Identification of proopiomelanocortin neurones in rat hypothalamus by in situ cDNA-mRNA hybridization

Detection of proopiomelanocortin mRNA by in situ hybridization with an oligonucleotide probe

Synthetic oligonucleotide probes can be easily obtained and used, in contrast to cDNA cloning to develop probes, and thus the present study was carried out to determine whether such probes could also be useful for in situ hybridization. A 24-base synthetic oligonucleotide complementary to part of the alpha-melanocyte-stimulating hormone (alpha-MSH) coding region of proopiomelanocortin (POMC) mRNA was 5'-end-labeled by using [gamma-32P]ATP with T4 polynucleotide kinase or was 3' tailed by using [alpha-32P]dATP or [3H]dCTP with terminal deoxynucleotidyltransferase. Blot analysis of pituitary poly(A)+ RNA showed that the oligonucleotide hybridized to a single species with a molecular size of approximately 1200 nucleotides, consistent with that determined previously for POMC mRNA. The oligonucleotide, regardless of labeling method, hybridized to cells in the pituitary intermediate lobe, but not in the posterior lobe. Only the 3H-labeled probe gave resolution of individual pituitary anterior lobe cells. The specificity of the hybridization was determined by showing that the intermediate lobe signal was blocked by prehybridization of the tissue with unlabeled alpha-MSH oligonucleotide probe. Furthermore, the hybridized probe exhibited a sharp sigmoid curve when melted off. Finally, the oligonucleotide probe detected, in situ, the haloperidol-induced elevation of intermediate lobe POMC mRNA. Thus, the oligonucleotide probe exhibited hybridization in an anatomically and biochemically specific manner, and it detected a tissue-specific change in mRNA levels in situ.

Tyrosine 3-hydroxylase in rat brain and adrenal medulla: hybridization histochemistry and immunohistochemistry combined with retrograde tracing

Rat brain and adrenal gland were analyzed by hybridization histochemistry using an RNA probe complementary to mRNA for tyrosine 3-hydroxylase (TyrOHase; tyrosine 3-monooxygenase, EC 1.14.16.2), by immunohistochemistry using TyrOHase antiserum, and by retrograde tracing using the fluorescent compound Fast blue. Cell bodies in the ventral mesencephalon contained mRNA for TyrOHase, and these cells were also TyrOHase immunoreactive. After injection of Fast blue into the striatum, such double-labeled cells in addition contained the retrograde tracer, showing that these cells send axonal projections to the injection site. These results show that hybridization histochemistry can be used to identify transmitter-specific neuron populations and that their projections can be established.

In situ hybridization to localize mRNA encoding the neurotransmitter synthetic enzyme glutamate decarboxylase in mouse cerebellum

Glutamate decarboxylase (GAD; EC 4.1.1.15) is responsible for the synthesis of the neurotransmitter gamma-aminobutyric acid (GABA). We have used a cDNA sequence encoding GAD to produce a single-stranded RNA hybridization probe for GAD mRNA. This probe detects GAD mRNA in individual cells in sections of mouse cerebellum. The specificity of in situ hybridization with this probe rests on four criteria: the distribution of labeled cells matched the results we and others obtain with GAD immunohistochemistry (Purkinje, Golgi II, stellate, and basket neurons were labeled, whereas granule cells and glia were not); a negative control probe having a sequence identical to GAD mRNA did not specifically label any cerebellar cells; prior treatment of the sections with RNase abolished specific labeling; the labeling showed the melting behavior typical of nucleic acid hybrids. Translation of GAD mRNA is apparently restricted to neuronal cell bodies since GAD mRNA was detectable in neuronal perikarya but not in terminals. Also, the choice of GABA as a neurotransmitter appears to be made at the level of transcription since granule neurons did not contain detectable GAD mRNA. The level of GAD mRNA varied among the classes of neurons as well as from cell to cell within each neuron type.

