mRNA and subcellular organelles successfully at any optional cross sections of light microscopic ISH studies, and can be another useful tool for the ultrastructural ISH study of mRNA.

RNA localization in development

Cytoplasmic RNA localization is an evolutionarily ancient mechanism for producing cellular asymmetries. This review considers RNA localization in the context of animal development. Both mRNAs and non-protein-coding RNAs are localized in Drosophila, Xenopus, ascidian, zebrafish, and echinoderm oocytes and embryos, as well as in a variety of developing and differentiated polarized cells from yeast to mammals. Mechanisms used to transport and anchor RNAs in the cytoplasm include vectorial transport out of the nucleus, directed cytoplasmic transport in association with the cytoskeleton, and local entrapment at particular cytoplasmic sites. The majority of localized RNAs are targeted to particular cytoplasmic regions by cis-acting RNA elements; in mRNAs these are almost always in the 3'-untranslated region (UTR). A variety of trans-acting factors--many of them RNA-binding proteins--function in localization. Developmental functions of RNA localization have been defined in Xenopus, Drosophila, and Saccharomyces cerevisiae. In Drosophila, localized RNAs program the antero-posterior and dorso-ventral axes of the oocyte and embryo. In Xenopus, localized RNAs may function in mesoderm induction as well as in dorso-ventral axis specification. Localized RNAs also program asymmetric cell fates during Drosophila neurogenesis and yeast budding.

Subcellular localization of preprogalanin messenger RNA in perikarya and axons of hypothalamo-posthypophyseal magnocellular neurons: an in situ hybridization study

The subcellular compartmentalization and axonal transport of oxytocin and vasopressin messenger RNAs have recently been reported in the rat hypothalamo-posthypophyseal system using in situ hybridization. So far, no data are available concerning the intracellular distribution of co-localized peptide transcripts, for example of galanin, which is synthesized in the vasopressinergic magnocellular neurons of the rat and which is up-regulated in these neurons under different conditions, including salt loading and colchicine injection. In the present study, using non-radioactive in situ hybridization and immunohistochemistry at the light and electron microscope levels, preprogalanin messenger RNA and galanin-like immunoreactivity were localized in the hypothalamo-posthypophyseal system. After salt loading, preprogalanin transcripts were found throughout the perikaryal cytoplasm, especially in the peripheral cytoplasm and in the perinuclear area. Since immunohistochemistry also showed galanin-like immunoreactivity preferentially in the perinuclear area of control rats, galanin synthesis may occur mainly in this cytoplasmic domain. Preprogalanin messenger RNA was also clustered in dendrites containing rough endoplasmic reticulum. The use of a new in situ hybridization method involving tyramide signal amplification, based on catalysed reporter deposition, allowed visualization of preprogalanin messenger RNA in axonal projections running through the internal layer of the median eminence after salt loading, but not in control or in colchicine-injected animals. The negative results obtained after colchicine injection indicate that the mechanism of messenger RNA transport may require an intact cytoskeleton. The labelling was found in non-dilated axon segments as well as in a subset of axonal swellings in the rostral aspect of the median eminence, but was restricted to a few swellings in its caudal part, with no labelling in the posterior pituitary. Thus, preprogalanin messenger RNA was segregated in the axons. The functional significance of messenger RNAs' exportation into axons is not known, but our results suggest that this phenomenon may not be limited to the two principal magnocellular hormone messenger RNAs, but may also involve co-existing peptide messenger RNAs.

An improved ultrastructural double-staining method for rat growth hormone and its mRNA using LR White resin: a technical note

An improved new method for the simultaneous visualization of mRNA and encoded protein in LR White resin-embedded specimens is described. This pre-embedding electron microscopical in situ hybridization (procedure) localized rat growth hormone mRNA specifically as high electron-density products on the polysomes of the rough endoplasmic reticulum. A subsequent post-embedding immunoreaction, using protein A colloidal gold particles, identified growth hormone as gold particles both in the cisternae of the rough endoplasmic reticulum and on the secretory granules. In our previous report, we used Epon resin for tissue embedment, which required an etching process using hydrogen peroxide or sodium periodate for immunoreactivity retrieval. In general, osmification and embedment in Epon resin are reported to decrease the immunoreactivity of the targeted protein, and the etching process using hydrogen peroxide or sodium periodate results in deosmification and shades off the signals of mRNA. To resolve these problems, we have recently used LR White resin for tissue embedment. In LR White resin-embedded tissues, retrieval of immunoreactivity using hydrogen peroxide or sodium periodate is not required, and, therefore, the gradation of the signals of mRNA can be avoided.

