Neuronal localization of prosomatostatin mRNA in the rat brain with in situ hybridization histochemistry

Individual neurons containing prosomatostatin mRNA were identified with in situ hybridization histochemistry. Our results demonstrate a widespread distribution of prosomatostatin mRNA in several regions of the rat central nervous system. Neurons containing this transcript were most abundant in the anterior olfactory nucleus, hypothalamus, hippocampus, and amygdala as well as in all regions of the cerebral cortex. Moreover, the distribution of mRNA-containing perikarya was coextensive with the location of neurons containing somatostatin-like immunoreactivity in all areas of the brain examined. Somatostatin neurons varied in their morphology and amount of hybridization signal from region to region. The widespread distribution and regional variations in neuronal morphology and the amount of hybridization signal are consistent with a neurotransmitter and/or a neuromodulator role for somatostatin in addition to its well-established neuroendocrine role. These results demonstrate that both the peptide and its mRNA are found in perikarya in the same areas and that they are therefore the sites of synthesis for somatostatin.

Recent developments in the use of synthetic oligonucleotides for in situ hybridization histochemistry

Synthetic oligonucleotides have been used with increasing frequency as probes for the detection and study of the regulation of specific mRNAs by in situ hybridization histochemistry. These probes can be easily obtained and used by the nonmolecular biologist, and they have been shown to be effective for the study of a wide range of mRNAs in neuronal and neuroendocrine tissues. Considerations in oligonucleotide probe design, synthesis, purification, and labeling are described in this article, and current procedures for tissue preparation and hybridization are discussed. In addition, control procedures and methods for the quantitation of in situ hybridization by image analysis are discussed. Finally, the combination of this technique with immunocytochemistry and retrograde tract-tracing is reviewed. The coupling of quantitative in situ hybridization with other neuronal markers, e.g., of connectivity, provides an increasingly valuable technology for exploring the regulation of gene expression in a rich anatomical context.

Quantitation of cellular resolution in situ hybridization histochemistry in brain by image analysis

A new method for relative quantitation of mRNA levels with single neuron resolution is described. Hybridized tissue sections are emulsion dipped, exposed, and developed. The resulting silver grains are visualized using dark-field microscopy at high magnification. The method relies on computer-based image analysis of sequentially located, high resolution, small fields containing the cell images, each of which is analyzed for mRNA content. Maps of cell distributions are constructed, with cell marks color-coded for relative mRNA levels, yielding previously unavailable information on regional distribution of quantitative cellular expression of specific mRNA in brain.

Autoradiographic differentiation of mu, delta, and kappa opioid receptors in the rat forebrain and midbrain

While there is an abundance of pharmacological and biochemical evidence to suggest the existence of multiple opioid receptors, their precise localization within the brain is unclear. To help clarify this issue, the present study examined the distributions of the mu, delta, and kappa opioid receptor subtypes in the rat forebrain and midbrain using in vitro autoradiography. Mu and delta receptors were labeled with the selective ligands 3H-DAGO (Tyr- D-Ala-Gly-MePhe-Gly-ol), and 3H-DPDPE (D-Pen2, D-Pen5-enkephalin), respectively, while the kappa receptors were labeled with 3H-(-)bremazocine in the presence of unlabeled DAGO and DPDPE. Based on previous findings in our laboratory, the labeling conditions were such that each ligand selectively occupied approximately 75% of each of the opioid sites. The results demonstrated that all 3 opioid receptor subtypes were differentially distributed in the rat brain. Mu binding was dense in anterior cingulate cortex, neocortex, amygdala, hippocampus, ventral dentate gyrus, presubiculum, nucleus accumbens, caudate putamen, thalamus, habenula, interpeduncular nucleus, pars compacta of the substantia nigra, superior and inferior colliculi, and raphe nuclei. In contrast, delta binding was restricted to only a few brain areas, including anterior cingulate cortex, neocortex, amygdala, olfactory tubercle, nucleus accumbens, and caudate putamen. Kappa binding, while not as widespread as observed with mu binding, was densely distributed in the amygdala, olfactory tubercle, nucleus accumbens, caudate putamen, medial preoptic area, hypothalamus, median eminence, periventricular thalamus, and interpeduncular nucleus. While all 3 opioid receptor subtypes could sometimes be localized within the same brain area, their precise distribution within the region often varied widely. For example, in the caudate putamen, mu binding had a patchy distribution, while delta and kappa sites were diffusely distributed, with delta sites being particularly dense ventrolaterally and kappa sites being concentrated ventromedially. These results support the existence of at least 3 distinct opioid receptors with possibly separate functional roles.

