In Vitro Modelling of Oral Microbial Invasion in the Human Colon

Recent advances in the human microbiome characterization have revealed significant oral microbial detection in stools of dysbiotic patients. However, little is known about the potential interactions of these invasive oral microorganisms with commensal intestinal microbiota and the host. In this proof-of-concept study, we proposed a new model of oral-to-gut invasion by the combined use of an in vitro model simulating both the physicochemical and microbial (lumen- and mucus-associated microbes) parameters of the human colon (M-ARCOL), a salivary enrichment protocol, and whole-metagenome shotgun sequencing. Oral invasion of the intestinal microbiota was simulated by injection of enriched saliva in the in vitro colon model inoculated with a fecal sample from the same healthy adult donor. The mucosal compartment of M-ARCOL was able to retain the highest species richness levels over time, while species richness levels decreased in the luminal compartment. This study also showed that oral microorganisms preferably colonized the mucosal microenvironment, suggesting potential oral-to-intestinal mucosal competitions. This new model of oral-to-gut invasion can provide useful mechanistic insights into the role of oral microbiome in various disease processes. IMPORTANCE Here, we propose a new model of oral-to-gut invasion by the combined use of an in vitro model simulating both the physicochemical and microbial (lumen- and mucus-associated microbes) parameters of the human colon (M-ARCOL), a salivary enrichment protocol, and whole-metagenome shotgun sequencing. Our study revealed the importance of integrating the mucus compartment, which retained higher microbial richness during fermentation, showed the preference of oral microbial invaders for the mucosal resources, and indicated potential oral-to-intestinal mucosal competitions. It also underlined promising opportunities to further understand mechanisms of oral invasion into the human gut microbiome, define microbe-microbe and mucus-microbe interactions in a compartmentalized fashion, and help to better characterize the potential of oral microbial invasion and their persistence in the gut.

Fungi participate in the dysbiosis of gut microbiota in patients with primary sclerosing cholangitis

OBJECTIVE

Patients with primary sclerosing cholangitis (PSC) were previously shown to display a bacterial gut dysbiosis but fungal microbiota has never been examined in these patients. The aim of this study was to assess the fungal gut microbiota in patients with PSC.

DESIGN

We analysed the faecal microbiota of patients with PSC and concomitant IBD (n=27), patients with PSC and no IBD (n=22), patients with IBD and no PSC (n=33) and healthy subjects (n=30). Bacterial and fungal composition of the faecal microbiota was determined using 16S and ITS2 sequencing, respectively.

RESULTS

We found that patients with PSC harboured bacterial dysbiosis characterised by a decreased biodiversity, an altered composition and a decreased correlation network density. These alterations of the microbiota were associated with PSC, independently of IBD status. For the first time, we showed that patients with PSC displayed a fungal gut dysbiosis, characterised by a relative increase in biodiversity and an altered composition. Notably, we observed an increased proportion of Exophiala and a decreased proportion of Saccharomyces cerevisiae. Compared with patients with IBD and healthy subjects, the gut microbiota of patients with PSC exhibited a strong disruption in bacteria-fungi correlation network, suggesting an alteration in the interkingdom crosstalk.

CONCLUSION

This study demonstrates that bacteria and fungi contribute to gut dysbiosis in PSC.

Specific changes in faecal microbiota are associated with familial Mediterranean fever

OBJECTIVES

Familial Mediterranean fever (FMF) can be complicated by AA amyloidosis (AAA), though it remains unclear why only some patients develop amyloidosis. We examined the gut microbiota composition and inflammatory markers in patients with FMF complicated or not by AAA.

METHODS

We analysed the gut microbiota of 34 patients with FMF without AAA, 7 patients with FMF with AAA, 19 patients with AAA of another origin, and 26 controls using 16S ribosomal RNA gene sequencing with the Illumina MiSeq platform. Associations between bacterial taxa and clinical phenotypes were evaluated using multivariate association with linear models statistical method. Blood levels of interleukin (IL)-1β, IL-6, tumour necrosis factor-α and adipokines were assessed by ELISA; indoleamine 2,3-dioxygenase (IDO) activity was determined by high-performance liquid chromatography.

RESULTS

Compared with healthy subjects, specific changes in faecal microbiota were observed in FMF and AAA groups. Several operational taxonomic units (OTUs) were associated with FMF. Moreover, two OTUs were over-represented in FMF-related AAA compared with FMF without AAA. Additionally, higher adiponectin levels and IDO activity were observed in FMF-related AAA compared with FMF without AAA (p<0.05).

CONCLUSION

The presence of specific changes in faecal microbiota in FMF and in FMF-related AAA suggests that intestinal microorganisms may play a role in the pathogenesis of these diseases. These findings may offer an opportunity to use techniques for gut microbiota manipulation.

Enterobacteriaceae are essential for the modulation of colitis severity by fungi

BACKGROUND

Host-microbe balance maintains intestinal homeostasis and strongly influences inflammatory conditions such as inflammatory bowel diseases (IBD). Here we focused on bacteria-fungi interactions and their implications on intestinal inflammation, a poorly understood area.

METHODS

Dextran sodium sulfate (DSS)-induced colitis was assessed in mice treated with vancomycin (targeting gram-positive bacteria) or colistin (targeting Enterobacteriaceae) and supplemented with either Saccharomyces boulardii CNCM I-745 or Candida albicans. Inflammation severity as well as bacterial and fungal microbiota compositions was monitored.

RESULTS

While S. boulardii improved DSS-induced colitis and C. albicans worsened it in untreated settings, antibiotic treatment strongly modified DSS susceptibility and effects of fungi on colitis. Vancomycin-treated mice were fully protected from colitis, while colistin-treated mice retained colitis phenotype but were not affected anymore by administration of fungi. Antibacterial treatments not only influenced bacterial populations but also had indirect effects on fungal microbiota. Correlations between bacterial and fungal relative abundance were dramatically decreased in colistin-treated mice compared to vancomycin-treated and control mice, suggesting that colistin-sensitive bacteria are involved in interactions with fungi. Restoration of the Enterobacteriaceae population by administrating colistin-resistant Escherichia coli reestablished both beneficial effects of S. boulardii and pathogenic effects of C. albicans on colitis severity. This effect was at least partly mediated by an improved gut colonization by fungi.

CONCLUSIONS

Fungal colonization of the gut is affected by the Enterobacteriaceae population, indirectly modifying effects of mycobiome on the host. This finding provides new insights into the role of inter-kingdom functional interactions in intestinal physiopathology and potentially in IBD.

