Biochemical characterisation and immunohistochemical localisation of the secretogranin II-derived peptide EM66 in the hypothalamus of the jerboa (Jaculus orientalis): modulation by food deprivation

Secretoneurin is a secretogranin-2 derived hormonal peptide in vertebrate neuroendocrine systems

Secretogranin-2 (SCG2) is a large precursor protein that is processed into several potentially bioactive peptides, with the 30-43 amino acid central domain called secretoneurin (SN) being clearly evolutionary conserved in vertebrates. Secretoneurin exerts a diverse array of biological functions including regulating nervous, endocrine, and immune systems in part due to its wide tissue distribution. Expressed in some neuroendocrine neurons and pituitary cells, SN is a stimulator of the synthesis and release of luteinizing hormone from both goldfish pituitary cells and the mouse LβT2 cell line. Neuroendocrine, paracrine and autocrine signaling pathways for the stimulation of luteinizing hormone release indicate hormone-like activities to regulate reproduction. Mutation of the scg2a and scg2b genes using TALENs in zebrafish reduces sexual behavior, ovulation, oviposition, and fertility. A single injection of the SNa peptide enhanced reproductive outcomes in scg2a/scg2b double mutant zebrafish. Evidence in goldfish suggests a new role for SN to stimulate food intake by actions on other feeding-related neuropeptides. Expression and regulation of the Scg2a precursor mRNA in goldfish gut also supports a role in feeding. In rodent models, SN has trophic-like properties promoting both neuroprotection and neuronal plasticity and has chemoattractant properties that regulate neuroinflammation. Data obtained from several cellular models suggest that SN binds to and activates a G-protein coupled receptor (GPCR), but a bona fide SN receptor protein needs to be identified. Other signaling pathways for SN have been reported which provides alternatives to the GPCR hypothesis. These include AMP-activated protein kinase (AMPK), extracellular signal-regulated kinases (ERK), mitogen-activated protein kinase (MAPK)and calcium/calmodulin-dependent protein kinase II in cardiomyocytes, phosphatidylinositol 3-kinase (PI3K) and Akt/Protein Kinase B (AKT, and MAPK in endothelial cells and Janus kinase 2/signal transducer and activator of transcription protein (JAK2-STAT) signaling in neurons. Some studies in cardiac cells provide evidence for cellular internalization of SN by an unknown mechanism. Many of the biological functions of SN remain to be fully characterized, which could lead to new and exciting applications.

Characterization of the EM66 Biomarker in the Pituitary and Plasma of Healthy Subjects With Different Gonadotroph Status and Patients With Gonadotroph Tumor

Granins and their derived-peptides are useful markers of secretion from normal and tumoral neuroendocrine cells. The need to identify new diagnostic markers for neuroendocrine tumors, including pituitary tumors prompted us to determine plasma levels of the secretogranin II-derived peptide EM66 in healthy volunteers with different gonadotroph status and to evaluate its usefulness as a circulating marker for the diagnosis of gonadotroph tumor. Using a radioimmunoassay, we determined plasma EM66 concentrations in healthy men and women volunteers in different physiological conditions in relation with the gonadotroph function. Our results revealed that in men, in women with or without contraception, in pregnant or post-menopausal women, plasma EM66 concentrations are not significantly different, and did not show any correlation with gonadotropin levels. In addition, stimulation or inhibition tests of the gonadotroph axis had no effect on EM66 levels, whatever the group of healthy volunteers investigated while gonadotropin levels showed the expected variations. Immunohistochemical experiments and HPLC analysis showed the occurrence of EM66 in pituitary gonadotroph, lactotroph and corticotroph tumors but not in somatotroph tumor. In patients with gonadotroph or lactotroph tumor, plasma EM66 levels were 1.48 (0.82-4.38) ng/ml and 2.49 (1.19-3.54) ng/ml, respectively. While median value of EM66 was significantly lower in patients with gonadotroph tumor compared to healthy volunteers [2.59 (0.62-4.95) ng/ml], plasma EM66 concentrations were in the same range as normal values and did not show any correlation with gonadotropin levels. These results show that plasma EM66 levels are independent of the activity of the gonadotroph axis in healthy volunteers and, while EM66 levels are reduced in gonadotroph tumors, plasma EM66 does not provide a helpful marker for the diagnosis of these tumors.