Pharmacological and anatomical evidence of selective mu, delta, and kappa opioid receptor binding in rat brain

While the distribution of opioid receptors can be differentiated in the rat central nervous system, their precise localization has remained controversial, due, in part, to the previous lack of selective ligands and insensitive assaying conditions. The present study analyzed this issue further by examining the receptor selectivity of [3H]DAGO (Tyr-D-Ala-Gly-MePhe-Gly-ol), [3H]DPDPE (2-D-penicillamine-5-D-penicillamine-enkephalin), [3H]DSLET (Tyr-D-Ser-Gly-Phe-Leu-Thr) and [3H](-)bremazocine, and their suitability in autoradiographically labelling selective subpopulations of opioid receptors in rat brain. The results from saturation, competition, and autoradiographic experiments indicated that the three opioid receptor subtypes can be differentiated in the rat brain and that [3H]DAGO and [3H]DPDPE selectively labelled mu and delta binding sites, respectively. In contrast, [3H]DSLET was found to be relatively non-selective, and labelled both mu and delta sites. [3H]Bremazocine was similarly non-selective in the absence of mu and delta ligands and labelled all three opioid receptor subtypes. However, in the presence of 100 nM DAGO and DPDPE, concentrations sufficient to saturate the mu and delta sites, [3H]bremazocine did label kappa sites selectively. The high affinity [3H]bremazocine binding sites showed a unique distribution with relatively dense kappa labelling in the hypothalamus and median eminence, areas with extremely low mu and delta binding. These results point to the selectivity, under appropriate conditions, of [3H]DAGO, [3H]DPDPE and [3H]bremazocine and provide evidence for the differential distribution of mu, delta, and kappa opioid receptors in rat brain.

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.

[3H]dynorphin A binding and kappa selectivity of prodynorphin peptides in rat, guinea-pig and monkey brain

We have previously demonstrated that [3H]dynorphin A selectively labels kappa opioid receptors in guinea-pig whole brain. In these current studies, using protection from inactivation by beta-chloronaltrexamine (beta-CNA), we are able to demonstrate that although dynorphin A prefers kappa receptors, it will label mu receptors when kappa receptors are not available, or present in only a small number. Thus, differences in numbers of mu and kappa receptors present in brain preparations are critical in determining the receptor binding profile of [3H]dynorphin A across species. Additionally, although all the prodynorphin derived peptides show kappa preference, the ability of the other prodynorphin derived peptides to compete with [3H]dynorphin A for its receptor varies across species. Consequently, in a highly enriched kappa preparation such as monkey cerebral cortex, [3H]dynorphin A appears to label kappa receptors with substantial selectivity, and the other prodynorphin-derived peptides show less ability to compete with dynorphin A for its receptor. In contrast, in a kappa-poor tissue such as rat brain, all of the prodynorphin-derived peptides, including dynorphin A-(1-8), show very similar potency. Thus, differences in mu and kappa receptor numbers across brain regions and species lead to differences in the receptor binding profile of dynorphin A.

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.

Correlation of [3H]diazepam binding density with anxiolytic locus in the amygdaloid complex of the rat

Using [3H]diazepam binding, high concentrations of receptors were found in the frontal cortex and lateral amygdala. Infusions of chlordiazepoxide into the lateral amygdala induced a release of responding measured during the component of a conditioned emotional response task previously associated with an aversive stimulus. The lateral amygdala appears to be an important component of the forebrain circuitry involved in the expression of anxiety and sensitive to benzodiazepine drugs.