Expression of tyrosine hydroxylase in magnocellular hypothalamic neurons of obese (fa / fa) and lean heterozygous (Fa / fa) Zucker rats

In the magnocellular hypothalamic neurons (MCN) of normal rats, tyrosine hydroxylase (TH) is expressed in response to hyperosmotic stimulation and co-exists with vasopressin. The present study shows that both Zucker obese (fa / fa) and heterozygous lean (Fa / fa) rats express TH in MCN independently of an osmotic challenge. The lack of L-DOPA and aromatic-L-aminoacid decarboxylase in the MCN showed the absence of mechanisms necessary for catecholamine synthesis in these cells. Therefore, TH in MCN seems to be functionally inactive and is not involved in catecholamine abnormalities observed in these rats. All TH-immunoreactive MCN co-expressed vasopressin mRNA while a part of them co-expressed oxytocin mRNA. This suggests a mechanism of regulation of TH expression in MCN which is different in Zucker rats and in dehydrated normal rats.

Signal amplification in the detection of single-copy DNA and RNA by enzyme-catalyzed deposition (CARD) of the novel fluorescent reporter substrate Cy3.29-tyramide

We demonstrate that the CAtalyzed Reporter Deposition method (CARD), utilizing the novel fluorescent reporter Cy3.29-tyramide, is successful in the Fluorescent in Situ Hybridization (FISH) detection of RNA and single-copy DNA. Histone 4 expression is detected in RNA extracts of 5-phase, synchronized HeLa cells by dot-blot analysis. Gene expression of histone 4 in HeLa cells is demonstrated by FISH via CARD, utilizing oligonucleotide probes. Fluorescence intensity measurements on CARD-amplified histone 4 RNA detection showed (a) a 25-fold amplification of the signal brightness by biotinylated oligonucleotide probes and (b) a sixfold amplification of the signal brightness by horseradish peroxidase (HRP)-labeled histone 4 probes vs the directly stained control. The sensitivity of the CARD method is demonstrated by the FISH detection of single-copy DNA on human corneal fibroblast and HeLa S5 interphase nuclei. Chromosomal localization of the single copy DNA is demonstrated on HeLa S3 metaphase chromosome spreads.

Simultaneous ultrastructural identification of growth hormone and its messenger ribonucleic acid using combined immunohistochemistry and non-radioisotopic in situ hybridization: a technical note

The present electron microscopical study is concerned with the simultaneous visualization of messenger ribonucleic acid (mRNA) and its encoded protein in the same specimen. Pre-embedding electron microscopical in situ hybridization (EM-ISH) on rat pituitary gland tissue localized growth hormone mRNA in the polysomes of the rough endoplasmic reticulum, and subsequent postembedding immunolabelling using protein A-colloidal gold particles identified growth hormone mainly in the secretory granules. We believe that our report provides the first simultaneous ultrastructural identification of mRNA and its encoded protein using combined pre-embedding EM-ISH and immunohistochemistry. In this method, the signals for mRNA were localized specifically as highly electron dense products on the polysomes of the endoplasmic reticulum, and those for its encoded protein were recognized as gold particles both in the cisternae of the reticulum and in the secretory granules. Our ultrastructural double labelling method for mRNA and protein may provide a tool to find important clues for elucidating the intracellular correlation of mRNA translation and secretion of translated protein, because of its high resolution, good morphological preservation, and the specific localization of the reaction products.

Non-isotopic electron microscope in situ hybridization for studying the functional sub-compartmentalization of the cell nucleus

Post-embedding electron microscope in situ hybridization using gold particles as label permits the clear identification of the cellular structures which contain the nucleic acid molecules under study. It has yielded information on the distribution of defined nucleic acid sequences of different origins-cellular or viral, DNA or RNA, single- or double-stranded molecules-which has revolutionized the study of the nucleus. Application of this powerful technique in combination with other refined techniques to studies on transcription and replication of cellular and viral genes has augmented our knowledge of the functional organization of the cell nucleus. One can now ask mechanistically meaningful questions concerning the successive steps of gene replication and expression not only under normal conditions of cell growth, but also when the cellular metabolism is altered by a drug treatment or a viral infection. This chapter aims (a) to present the established methods of post-embedding electron microscope in situ hybridization for localizing, precisely and specifically, a nucleic acid target in its normal environment and (b) to present some contributions of this technique to investigations of the functional compartmentalization of the cell nucleus and to elucidate the cell-virus relationships in infected cells.