Genetic deficiency of indoleamine 2,3-dioxygenase promotes gut microbiota-mediated metabolic health

The association between altered gut microbiota, intestinal permeability, inflammation and cardiometabolic diseases is becoming increasingly clear but remains poorly understood1,2. Indoleamine 2,3-dioxygenase is an enzyme induced in many types of immune cells, including macrophages in response to inflammatory stimuli, and catalyzes the degradation of tryptophan along the kynurenine pathway. Indoleamine 2,3-dioxygenase activity is better known for its suppression of effector T cell immunity and its activation of regulatory T cells3,4. However, high indoleamine 2,3-dioxygenase activity predicts worse cardiovascular outcome5-9 and may promote atherosclerosis and vascular inflammation6, suggesting a more complex role in chronic inflammatory settings. Indoleamine 2,3-dioxygenase activity is also increased in obesity10-13, yet its role in metabolic disease is still unexplored. Here, we show that obesity is associated with an increase of intestinal indoleamine 2,3-dioxygenase activity, which shifts tryptophan metabolism from indole derivative and interleukin-22 production toward kynurenine production. Indoleamine 2,3-dioxygenase deletion or inhibition improves insulin sensitivity, preserves the gut mucosal barrier, decreases endotoxemia and chronic inflammation, and regulates lipid metabolism in liver and adipose tissues. These beneficial effects are due to rewiring of tryptophan metabolism toward a microbiota-dependent production of interleukin-22 and are abrogated after treatment with a neutralizing anti-interleukin-22 antibody. In summary, we identify an unexpected function of indoleamine 2,3-dioxygenase in the fine tuning of intestinal tryptophan metabolism with major consequences on microbiota-dependent control of metabolic disease, which suggests indoleamine 2,3-dioxygenase as a potential therapeutic target.

Specificities of the intestinal microbiota in patients with inflammatory bowel disease and Clostridium difficile infection

Clostridium difficile infection (CDI) is a common complication in inflammatory bowel disease (IBD) and has been associated with poor IBD outcome. Intestinal microbiota composition in IBD patients with CDI has not been specifically evaluated to date. The fecal microbiota of 56 IBD patients, including 8 in flare with concomitant CDI, 24 in flare without CDI, and 24 in remission, as well as 24 healthy subjects, was studied using 16S sequencing. Analysis was performed using the Qiime pipeline. Compared to IBD patients without CDI, IBD patients with CDI had more pronounced dysbiosis with higher levels of Ruminococcus gnavus and Enterococcus operational taxonomic units (OTUs) and lower levels of Blautia and Dorea OTUs. Correlation network analysis suggested a disrupted ecosystem in IBD patients in flare, particularly in those with CDI. In patients with IBD, CDI is associated with a more pronounced intestinal dysbiosis with specific alterations in intestinal microorganisms.

Predictors of responses to immune checkpoint blockade in advanced melanoma

Immune checkpoint blockers (ICB) have become pivotal therapies in the clinical armamentarium against metastatic melanoma (MMel). Given the frequency of immune related adverse events and increasing use of ICB, predictors of response to CTLA-4 and/or PD-1 blockade represent unmet clinical needs. Using a systems biology-based approach to an assessment of 779 paired blood and tumor markers in 37 stage III MMel patients, we analyzed association between blood immune parameters and the functional immune reactivity of tumor-infiltrating cells after ex vivo exposure to ICB. Based on this assay, we retrospectively observed, in eight cohorts enrolling 190 MMel patients treated with ipilimumab, that PD-L1 expression on peripheral T cells was prognostic on overall and progression-free survival. Moreover, detectable CD137 on circulating CD8⁺ T cells was associated with the disease-free status of resected stage III MMel patients after adjuvant ipilimumab + nivolumab (but not nivolumab alone). These biomarkers should be validated in prospective trials in MMel.The clinical management of metastatic melanoma requires predictors of the response to checkpoint blockade. Here, the authors use immunological assays to identify potential prognostic/predictive biomarkers in circulating blood cells and in tumor-infiltrating lymphocytes from patients with resected stage III melanoma.

Fungal microbiota dysbiosis in IBD

OBJECTIVE

The bacterial intestinal microbiota plays major roles in human physiology and IBDs. Although some data suggest a role of the fungal microbiota in IBD pathogenesis, the available data are scarce. The aim of our study was to characterise the faecal fungal microbiota in patients with IBD.

DESIGN

Bacterial and fungal composition of the faecal microbiota of 235 patients with IBD and 38 healthy subjects (HS) was determined using 16S and ITS2 sequencing, respectively. The obtained sequences were analysed using the Qiime pipeline to assess composition and diversity. Bacterial and fungal taxa associated with clinical parameters were identified using multivariate association with linear models. Correlation between bacterial and fungal microbiota was investigated using Spearman's test and distance correlation.

RESULTS

We observed that fungal microbiota is skewed in IBD, with an increased Basidiomycota/Ascomycota ratio, a decreased proportion of Saccharomyces cerevisiae and an increased proportion of Candida albicans compared with HS. We also identified disease-specific alterations in diversity, indicating that a Crohn's disease-specific gut environment may favour fungi at the expense of bacteria. The concomitant analysis of bacterial and fungal microbiota showed a dense and homogenous correlation network in HS but a dramatically unbalanced network in IBD, suggesting the existence of disease-specific inter-kingdom alterations.

CONCLUSIONS

Besides bacterial dysbiosis, our study identifies a distinct fungal microbiota dysbiosis in IBD characterised by alterations in biodiversity and composition. Moreover, we unravel here disease-specific inter-kingdom network alterations in IBD, suggesting that, beyond bacteria, fungi might also play a role in IBD pathogenesis.

CARD9 impacts colitis by altering gut microbiota metabolism of tryptophan into aryl hydrocarbon receptor ligands

Complex interactions between the host and the gut microbiota govern intestinal homeostasis but remain poorly understood. Here we reveal a relationship between gut microbiota and caspase recruitment domain family member 9 (CARD9), a susceptibility gene for inflammatory bowel disease (IBD) that functions in the immune response against microorganisms. CARD9 promotes recovery from colitis by promoting interleukin (IL)-22 production, and Card9(-/-) mice are more susceptible to colitis. The microbiota is altered in Card9(-/-) mice, and transfer of the microbiota from Card9(-/-) to wild-type, germ-free recipients increases their susceptibility to colitis. The microbiota from Card9(-/-) mice fails to metabolize tryptophan into metabolites that act as aryl hydrocarbon receptor (AHR) ligands. Intestinal inflammation is attenuated after inoculation of mice with three Lactobacillus strains capable of metabolizing tryptophan or by treatment with an AHR agonist. Reduced production of AHR ligands is also observed in the microbiota from individuals with IBD, particularly in those with CARD9 risk alleles associated with IBD. Our findings reveal that host genes affect the composition and function of the gut microbiota, altering the production of microbial metabolites and intestinal inflammation.

