Catia Sternini

Distribution and characterization of calcitonin gene-related peptide immunoreactivity in the digestive system of normal and capsaicin-treated rats

The distribution and characterization of calcitonin gene-related peptide immunoreactivity in the digestive system of normal, capsaicin-treated, and littermate control rats were studied by radioimmunoassay, chromatography, and immunohistochemistry. The highest concentrations of calcitonin gene-related peptide immunoreactivity were found in the stomach (45 +/- 2.8 pmol/g wet wt, nonsecretory region; 38.7 +/- 4.4 pmol/g wet wt, secretory region) and rectum (30.9 +/- 1.6 pmol/g wet wt). Significant amounts of peptide were also found in the other regions of the gut and in the pancreas. Neonatal treatment with capsaicin, which causes a permanent degeneration of most of the small-diameter sensory neurons, reduced calcitonin gene-related peptide content by greater than 95% in the esophagus and stomach, by 60% in the pancreas, and by less than 50% in the intestine, when compared with littermate controls. Separation of extracts from the gut, pancreas, and brain by chromatography gave major peaks corresponding to the predicted rat calcitonin gene-related peptide and small unidentified peaks, which presumably arise from metabolism of the peptide. Immunohistochemical studies demonstrated that in the esophagus and stomach, calcitonin gene-related peptide immunoreactivity is restricted to nerve fibers, whereas in the intestine it is localized in both nerve fibers and enteric ganglion cells. In capsaicin-treated rats there was a virtually complete elimination of calcitonin gene-related peptide immunoreactive fibers innervating the esophagus and stomach, whereas in the small and large intestine there was a dramatic reduction and often a complete elimination of those associated with blood vessels and a slighter reduction of the nonvascular immunoreactive fibers. The results of this study indicate that calcitonin gene-related peptide immunoreactive nerve fibers innervating the rat digestive system originate from both intrinsic (enteric) and extrinsic (presumably sensory) sources and that both the intrinsic and extrinsic components appear to contain a substance that corresponds to the predicted calcitonin gene-related peptide.

A novel α subunit in rat brain GABAA receptors

Abstract Two cDNAs (α1 and α4) from rat brain cDNA libraries encode isoforms of the a subunit of the GABA/benzodiazepine receptor, which differ at 30% of their amino acid residues. Northern blot analysis and in situ hybridization histochemistry show that α1 and α4 mRNAs have distinct sizes and distinct regional and cellular distributions in rat brain: both mRNAs are found in the cortex and hippocampus; however, only the α1 mRNA is detected in the cerebellum. We injected RNA transcribed from αa1 and α4 cDNAs into Xenopus oocytes, together with an RNA for a rat β subunit. We obtained GABA-dependent inward currents that were reversibly blocked by picrotoxin. Picrotoxin alone, applied to oocytes producing the α and β polypeptides, elicited an outward current. We suggest that these polypeptides together produce GABA-gated ion channels that can also open spontaneously.

Enteroendocrine cells: a site of ‘taste’ in gastrointestinal chemosensing

Purpose of reviewThis review discusses the role of enteroendocrine cells of the gastrointestinal tract as chemoreceptors that sense lumen contents and induce changes in gastrointestinal function and food intake through the release of signaling substances acting on a variety of targets locally or at a distance. Recent findingsRecent evidence supports the concept that chemosensing in the gut involves G protein-coupled receptors and effectors that are known to mediate gustatory signals in the oral cavity. These include sweet-taste and bitter-taste receptors, and their associated G proteins, which are expressed in the gastrointestinal mucosa, including selected populations of enteroendocrine cells. In addition, taste receptor agonists elicit a secretory response in enteroendocrine cells in vitro and in animals in vivo, and induce neuronal activation. SummaryTaste-signaling molecules expressed in the gastrointestinal mucosa might participate in the functional detection of nutrients and harmful substances in the lumen and prepare the gut to absorb them or initiate a protective response. They might also participate in the control of food intake through the activation of gut–brain neural pathways. These findings provide a new dimension to unraveling the regulatory circuits initiated by luminal contents of the gastrointestinal tract.