Patterns of gene expression in the murine brain revealed by in situ hybridization of brain-specific mRNAs

Biochemical differences between neuronal cell populations of the mammalian brain, including selection of neurotransmitters and distinct neural antigens, suggest that the regulation of gene expression plays an important role in defining brain function. Here we describe the use of in situ hybridization to identify cDNA clones of highly regulated mRNA species and to define directly their pattern of gene expression in brain at both gross morphological and cellular levels. One of the selected cDNA clones, pMuBr2, detected a single 3.0 kb mRNA species, which from in situ hybridization appears specific to oligodendroglia cells. Three other cDNA clones, pMuBr3, 8 and 85, identified polyadenylated mRNA transcripts expressed by neuronal cells of the murine brain. Viewed at the gross morphological level, the mRNAs hybridizing to these cDNA sequences exhibit different patterns of abundance distinguishing such brain structures as pons, anterior thalamus, hippocampus, basal ganglia and anterior lobe of the neuroendocrine pituitary gland. At the cellular level, in situ hybridization revealed that these mRNAs are differentially expressed by morphologically and functionally distinct neurons of the cerebellum and hippocampal formation. When examined in the context of known brain function, however, the regulated expression of the neuron-specific mRNAs does not correlate simply with known cellular morphology or previously demonstrated neuronal relationships suggesting novel patterns of gene expression which may contribute to brain function.

Suprachiasmatic nucleus vasopressin messenger RNA: circadian variation in normal and Brattleboro rats

In situ hybridization of an oligonucleotide probe complementary to vasopressin messenger RNA (mRNA) in sections from normal or Brattleboro rat hypothalami revealed hybridization densities in each of three vasopressin-rich nuclei: the supraoptic, paraventricular, and suprachiasmatic. When entrained to a daily light-dark cycle, each rat strain displayed diurnal variation in hybridizable mRNA in the suprachiasmatic, but not in the supraoptic or paraventricular nuclei. The higher values for suprachiasmatic mRNA in the morning correlate well with previously elucidated morning increases in vasopressin immunoreactivity in the cerebrospinal fluid. These results support the utility of in situ hybridization techniques for elucidating physiological influences on regional peptidergic function, are consistent with a prominent role for vasopressinergic suprachiasmatic neurons in generating the cerebrospinal fluid vasopressin rhythm, and suggest that regulation of this mRNA rhythm is not dependent on release of intact peptide.

Detection of the mRNA coding for enkephalin precursor in the rat brain and adrenal by using an 'in situ' hybridization procedure

The messenger RNA coding for preproenkephalin A (PPA) has been detected in tissue sections of the rat brain and adrenal by using two rat PPA cDNAs labeled with 32P or 35S as probes. In the brain, neurons were labeled in areas known to correspond to sites of synthesis of enkephalins, including the caudate-putamen, the nucleus accumbens, the olfactory cortex, the hypothalamus, the brainstem and the granular layer of the cerebellum. The presence of the PPA mRNA in the normal rat adrenal medulla shows transcription of the PPA gene in such cells despite the absence of enkephalin immunoreactivity in them. These results demonstrate in situ hybridization as an efficient technique to detect the site of synthesis of PPA.

Rapid, high-resolution in situ hybridization histochemistry with radioiodinated synthetic oligonucleotides

In situ hybridization histochemistry is a valuable technique for localizing specific messenger RNA (mRNA) and detecting changes in gene expression. Generally, the mRNA of interest has been detected by probes obtained from cloned DNA and labelled to high specific activity by nick translation. Such probes have a number of disadvantages which can be circumvented by the use of short synthetic oligonucleotides designed to be complementary to a known mRNA sequence. We report here that synthetic oligonucleotides complementary to part of the mRNA coding for rat arginine-vasopressin (AVP) can be labelled to high specific activity with [125I], using either the primer extension method with the Klenow fragment of DNA polymerase I or the 3'-tailing method with terminal deoxynucleotidyl transferase. Both AVP probes hybridized well to the magnocellular neurons of the hypothalamic paraventricular and supraoptic nuclei. A strong autoradiographic signal was present by 2 days, with grains largely confined to the perikaryon. These results compare favorably to those obtained with [32P]- or [3H]-labelled probes. Given the ease of the 3'-tailing method, [125I]-labelled oligonucleotides appear to be especially useful probes for in situ hybridization histochemistry.

In situ hybridization histochemistry for the analysis of gene expression in the endocrine and central nervous system tissues: a 3-year experience