NKp30 isoforms and NKp30 ligands are predictive biomarkers of response to imatinib mesylate in metastatic GIST patients

Despite effective targeted therapy acting on KIT and PDGFRA tyrosine kinases, gastrointestinal stromal tumors (GIST) escape treatment by acquiring mutations conveying resistance to imatinib mesylate (IM). Following the identification of NKp30-based immunosurveillance of GIST and the off-target effects of IM on NK cell functions, we investigated the predictive value of NKp30 isoforms and NKp30 soluble ligands in blood for the clinical response to IM. The relative expression and the proportions of NKp30 isoforms markedly impacted both event-free and overall survival, in two independent cohorts of metastatic GIST. Phenotypes based on disbalanced NKp30B/NKp30C ratio (ΔBC^low) and low expression levels of NKp30A were identified in one third of patients with dismal prognosis across molecular subtypes. This ΔBC^low blood phenotype was associated with a pro-inflammatory and immunosuppressive tumor microenvironment. In addition, detectable levels of the NKp30 ligand sB7-H6 predicted a worse prognosis in metastatic GIST. Soluble BAG6, an alternate ligand for NKp30 was associated with low NKp30 transcription and had additional predictive value in GIST patients with high NKp30 expression. Such GIST microenvironments could be rescued by therapy based on rIFN-α and anti-TRAIL mAb which reinstated innate immunity.

Gastric electrical stimulation modulates hypothalamic corticotropin-releasing factor-producing neurons during post-operative ileus in rat

High-frequency/low-energy gastric electrical stimulation (GES) is an efficient therapy to treat gastric emptying-related disorders but its mechanism of action remains poorly understood. We aimed to assess the effects of high-frequency/low-energy GES on corticotropin-releasing factor (CRF)-producing neurons in the paraventricular nucleus of the hypothalamus (PVN), which are involved in gastric ileus induced by laparotomy. Two electrodes were implanted in the rat gastric antrum during laparotomy, then stimulation (amplitude: 2 mA; pulse duration 330 micros; frequency: 2 Hz; 1 min ON/2 min OFF) or sham stimulation (control group) were applied. Using immunohistochemistry, the number of c-Fos protein-expressing neurons (c-Fos protein-immunoreactive cells, Fos-IR) was quantified in the PVN after 1 h of stimulation. The number of neurons expressing simultaneously c-Fos protein and CRF mRNA was measured by means of immunocytochemistry combined with in situ hybridization. Finally, c-Fos and CRF mRNA levels in the hypothalamus were determined by in situ hybridization or quantitative reverse transcriptase-polymerase chain reaction. Fos-IR in the PVN was significantly decreased 1 h after GES (P<0.05) but was not affected by sub-diaphragmatic vagotomy. The number of neurons containing c-Fos protein and CRF mRNA was lower in the GES group compared with the control group (P<0.05). In addition, c-Fos and CRF mRNA levels in the PVN were significantly decreased by GES (P<or=0.05). It is concluded that acute GES reduces the number of CRF-producing neurons and decreases CRF expression in the PVN during post-operative gastric ileus.

Galanin modulates the activity of proopiomelanocortin neurons in the isolated mediobasal hypothalamus of the male rat

It has become apparent that galanin as well as proopiomelanocortin-derived peptides, such as beta-endorphin, play an important role in the hypothalamic circuitry that regulates neuroendocrine functions and appetite behavior. We have recently shown that GalR1 and GalR2 galanin receptor mRNAs are expressed in proopiomelanocortin neurons of the arcuate nucleus, suggesting a direct modulatory action of galanin on the proopiomelanocortin neuronal system. In the present study, we investigated the effect of galanin on beta-endorphin release and proopiomelanocortin mRNA expression from male rat mediobasal hypothalamic fragments incubated ex vivo. Galanin induced a decrease of spontaneous beta-endorphin release within the first 30-60 min of incubation and this effect was blocked by the galanin receptor antagonist galantide. Co-incubation of galanin with FK-506 (tacrolimus), a calcineurin inhibitor, suppressed the inhibitory effect of galanin on beta-endorphin release, suggesting that calcineurin is involved in the galanin-evoked decrease in beta-endorphin release. Measurement of beta-endorphin levels in the tissues at the end of the incubation period (120 min) revealed that galanin caused a two-fold increase of beta-endorphin peptide concentration in the mediobasal hypothalamic tissues. Concurrently, galanin induced an increase in the mean density of silver grains overlying proopiomelanocortin neurons after 60 min of incubation, an effect antagonized by galantide. Finally, reverse transcription-polymerase chain reaction analysis revealed that the mRNAs for the three galanin receptor subtypes (i.e. GalR1, GalR2, and GalR3) were expressed in the incubated mediobasal hypothalamic fragments. Taken as a whole, our results indicate that galanin plays a modulatory role on proopiomelanocortin neurons and this interrelation contributes to the elucidation of the neural circuitry that controls, among others, gonadotropin-releasing hormone function.

Evidence that TGF beta may directly modulate POMC mRNA expression in the female rat arcuate nucleus

The purpose of the present study was to determine whether TGF beta, a cytokine secreted by hypothalamic astrocytes, was able to regulate POMC neurons in the arcuate nucleus. In a first set of experiments, mediobasal hypothalamic fragments were exposed to TGF beta(1), and the relative POMC mRNA expression was assessed by in situ hybridization using a radiolabeled POMC riboprobe. The results showed that 4 x 10(-10) M TGF beta(1) was efficient in decreasing significantly the amounts of POMC mRNA (P < 0.01). Interestingly, the decrease of relative POMC mRNA levels was higher in the rostral than in the caudal parts of the arcuate nucleus. In a second set of experiments, we examined the occurrence of TGF beta receptors expression in arcuate POMC neurons. Dual labeling in situ hybridization and in situ hybridization, coupled to immunohistochemical labeling, were performed to examine mRNA expression of the type I serine-threonine kinase receptor for TGF beta and the presence of type II receptor for TGF beta, respectively, in POMC neurons. The results indicated that TGF beta receptor I mRNA and TGF beta receptor II protein were expressed in numerous POMC neurons. Regional analysis revealed that the highest proportion of POMC neurons expressing TGF beta receptors was located in the rostral part of the arcuate nucleus. Using dual labeling immunohistochemistry, we also found that Smad2/3 immunoreactivity, a TGF beta(1) downstream signaling molecule, was present in the cytoplasm and nucleus of some POMC (beta-endorphin) neurons. We next examined whether the number of POMC neurons expressing TGF beta-RI mRNA was affected by sex steroids. Quantification of the number of POMC neurons expressing TGF beta receptor I mRNA in ovariectomized, ovariectomized E2-treated, and ovariectomized E2 plus progesterone-treated animals revealed that estrogen treatment decreased the expression of TGF beta receptor I mRNA in POMC neurons located in the rostral half of the arcuate nucleus, an effect reversed by progesterone in a subset of the most rostral cells. Taken together, these data reveal that TGF beta(1) may directly modulate the activity of POMC neurons through the activation of TGF beta receptors. Therefore, the present study provides additional evidence for the involvement of TGF beta(1) in the regulation of neuroendocrine functions and supports the existence of a glial-to-neurons communication within the arcuate nucleus.