Ovulatory Induction of SCG2 in Human, Nonhuman Primate, and Rodent Granulosa Cells Stimulates Ovarian Angiogenesis

The luteinizing hormone (LH) surge is essential for ovulation, but the intrafollicular factors induced by LH that mediate ovulatory processes (e.g., angiogenesis) are poorly understood, especially in women. The role of secretogranin II (SCG2) and its cleaved bioactive peptide, secretoneurin (SN), were investigated as potential mediators of ovulation by testing the hypothesis that SCG2/SN is induced in granulosa cells by human chorionic gonadotropin (hCG), via a downstream LH receptor signaling mechanism, and stimulates ovarian angiogenesis. Humans, nonhuman primates, and rodents were treated with hCG in vivo resulting in a significant increase in the messenger RNA and protein levels of SCG2 in granulosa cells collected early during the periovulatory period and just prior to ovulation (humans: 12 to 34 hours; monkeys: 12 to 36 hours; rodents: 4 to 12 hours post-hCG). This induction by hCG was recapitulated in an in vitro culture system utilizing granulosa-lutein cells from in vitro fertilization patients. Using this system, inhibition of downstream LH receptor signaling pathways revealed that the initial induction of SCG2 is regulated, in part, by epidermal growth factor receptor signaling. Further, human ovarian microvascular endothelial cells were treated with SN (1 to 100 ng/mL) and subjected to angiogenesis assays. SN significantly increased endothelial cell migration and new sprout formation, suggesting induction of ovarian angiogenesis. These results establish that SCG2 is increased in granulosa cells across species during the periovulatory period and that SN may mediate ovulatory angiogenesis in the human ovary. These findings provide insight into the regulation of human ovulation and fertility.

Granin-derived peptides

The granin family comprises altogether 7 different proteins originating from the diffuse neuroendocrine system and elements of the central and peripheral nervous systems. The family is dominated by three uniquely acidic members, namely chromogranin A (CgA), chromogranin B (CgB) and secretogranin II (SgII). Since the late 1980s it has become evident that these proteins are proteolytically processed, intragranularly and/or extracellularly into a range of biologically active peptides; a number of them with regulatory properties of physiological and/or pathophysiological significance. The aim of this comprehensive overview is to provide an up-to-date insight into the distribution and properties of the well established granin-derived peptides and their putative roles in homeostatic regulations. Hence, focus is directed to peptides derived from the three main granins, e.g. to the chromogranin A derived vasostatins, betagranins, pancreastatin and catestatins, the chromogranin B-derived secretolytin and the secretogranin II-derived secretoneurin (SN). In addition, the distribution and properties of the chromogranin A-derived peptides prochromacin, chromofungin, WE14, parastatin, GE-25 and serpinins, the CgB-peptide PE-11 and the SgII-peptides EM66 and manserin will also be commented on. Finally, the opposing effects of the CgA-derived vasostatin-I and catestatin and the SgII-derived peptide SN on the integrity of the vasculature, myocardial contractility, angiogenesis in wound healing, inflammatory conditions and tumors will be discussed.

A potential role for the secretogranin II-derived peptide EM66 in the hypothalamic regulation of feeding behaviour

EM66 is a conserved 66-amino acid peptide derived from secretogranin II (SgII), a member of the granin protein family. EM66 is widely distributed in secretory granules of endocrine and neuroendocrine cells, as well as in hypothalamic neurones. Although EM66 is abundant in the hypothalamus, its physiological function remains to be determined. The present study aimed to investigate a possible involvement of EM66 in the hypothalamic regulation of feeding behaviour. We show that i.c.v. administration of EM66 induces a drastic dose-dependent inhibition of food intake in mice deprived of food for 18 hours, which is associated with an increase of hypothalamic pro-opiomelanocortin (POMC) and melanocortin-3 receptor mRNA levels and c-Fos immunoreactivity in the POMC neurones of the arcuate nucleus. By contrast, i.c.v. injection of EM66 does not alter the hypothalamic expression of neuropeptide Y (NPY), or that of its Y1 and Y5 receptors. A 3-month high-fat diet (HFD) leads to an important decrease of POMC and SgII mRNA levels in the hypothalamus, whereas NPY gene expression is not affected. Finally, we show that a 48 hours of fasting in HFD mice decreases the expression of POMC and SgII mRNA, which is not observed in mice fed a standard chow. Taken together, the present findings support the view that EM66 is a novel anorexigenic neuropeptide regulating hypothalamic feeding behaviour, at least in part, by activating the POMC neurones of the arcuate nucleus.