We report our experience in development of the in situ hybridization (ISH) procedure to detect messenger RNAs (mRNAs) coding for various molecules involved in endocrine glands and central nervous system activity, including mRNAs coding for endorphin precursors [preproenkephalin A (PPA), pro-opiocortin (POMC)], vasopressin, and transferrin. Various conditions of fixation and handling of the tissues were tested to establish optimal parameters for mRNA detection. Double-stranded DNA probes labeled by nick translation, synthetic oligonucleotides labeled at their 5' end, as well as single-stranded RNA probes were used, after incorporation of 32P- or 35S-labeled nucleotides. Specific requirements for efficient and reproducible ISH investigations are discussed. Cells expressing the PPA gene in the adrenal medulla and in the brain were detected by ISH. The results show that ISH is as sensitive as immunohistochemistry in detecting peptide-producing cells in the adrenal and that it allows detection of PPA cell bodies in brain in conditions in which they are inconstantly detected by immunohistochemistry. Unilateral destruction of substantia nigra provokes a dramatic decrease in the number of neurons expressing the PPA gene in the contralateral striatum. Cells expressing the POMC gene were detected in the pituitary of various species including man and in the rat arcuate nucleus. Neurons containing vasopressin mRNA were visualized in the supraoptic paraventricular and suprachiasmatic nucleus of the adult rat by using a synthetic oligonucleotide probe. Transferrin gene expression was shown in the central nervous system of the rat brain in two cell populations, the oligodendrocytes and the epithelial cells of the choroid plexus, by demonstration of simultaneous presence in them of transferrin immunoreactivity together with transferrin mRNA. These results show that the ISH procedure is a technique that can be routinely used to investigate gene transcription anatomically in complex heterocellular tissues such as the endocrine glands and the nervous system.

Location of gene expression in CNS using hybridization histochemistry

In this chapter we have placed heavy emphasis on our own recent work to lay out a workable recipe for hybridization histochemistry. Only a trickle of papers followed the initial benchmark excursions into in situ labeling of tissue sections. Our own entry into this field was as late starters in 1978, but since then a confluence of important questions and technical advances has served to make hybridization histochemistry much more attractive and universally applicable as a research tool. Hybridization histochemistry allows the location of anatomical sites of gene expression and viral replication with unique specificity and is able to solve some problems for which there is no other suitable technique available in the central nervous system. For example, allowing that peptides may enter neurons by a variety of mechanisms and then be christened neuroendocrine peptides, it has become a compelling issue to know which cells are manufacturing the peptide. Thus, much can be learned by the approach elegantly demonstrated by Gee et al., of locating mRNA and its peptide product within the same neuron. The intracellular location of specific mRNA for a neuropeptide in a cell body indicates a very high probability that the peptide is secreted as a neurotransmitter or a neuromodulator from sites associated with the cell body. Our introduction of the use of whole mouse sections and large sections of brain of large animals in hybridization histochemistry has great potential in locating hormonal, enzymatic, and growth factor gene expression. The technique has been applied most elegantly by others to developmental studies and for the examination of viral infection. Resolution down to a single cell in heterogeneous tissue was beyond the original expectation of the capability of 32P-labeled probes and single cells in sections shown in Fig. 2 is probably the limit of resolution with this isotope. There is no reason why other isotopes, fluorescent labels, or labels suitable for EM should not take the resolution of the technique to intracellular. The horizon of application is widened enormously by the successful application of synthetic oligonucleotide probes, and at the same time unshackles the procedure from dependence upon a fully functional molecular biology laboratory. Although hybridization is a valuable research tool which we have applied to location of neuropeptides in the brain, it should soon find a niche in many fields and in a short time should become a key diagnostic tool.(ABSTRACT TRUNCATED AT 400 WORDS)

Gene expression in hypothalamic neurons: luteinizing hormone releasing hormone

In situ hybridization allows the detection and measurement of specific messenger RNAs in individual hypothalamic neurons, and has shown, among magnocellular neurons, not only which cells express the genes for oxytocin and vasopressin but also how they change with physiological stimulation. With this technique, neurons expressing a gene for luteinizing hormone releasing hormone-like messenger RNA have been discovered in the preoptic area and diagonal bands of the rat forebrain. Seven days of estrogen treatment of ovariectomized female rats increases the LHRH-like messenger RNA in this neuronal system.

In situ cDNA:mRNA hybridization: development of a technique to measure mRNA levels in individual cells

In this article we have described our protocol for in situ cDNA:mRNA hybridization and a variety of methodological considerations we have entertained to optimize the procedure. It should be stressed that each different system will have its own special characteristics and require optimization to obtain maximal and reproducible signals. We believe that by following a methodological logic as outlined here, researchers should be able to establish the in situ cDNA:mRNA hybridization protocol with their probes and tissue systems.