Comparative distribution of pituitary adenylate cyclase-activating polypeptide (PACAP) binding sites and PACAP receptor mRNAs in the rat brain during development

The distribution and density of pituitary adenylate cyclase-activating polypeptide (PACAP) binding sites as well as PACAP-specific receptor 1 (PAC1-R), vasoactive intestinal polypeptide/PACAP receptor 1 (VPAC1-R), and VPAC2-R mRNAs have been investigated in the rat brain from embryonic day 14 (E14) to postnatal day 8 (P8). Significant numbers of binding sites for the radioiodinated, 27-amino-acid form of PACAP were detected as early as E14 in the neuroepithelia of the metencephalon and the myelencephalon. From E14 to E21, the density of binding sites in the germinative areas increased by 3- to 5-fold. From birth to P12, the density of binding sites gradually declined in all neuroepithelia except in the external granule cell layer of the cerebellum, where the level of binding sites remained high during the first postnatal weeks. Only low to moderate densities of PACAP binding sites were found in regions other than the germinative areas, with the exception of the internal granule cell layer of the cerebellum, which contained a high density of sites. The localization of PACAP receptor mRNAs was investigated by in situ hybridization using [(35)S] uridine triphosphate-specific riboprobes. The evolution of the distribution of PAC1-R and VPAC1-R mRNAs was very similar to that of PACAP binding sites, the concentration of VPAC1-R mRNA being much lower than that of PAC1-R mRNA. In contrast, intense expression of VPAC2-R mRNA was observed in brain regions other than germinative areas, such as the suprachiasmatic, ventral thalamic, and dorsolateral geniculate nuclei. The discrete localization of PACAP binding sites as well as PAC1-R and VPAC1-R mRNAs in neuroepithelia during embryonic life and postnatal development strongly suggests that PACAP, acting through PAC1-R and/or VPAC1-R, may play a crucial role in the regulation of neurogenesis in the rat brain.

Expression of GalR1 and GalR2 galanin receptor messenger ribonucleic acid in proopiomelanocortin neurons of the rat arcuate nucleus: effect of testosterone

Previous studies have shown that galanin-containing fibers make synaptic contacts with POMC neurons in the arcuate nucleus. However, the ability of POMC neurons to express galanin receptors has never been assessed. The present study was designed to investigate whether POMC neurons express galanin receptor messenger RNA (mRNA) and whether testosterone could modulate galanin receptor gene expression. A dual-labeling in situ hybridization histochemistry, using 35S-labeled (galanin receptors GalR1 or GalR2) and digoxigenin-labeled (POMC) riboprobes, was performed on brain sections from intact, castrated, and testosterone-replaced adult male rats. For analysis, the arcuate nucleus was divided into four rostro-caudal areas. The results revealed that both GalR1 and GalR2 mRNAs were expressed in POMC neurons. Most POMC neurons expressing galanin receptor mRNAs were found in the rostral parts of the nucleus. Castration reduced the labeling density of galanin receptor mRNAs in POMC neurons, and testosterone prevented the effects of castration in all rostro-caudal subdivisions of the arcuate nucleus. Taken together, these data indicate that galanin can directly modulate the activity of POMC neurons, via an action on GalR1 or GalR2 receptors, particularly in the rostral-arcuate nucleus. In addition, testosterone can modulate the expression of GalR1 and GalR2. Because POMC neurons located in the rostral part of the nucleus are known to project preferentially to the preoptic area, POMC neurons expressing the galanin receptor genes may play an important role in the regulation of the GnRH neuroendocrine axis.

Molecular cloning, characterization of cDNA, and distribution of mRNA encoding the frog prohormone convertase PC1

Prohormone convertases (PCs) are calcium-dependent serine endoproteases of the subtilisin/kexin family that play a key role in the posttranslational processing of precursors for biologically active peptides. In this study, we have characterized the cDNA encoding PC1 in the European green frog Rana ridibunda. A frog brain cDNA library was screened by using a heterologous probe at low stringency, and a 2.3-kb cDNA clone encoding PC1 was isolated. This cDNA encodes a 736-residue protein with a 26-amino-acid signal peptide. Comparative structural analysis revealed that frog PC1 exhibits a high degree of amino acid identity with its mammalian counterparts, in particular in the subtilisin-like catalytic domain. Northern blot analysis resolved two major transcripts of 3.0 kb and 5.0 kb that were expressed differentially in the brain and pituitary. In situ hybridization studies showed that, in the frog brain, the highest densities of PC1 mRNA are present in the amygdala, the hypothalamus, and the anterior preoptic area. High concentrations of PC1 mRNA also were found in the pars distalis and pars intermedia of the pituitary, whereas the pars nervosa was devoid of hybridization signal. The wide distribution of PC1 mRNA in the brain and pituitary suggests that, in frog, PC1 is involved in the processing of a number of hormone and neuropeptide precursors.

A cloned frog vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating polypeptide receptor exhibits pharmacological and tissue distribution characteristics of both VPAC1 and VPAC2 receptors in mammals

Three receptor subtypes for the neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) have been identified in mammals: the PAC1 receptor (PAC1-R) which is selectively activated by PACAP, and two VPAC receptors (VPAC1-R and VPAC2-R), which are equally stimulated by PACAP and VIP. The structures of PACAP and VIP have been well conserved during evolution, but little is known about VIP/PACAP receptors in nonmammalian species. An amphibian VIP/PACAP receptor complementary DNA (cDNA) has been cloned and characterized from a frog (Rana ridibunda) pituitary cDNA library. The predicted protein contains seven putative transmembrane domains and exhibits the highest sequence identity (65%) with the human VPAC1-R. The cloned cDNA was transiently expressed in LLC-PK1 cells, and its pharmacological profile was determined in comparison with the human VPAC1-R. Both PACAP and VIP stimulated cAMP accumulation through the cloned receptor with an EC50 of about 30 nM. In contrast, secretin, at concentrations that stimulate the human VPAC1-R, had no effect on cAMP production. RT-PCR analysis revealed the widespread distribution of this frog VIP/PACAP receptor in peripheral tissues. In situ hybridization histochemistry using a complementary RNA probe showed that the receptor gene is highly expressed in several hypothalamic and thalamic nuclei and to a lesser extent in the pallium and striatum. In the pituitary, the highest messenger RNA levels were detected in the distal lobe. Taken together, these data show that the cloned frog receptor shares several common features with both the VPAC1-R and VPAC2-R of mammals; the frog receptor exhibits the highest sequence identity with mammalian VPAC1-R, but the lack of effect of secretin and the brain distribution of the receptor are reminiscent of the characteristics of the mammalian VPAC2-R. The sequence of the frog receptor should thus prove useful to decipher the structure-activity relationships of the VIP/PACAP receptor family.