Stimulatory effect of the secretogranin-ll derived peptide secretoneurin on food intake and locomotion in female goldfish (Carassius auratus)

Secretoneurin (SN) is a conserved peptide derived by proteolytic processing from the middle domain of the ∼600 amino acid precursor secretogranin-II (SgII). Secretoneurin is widely distributed in secretory granules of endocrine cells and neurons and has important roles in reproduction as it stimulates luteinizing hormone release from the pituitary. A potential new role of SN in goldfish feeding is the subject of this study. Firstly, we established that acute (26 h; p<0.0001) and short-term (72 h; p=0.016) fasting increased SgIIa precursor mRNA levels 1.25-fold in the telencephalon, implicating SN in the control of feeding. Secondly, we determined that intracerebroventricular injections of the type A SN (SNa; 0.2 and 1 ng/g BW) increased food intake and locomotor behavior by 60 min. Fish injected with the lower and higher doses of SNa (0.2 and 1 ng/g) respectively exhibited significant 1.77- and 2.58-fold higher food intake (p<0.0001) than the saline-injected control fish. Locomotor behavior was increased by 1.35- and 2.26-fold for 0.2 ng/g SNa (p=0.0001) and 1 ng/g SNa (p<0.0001), respectively. Injection of 1 ng/g SNa increased mRNA levels of hypothalamic neuropeptide Y 1.36-fold (p=0.038) and decreased hypothalamic cocaine-and amphetamine-regulated transcript by 33% (p=0.01) at 2h and 5h post-injection, respectively. These data suggest interactions of SNa with stimulatory and inhibitory pathways of food intake control in fish.

Impact of aflatoxin B1 on hypothalamic neuropeptides regulating feeding behavior

The presence of mycotoxins in food is a major problem of public health as they produce immunosuppressive, hepatotoxic and neurotoxic effects. Mycotoxins also induce mutagenic and carcinogenic effects after long exposure. Among mycotoxins that contaminate food are aflatoxins (AF) such as AFB1, which is the most powerful natural carcinogen. The AF poisoning results in symptoms of depression, anorexia, diarrhea, jaundice or anemia that can lead to death, but very few studies have explored the impact of AF on neuroendocrine regulations. To better understand the neurotoxic effects of AF related to anorexia, we explored in rat the impact of AFB1 on the major hypothalamic neuropeptides regulating feeding behavior, either orexigenic (NPY, Orexin, AgRP, MCH) or anorexigenic (α-MSH, CART, TRH). We also studied the effect of AFB1 on a novel neuropeptide, the secretogranin II (SgII)-derived peptide EM66, which has recently been linked to the control of food intake. For this, adult male rats were orally treated twice a week for 5 weeks with a low dose (150 μg/kg) or a high dose (300 μg/kg) of AFB1 dissolved in corn oil. Repeated exposure to AFB1 resulted in reduced body weight gain, which was highly significant for the high dose of AF. Immunocytochemical and quantitative PCR experiments revealed a dose-related decrease in the expression of all the hypothalamic neuropeptides studied in response to AFB1. Such orexigenic and anorexigenic alterations may underlie appetite disorders as they are correlated to a dose-dependent decrease in body weight gain of treated rats as compared to controls. We also found a decrease in the number of EM66-containing neurons in the arcuate nucleus of AFB1-treated animals, which was associated with a lower expression of its precursor SgII. These findings show for the first time that repeated consumption of AFB1 disrupts the hypothalamic regulation of neuropeptides involved in feeding behavior, which may contribute to the lower body weight gain associated to AF exposure.

Differential expression and processing of secretogranin II in relation to the status of pheochromocytoma: implications for the production of the tumoral marker EM66