Changes in the ultrastructural distribution of prolactin and growth hormone mRNAs in pituitary cells of female rats after estrogen and bromocriptine treatment, studied using in situ hybridization with biotinylated oligonucleotide probes

The expression and distribution of prolactin (PRL) mRNA and their alterations induced by estrogen and bromocriptine were investigated using non-radioisotopic in situ hybridization (ISH) at the electron microscopic (EM) level. Our EM-ISH studies using biotinylated oligonucleotide probes showed that estrogen induced whirling changes of the rough endoplasmic reticulum (RER) of female rat PRL cells and increased transcription of PRL genes located on the polysomes of the whirling RER. The presence of mammosomatotroph cells in the rat pituitary gland was also verified in our EM-ISH studies. After bromocriptine administration, PRL cells contained many secretory granules due to the inhibition of secretion. Pre- and post-embedding EM-ISH and northern hybridization studies revealed that bromocriptine induced the distorted, vesiculated, and dilated RER, and also the suppressed PRL mRNA expression. The activity of protein kinase C (PKC), which mediates PRL gene expression, tended to be elevated by estrogen and suppressed by bromocriptine. Therefore, it is considered that the ultrastructural and quantitative changes in PRL mRNA expression evoked by estrogen and bromocriptine may be mediated by the intracellular signal transduction system, including PKC.

Developmental expression of tryptophan hydroxylase mRNAs in the rat pineal gland: an in situ hybridization study

The expression of messenger RNAs encoding for tryptophan hydroxylase (TPOH), the first enzyme involved in serotonin and melatonin synthesis, has been investigated by in situ hybridization during the development of the rat pineal gland. TPOH mRNAs were detected as early as the twentieth day of gestation (E20) in the rat embryo before any nerve ending was observed in the pineal gland. After birth, their expression increased strongly, and attained a plateau during the second week. This coincides with the setting up of sympathetic innervation. From day 17 (D17), the TPOH mRNA expression diminished. These results indicate that noradrenergic innervation is not involved in the initiation of rat pinealocyte differentiation, but might modulate cell maturation. This study showed the existence of three types of cells arranged in patches in the young rat pineal gland (D6): regions in which cells expressed TPOH mRNAs, regions in which cells expressed vimentin, an intermediate filament protein present in the cytoskeleton of immature cells, and regions in which both TPOH mRNAs and vimentin are expressed. In older rat pineal gland (D20), almost all cells express TPOH mRNAs, and some cells still express vimentin. This suggests that all cells do not reach the same level of differentiation at the same time in the rat pineal gland.

Ultrastructural distribution of growth hormone and prolactin mRNAs in normal rat pituitary cells: a comparison between preembedding and postembedding methods

In situ hybridization (ISH) at the electron microscopic level is essential for elucidating the intracellular distribution and role of mRNA in protein synthesis. We describe our electron microscopic ISH method using biotinylated oligonucleotide probes for rat growth hormone and prolactin mRNAs and compare the preembedding method with the postembedding method. Preembedding electron microscopic ISH localized rat growth hormone and prolactin mRNAs on the polysomes of the rough endoplasmic reticulum (RER). Rat growth hormone mRNA was distributed diffusely on the RER, whereas rat prolactin mRNA was scattered and distributed focally. Thus there might be a specific translational site for prolactin mRNA on the RER. Rat growth hormone mRNA signals were also recognized on the polysomes of the RER, using the postembedding method with streptavidin gold conjugate. The hybridization signal intensity using the postembedding method was lower, and non-specific signals were more frequent, in comparison with the preembedding method. The preembedding method thus appears to be easier and better than the postembedding method from the viewpoint of utility and preservation of mRNA. Electron microscopic ISH is considered to be an important tool for evaluating the intracellular localization of mRNA and the site of specific hormone synthesis on the RER.