The opioid system in the gastrointestinal tract

µ‐, δ‐ and κ‐opioid receptors (ORs) mediate the effects of endogenous opioids and opiate drugs. Here we report (1) the distribution of µOR in the guinea‐pig and human gastrointestinal tract in relation to endogenous ligands, to functionally distinct structures in the gut and to δOR and κOR; and (2) the ligand‐induced µOR endocytosis in enteric neurones using in vitro and in vivo models. In the guinea pig, µOR immunoreactivity is confined mainly to the myenteric plexus. µOR myenteric neurones are most numerous in the small intestine, followed by the stomach and the proximal colon. µOR immunoreactive fibres are dense in the muscle layer and the deep muscular plexus, where they are in close association with interstitial cells of Cajal. This distribution closely matches the pattern of enkephalin. µOR enteric neurones comprise functionally distinct populations of neurones of the ascending and descending pathways of the peristaltic reflex. In human gut, µOR immunoreactivity is localized to myenteric and submucosal neurones and to immune cells of the lamina propria. δOR immunoreactivity is located in both plexuses where it is predominantly in varicose fibres in the plexuses, muscle and mucosa, whereas κOR immunoreactivity appears to be confined to the myenteric plexus and to bundles of fibres in the muscle. µOR undergoes endocytosis in a concentration‐dependent manner, in vitro and in vivo. Pronounced µOR endocytosis is observed in neurones from animals that underwent abdominal surgery that has been shown to induce delay in gastrointestinal transit. We can conclude that all three ORs are localized to the enteric nervous system with differences among species, and that µOR endocytosis can be utilized as a means to visualize enteric neurones activated by opioids and sites of opioid release.

Localization of calcitonin gene-related peptide-like immunoreactivity in neurons of the rat gastrointestinal tract

Calcitonin gene-related peptide (CGRP)-like immunoreactivity was localized in neuronal processes and somata of the rat gastrointestinal tract. Varicose processes were observed in the myenteric and submucosal plexuses, smooth muscles, submucosa, mucosa and around blood vessels. Immunoreactive somata were visualized in the myenteric and submucosal ganglia of the intestine in colchicine-treated rats. These observations, together with previous neuroanatomical and pharmacological studies, suggest that CGRP may be involved in regulatory functions of the gastrointestinal tract.

Somatostatin 2A receptor is expressed by enteric neurons, and by interstitial cells of Cajal and enterochromaffin-like cells of the gastrointestinal tract.

Somatostatin exerts multiple effects by activating distinct G protein‐coupled receptors. Here we report the cellular sites of expression of the somatostatin subtype 2A (sst2A) receptor in the rat enteric nervous system by using a C‐terminus‐specific, affinity‐purified antiserum and immunohistochemistry. Antibody specificity was confirmed by the cell surface staining of human embryonic kidney 293 cells expressing the sst2A receptor, the lack of staining of cells expressing the somatostatin subtype 2B receptor, and the abolition of staining by preincubating the antiserum with the C‐terminus peptide used for immunization, sst2A(361‐369). The sst2A receptor antibody recognized a broad 80 kDa band on Western blots of membranes prepared from cells transfected with sst2A receptor cDNA; following receptor membrane deglycosylation, the antibody detected an additional 40 kDa band. In the enteric nervous system, the sst2A antibody primarily stained neurons of the myenteric and submucosal plexuses, and abundant fibers distributed to the muscle, mucosa, and vasculature. Immunoreactive staining was also observed in non‐neuronal cells, including presumed interstitial cells of Cajal of the intestine and enterochromaffin‐like cells of the stomach. Fibers expressing sst2A receptor immunoreactivity were often in close proximity to D cells of the gastric and intestinal mucosa. Colocalization of somatostatin and sst2A receptor immunoreactivities was not observed in endocrine cells nor in enteric neurons. Double‐label immunohistochemistry revealed colocalization of sst2A and vasoactive intestinal peptide immunoreactivities in enteric neurons. The multiple types of cells expressing the sst2A receptor, including enteric neurons and non‐neuronal structures, in addition to the relationship between somatostatin and sst2A receptor elements, provide evidence that the sst2A receptor mediates somatostatin effects in the gastrointestinal tract via neuronal and paracrine pathways. J. Comp. Neurol. 386:396‐408, 1997.

Independent cellular and ontogenetic expression of mRNAS encoding three α polypeptides of the rat GABAA receptor

Previous studies have shown that several distinct but related polypeptides can serve as alpha subunits of functional GABAA receptors. Furthermore, the diversity of these polypeptides at least partially accounts for the functional heterogeneity of GABAA receptors. In this paper, we report the results of in situ hybridization studies using probes derived from our recently reported cDNAs for alpha 1, alpha 2, and alpha 4 GABAA receptor polypeptides. We show that the mRNAs that encode these isoforms have distinct regional and cellular distributions and are present at widely varying levels within the rat brain. In addition, our Northern blot analyses indicate that each of these three alpha mRNAs has a distinct pattern of ontogenetic regulation. Differential regulation of alpha polypeptide isoforms may lead to changes in GABAA receptor function during ontogeny as well as to distinct cellular responses to GABA and GABA-related drugs.