We have previously demonstrated that measurement of tissue concentrations of the secretogranin II (SgII or SCG2 as listed in the HUGO database)-derived peptide EM66 may help to discriminate between benign and malignant pheochromocytomas and that EM66 represents a sensitive plasma marker of pheochromocytomas. Here, we investigated the gene expression and protein production of SgII in 13 normal adrenal glands, and 35 benign and 16 malignant pheochromocytomas with the goal to examine the molecular mechanisms leading to the marked variations in the expression of EM66 in tumoral chromaffin tissue. EM66 peptide levels were 16-fold higher in benign than in malignant pheochromocytomas and had an area under the receiver-operating characteristic curve of 0.95 for the distinction of benign and malignant tumors. Q-PCR experiments indicated that the SgII gene was significantly underexpressed in malignant tumors compared with benign tumors. Western blot analysis using antisera directed against SgII and SgII-derived fragments revealed lower SgII protein and SgII-processing products in malignant tumors. Western blot also showed that low p-cAMP-responsive element-binding (CREB) concentrations seemed to be associated with the malignant status. In addition, the prohormone convertase PC1 and PC2 genes and proteins were overexpressed in benign pheochromocytomas compared with malignant pheochromocytomas. Low concentrations of EM66 found in malignant tumors are associated with reduced expression and production of SgII and SgII-derived peptides that could be ascribed to a decrease in SgII gene transcription, probably linked to p-CREB down-regulation, and to lower PC levels. These findings highlight the mechanisms leading to lower concentrations of EM66 in malignant pheochromocytoma and strengthen the notion that this peptide is a suitable marker of this neuroendocrine tumor.

Granins and granin-related peptides in neuroendocrine tumours

This review focus on neuroendocrine tumours (NETs), with special reference to the immunohistochemical analysis of granins and granin-related peptides and their usefulness in identifying and characterizing the great diversity of NET types. Granins, their derived peptides, and complex protein-processing enzyme systems that cleave granins and prohormones, have to some extent cell-specific expression patterns in normal and neoplastic NE cells. The marker most commonly used in routine histopathology to differentiate between non-NETs and NETs is chromogranin (Cg) A, to some extent CgB. Other members of the granin family may also be of diagnostic value by identifying special NET types, e.g. secretogranin (Sg) VI was only found in pancreatic NETs and phaeochromocytomas. SgIII has recently arisen as an important NET marker; it was strongly expressed in NETs, with some exceptions--phaeochromocytomas expressed few cells and parathyroid adenomas none. Some expression patterns of granin-related peptides seem valuable in differentiating between some benign and malignant NETs, some may also provide prognostic information, among which: well-differentiated NET types expressed more CgA epitopes than the poorly differentiated ones, except insulinomas, where the opposite was noted; medullary thyroid carcinomas containing few cells immunoreactive to a CgB antibody were related to a bad prognosis; C-terminal secretoneurin visualized a cell type related to malignancy in phaeochromocytomas. Further research will probably establish new staining patterns with marker functions for granins in NETs which may be of histopathological diagnostic value.

Chromogranins A and B and secretogranin II as prohormones for regulatory peptides from the diffuse neuroendocrine system

Chromogranin A (CgA), chromogranin B (CgB), and secretogranin II (SgII) belong to a family of uniquely acidic secretory proteins in elements of the diffuse neuroendocrine system. These "granins" are characterized by numerous pairs of basic amino acids as potential sites for intra- and extragranular processing. In response to adequate stimuli, the granins are coreleased with neurotransmitters and hormones and appear in the circulation as potential modulators of homeostatic processes. This review is directed towards functional aspects of the secreted CgA, CgB, and SgII and their biologically active sequences. Widely different effects and targets have been reported for granin-derived peptides. So far, the CgA peptides vasostatin-I, pancreastatin, and catestatin, the CgB peptides CgB(1-41) and secretolytin, and the SgII peptide secretoneurin are the most likely candidates for granin-derived regulatory peptides. Most of their effects fit into patterns of direct or indirect modulations of major functions, in particular associated with inflammatory conditions.

Granin-derived peptides as diagnostic and prognostic markers for endocrine tumors