Effects of an acute immobilization stress upon proopiomelanocortin (POMC) mRNA levels in the mediobasal hypothalamus: a quantitative in situ hybridization study

The aim of this study was to examine by quantitative in situ hybridization the effects of an acute stress on the expression of the POMC gene in the mediobasal hypothalamus (MBH) of the rat. In control animals, the highest levels of POMC mRNA were observed in the posterior periventricular region of the MBH. Lower levels were found in the anterior and posterior arcuate nucleus. At the end of a one hour immobilization, a small decrease (-8%) was observed in the periventricular region only. Four hours after the end of immobilization, increases in POMC mRNA levels were detected in the anterior part (7%), in the posterior part (25%) and in the periventricular region (13%) of the MBH. These results suggest that MBH POMC-derived peptides might be an important component in the central response to stress.

Effects of intranigral injections of colchicine on the expression of some neuropeptides in the rat forebrain: an immunohistochemical and in situ hybridization study

In the present study, we describe the neurochemical effects of intranigral injections of colchicine in the rat forebrain using immunohistochemistry and in situ hybridization. The observations on the injected side are compared to the contralateral one and to the sham-operated rats. We demonstrate that such injections are able to strongly enhance the immunoreactivity for Met-enkephalin (ME), substance P (SP) and neuropeptide Y (NPY) in numerous nerve cell bodies of the limbic system (injected side), whereas the levels of the corresponding mRNAs are differently modified according to the region examined. A clear correlation between the enhancement of the immunostaining for ME and SP and that of the preproenkephalin (PPA) and preprotachychinin gene transcripts was observed in neuronal perikarya of the medial amygdaloid nucleus (SP), of the dorsolateral hypothalamus (ME) and of the ventromedial hypothalamic nucleus (SP). These observations are interpreted as an induction--or increased expression--of neuropeptide genes in neuronal perikarya postsynaptic to nerve fibers originating in the midbrain and brain stem. In this case, colchicine is thought to block the electrophysiological activity of ascending nerve fibers (anterograde and postsynaptic effect). In the case where the enhancement of the immunoreactivity for the studied neuropeptides was associated with no change or a decreased expression of the corresponding genes in the same brain areas, colchicine may have blocked the axoplasmic transport of peptides in nerve fibers projecting to the midbrain and/or brain stem (6). This may result in a retrograde accumulation of peptides in the nerve cell bodies of origin and, eventually, in a negative feedback regulation of the corresponding encoding genes in these perikarya (retrograde and presynaptic effect of colchicine). The drastic behavioral effects of bilateral intranigral injections of colchicine, on ingestive behavior in particular, have been studied in a following paper.

Fine-structural localization of proenkephalin mRNAs in the hypothalamic magnocellular dorsal nucleus of the guinea pig: a comparison of radioisotopic and enzymatic in situ hybridization methods at the light- and electron-microscopic levels

With the aim of localizing proenkephalin mRNAs in neurons of the hypothalamic magnocellular dorsal nucleus of the guinea pig, we compared the in situ hybridization signals obtained on Vibratome sections with a method employing either a biotinylated or a digoxigenin-labeled oligonucleotide detected by means of the alkaline phosphatase reaction. Since the hybridization approach using the biotinylated probe was more sensitive than the digoxigenin method, the ultrastructural localization of hybrids in neurons of the magnocellular dorsal nucleus was studied by the use of the former procedure, and was further compared with results of in situ hybridization using a 35S-labeled probe. Biotin was detected via an amplified avidin-biotin-peroxidase complex. Radioactive hybrids were localized over extended cytoplasmic compartments rich in rough endoplasmic reticulum and also in nuclear indentations. The method based on biotinylated probe proved to be sensitive and provided high-resolution labeling in well-preserved specimens. Proenkephalin mRNAs were clearly localized within circumscribed cytoplasmic compartments. The immunoprecipitates were mainly observed within the rough endoplasmic reticulum, especially at the periphery of the cell. The reticulum was dominated by elongated parallel cisternae. The labeling also appeared in a paranuclear position, mainly in nuclear indentations. The labeling was found on the outer surface of the endoplasmic lamellae. The remainder of the reticulum was unlabeled. Neuronal processes were free of labeling.