Detection of preprocholecystokinin and preproenkephalin A mRNAs in rat brain by hybridization histochemistry using complementary RNA probes

The distributions of mRNAs encoding preprocholecystokinin and preproenkephalin A in the rat brain were examined by in situ hybridization histochemistry. Complementary RNA probes 0.5-1.0 kilobase in length were synthesized in vitro with 35S-ribonucleotides using SP6 polymerase and a transcription vector containing the SP6 promotor. Following hybridization to fixed tissue sections, signals were detected by autoradiography after relatively short exposure times. These studies demonstrate that neuropeptide mRNAs can be detected within specific cells in the brain and that the patterns of hybridization match the localization of the peptides visualized by immunohistochemistry. Minimum numbers of mRNA copies encoding the peptides were determined by quantitative autoradiography.

Structure of the rat pro-opiomelanocortin (POMC) gene

The gene encoding pro-opiomelanocortin (POMC) presents unique regulatory features. In particular, glucocorticoids inhibit transcription of the POMC gene in the anterior pituitary, but not in the intermediate pituitary. In order to study the mechanism leading to transcriptional inhibition of POMC by glucocorticoid and the interaction of the glucocorticoid receptor complex with specific DNA sequences along the POMC gene, we have cloned the rat POMC gene and determined its structure. The gene is composed of three exons and appears to be present at a single copy per haploid genome. Besides the usual regulatory signals like 'TATA' and 'CCAAT' boxes, the upstream region contains sequences homologous to known enhancer sequences and to the glucocorticoid receptor binding site observed in glucocorticoid-responsive genes.

Changes in the processing of beta-endorphin in the hypothalamus and pituitary gland of female rats during sexual maturation

Puberty in the female rat is accompanied by a marked attenuation of the opioid inhibition of luteinizing hormone secretion. One factor which may contribute to this altered role is a change in the metabolism of opioid peptides during sexual maturation. beta-Endorphin undergoes a considerable degree of metabolism through both C-terminal proteolysis and N-acetylation, and these metabolites do not possess opioid activity. The processing of beta-endorphin in the hypothalamus and in the anterior and neurointermediate lobes of the pituitary gland in prepubertal and adult female rats was studied using gel filtration and high performance liquid chromatography coupled with radioimmunoassay. In the anterior lobe, high molecular weight precursors of beta-endorphin (pro-opiomelanocortin and beta-lipotropin) were present in prepubertal (28 days old) rats, but little authentic beta-endorphin was detected. In contrast, only beta-lipotropin and beta-endorphin were present in mature (70 days old) animals. Only beta-endorphin-sized peptides were present in the neurointermediate lobes of both prepubertal and adult rats. However, the proportion of N-acetylated metabolites was higher in sexually mature animals. In the hypothalamus, only beta-endorphin-sized peptides were present in both juvenile and adult animals. However, C-terminal proteolysis increased with age (no acetylated metabolites were detectable in this tissue). The proportion of the total beta-endorphin-like immunoreactivity attributable to beta-endorphin was lower in young adult (first dioestrus after vaginal opening) (55%) and mature (dioestrus, 61-64 days old) rats (56%) compared to prepubertal (30 days old) animals (75%) and the proportions of non-acetylated metabolites [beta-endorphin-(1-27) in young adults and beta-endorphin-(1-26) in adults] were increased concomitantly. These changes were correlated with a reduced luteinizing hormone response to the opiate antagonist naloxone in adult compared to prepubertal rats. beta-Endorphin is processed differently in the two lobes of the pituitary gland and in the hypothalamus and the degree of metabolism increases as the rat reaches sexual maturity. The increased metabolism of beta-endorphin in the hypothalamus, the site most likely to be involved in the control of luteinizing hormone secretion, results in a reduction in the relative proportion of the opioid active parent peptide. Thus, increased inactivation of beta-endorphin may contribute to the attenuation of the opioid inhibition of luteinizing hormone secretion observed during puberty.

Hybridization histochemistry

In this review we have used our own recent work as a flagship to illustrate the recent renaissance of interest in hybridization histochemistry. A trickle of papers followed the initial key excursion into the in situ labeling of tissue sections (48-50). Our own entry into this field started in 1978 and since then a confluence of important questions and technical advances has served to make hybridization histochemistry much more attractive as a research tool. Hybridization histochemistry is able to solve some problems for which there is no other suitable technique at this time. Hybridization histochemistry provides the location of anatomical sites of gene expression, and viral replication, with uniquely high specificity. We have taken 32P-labeled probes to what appears to be their limit of resolution, which is single cells in thin sections. While 32P has clear disadvantages, exposure time is relatively short and the use of fast-X-ray film to preview the results and estimate exposure time for emulsion has been turned to advantage. Our introduction (27) of the use of whole-mouse sections in hybridization histochemistry has great potential in hormonal, enzymatic, and growth factor gene expression and will no doubt prove of great use in developmental studies and examination of viral infection. The use of synthetic DNA (synthetic oligonucleotides) unshackles the technique from the need for an associated molecular biology laboratory and at once widens the horizon of application of the technique. Although hybridization histochemistry is a valuable research tool which will soon find a niche in many fields, in a short time it should become a key diagnostic aid. It may well become the method of preference for detection of the expression of oncogenes and other cancer-related genes and for viruses which for other reasons are difficult to detect.