Cloning of the cDNA encoding the urotensin II precursor in frog and human reveals intense expression of the urotensin II gene in motoneurons of the spinal cord

Urotensin II (UII) is a cyclic peptide initially isolated from the caudal neurosecretory system of teleost fish. Subsequently, UII has been characterized from a frog brain extract, indicating that a gene encoding a UII precursor is also present in the genome of a tetrapod. Here, we report the characterization of the cDNAs encoding frog and human UII precursors and the localization of the corresponding mRNAs. In both frog and human, the UII sequence is located at the C-terminal position of the precursor. Human UII is composed of only 11 amino acid residues, while fish and frog UII possess 12 and 13 amino acid residues, respectively. The cyclic region of UII, which is responsible for the biological activity of the peptide, has been fully conserved from fish to human. Northern blot and dot blot analysis revealed that UII precursor mRNAs are found predominantly in the frog and human spinal cord. In situ hybridization studies showed that the UII precursor gene is actively expressed in motoneurons. The present study demonstrates that UII, which has long been regarded as a peptide exclusively produced by the urophysis of teleost fish, is actually present in the brain of amphibians and mammals. The fact that evolutionary pressure has acted to conserve fully the biologically active sequence of UII suggests that the peptide may exert important physiological functions in humans.

Hepatic and extra-hepatic transcription of inter-alpha-inhibitor family genes under normal or acute inflammatory conditions in rat

The expression and level of the mRNAs for the five genes that code for a set of plasma proteins collectively referred to as the inter-alpha-inhibitor family have been studied in rat under a normal condition or in the course of a turpentine-induced, systemic inflammation. In healthy rats, all five mRNAs [H1, H2, H3, H4, and alpha1-microglobulin/bikunin precursor (AMBP)] are expressed primarily in liver and two of them (H2 and H3) are found to a lower extent in brain. By in situ hybridization onto sections of a normal brain, the H3 mRNA has been precisely localized to the hypothalamus, amygdala, pontine area, optic tectum, and cerebellum. By reverse transcriptase-polymerase chain reaction of total RNAs obtained from a panel of organs, low amounts of one or more mRNA(s) could be detected in other locations (e.g., intestine and stomach). Furthermore, the extrahepatic expressions of several of these genes are up- or downregulated at 20 h after the start of a turpentine-induced inflammation. In liver, the contents of H3 and H4 mRNA are upregulated, whereas those of AMBP and H2 are downregulated during the acute phase. This is accounted for by changes in gene transcription, the kinetics of which is gene-specific. This behavior of H1, H2, H3, H4, and AMBP mRNAs in rat liver is in keeping with more limited analyses made at mRNA and/or protein levels in other species (human, pig) suffering from an acute inflammation. Therefore, the inflammation-associated regulation of these five genes that is conserved between species indicates that the inter-alpha-inhibitor family members are likely to be important partners of the acute phase response.

Interrelations between hypothalamic somatostatin and proopiomelanocortin neurons

Somatostatin receptors were visualized by [125I]-Tyr0-DTrp8-somatostatin radioautography on 35% of arcuate neurons containing proopiomelanocortin (POMC) mRNA, as identified by in situ hybridization using a [35S] labelled riboprobe on 5 microm-thick consecutive sections. Furthermore, double immunohistochemical staining revealed contacts of beta-endorphin or alpha-MSH containing fibres with a majority of somatostatin perikarya in the anterior hypothalamic periventricular nucleus. Taken together, these data indicate that hypothalamic somatostatin and POMC neurons are interconnected. The results are discussed in term of intrahypothalamic control of GH secretion.

Visualization of gamma-aminobutyric acid A receptors on proopiomelanocortin-producing neurons in the rat hypothalamus

It has recently been shown that gamma-aminobutyric acid (GABA) and central-type benzodiazepine receptor agonists inhibit the expression of the POMC gene and the release of POMC-derived peptides from hypothalamic neurons. To determine whether the inhibitory effect of GABA could be accounted for by a direct action on POMC neurons, we investigated the localization of the beta 1-subunit of the GABAA-benzodiazepine-receptor complex in the arcuate nucleus. Using a monoclonal antibody raised against a synthetic fragment of the beta 1-subunit, we demonstrate the presence of GABAA receptor on POMC neurons. The proportion of POMC neurons that exhibit immunoreactivity for the beta 1-subunit of the GABAA receptor was not significantly different in the posterior portion (73.0-76.0%) and anterior portion (61.3-62.7%) of the arcuate nucleus. The data also revealed that in the arcuate nucleus, a majority of neurons that were immunostained by the antibody to the beta 1-subunit were not POMC positive. The present results support the concept that GABAA and central-type benzodiazepine receptor agonists exert a direct inhibitory action on POMC neurons. The data also indicate the existence of subsets of POMC neurons within the arcuate nucleus.

Characterization of alpha-melanocyte-stimulating hormone (alpha-MSH)-like peptides in discrete regions of the rat brain. In vitro release of alpha-MSH from perifused hypothalamus and amygdala

The neuropeptide alpha-melanocyte-stimulating hormone (alpha-MSH) is synthesized by discrete populations of hypothalamic neurons which project in different brain regions including the cerebral cortex, hippocampus and amygdala nuclei. The purpose of the present study was to identify the alpha-MSH-immunoreactive species contained in these different structures and to compare the ionic mechanisms underlaying alpha-MSH release at the proximal and distal levels, i.e. within the hypothalamus and amygdala nuclei, respectively. The molecular forms of alpha-MSH-related peptides stored in discrete areas of the brain were characterized by combining high-performance liquid chromatography (HPLC) separation and radioimmunoassay detection. In mediobasal and dorsolateral hypothalamic extracts, HPLC analysis confirmed the existence of a major immunoreactive peak which co-eluted with the synthetic des-N alpha-acetyl alpha-MSH standard. In contrast, 3 distinct forms of immunoreactive alpha-MSH, which exhibited the same retention times as synthetic des-, mono- and di-acetyl alpha-MSH, were resolved in amygdala nuclei, hippocampus, cortex and medulla oblongata extracts. The proportions of acetylated alpha-MSH (authentic alpha-MSH plus diacetyl alpha-MSH) contained in these extrahypothalamic structures were, respectively, 78, 80, 60 and 92% of the total alpha-MSH immunoreactivity. In order to compare the ionic mechanisms underlaying alpha-MSH release from hypothalamic and extrahypothalamic tissues, we have investigated in vitro the secretion of alpha-MSH by perifused slices of hypothalamus and amygdala nuclei. High potassium concentrations induced a marked increase of alpha-MSH release from both tissue preparations. However, a higher concentration of KCl was required to obtain maximal stimulation of amygdala nuclei (90 mM) than hypothalamic tissue (50 mM).(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical Localization and Biochemical Characterization of alpha-Melanocyte-Stimulating Hormon in the Brain of the Rainbow Trout, Salmo gairdneri