Time of origin of opioid peptide-containing neurons in the rat hypothalamus

By using a combined technique of immunocytochemistry and [3H]thymidine autoradiography, we have determined the "birth date" of opioid peptide-containing neurons in several hypothalamic nuclei and regions. These include proopiomelanocortin (POMC) neurons (represented by ACTH immunoreactivity) in the arcuate nucleus; dynorphin A neurons in the supraoptic and paraventricular nuclei and the lateral hypothalamic area; and leu-enkephalin neurons in the periventricular, ventromedial, and medial mammillary nuclei, as well as in preoptic and perifornical areas. Arcuate POMC neurons were born very early in embryonic development, with peak heavy [3H]thymidine nuclear labelling occurring on embryonic day E12. Supraoptic and paraventricular dynorphin A neurons were also labelled relatively early (peak at E13). The lateral hypothalamic dynorphin A neurons showed peak heavy labelling also on day E12. By contrast, leu-enkephalin neurons in the periventricular nucleus and medial preoptic area exhibited peak heavy nuclear labelling on day E14. Furthermore, perifornical and ventromedial leu-enkephalin neurons were also born relatively early (peak on days E12 and E13, respectively). However, the leu-enkephalin neurons in the medial mammillary nucleus were born the latest of all cell groups studied (i.e., peak at E15). The results indicate a differential genesis of these opioid peptide-containing neuronal groups in different hypothalamic nuclei and regions.

Development of hypothalamic opioid neurons: a combined immunocytochemical and [3H]thymidine autoradiographic study

Using a combined technique of immunocytochemistry and [3H]thymidine autoradiography, we have determined the "birth-date" of opioid peptide containing neurons in three hypothalamic nuclei. These include proopiomelanocortin neurons (indicated by ACTH immunoreactivity) in the arcuate nucleus, dynorphin A neurons in the supraoptic nucleus, and [Leu]enkephalin neurons in the periventricular nucleus. Arcuate proopiomelanocortin neurons were born very early in embryonic development, with peak heavy [3H]thymidine nuclear labelling occurring on embryonic day E12. Supraoptic dynorphin A neurons were also labelled relatively early (peak at E13). By contrast, [Leu]enkephalin neurons in the periventricular nucleus exhibited peak heavy nuclear labelling on day E14. The results indicate a differential genesis of these three opioid peptide containing neuronal groups in three different hypothalamic nuclei.

Analysis of opioid and non-opioid end products of pro-dynorphin in the substantia nigra of the rat

The substantia nigra is among the richest pro-dynorphin terminal field regions in the rat brain. We therefore contrasted processing in this area to the known processing in the posterior pituitary. Fractionation of acid extracts of the posterior pituitary by gel filtration followed by analysis by radioimmunoassay indicated that the molar ratio of dynorphin A(1-17) to dynorphin A(1-8) averaged 1:2. The levels of dynorphin A-related end products to alpha-neo-endorphin and bridge peptide (a 2K nonopioid end product of pro-dynorphin) were approximately equimolar; however, the levels of dynorphin B-sized material were 50% lower than dynorphin A levels. Similar analyses of acid extracts of the substantia nigra also indicated that the levels of dynorphin A, alpha-neo-endorphin, and bridge peptide were approximately equimolar. In this terminal field the levels of dynorphin B-sized material were approximately 60% lower than dynorphin A. A striking feature of the nigral system was that the molar ratio of dynorphin A(1-17) to dynorphin A(1-8) averaged 1:16. Thus, in the nigra, dynorphin A(1-17) is primarily a biosynthetic intermediate rather than as an end product.