Vasopressin mRNA in situ hybridization: localization and regulation studied with oligonucleotide cDNA probes in normal and Brattleboro rat hypothalamus

Hybridizable vasopressin mRNA may be quantitatively localized in situ in sections from rat hypothalamus. Radiolabeled oligonucleotide cDNA probes, synthesized by chemical and enzymatic means, provide strong hybridization in zones known to contain vasopressin cell bodies. Multiple single-stranded 32P-, 35S-, or 3H-labeled oligonucleotides demonstrate localized hybridization that increases as probes are lengthened from 8 to 75 bases. Competition studies, RNase experiments, anatomic localization, and use of multiple probes all support hybridization specificity. An approximate doubling of hybridizable mRNA in both supraoptic and paraventricular nuclei can be detected with dehydration of the animals. Hybridizable mRNA densities are virtually normal in hypothalamic nuclei of Brattleboro rats given free access to water. These methods can provide insight into regional mRNA dynamics and may reflect functional activity of peptidergic neurons.

Pro-opiocortin peptides in rat cerebrospinal fluid

Cerebrospinal fluid (CSF) taken from rats implanted with chronic cisternal cannulae was subjected to gel filtration chromatography on Sephadex G-50. Fractions were monitored using radioimmunoassays for N-terminal pro-opiocortin (N-POC), gamma 3-melanotropin (gamma 3-MSH), C-terminal adrenocorticotropin (C-ACTH), alpha-endorphin, beta-endorphin, gamma-lipotropin (gamma-LPH) and alpha-MSH. Two peaks which corresponded in elution position to rat N-POC (1-74) and gamma 3-MSH were detected. The major C-ACTH-immunoreactive (IR) peak was found to correspond to 14k ACTH. While no alpha-endorphin immunoreactivity was detected in rat CSF, three beta-endorphin-IR peaks were identified in positions expected for beta-LPH, beta-endorphin (1-31) and beta-endorphin (1-27), as well as a major peak of activity with the elution characteristics and cross-reactivity of rat gamma-LPH. HPLC of the alpha-MSH-IR material in rat CSF revealed the presence of a major peak of immunoreactivity whose retention time did not correspond to the known oxidised and reduced forms of alpha-MSH and its desacetylated and diacetylated derivatives. The identity of this peak is unknown.

The effect of the estrous cycle and estrogen on the release of immunoreactive alpha-melanocyte-stimulating hormone

Circulating levels and tissue content of alpha-MSH were measured on the morning of various days of the estrous cycle, and on the afternoon of proestrus in freely moving conscious rats. No surges of alpha-MSH were detected by RIA in the morning of various days of the cycle. The neurointermediate lobe content of alpha-MSH was slightly elevated on diestrus 1 as compared to the levels on diestrus 11 and proestrus but not to estrous levels. No changes in alpha-MSH content were detected in the anterior pituitary, the median eminence, mediobasal hypothalamus and the preoptic area at various stages of the estrous cycle. Plasma alpha-MSH levels were slightly elevated at 1500 hr of proestrus which was followed three hours later by a decline. This profile of plasma alpha-MSH on the afternoon of proestrus was reproduced by the SC administration of estradiol benzoate to long-term ovariectomized rats. These data suggest that, contrary to the results obtained by bioassay of alpha-MSH no surges of alpha-MSH occur on any day of the cycle, although a slight elevation on the afternoon of proestrus was detected. The altered pattern of release of this peptide on the afternoon of proestrus may be induced by estrogen.

N-acetyl endorphin in rat spermatogonia and primary spermatocytes

In previous reports modest levels of beta-endorphin have been found by radioimmunoassay in rat testis, and localized by immunofluorescence to the interstitial cells. We have confirmed these previous reports and extended them by showing that the majority of testicular endorphins are acetylated forms, N-acetyl gamma-endorphin, N-acetyl alpha-endorphin, and N-acetyl beta-endorphin1-27. In addition, N-acetylated endorphins are not found in interstitial cells, but are confined to spermatogonia and primary spermatocytes.