Abstract The distribution of alpha-melanocyte-stimulating hormone (alpha-MSH)-like immunoreactivity in the central nervous system of the rainbow trout Salmo gairdneri was investigated by indirect immunofluorescence and peroxidase-antiperoxidase techniques, using a highly specific antiserum generated in rabbits against synthetic alpha-MSH. Immunoreactive perikarya were exclusively observed in the basal hypothalamus within the pars anterioris of the nucleus lateralis tuberis. In this region, a moderate number of small stained cell bodies were observed surrounding the dorsal wall of the anterior infundibular recess. These immunoreactive cells were organized in rostro-caudal rows extending over the whole portion of the nucleus. Positive fibres originating from these perikarya were visualized in the dorsal posterior lobe and the ventral hypothalamus. A dense tract of immunoreactive fibres projected ventrally through the pituitary stalk and terminated in the neurohypophysis. The concentrations of alpha-MSH in different regions of the brain were measured by means of a sensitive and specific radioimmunoassay. The dilution curves obtained with synthetic alpha-MSH and serial dilutions of diencephalon, mesencephalon, medulla oblongata, telencephalon or pituitary extracts were strictly parallel. The highest concentration of alpha-MSH in brain was found in the diencephalon (1.31 +/- 0.07 ng/mg protein). In contrast alpha-MSH was not detectable in cerebellar extracts. Reverse-phase high-performance liquid chromatography and radioimmunoassay were used to characterize alpha-MSH-like peptides in the trout brain and pituitary. Two major forms of immunoreactive alpha-MSH were resolved by high performance liquid chromatography in hypothalamic extracts; these peptides exhibited the same retention times as des-Na-acetyl alpha-MSH and its sulfoxide derivative, respectively. Additional peaks of alpha-MSH immunoreactive material were detected in pituitary extract. These latter peptides coeluted with authentic alpha-MSH, diacetyl alpha-MSH and their sulfoxide forms. These results provide the first evidence for the presence of alpha-MSH in the brain of a teleostean fish. Our data indicate that, in the brain, the immunoreactivity corresponds to the non-acetylated form of alpha-MSH, while three different types of alpha-MSH-like molecules (namely deacetylated, monoacetylated, and diacetylated forms) coexist in the pituitary. It thus appears that, in salmonoid fish, mono- or diacetylation of the N-terminal serine residue of aL-MSH only occurs at the pituitary level.

NPY-like peptides occur in the nervous system and midgut of the migratory locust, Locusta migratoria and in the brain of the grey fleshfly, Sarcophaga bullata

The distribution of the NPY-like substances in the nervous system and the midgut of the migratory locust, Locusta migratoria and in the brain of the grey fleshfly, Sarcophaga bullata was determined by immunocytochemistry using an antiserum directed against synthetic porcine NPY. The peroxidase-antiperoxidase procedure revealed that NPY immunoreactive cell bodies and nerve fibers were observed in the brain, optic lobes, corpora cardiaca, suboesophageal ganglion and ventral nerve cord of the locust and in the brain, optic lobes and suboesophageal ganglion of the fleshfly. In the locust midgut, numerous endocrine cells and nerve fibers penetrating the outer musculature contained NPY-like immunoreactivity. The concentrations of NPY immunoreactive material in acetic acid extracts of locust brain, optic lobes, thoracic ganglia, ovaries and midguts was measured using a specific radioimmunoassay technique. The dilution curves of the crude tissue extracts were parallel to the standard curve. The highest amount of NPY-like immunoreactivity was found in the locust ovary and midgut. Reverse-phase high-performance liquid chromatography (RP-HPLC) and radioimmunoassay were used to characterize the NPY-like substances in the locust brain and midgut. HPLC-analysis revealed that NPY-immunoreactivity in the locust brain eluted as three separate peaks. The major peak corresponded to a peptide less hydrophobic than synthetic porcine NPY. RP-HPLC analysis of midgut extracts revealed the presence of an additional NPY-immunoreactive peak which had a retention time similar to the porcine NPY standard. The present data show the existence of a widespread network of NPY immunoreactive neurons in the nervous system of the locust and the fleshfly. Characterization of the immunoreactive substances indicates that peptides similar but not identical to porcine NPY are present in the central nervous system and midgut of insects.

Alpha-melanocyte-stimulating hormone (alpha-MSH) in the brain of the cartilagenous fish. Immunohistochemical localization and biochemical characterization

The distribution of immunoreactive alpha-melanocyte-stimulating hormone (alpha-MSH) in the central nervous system and pituitary of the elasmobranch fish Scyliorhinus canicula was determined by the indirect immunofluorescence and the peroxidase-antiperoxidase methods using a highly specific antiserum. Perikarya containing alpha-MSH-like immunoreactivity were localized in the dorsal portion of the posterior hypothalamus, mainly in the tuberculus posterioris and sacci vasculosus nuclei. Immunoreactive alpha-MSH cell bodies were found in the dorsal wall and ventral region of the caudal part of the tuberculum posterioris. These structures were densely innervated by fine beaded immunoreactive fibers. Some alpha-MSH immunoreactive cells were occasionally detected in the ventral part of the nucleus periventricularis. Scattered cell bodies and fibers were also observed in the dorsal wall of the posterior recess. Outside the hypothalamus very few fibers were detected in the dorsal thalamus and mesencephalon. No immunoreactivity was found in any other parts of the brain. The alpha-MSH immunoreactive material localized in the brain was characterized by combining high-performance liquid chromatography (HPLC) analysis and radioimmunological detection. Brain and pituitary extracts exhibited displacement curves which were parallel to that obtained with synthetic alpha-MSH. The concentrations of alpha-MSH immunoreactive material were determined in 5 different regions of the brain. The highest concentration was found in the hypothalamus. HPLC analysis resolved two major forms of immunoreactive alpha-MSH in the hypothalamus, which had been same retention times as des-N alpha-acetyl-alpha-MSH and its sulfoxide derivative. These results provide the first evidence for the presence of alpha-MSH-like peptides in the fish brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Coexistence of melanin-concentrating hormone and alpha-melanocyte-stimulating hormone immunoreactivities in the central nervous system of the locust, Locusta migratoria

The distribution of melanin concentrating hormone (MCH) in the central nervous system of the locust Locusta migratoria was studied by the indirect immunofluorescence technique, using antibodies against salmon MCH. Most MCH-immunoreactive perikarya were found in the optic lobes at both sides of the brain, dorsally with respect to the lamina ganglionaris. The same neurons also contain alpha-melanocyte-stimulating hormone (alpha-MSH)-like material. In addition, a moderate number of MCH-like neurons, which were devoid of alpha-MSH-immunoreactive substances, was observed in the pars intercerebralis. Bright immunofluorescent fibers were visualized in various regions of the central nervous system of the locust: the optic lobes, the ocelli, the proto-and deuterocerebrum, the subesophageal connectives and the corpora cardiaca. In the ventral nerve cord and the subesophageal ganglion, where alpha-MSH-like cell bodies were encountered, MCH immunoreactive perikarya were absent and immunoreactive fibers were scarce. The coexistence of MCH and alpha-MSH-immunoreactive material within the same specific neurons might indicate an evolutionary relationship of both peptides.