Chromogranin A-like immunoreactivity (CgA-LI) has been, and remains, the most widely used diagnostic and prognostic marker for endocrine tumors. The availability of assay kits combined with moderately high sensitivity and specificity has meant that there has been no great incentive to develop alternative markers. However, circulating concentrations of CgA-LI are elevated in several non-neoplastic diseases and in patients receiving acid-suppression therapy which may lead to false positive diagnosis. Additionally, certain endocrine tumors, such as rectal carcinoids, do not express the CgA gene so that there is a need for additional markers to complement CgA measurements. Plasma concentrations of the CgA-derived peptide, pancreastatin, measured with antisera of defined regional specificity, have a prognostic value in patients with metastatic midgut carcinoid tumors receiving somatostatin analog therapy or hepatic artery chemoembolization. Other CgA-derived peptides with potential as tumor markers are vasostatin-1, WE-14, catestatin, GE-25, and EL-35 but their value has yet to be fully assessed. Circulating concentrations of chromogranin B-like immunoreactivity (CgB-LI) are not elevated in non-neoplastic diseases and measurements of CCB, the COOH-terminal fragment of CgB, may be useful as a biochemical marker for neuroendocrine differentiation in lung tumors. Antisera to the secretogranin II-derived peptide, secretoneurin detects carcinoid tumors of the appendix with greater frequency than antisera to CgA and are of value in identifying therapy-resistant carcinoma of the prostate (clinical stage D3). Measurement of concentrations of a second secretogranin II-derived peptide, EM-66 in tumor tissue has been used to differentiate between benign and malignant pheochromocytoma. These examples point to a limited although potentially valuable role for granin-derived peptides as tumor markers.

New insights into granin-derived peptides: evolution and endocrine roles

The granin protein family is composed of two chromogranin and five secretogranin members that are acidic, heat-stable proteins in secretory granules in cells of the nervous and endocrine systems. We report that there is little evidence for evolutionary relationships among the granins except for the chromogranin group. The main granin members, including chromogranin A and B, and secretogranin II are moderately conserved in the vertebrates. Several small bioactive peptides can be generated by proteolysis from those homologous domains existing within the granin precursors, reflecting the conservation of biological activities in different vertebrates. In this context, we focus on reviewing the distribution and function of the major granin-derived peptides, including vasostatin, bovine CgB(1-41) and secretoneurin in vertebrate endocrine systems, especially those associated with growth, glucose metabolism and reproduction.

Molecular cloning, mapping, and polymorphism of the porcine SCG2 gene

The secretogranin II (SCG2) gene is associated with the synthesis and secretion of follicle-stimulating hormone and luteinizing hormone. In the present study, we have determined the complete cDNA sequence of pig SCG2, which was submitted to GenBank with accession no. AY870646. Its complete open reading frame of 1,851 nucleotides encodes 616 amino acids. The predicted protein shares 80-87% identity with mouse, human, and bovine SCG2 proteins, and all four species share almost complete identity in the secretoneurin and EM66 domains. Pig SCG2 is a protein of 589 amino acids and 68,132 Da, preceded by a signal peptide of 27 residues. It contains nine pairs of dibasic residues, which are used as potential cleavage sites for generation of physiologically active peptides. Analysis of the SCG2 gene across the INRA-Minnesota porcine radiation hybrid panel indicates close linkage with microsatellite marker SW2608, located on Sus scrofa chromosome 15 (SSC15) q25, which harbors several QTL for ovulation rate and meat quality. Comparative sequencing and EST analysis revealed nine SNPs in porcine SCG2 cDNA, including seven SNPs in the coding region and two SNPs in the 3' UTR. Four nonsynonymous SNPs (G622A, G1671T, C1718T, and A1790C) resulted in amino acid substitutions of Ala-->Thr, Glu-->Asp, Pro-->Leu, and Asn-->Thr, respectively.

Chromogranins A and B and secretogranin II: evolutionary and functional aspects

Chromogranins/secretogranins or granins are a class of acidic, secretory proteins that occur in endocrine, neuroendocrine, and neuronal cells. Granins are the precursors of several bioactive peptides and may be involved in secretory granule formation and neurotransmitter/hormone release. Characterization and analysis of chromogranin A (CgA), chromogranin B (CgB), and secretogranin II (SgII) in distant vertebrate species confirmed that CgA and CgB belong to related monophyletic groups, probably evolving from a common ancestral precursor, while SgII sequences constitute a distinct monophyletic group. In particular, selective sequences within these proteins, bounded by potential processing sites, have been remarkably conserved during evolution. Peptides named vasostatin, secretolytin and secretoneurin, which occur in these regions, have been shown to exert various biological activities. These conserved domains may also be involved in the formation of secretory granules in different vertebrates. Other peptides such as catestatin and pancreastatin may have appeared late during evolution. The function of granins as propeptide precursors and granulogenic factors is discussed in the light of recent data obtained in various model species and using knockout mice strains.