Prodynorphin peptide immunocytochemistry in rhesus monkey brain

The present study describes the immunocytochemical distribution of peptides derived from the prodynorphin precursor in the brain of the rhesus monkey (Macaca mulatta). Animals were treated with colchicine (intracerebroventricularly) prior to perfusion to enhance the observation of perikaryal immunoreactivity. Using antisera generated against dynorphin A(1-17), dynorphin B(1-13), and prodynorphin(186-208) (or bridge peptide), the anatomical distribution of dynorphin systems was mapped. The results indicate a widespread neuronal localization of immunoreactivity from the cerebral cortex to the caudal medulla. Anti-dynorphin B and anti-bridge peptide sera proved useful for the demonstration of neuronal perikarya, while the dynorphin A antiserum was best for localizing terminal projection fields. Immunoreactive perikarya are located in numerous brain loci, including the cingulate cortex, caudate nucleus, amygdala, hypothalamus (especially the magnocellular nuclei), thalamus, substantia grisea centralis, parabrachial nucleus, nucleus tractus solitarius, and other nuclei. In addition, fiber and terminal immunoreactivity are seen in varying densities in the striatum and pallidum, substantia innominata, hypothalamus, substantia nigra pars reticulata, parabrachial nucleus, spinal trigeminal nucleus, and other areas. The distribution of prodynorphin peptides in the brain of the monkey is similar to that described for the rat brain; however, significant differences also exist. Other interspecies differences in the anatomy of prodynorphin and proenkephalin neuronal systems in the monkey and human brain are further discussed.

Combined autoradiographic-immunocytochemical analysis of opioid receptors and opioid peptide neuronal systems in brain

Using adjacent section autoradiography-immunocytochemistry, the distribution of [3H]naloxone binding sites was studied in relation to neuronal systems containing [Leu]enkephalin, dynorphin A, or beta-endorphin immunoreactivity in rat brain. Brain sections from formaldehyde-perfused rats show robust specific binding of [3H]naloxone, the pharmacological (mu-like) properties of which appear unaltered. In contrast, specific binding of the delta ligand [3H]D-Ala2,D-Leu5-enkephalin was virtually totally eliminated as a result of formaldehyde perfusion. Using adjacent section analysis, we have noted associations between [3H]naloxone binding sites and one, two, or all three opioid systems in different brain regions; however, in some areas, no apparent relationship could be observed. Within regions, the relationship was complex; for example, in caudate-putamen, patches of opioid receptors did not correspond to the distribution of enkephalin immunoreactivity, but there was a correspondence between subcallosal streaks of binding sites and enkephalin. The complexity of the association between [3H]naloxone binding sites and the multiple opioid systems, and previous reports of colocalization of mu and kappa receptors in rat brain, are inconsistent with a simple-one-to-one relationship between a given opioid precursor and opioid receptor subtype. Instead, since differential processing of the three precursors gives rise to peptides of varying receptor subtype potencies and selectivities, the multiple peptide-receptor relationships may point to a key role of post-translational processing in determining the physiological consequences of opioid neurotransmission.

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.

Proopiomelanocortin peptide immunocytochemistry in rhesus monkey brain

The immunocytochemical distribution of proopiomelanocortin (POMC) peptides (beta-endorphin, ACTH, alpha-MSH, 16K fragment) was studied in the brain of the rhesus monkey (Macaca mulatta). Some animals were administered colchicine intracerebroventricularly prior to sacrifice to enhance the visualization of perikaryal immunoreactivity. Immunoreactive perikarya are localized to hypothalamic infundibular nucleus, giving rise to several distinct projections. Rostral projections extend through midline diencephalic and preoptic areas, and enter the telencephalon. Along this course, immunoreactive fibers are seen in midline hypothalamic and preoptic nuclei, nucleus of the diagonal band, olfactory tubercle, nucleus accumbens, bed nucleus of stria terminalis, septum, and other limbic structures in telencephalon. Caudal to the anterior commissure, some fibers ascend dorsally to enter the midline thalamus, which they innervate. Lateral projections of the infundibular perikarya course through the medial-basal hypothalamus, dorsal to the optic tracts, and enter the amygdala region where they innervate more medially situated amygdaloid nuclei. Caudal projections of the POMC neurons also extend through midline diencephalon, some coursing along a periventricular path to innervate midline hypothalamic and thalamic nuclei. This projection extends into the mesencephalic substantia grisea centralis and may also contribute to the innervation of more dorsally situated nuclei in the pons and medulla, such as the parabrachial nuclei and nucleus tractus solitarius. Other caudal projections originating in the hypothalamus course through the ventral tegmentum of mesencephalon and pons and may contribute to the innervation of midline raphe and other ventrally situated nuclei in the pons and medulla. The distribution of immunoreactive perikarya and fibers in the brain of rhesus monkey is strikingly similar to that found in the rat brain. However, subtle differences appear to exist in the innervation patterns of particular brain regions.