Detection of the messenger RNAs coding for the opioid peptide precursors in pituitary and adrenal by "in situ' hybridization: study in several mammal species

The messenger RNAs coding for opioid peptide precursors have been detected and mapped in histological sections by "in situ' hybridization using specific DNA probes labelled with 32P. Using bovine preproenkephalin A (PPA) cDNA, PPA mRNA was detected in adrenal medulla of bull, hamster and guinea pig. No signal was detected in adrenal of man, rat and cat. The pro-opiomelanocortin (POMC) mRNA was detected in pituitary of man, bull, cat, rat and pig, in all cells of the intermediate lobe as well as in scattered cells of the anterior lobe producing POMC. Adequate controls demonstrated the specificity of the labelling. These results provide evidence of the expression of the gene coding for PPA in the adrenal and for POMC in the pituitary. They show cross-hybridization of one DNA probe with mRNAs of various mammals and then provide evidence that one single probe can be used to analyze expression of a given gene in tissues of several animal species by "in situ' hybridization.

In situ hybridization of putative somatostatin mRNA within hypothalamus of the rat using synthetic oligonucleotide probes

The distribution of mRNA with high sequence homology to somatostatin mRNA within the periventricular hypothalamus of rat was assessed using in situ hybridization techniques with synthetic oligodeoxyribonucleotide probes, complementary to the 3' coding region of rat somatostatin mRNA. The probes (22- and 24-mers) were 5'-end labeled using T4 polynucleotide kinase and gamma-32P-ATP. They were used either individually or after ligation with T4 DNA ligase to form a 46-mer. Serial tissue sections (less than 10 microns) were taken from the level of the preoptic/anterior hypothalamus through the paraventricular hypothalamus. In situ hybridizations were conducted at room temperature in hybridization buffer. Neurons immunoreactive with antiserum raised against somatostatin were identified in alternate sections using standard immunocytochemical procedures. The anatomical location of the hybridization signal was determined by autoradiography. Our results show that the peri- and paraventricular hypothalamus is rich in transcripts putatively coding for somatostatin and that these transcripts are co-distributed with neurons immunoreactive with antisomatostatin immunoglobulin.

Localization of vasoactive intestinal peptide immunoreactivity in human foetus and newborn infant spinal cord

Using an indirect immunofluorescence method the distribution of vasoactive intestinal peptide (VIP) immunoreactivity was studied in human foetus and newborn infant spinal cord and dorsal root ganglia. Further, for comparison some newborn infant brains were also investigated. Vasoactive intestinal peptide-like immunoreactive fibres were exclusively found in the caudal spinal cord and corresponding dorsal root ganglia. No immunoreactive cell bodies were detected. The first appearance of VIP-like immunoreactive fibres in both spinal cord and dorsal root ganglia was suggested during the fourth month of foetal life. Most immunolabelled fibres, concentrated in the sacral segment, were distributed in the Lissauer tract, along the dorsolateral gray border, in the intermediolateral areas and near the central canal in the dorsolateral commissure. A few VIP-like immunoreactive fibres were also seen in the dorsal funiculus and occasionally in the ventral gray horn and ventral roots. Further, a large population of VIP-like immunoreactive fibres occurs longitudinally in dorsal root, in ganglia and in the spinal nerve exit zone. These findings indicate the early appearance of VIP-like immunoreactive fibres in the human foetus spinal cord and corresponding ganglia. Moreover, they emphasize that in both foetus and newborn infant spinal cord VIP-like immunoreactive fibre distribution is limited to the lumbosacral segment.

In situ hybridization histochemistry with synthetic oligonucleotides: strategies and methods

In situ hybridization histochemistry is a useful method for localizing specific mRNA and studying the regulation of gene expression in an anatomical context. Previously, classical recombinant DNA and microbiological techniques have been required to identify and nick-translate the cloned DNAs necessary for in situ hybridization experiments. These requirements can be circumvented by the use of synthetic oligonucleotides complementary to the mRNA of interest. Compared to cloned cDNA probes, oligonucleotides are easy to manufacture, penetrate tissue much more easily, can be made to correspond to a sequence at any point in a known cDNA structure, and allow for the design of more precise controls for in situ studies. We describe a number of considerations in oligonucleotide probe design, including unique probe design from cDNA sequences and mixed probe design from protein primary structure data. The issues of species specificity, G-C content, probe length, tissue-specific mRNA expression, repeated sequences, non-coding region specific probes, and gene family homologies are discussed in an in situ hybridization context. Alternative strategies for mixed probe design are also considered. Information on the synthesis, purification, and sequence confirmation of oligonucleotides is then presented, followed by methods for labeling and using these probes for in situ hybridization histochemistry. The special considerations of specificity controls are addressed, including combined in situ hybridization histochemistry and immunocytochemistry, competition studies, the use of multiple hybridization probes, Tm studies, and Northern analysis of extracted RNA. The current and future directions of research with this technique are considered, with emphasis on the need to improve quantitation in order to facilitate the study of gene expression and regulation at the single cell level.