Vasopressin mRNA in the cerebellum and circumventricular organs: a quantitative in situ hybridization study

To answer the question as to whether vasopressin is synthesized in brain structures other than the supraoptic and paraventricular nuclei of the hypothalamus, vasopressin mRNA was detected by in situ hybridization in the pituitary, cerebellum, dentate gyrus, habenula and circumventricular organs. The highest levels (0.3-0.2 pmol/g), measured by quantitative autoradiography, were observed in the pituitary intermediate lobe and the granular layers of the cerebellum and dentate gyrus. Lower levels (0.15-0.08 pmol/g) were found in the medial habenula, adenohypophysis, area postrema, pineal, subfornical and subcommissural organs.

Discrete expression of Ca2+/calmodulin-sensitive and Ca(2+)-insensitive adenylyl cyclases in the rat brain

Physiological studies and inferences from invertebrate models implicate Ca2+/calmodulin-sensitive adenylyl cyclase with memory processes. However, Ca2+/calmodulin-insensitive adenylyl cyclase also occurs in brain, and its neuronal functions are less clear. Two oligonucleotide probes, based on rat cDNAs for Types I and II adenylyl cyclase, which appear to correspond to these functional forms, were used to conduct in situ hybridization analysis of the relative abundance and localization of these two species in the rat brain as a first step in evaluating their neuronal role. Quite discrete patterns of expression were encountered; in some areas, both species were co-expressed, but in others, little overlap was observed. The differential expression of the two mRNAs suggests that discrete roles may be fulfilled by the two adenylyl cyclases in neural tissues.

Adaptation of a non-radioactive in situ hybridization method to electron microscopy: detection of tenascin mRNAs in mouse cerebellum with digoxigenin-labelled probes and gold-labelled antibodies

In this study we describe a method for the detection of mRNAs at the ultrastructural level using a non-radioactive in situ hybridization method based on digoxigenin-labelled cRNA probes and gold-labelled digoxigenin-specific antibodies. We applied this protocol to an analysis of the expression of the extracellular matrix protein tenascin in the developing cerebellar cortex of the mouse. To gain an impression of the sensitivity attainable with digoxigenin-labelled probes, we first established at the light microscopic level that the hybridization signal obtained with the non-radioactive probe is as sensitive as that obtained with a 35S-labelled probe. The non-radioactive hybridization protocol was then combined with electron microscopic post-embedding and immunogold detection techniques. Tenascin-specific, digoxigenin-labelled cRNA probes were hybridized to ultrathin sections of Lowicryl K4M-embedded tissue and the probe/target mRNA hybrids were detected using gold-labelled antibodies to digoxigenin. In agreement with the observations from in situ hybridization at the light microscopic level, specific labelling was observed in Golgi epithelial cells in the region of the Purkinje cell layer and cells in the internal granular layer, which could be identified as astrocytes by ultrastructural criteria. Labelling was detectable in association with free ribosomes and ribosomes of the rough endoplasmic reticulum. In addition, focal hybridization signals were occasionally found in the nucleus. No signal was observed in Golgi epithelial cells or astrocytes using sense or in any other cerebellar cell type using either sense or anti-sense probes. The described in situ hybridization technique uses ultrastructural criteria to associate the presence of a given mRNA species with a particular cell type. Additionally, it provides information about the target mRNA's subcellular distribution, thus offering the possibility to study intracellular transport of particular mRNAs.

Somatotopic organization of tyrosine hydroxylase expression in the rat locus coeruleus: long term effect of RU24722

Tyrosine hydroxylase (TH) tissue concentration was determined by immunostaining of tissue sections directly transferred onto nitrocellulose membranes in the restricted region of the noradrenergic perikarya of the locus coeruleus (LC) along its postero-anterior axis. TH containing cells were systematically counted on adjacent post fixed sections stained by immunohistochemistry. The absolute quantity of TH was estimated in each section and was found to be linearly related to the number of TH immuno-positive cells found in the adjacent section. The ratio between these two parameters was thus used as an index of the cellular concentration of TH in noradrenergic cells. In the LC of control rats, the TH cellular concentration was lower (-39%) in the anterior than in the posterior half of the structure. Three days after an injection of 20 mg/kg of RU24722, an eburnamine derivative known to increase the quantity of TH in the LC, increases in quantities of TH were found in both portions of the LC. Moreover in the posterior LC the increase in the amount of TH resulted from a significant increase in the number of TH-immunopositive cells. In the anterior part, however, it was primarily the result of a significant increase in TH cellular concentration. Throughout the LC there was an increase in the cellular concentration of TH which was inversely proportional to the concentrations found in control animals. TH mRNA content was measured by a quantitative in situ hybridization in sections of both the posterior and anterior LC one day after a single injection of RU24722 at the same dose. The quantity of TH mRNA was significantly increased in both parts. The number of TH mRNA-expressing neurons also increased, especially in the anterior LC. Thus the effects at the level of TH protein and TH mRNA were strikingly parallel though increase in TH protein occurred later than the increase in the TH mRNA. These results suggest that in the rat LC: (1) there is a significant population of 'sleeping cells' in which TH expression is either inactivated or, at a low level of activation; (2) TH cellular concentration could exert a retrocontrol on its own expression in cells of the LC that contained TH and (3) TH expression appears to be regulated by different selective mechanisms in these two different subpopulations of noradrenergic cells within the LC.