Immunohistochemical distribution of the secretogranin II-derived peptide EM66 in the rat hypothalamus: A comparative study with jerboa

EM66 is a 66-amino acid peptide derived from secretogranin II, a member of granin acidic secretory protein family, by proteolytic processing. EM66 has been previously characterized in the jerboa (Jaculus orientalis) hypothalamus and its potential implication in the neuroendocrine regulation of feeding behaviour has been demonstrated. In the present study, an immunohistochemical analysis of the localization of EM66 within hypothalamic structures of rat was performed and compared to the distribution of EM66 in the jerboa hypothalamus. In the rat hypothalamus, as in the jerboa, EM66 immunostaining was detected in the parvocellular paraventricular, preoptic and arcuate nuclei, as well as the lateral hypothalamus which displayed an important density of EM66-producing neurones. However, unlike jerboa, the suprachiasmatic and supraoptic nuclei of the rat hypothalamus were devoid of cellular EM66-immunolabeling. Thus, the novel peptide EM66 may exert common neuroendocrine activities in rat and jerboa, e.g. control of food intake, and species-specific roles in jerboa such as the regulation of biological rhythms and hydromineral homeostasis. These results suggest the existence of differences between jerboas and rats in neuroendocrine regulatory mechanisms involving EM66.

Expression and processing of the neuroendocrine protein secretogranin II in benign and malignant pheochromocytomas

The aim of the present study was to compare the expression levels of secretogranin II (SgII), prohormone convertases (PC)1 and PC2, and the proteolytic processing of SgII in benign versus malignant pheochromocytomas. Quantitative (Q)-PCR experiments indicated that SgII, PC1, and PC2 mRNAs were overexpressed in pheochromocytoma compared to non-tumoral chromaffin cells (P<0.001) and in benign compared to malignant tumors (P<0.01). Western blot analysis using a human SgII antiserum revealed the occurrence of a 97-kDa band corresponding to the expected size of SgII, with significantly higher quantities in benign than in malignant tumors (P<0.05). Using antisera directed against sequential regions of SgII (N-terminal, secretoneurin [SN], EM66, internal, and C-terminal sequences), we observed distinct processing profiles between benign and malignant pheochromocytomas. In contrast, using PC1 and PC2 antisera no differences between the two types of tumors were found. RIA measurement showed that EM66 median values between benign and malignant chromaffin cell tumors were significantly different (128.5 vs. 6.3 ng/mg protein, respectively; P<0.001). Taken together, these results indicate that, in pheochromocytoma, malignancy is associated with reduced PC1, PC2, and SgII mRNA expression and decreased levels of processing products of SgII, in line with the low concentrations of EM66 that occur in malignant tumors. These data support the notion that SgII-processing products, such as EM66, could represent prognostic markers of pheochromocytomas.

Immunocytochemical detection of cholecystokinin and corticotrophin-releasing hormone neuropeptides in the hypothalamic paraventricular nucleus of the jerboa (Jaculus orientalis): modulation by immobilisation stress

The hypothalamic response to an environmental stress implicates the corticotrophin-releasing hormone (CRH) neuroendocrine system of the hypothalamic parvicellular paraventricular nucleus (PVN) in addition to other neuropeptides coexpressed within CRH neurones and controlling the hypothalamo-pituitary-adrenal (HPA) axis activity as well. Such neuropeptides are vasopressin, neurotensin and cholecystokinin (CCK). It has previously been demonstrated that the majority of the CRH neuronal population coexpresses CCK after a peripheral stress in rats. In the present study, we explored such neuroendocrine plasticity in the jerboa in captivity as another animal model. In particular, we studied CCK and CRH expression within the hypothalamic PVN by immunocytochemistry in control versus acute immobilisation stress-submitted jerboas. The results show that CCK- and CRH-immunoreactive neuronal systems are located in the hypothalamic parvicellular PVN. The number of CCK-immunoreactive neurones within the PVN was significantly increased (138% increase) in stressed animals compared to controls. Similarly, the number of CRH-containing neurones was higher in stressed jerboas (128%) compared to controls. These results suggest that the neurogenic stress caused by immobilisation stimulates CCK as well as CRH expression in jerboas, which correlates well with previous data obtained in rats using other stressors. The data obtained also suggest that, in addition to CRH, CCK is another neuropeptide involved in the response to stress in jerboa, acting by controlling HPA axis activity. Because CCK is involved in the phenotypical plasticity of CRH-containing neurones in response to an environmental stress, we also explored their coexpression by double immunocytochemistry within the PVN and the median eminence (i.e. the site of CRH and CCK corelease in the rat) following jerboa immobilisation. The results show that CCK is not coexpressed within CRH neurones in either control or stressed jerboa, suggesting differences between jerboas and rats in the neuroendocrine regulatory mechanisms of the stress response involving CRH and CCK. The adaptative physiological mechanisms to environmental conditions might vary from one mammal species to another.