Chemical anatomy of the brain

The development of sensitive histochemical-neuroanatomical techniques has made it possible to analyze the content of specific compounds in single nerve cells and their processes. In consequence, it has been possible to construct detailed maps of the distribution of various types of neurons on the basis of their transmitter substance. There are now many examples of neurons containing both a classical transmitter and a peptide. In some instances the peptides seem to support the action of the classical transmitters. This interaction may have applications in the prevention and treatment of nervous disease states.

Bilateral alpha-melanocyte stimulating hormonergic fiber system from zona incerta to cerebral cortex: combined retrograde axonal transport and immunohistochemical study

We employed a highly sensitive combination method of retrograde tracing and immunohistochemistry to identify an alpha-melanocyte-stimulating hormone (alpha-MSH)-containing fiber pathway from zona incerta to cerebral cortex. Biotin-horseradish peroxidase injected into the parietal cortex of the rat labeled a number of neurons in the zona incerta bilaterally, and simultaneous staining with an alpha-MSH antiserum revealed that a part of these neurons are alpha-MSHergic.

Histone RNA in amphibian oocytes visualized by in situ hybridization to methacrylate-embedded tissue sections

We present an in situ hybridization method for detecting cellular RNAs in tissue sections using methacrylate as the embedding medium. The technique offers the advantage of superior morphological preservation compared with previously published procedures. Since sections can be cut 1 micron or less in thickness, full advantage is taken of the short path length of 3H electrons. Applying this procedure to developing amphibian oocytes, we investigated the accumulation and localization of RNA complementary to the histone genes and their adjacent spacers. Histone RNA begins to accumulate in the cytoplasm of late pachytene-early diplotene oocytes, rapidly reaching a maximum concentration during Dumont stage 1. After this stage the concentration of histone RNA declines. RNA transcribed from histone coding regions is located almost exclusively in the cytoplasm of oocytes. Transcripts of the spacer regions, which are known to be synthesized on oocyte lampbrush chromosomes, do not accumulate in the oocytes. [3H]RNA complementary to U2 small nuclear RNA, used in these experiments as a control, hybridized predominantly to the nucleus of the oocytes.

Characterization and localization of proopiomelanocortin messenger RNA in the adult rat testis

Northern blot analysis of total RNA and polyadenylated RNA isolated from adult rat testes showed that a proopiomelanocortin (POMC)-like messenger RNA molecule is present in these extracts. The testicular POMC messenger RNA is comparable in length to amygdala and midbrain POMC messenger RNA and appears to be at least 200 nucleotides shorter than POMC messenger RNA found in the hypothalamus and anterior and intermediate lobes of the pituitary gland. Hybridization in situ showed that POMC messenger RNA is located in Leydig cells, which are the only testicular cells that contain immunostainable POMC-derived peptides. These results suggest that local synthesis of POMC occurs in the testis.

Tissue distribution of messenger RNAs coding for opioid peptide precursors and related RNA

All of the endogenous opioid peptides thus far identified are derived from three types of precursors, i.e. the corticotropin/beta-lipotropin precursor, preproenkephalin A and preproenkephalin B. Poly(A)-containing RNA from various bovine and porcine tissues has been subjected to blot hybridization analysis with the use of cDNA probes specific for the three opioid peptide precursors. Analysis with a corticotropin/beta-lipotropin precursor cDNA probe has revealed, in addition to the pituitary mRNA, a smaller hybridizable RNA species present in bovine extrapituitary tissues, such as the adrenal medulla, thyroid, thymus, duodenum and lung. The hypothalamus contains both these RNA species. DNA complementary to the smaller RNA species from the bovine adrenal medulla has been cloned. Analysis of the cloned cDNA, in conjunction with endonuclease S1 mapping of poly(A)-rich RNA from the adrenal medulla, has indicated that the smaller RNA species represents the 3'-terminal 712-729 nucleotides, excluding the poly(A) tail, of the pituitary corticotropin/beta-lipotropin precursor mRNA, having heterogeneous start sites. Analysis with a preproenkephalin A cDNA probe has shown the presence of hybridizable RNA in the bovine hypothalamus, duodenum and pituitary neurointermediate lobe in addition to the adrenal medulla. The hybridizable RNA species from all these tissues are indistinguishable in size. RNA hybridizable with a preproenkephalin B cDNA probe has been found in the porcine spinal cord and ileum besides the hypothalamus, and these RNA species exhibit an indistinguishable size. The results presented indicate that each opioid peptide precursor is synthesized in different tissues.