Gamma-melanotropin response to ovine corticotropin releasing factor in normal humans

Plasma gamma-melanotropin was measured by a gamma 3MSH-specific radioimmunoassay before and after a single bolus intravenous infusion of ovine corticotropin releasing factor (oCRF; 0.1 microgram/kg) in seven normal men. A significant increase of gamma 3MSH was observed 15 minutes post-oCRF infusion, which paralleled a similar increase in plasma cortisol. Gel filtration chromatography revealed that the observed increase was attributable to elevations of 9K and 4K forms of gamma 3MSH immunoreactivity. Affinity chromatography demonstrated that the majority of gamma 3MSH immunoreactivity in human plasma is glycosylated. As the smaller forms of gamma 3MSH are felt to have endocrine activity at the adrenal cortex, these changes may be physiologically relevant.

Coexistence of melanin-concentrating hormone (MCH) and alpha-melanocyte-stimulating hormone (alpha-MSH) in the preoptic nucleus of the frog brain

Coexistence of MCH- and alpha-MSH-like peptides in specific neurons of the frog hypothalamus has been investigated on serial frozen sections using the indirect immunofluorescence method. In the anterior region of the preoptic nucleus, perikarya containing MCH- and alpha-MSH-immunoreactive materials were co-distributed and the two peptides were generally co-sequestered within the same neurons. In contrast, alpha-MSH immunoreactive neurons of the ventral infundibular nucleus did not contain any MCH-like peptide. These data suggest that MCH and alpha-MSH are transported by the same nerve fibers originating from preoptic perikarya and are likely released together by axon terminals. Since MCH and alpha-MSH exert antagonistic hormonal activities on dermal melanophores, our results suggest that the two regulatory peptides may also interact in the central nervous system.

Localization of melanin-concentrating hormone-like immunoreactivity in the brain and pituitary of the frog Rana ridibunda

The distribution of melanin-concentrating hormone (MCH) in the central nervous system of the frog Rana ridibunda was determined by the indirect immunofluorescence technique using antibodies against synthetic salmon MCH, generated in rabbits. The most prominent group of MCH-like containing perikarya was detected in the preoptic nucleus. Comparatively, a moderate number of cell bodies was observed in the dorsal infundibular nucleus and in the ventral thalamic area. Brightly immunofluorescent nerve bundles were found in the preoptic nucleus and in the ventral infundibular nucleus, coursing towards the internal zone of the median eminence and the pituitary stalk. An intense network of immunofluorescent fibers was localized in the neural lobe of the pituitary. The subcellular localization of MCH-like material was studied in the neurohypophysis using the immunogold technique. It was demonstrated that MCH-like material was contained in dense core vesicles (80-90 mm in diameter) within specific nerve terminals. The present findings indicate that, in amphibians, MCH-like peptide is located in specific hypothalamic neurons. Our data suggest that MCH may be released by neurohypophyseal nerve endings as a typical neurohormone.

Pro-opiomelanocortin peptides in the human hypothalamus: comparative study between normal subjects and Parkinson patients

The concentrations of gamma 3-melanotropin-, alpha-melanotropin-, corticotropin-, gamma-lipotropin- and beta-endorphin-immunoreactivities were determined simultaneously, before and after gel exclusion chromatography, in whole hypothalamic extracts of normal subjects and Parkinson patients. All five immunoreactivities were present and were all significantly correlated to each other. Shorter peptides (alpha-melanotropin, gamma 3-melanotropin, beta-endorphin and a lipotropin37-58-like peptide) were the dominant products. Whereas the dopamine content was significantly reduced in Parkinson patients, there was no significant difference for any peptide between normal subjects and Parkinson patients, either in tissue concentrations or in chromatographic patterns.

In vitro study of frog (Rana ridibunda Pallas) neurointermediate lobe secretion by use of a simplified perifusion system. III. Effect of neuropeptides on alpha-MSH secretion

It has been previously demonstrated that thyrotropin-releasing hormone (TRH) stimulates in vitro the release of alpha-melanocyte-stimulating hormone (alpha-MSH) in frog. In the present study, the effects of various neuropeptides on spontaneous and/or TRH-induced alpha-MSH secretion were investigated, using a well-defined perifusion system technique. Vasoactive intestinal peptide, (VIP) a neurohormone which stimulates TRH target cells in mammals, was totally devoid of effect on frog melanotrophs although VIP-like material could be detected in neurointermediate lobe extracts. Somatostatin-like immunoreactive material was found in high concentrations in the frog neurointermediate lobe complex, but synthetic somatostatin (from 10(-10) to 10(-6) M) did not modify the spontaneous release of alpha-MSH. At doses of 10(-8) and 10(-6) M, synthetic somatostatin did not modify TRH-induced alpha-MSH secretion. Morphine (10(-5) M) and opioid peptides (10(-10) to 10(-6) M) had no effect on spontaneous alpha-MSH secretion. In addition, methionine enkephalin (10(-5) M) did not modify the stimulatory effect of TRH on alpha-MSH secretion. From these results we conclude that, among the neuropeptides which modulate prolactin secretion in mammals, only TRH is involved in alpha-MSH secretion in the frog.

In vitro study of frog (Rana ridibunda Pallas) neurointermediate lobe secretion by use of a simplified perifusion system. II. Lack of action of thyroxine on TRH-induced alpha-MSH secretion

Thyrotropin-releasing hormone (TRH) stimulates alpha-melanocyte-stimulating hormone (alpha-MSH) secretion in amphibia as well as thyrotropin-stimulating hormone (TSH) and prolactin secretions in mammals. Since thyroid hormones regulate the stimulatory effect of TRH on TSH and prolactin, the possible role of thyroxine (T4) in the control of alpha-MSH secretion in amphibia, has been investigated. Neurointermediate lobes of Rana ridibunda were perifused in amphibian culture medium for 7 hr and the amounts of alpha-MSH released into the effluent perfusate were measured by radioimmunoassay. In vivo treatment with T4 (0.5 mg/kg twice a day for 9 days) did not modify the in vitro response of the neurointermediate lobes to TRH (10(-9) to 10(-7) M). In addition, prolonged infusion of T4 in vitro did not alter spontaneous and TRH-induced alpha-MSH release. In spite of the inhibitory effect of T4 on TRH-induced TSH and prolactin secretions in mammals, the present data show that, in frogs, thyroid hormone does not modulate the stimulation of alpha-MSH secretion induced by TSH.