Involvement of multiple signaling pathways in PACAP-induced EM66 secretion from chromaffin cells

Secretoneurin (SN) and EM66 are two highly conserved peptides that derive from the processing of secretogranin II (SgII), one of the major constituents of chromaffin cell secretory vesicles. It has been shown that PACAP regulates SgII gene transcription and SN release in bovine adrenochromaffin cells. The aim of the present study was to localize and characterize EM66 in the bovine adrenal gland, and to examine the signaling pathways activated by PACAP to regulate the secretion of EM66 from cultured chromaffin cells. Double immunohistochemical labeling showed an intense EM66-immunoreactive (EM66-IR) signal in TH-positive medullary chromaffin cells of the adrenal gland. HPLC analysis combined with RIA detection revealed, in adrenal medulla extracts and cultured chromaffin cell media, the presence of a major EM66-IR peak co-eluting with the recombinant peptide. PACAP dose-dependently stimulated EM66 release from chromaffin cells (ED(50)=4.8 nM). The effect of PACAP on EM66 secretion was observed after 6 h of treatment and increased to reach a 2.6-fold stimulation at 48 h. The nonselective calcium channel blocker NiCl(2), the cytosolic calcium chelator BAPTA-AM and the L-type calcium channel blocker nimodipine significantly inhibited the stimulatory effect of PACAP on EM66 release. The secretory response to PACAP was also significantly lowered by the protein kinase A inhibitor H89 and by the protein kinase C inhibitor chelerythrine. Concomitant administration of chelerythrine, H89, NiCl(2) and BAPTA totally abolished PACAP-stimulated EM66 secretion. The MAPK inhibitors U0126 and SB203580 respectively decreased by 63% and 72% PACAP-evoked EM66 release. These results indicate that, in bovine adrenal medulla, SgII is processed to generate the EM66 peptide and that PACAP activates multiple signaling pathways to regulate EM66 release from chromaffin cells, suggesting that EM66 may act downstream of the trans-synaptic stimulation of the adrenal medulla by neurocrine factors.

Vasopressin-containing neurons of the hypothalamic parvocellular paraventricular nucleus of the jerboa: plasticity related to immobilization stress

The corticotropin-releasing hormone (CRH) neurons of the hypothalamic parvocellular paraventricular nucleus (PVN) have a high potential for phenotypical plasticity, allowing them to rapidly modify their neuroendocrine output, depending upon the type of stressors. Indeed, these neurons coexpress other neuropeptides, such as cholecystokinin (CCK), vasopressin (VP), and neurotensin, subserving an eventual complementary function to CRH in the regulation of the pituitary. Unlike in rats, our previous data showed that in jerboas, CCK is not coexpressed within CRH neurons in control as well as stressed animals. The present study explored an eventual VP participation in the phenotypic plasticity of CRH neurons in the jerboa. We analyzed the VP expression within the PVN by immunocytochemistry in male jerboas submitted to acute stress. Our results showed that, contrary to CRH and CCK, no significant change concerned the number of VP-immunoreactive neurons following a 30-min immobilization. The VP/CRH coexpression within PVN and median eminence was investigated by double immunocytochemistry. In control as well as stressed animals, the CRH-immunopositive neurons coexpressed VP within cell bodies and terminals. No significant difference in the number of VP/CRH double-labeled cells was found between both groups. However, such coexpression was quantitatively more important into the posterior PVN as compared with the anterior PVN. This suggests an eventual autocrine/paracrine or endocrine role for jerboa parvocellular VP which is not correlated with acute immobilization stress. VP-immunoreactive neurons also coexpressed CCK within PVN and median eminence of control and stressed jerboas. Such coexpression was more important into the anterior PVN as compared with the posterior PVN. These results showed the occurrence of at least two VP neuronal populations within the jerboa PVN. In addition, the VP expression did not depend upon acute immobilization stress. These data highlight differences in the neuroendocrine regulatory mechanisms of the stress response involving CRH/CCK or VP. They also underline that adaptative physiological mechanisms to stress might vary from one mammal species to another.