Calcitonin gene-related peptide immunoreactivity in the biliary pathway and liver of the guinea-pig: distribution and colocalization with substance P

SummaryCalcitonin gene-related peptide immunoreactivity was localized immunohistochemically in nerve fibers innervating the biliary pathway and liver of the guinea-pig. Immunoreactive fibers are present in all layers of the gallbladder and biliary tract and are particularly numerous around blood vessels. In the liver, immunoreactive processes are usually restricted to the interlobular space and porta hepatis, and only a few, very thin, beaded processes were observed in the hepatic parenchyma. A rich innervation is also associated with the vena portae. Positive ganglion cell bodies were not visualized within the ganglionated plexus of the biliary system, whereas they were found in the myenteric and submucosal plexus in the cranial portion of the duodenum corresponding to the sphincter of Oddi. The vast majority, if not all, of calcitonin gene-related peptide-immunoreactive fibers contain substance P immunoreactivity; however, there are some substance P-containing fibers lacking calcitonin gene-related peptide immunoreactivity. The lack of co-occurrence of calcitonin gene-related peptide and substance P immunoreactivities in intrinsic ganglion cells suggests that these two peptides are coexpressed in the extrinsic component of the innervation of the hepatobiliary system.

Expression of cholecystokinin a receptors in neurons innervating the rat stomach and intestine

BACKGROUND & AIMS Two distinct receptors, cholecystokinin (CCK)-A and CCK-B, mediate CCK effects in the digestive system. The aim of this study was to elucidate the cellular sites of expression of CCK-A receptor in the rat stomach and small intestine. METHODS We developed and characterized an antibody to the N-terminal region (LDQPQPSKEWQSA) of rat CCK-A receptor and used it for localization studies with immunohistochemistry. RESULTS Specificity of the antiserum was demonstrated by (1) detection of a broad band at 85-95 kilodaltons in Western blots of membranes from CCK-A receptor CHO-transfected cells; (2) cell surface staining of CCK-A receptor-transfected cells, (3) translocation of CCK-A receptor immunostaining in CCK-A receptor-transfected cells after exposure to CCK; and (4) abolition of tissue immunostaining by preadsorbtion of the antibody with the peptide used for immunization. CCK-A receptor immunoreactivity was localized to myenteric neurons and to fibers in the muscle and mucosa. In the stomach, myenteric neurons and mucosal fibers were abundant. Many CCK-A receptor myenteric neurons contained the inhibitory transmitter vasoactive intestinal polypeptide, and some were immunoreactive for the excitatory transmitter substance P. Subdiaphragmatic vagotomy reduced the density of CCK-A receptor fibers in the gastric mucosa by approximately 50%, whereas celiac/superior mesenteric ganglionectomy had no detectable effect on fiber density. CONCLUSIONS CCK-A receptor is expressed in functionally distinct neurons of the gastrointestinal tract. CCK-A receptor may mediate reflexes stimulated by CCK through the release of other transmitters from neurons bearing the receptor.

Expression of substance P/neurokinin A-encoding preprotachykinin messenger ribonucleic acids in the rat enteric nervous system

The cellular localization of substance P/neurokinin A-encoding preprotachykinin mRNAs in the rat enteric nervous system was studied by means of in situ hybridization histochemistry using 35S- or 3H-labeled single-stranded ribonucleic acid (RNA) probes which recognize all three preprotachykinin mRNA species, alpha, beta, and gamma. Substance P/neurokinin A-encoding mRNAs are expressed in neurons within the myenteric plexus of the esophagus and stomach, being more numerous in the latter, and in ganglion cells distributed to both the myenteric and submucosal plexuses of the intestine. Specificity of the hybridization was demonstrated by the lack of specific signal above background in sections incubated with a sense RNA probe or pretreated with ribonuclease A before hybridization. Ribonucleic acid blot hybridization analysis of RNA extracts from both the muscle layer-myenteric plexus and submucosal layer preparations of the duodenum demonstrated a single band of hybridization at 1.3 kb. Solution hybridization-nuclease protection assays showed multiple preprotachykinin-encoding transcripts in these RNA extracts, with an abundance level of gamma-mRNA greater than beta-mRNA much greater than alpha-mRNA, which is similar to that observed in the rat brain. Our results indicate that the preprotachykinin gene encoding the tachykinin peptides, substance P and neurokinin A, is transcribed in a population of enteric neurons that have a regional distribution comparable to the previously described tachykinin-like immunoreactive neurons, suggesting that specific mRNAs and the posttranslationally processed peptides are localized in the same structures.