Amplification of the in situ hybridization signal by silver postintensification: the biotin-dUTP-streptavidin-peroxidase diaminobenzidine-silver-gold detection system

Frozen and vibratome sections from the adrenal gland of the rat were hybridized in situ using a biotinylated oligonucleotide probe specific for tyrosine hydroxylase (TH) messenger ribonucleic acid (mRNA). Hybridization was detected using the streptavidin-peroxidase-diaminobenzidine (DAB) system in combination with silver-gold postintensification. The signal appeared as a black coloration and was localized to the cytoplasm of catecholamine-synthesizing chromaffin cells in the adrenal medulla. This coloration was due to the deposition of the silver-gold intensified DAB chromogen onto the probe hybridized to mRNA in carrier organelles. Compared with the conventional peroxidase-DAB labelling, the silver-gold amplified version was more sensitive in detecting TH mRNA. Using this modification, we were able to adapt the procedure to electron microscopy, thereby further localizing the hybridized signal to ribosomes. Because this hybridization detection system produces grains, not just color, this method has the potential for measurement of changes in mRNA levels at the ultrastructural level.

Enkephalin-containing nerve cell bodies in the substantia nigra of the rat: demonstration by immunohistochemistry and in situ hybridization

The use of a new and very sensitive immunohistochemical method, combined with intracerebral injections of colchicine, has allowed us to show that a number of nerve cell bodies immunoreactive for Met-enkephalin are present in several mesencephalic nuclei of the rat, including the different subdivisions of the substantia nigra (SN). The existence of numerous neuronal somata of this kind in the medial part of the SN pars compacta and in the lateral half of the pars reticulata is rather new. The latter has been ascertained by demonstrating a perikaryal immunoreactivity for synenkephalin in the same regions of the SN. In addition, by in situ hybridization, we have shown that neuronal cell bodies expressing the preproenkephalin A (PPA) gene are also present in the same regions of the SN. However, the fact that a strong radioautographic reaction was found only in rats which received an intranigral injection of 6-hydroxydopamine indicates that these neurons are probably not dopaminergic and that an induction of the PPA gene occurs in these animals.

Detection of FGF-beta mRNA in chondrosarcoma cells by a new in situ hybridization technique with synthetic oligonucleotide probes

Fibroblast growth factor beta (FGF-beta) is a potent mitogenic and angiogenic factor produced by a large number of normal and transformed cells. In this paper we report a new application of the in situ hybridization procedure which has allowed the detection of FGF-beta mRNA in chondrosarcoma cells using 35S-labelled synthetic oligonucleotide probes.

Evidence for a colocalization of oxytocin mRNA and galanin in magnocellular hypothalamic neurons: a study combining in situ hybridization and immunohistochemistry

The possible colocalization of oxytocin (OT) and galanin (GAL) was studied by combining, on the same cryostat sections, in situ hybridization (ISH) for OT mRNA with a tritiated oligonucleotide probe and immunohistochemistry (ICC) of GAL. Many cells were either labelled by ISH (OT mRNA containing cells), or by ICC (GAL containing cells). Moreover, some magnocellular neurons in the supraoptic and paraventricular nuclei were labelled for both OT mRNA and GAL. These results demonstrate that some magnocellular neurons of the rat hypothalamus contain both GAL and OT. This approach is suitable for studying the intracellular distribution of OT gene expression and mature GAL under different physiological or experimental conditions.