Mapping of neurons in the central nervous system of the guinea pig by use of antisera specific to the molluscan neuropeptide FMRFamide

Immunoreactive neurons were mapped in the central nervous system of colchicine-treated and untreated guinea pigs with the use of two antisera to the molluscan neuropeptide FMRFamide. These antisera were especially selected for their incapability to react with peptides of the pancreatic polypeptide family. Only one group of perikarya was stained by both antisera; this group was mainly located in the nucleus dorsomedialis hypothalami and extended to the nucleus paraventricularis and nucleus periventricularis hypothalami. The perikarya were found to project fibers to all regions of the hypothalamus, to the septum, nucleus proprius striae terminalis, nucleus paraventricularis thalami, nucleus centralis thalami, nucleus reuniens, medial, central and basal amygdala, area praetectalis, area tegmentalis ventralis of Tsai, substantia grisea centralis mesencephali, formatio reticularis mesencephali, nucleus centralis superior, locus coeruleus, nuclei parabrachiales, nucleus raphe magnus, A 5-region, vagus-solitarius complex, ventral medulla, nucleus spinalis nervi trigemini, and substantia gelatinosa of the spinal cord. In many brain regions FMRFamide-immunoreactive processes were found in close contact with blood vessels.

Detection of the messenger RNA coding for preproenkephalin A in bovine adrenal by in situ hybridization

The messenger RNA (mRNA) coding for the adrenal precursor of enkephalins (preproenkephalin-A) has been detected in bovine adrenal medulla cells using in situ hybridization with 32P-labelled preproenkephalin A (PPA) complementary DNA. In formaldehyde- and Carnoy-fixed tissue sections, an intense elective labelling restricted to the cells located at the periphery of the adrenal medulla can be detected after hybridization procedure, using X-ray film and classical autoradiographic procedure. Adequate controls show that this labelling is obtained only using PPA complementary DNA, inserted or not in its vector. Distribution of PPA mRNA appears identical to that of its immunoreactive end products, namely Met-enkephalin and BAM22 peptide, detected by immunohistochemistry. Norepinephrine, detectable using monoamine histofluorescence, appears restricted to the cells of the center of the gland unlabelled for PPA mRNA and its end-products. Cultured bovine adrenomedullary cells that exhibited enkephalin immunoreactivity also contain PPA mRNA located in their cytoplasm.

Three tachykinins in mammalian brain

Two polypeptide precursors to the neuropeptide substance P have recently been identified. One of them (β-preprotachykinin) contains amino acid sequences corresponding not only to substance P but also to substance K, a novel, related peptide. A third substance P-like peptide, neuromedin K, has recently been isolated from spinal cord. The existence in vertebrates of three members of the tachykinin family of peptides may account for pharmacological observations suggesting the presence of more than one type of substance P receptor in the nervous system.

Visualisation of messenger RNA directing peptide synthesis by in situ hybridisation using a novel single-stranded cDNA probe potential for the investigation of gene expression and endocrine cell activity

The neuropeptide tyrosine precursor (pre-pro-NPY) messenger RNA (mRNA) has been localised in formaldehyde-fixed human phaeochromocytoma tissue using a sensitive in situ hybridisation procedure and a novel single-stranded cDNA probe. The reaction product was revealed by avidin-biotin-peroxidase complex and streptavidin-gold complex with silver enhancement. This technique may be applied for the determination of biosynthetic activity of endocrine and neuronal cell bodies. This is largely due to its rapidity by comparison with conventional autoradiographic procedures, to the permanence of the reaction product and to the sensitivity of the visualisation steps.

Brain peptides: what, where, and why?

Within the past decade, a large number of peptides have been described within the vertebrate central nervous system. Some of these peptides were previously known to be present in nonneural vertebrate tissues, as well as in lower species, in which they may serve as primitive elements of intercellular communication prior to the development of neuronal or endocrine systems. In vertebrates, these peptides are thought to have neurotransmitter or neuromodulatory roles and appear to be involved in the regulation of a number of homeostatic systems, although the mechanisms of their actions are still unclear.