Biological and immunological characterization of alpha-melanocyte-stimulating hormone (alpha-MSH) in two neuronal systems of the rat brain

Recent immunocytochemical studies have demonstrated the existence of two different neuronal systems containing alpha-MSH-like material in the brain: one originating from the arcuate nucleus and the other one from the dorsolateral hypothalamus. The aim of the present study was to further characterize alpha-MSH in these two discrete regions of the rat diencephalon. Intracerebroventricular administration of colchicine resulted in a marked decrease in the number of ACTH and beta-endorphin nerve fibers and a significant reduction in ACTH and beta-endorphin content in the dorsolateral hypothalamus. Conversely, colchicine treatment did not alter alpha-MSH, ACTH or beta-endorphin content in the arcuate nucleus and did not significantly affect alpha-MSH concentration in the dorsal region. Reverse-phase high-performance liquid chromatography showed that the major alpha-MSH-like compound localized in the dorsal hypothalamus co-migrated exactly with synthetic alpha-MSH, whereas the arcuate nucleus contained 5 peptides cross-reacting with alpha-MSH antibodies, 4 of them being different from standard alpha-MSH. Significant amounts of biologically active melanotropin, which migrated on Sephadex G-25 columns like synthetic alpha-MSH, were also detected in both the arcuate nucleus and dorsolateral hypothalamus. Taken together, these data demonstrate that the alpha-MSH cell bodies located in the dorsolateral hypothalamus specifically produce authentic alpha-MSH, whereas the alpha-MSH cell bodies in the arcuate nucleus also contain ACTH, beta-endorphin and several peptides immunologically related but not identical to alpha-MSH.

Catecholaminergic control of alpha-melanocyte-stimulating hormone (alpha MSH) release by frog neurointermediate lobe in vitro: evidence for direct stimulation of alpha MSH release by thyrotropin-releasing hormone

The role of dopaminergic and adrenergic innervation of the intermediate lobe of amphibian pituitary in the release of alpha MSH has been studied in vitro. Neurointermediate lobes of frog (Rana ridibunda Pallas) have been perifused in amphibian culture medium (ACM) for 5-7 h. alpha MSH released in the effluent perifusate was measured by means of a sensitive and specific RIA. No significant morphological alteration of neurointermediate lobe cells was observed during the perifusion experiment, even at the electron microscopic level. The existence of dopaminergic receptors, responsible for an inhibition of frog melanotrophs, was shown using the dopaminergic agonists apomorphine (10(-6) M) and bromo-2-ergocryptine (10(-8) and 10(-7) M), which initiated a marked reduction of alpha MSH secretion. The effect of apomorphine was obliterated by the dopaminergic antagonist haloperidol. Haloperidol itself induced a dose-related stimulation, and the monoamine oxidase inhibitor nialamide (4 x 10(-3) M) inhibited alpha MSH secretion. In addition, haloperidol led to a complete reversal of the inhibitory effect of nialamide on alpha MSH secretion. These results demonstrate the existence, in the parenchyme of the intermediate lobe, of dopaminergic nerve fibers that are functionally active. The beta-adrenergic agonist isoproterenol was responsible for a dose-related stimulation of alpha MSH secretion; the stimulatory effect was reversed by the beta-adrenergic antagonist propranolol. TRH is a potent stimulator of alpha MSH secretion in amphibians. Since haloperidol and propranolol did not abolish the stimulation of alpha MSH release induced by TRH, it appeared that TRH action was not mediated via an inhibition of dopamine release or via a stimulation of adrenergic nerve fibers.

Effect of aldosterone antagonists on mineralocorticoid synthesis in vitro. Inhibition of aldosterone production by prorenoate-K

A perifusion technique using frog adrenal glands has been applied to investigate the effects of long-term administration of a new aldosterone antagonist (potassium prorenoate; SC 23992) on mineralocorticoid production. Whatever the duration of administration of potassium prorenoate, at a constant concentration of 5 X 10(-4) M, a significant inhibition of aldosterone output occurred during the passage of the compound. The inhibition was immediate (lag period less than 10 min); the amplitude of the inhibition was constant during the whole experiment and ranged from 77 to 89%; the aldosterone output returned to a regular basal value 80-100 min after the end of infusion of potassium prorenoate. We have also investigated the effect of a concentration gradient of potassium prorenoate (similar to the concentration gradient of aldosterone antagonist observed in plasma after a single oral administration of the molecule) upon aldosterone production over 12 h. From this study, we have established the existence of a highly significant correlation between the extent of the inhibition of aldosterone production and the concentration of the aldosterone antagonist. Finally we have observed that potassium prorenoate blocked the stimulation of aldosterone secretion induced by synthetic ACTH and significantly reduced the angiotensin-induced aldosterone stimulation. The present results indicate that, besides the well-known competitive inhibition of aldosterone binding exerted by potassium prorenoate at the renal receptor site, a direct inhibition of aldosterone biosynthesis also accounts for the pharmacological activity of this aldosterone antagonist.

Effect of hypophysectomy and pituitary stalk transection on alpha-melanocyte-stimulating hormone-like immunoreactivity in the brain of the frog, Rana ridibunda Pallas

The existence of an alpha-MSH-like molecule in the frog brain led us to investigate the role of the pituitary gland in the maintenance of the alpha-MSH content in 3 different regions of the brain. Acetic acid extracts of hypothalamus, rhombencephalon and telencephalon were analyzed by means of a highly specific radioimmunoassay for alpha-MSH in normal, sham-operated, pituitary disconnected and hypophysectomized frogs. Transection of the pituitary stalk gave rise to a significant decrease in alpha-MSH content in the intermediate lobe of the pituitary gland (-71% after 3 days), but did not affect alpha-MSH content in the distal lobe or in the brain. Eight days after total hypophysectomy, an alpha-MSH immunoreactive compound, co-eluting with synthetic alpha-MSH on Sephadex G-25, was found in the 3 brain regions studied. Removal of the whole pituitary gland did not significantly modify alpha-MSH content in the hypothalamus and the telencephalon. A slight increase in alpha-MSH was even observed in the rhombencephalon of hypophysectomized animals. Furthermore, no modification in alpha-MSH immunoreactivity occurred in any region of hypophysectomized animals. These results demonstrate the existence of alpha-MSH-like material in the brain of Rana ridibunda and establish that brain alpha-MSH in the frog is not of pituitary origin.

Immunohistochemical localization of gamma-endorphin in the rat pituitary gland and hypothalamus

To gain more information about cells and organelles involved in the secretion of gamma-endorphin in the rat pituitary gland, an immunohistochemical localization of this peptide was conducted at both light and electron microscopic levels. Using an antiserum to gamma-endorphin which shows little cross-reactivity with beta-lipotropin (beta-LPH) and beta-endorphin, it has been demonstrated that gamm-endorphin is present in all cells of the intermediate lobe and the corticotropic cells of the anterior lobe. At the electron microscopic level, staining for gamma-endorphin was restricted to the secretory granules which also contain ACTH and beta-LPH, suggesting that all of these peptides are released concomitantly during exocytosis. In the hypothalamus, immunostaining possibly related to both gamma- and beta-endorphin but not to beta-LPH was also observed in nerve fibers and not in cell bodies.