Anatomical relationship between opioid peptides and receptors in rhesus monkey brain

To determine whether opioid peptide-receptor pharmacological association found in vitro (e.g., enkephalin-delta, dynorphin-kappa) predict anatomical relationships in situ, immunocytochemical and receptor autoradiographic studies were carried out on adjacent sections from the same brains of formaldehyde-perfused rhesus monkeys. Apparent mu and kappa opioid receptors (labeled, respectively, by [3H] naloxone and [3H]bremazocine under different incubation conditions), but not delta opioid receptors (labeled by [3H]D-Ala2, D-Leu5-enkephalin), survived the fixation procedure, and were found to be colocalized throughout the brain. We have observed complex associations between these binding sites and one, two, or all three opioid peptide systems (i.e., proopiomelanocortin, proenkephalin, and prodynorphin) in different brain regions. These multiple opioid peptide-receptor subtype associations are apparent, for example, in neural systems involved in the processing of pain stimuli, and may be important for mediating different types of analgesia. Since differential processing of proenkephalin and prodynorphin can give rise to opioids of varying receptor selectivities, the colocalization of opioid receptor subtypes may signify that such processing is a key regulatory event in determining which receptor subtype is activated and, thus, the physiological consequences of opioid neurotransmission.

Detection of multiple strains of latent herpes simplex virus type 1 within individual human hosts

One hundred and fifteen isolates of herpes simplex virus were recovered from parallel explant cultures of trigeminal and vagus ganglia and trigeminal nerve roots derived from 20 unselected human cadavers. Restriction enzyme patterns of strains recovered from 18 of 20 individuals could be differentiated from individual to individual, although all isolates from a single host were identical. Isolates from two individuals differed among themselves in the number and location of certain restriction enzyme sites.

Recovery of herpes simplex virus genetic information from human trigeminal ganglion cells following superinfection with herpes simplex virus type 2 temperature-sensitive mutants

Explant cultures of human trigeminal ganglia were derived from 36 individuals. Those cultures which failed to release herpes simplex virus (HSV) spontaneously were superinfected at various times after establishment in vitro with a range of HSV-2 temperature-sensitive (ts) mutants. Eight cultures from six individuals contained HSV-specific genetic information which could be detected or rescued following superinfection. Restriction enzyme analysis of ts+ virus recovered from the ganglia of two individuals following superinfection was identical to that of endogenous HSV-1 spontaneously released from parallel cultures. Retrieval of ts+ virus by this technique suggests products of the superinfecting virus activated expression of whole genomes or that spontaneous virus expression occurred unrelated to the act of superinfection.

Colocalization of proenkephalin peptides in rat brain neurons

A serial, thin-section immunocytochemical study of the anatomical distribution of Leu-enkephalin and BAM-22P (an adrenal proenkephalin peptide) demonstrated that both immunoreactivities occur within the same neurons throughout brain. However, neither peptide immunoreactivity could be observed in neurons containing dynorphin A immunoreactivity. These results are consistent with the possibility that the enkephalin precursor in brain is similar to that sequenced in adrenal, but fail to support the hypothesis that the dynorphin precursor is a major source of Leu-enkephalin in brain.