Molecular cloning of chicken vasoactive intestinal polypeptide receptor complementary DNA, tissue distribution and chromosomal localization

Research Note: Association of VIPR-1 gene polymorphism with growth traits in meat type Japanese quail (Coturnix Japonica)

This study aimed to analyze the polymorphism of the vasoactive intestinal peptide receptor-1 (VIPR-1) gene and its association with growth traits in quail using the PCR-RFLP and sequencing techniques. Genomic DNA was extracted from blood samples of 36 female Savimalt (SV) quails and 49 female French Giant (FG) quails. Growth traits were measured and used for VIPR-1 gene analysis, as body weight (BW), tibia length (TL), chest width (CW), chest depth (CD), sternum length (SL), body length (BL), and tibia circumference (TC). The results showed that 2 SNPs (BsrD I and HpyCH4 IV) were detected in exon 4 to 5 and exon 6 to 7 of the VIPR-1 gene, respectively. The results of association showed that the BsrD I site was not significantly associated with growth traits at 3 or 5 wk of age in the SV strain (P < 0.05), while the BsrD I site was significantly associated with BL at 3 or 5 wk of age in FG (P < 0.05). The HpyCH4 IV site was significantly associated with TL, CW, CD, SL, and BL at 3 wk of age in the SV strain (P < 0.05), while the HpyCH4 IV site was significantly correlated with BW, CW, SL, and BL at 5 wk of age in SV (P < 0.05). The HpyCH4 IV site was significantly associated with TL and TC at 3 wk of age in FG (P < 0.05), while the HpyCH4 IV site was significantly associated with TC at 5 wk of age in FG (P < 0.05). Four haplotype combinations based on 2 SNPs showed significantly association with BW, CW, CD, SL, BL, and TC at 3 or 5 wk of age in SV (P < 0.05). There was not significant association between 3 haplotype combinations with growth trait at 3 or 5 wk of age in FG (P > 0.05). In conclusion, the VIPR-1 gene could be used as a molecular genetic marker to improve growth traits in quail.

The anorexigenic effect of vasoactive intestinal polypeptide in Japanese quail is associated with molecular changes in the arcuate and dorsomedial hypothalamic nuclei

Vasoactive intestinal polypeptide (VIP) is involved in gastric smooth muscle relaxation, vasodilation, and gastric secretions. It is also associated with appetite regulation, eliciting an anorexigenic response in mammals, birds, and fish; however, the molecular mechanism mediating this response is not well understood. The aim of the present study was thus to investigate hypothalamic mechanisms mediating VIP-induced satiety in 7-d old Japanese quail. In experiment 1, chicks that received intracerebroventricular (ICV) injection of VIP had reduced food intake for up to 180 min after injection and reduced water intake for 90 min. In experiment 2, VIP-treated chicks that were food restricted did not reduce water intake. In experiment 3, there was increased c-Fos immunoreactivity in the arcuate (ARC) and dorsomedial (DMN) nuclei of the hypothalamus in VIP-injected quail. In experiment 4, ICV VIP was associated with decreased neuropeptide Y mRNA in the ARC and DMN and an increase in corticotropin releasing factor mRNA in the DMN. In experiment 5, VIP-treated chicks displayed fewer feed pecks and locomotor behaviors. These results demonstrate that central VIP causes anorexigenic effects that are likely associated with reductions in orexigenic tone involving the ARC and DMN.

Daily, circadian and seasonal changes of rhodopsin-like encephalic photoreceptor and its involvement in mediating photoperiodic responses of Gambel's white-crowned Sparrow, Zonotrichia leucophrys gambelii

Extra-retinal, non-pineal, encephalic photoreceptors (EP) play important roles in mediating development of the reproductive system by the annual change in day length (photoperiodic gonadal response - PGR) in birds. However, the distribution of rhodopsin-like EPs and their functional daily, circadian and seasonal changes are still unclear in the avian brain. This study identifies two novel groups of rhodopsin-immunoreactive cells in the nucleus paraventricularis magnocellularis (PVN) of the hypothalamus and in the medial basal hypothalamus (MBH) in a seasonally breeding species, Gambel's white-crowned sparrow (Zonotrichia leucophrys gambelii). In the PVN, rhodopsin-ir cell number showed both daily and circadian changes with more labeled cells apparent in the night phase in photosensitive birds, while only circadian changes were observed involving fewer labeled cells in the night phase in photorefractory birds. Single long day photo-stimulation significantly decreased the rhodopsin-ir cell number only in photosensitive birds, coincident with a rise in plasma levels of luteinizing hormone (LH). In the MBH, rhodopsin-ir cell number did not show daily, circadian or single long day induced changes in either photoperiodic states. But, overall these rhodopsin expressing neurons significantly increased from photosensitive to photorefractory states. In the median eminence (ME), more intense rhodopsin-ir was detected in photorefractory birds compared to photosensitive birds. For expression of GnRH and vasoactive intestinal polypeptide (VIP), seasonal differences were found with opposite relationships, consistent with previous studies. Our results suggest different roles of the two groups of rhodopsin-like EPs in the regulation of PGR in white-crowned sparrows.

Reproductiveaxis gene regulation during photostimulation and photorefractoriness in Yangzhou goose ganders

Background

The Yangzhou goose is a long-day breeding bird that has been increasingly produced in China. Artificial lighting programs are used for controlling its reproductive activities. This study investigated the regulations of photostimulation and photorefractoriness that govern the onset and cessation of the breeding period.

Results

Increasing the daily photoperiod from 8 to 12 h rapidly stimulated testis development and increased plasma testosterone concentrations, with peak levels being reached 2 months after the photoperiod increase. Subsequently, testicular activities, testicular weight, spermatogenesis, and plasma testosterone concentrations declined steadily and reached to the nadir at 5 months after the 12-hour photoperiod. Throughout the experiment, plasma concentrations of triiodothyronine and thyroxine changed in reciprocal fashions to that of testosterone. The stimulation of reproductive activities caused by the increasing photoperiod was associated with increases in gonadotropin-releasing hormone (GnRH), but decreases in gonadotropin-inhibitory hormone (GnIH) and vasoactive intestinal peptide (VIP) gene messenger RNA (mRNA) levels in the hypothalamus. In the pituitary gland, the levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) mRNA abruptly increased during the longer 12-hour photoperiod. The occurrence of photorefractoriness was associated with increased GnIH gene transcription by over 250-fold, together with increased VIP mRNA levels in the hypothalamus, and then prolactin and thyroid-stimulating hormone in the pituitary gland. FSH receptor, LH receptor, and StAR mRNA levels in the testis changed in ways paralleling those of testicular weight and testosterone concentrations.

Conclusions

The seasonal reproductive activities in Yangzhou geese were directly stimulated by a long photoperiod via upregulation of GnRH gene transcription, downregulation of GnIH, VIP gene transcription, and stimulation of gonadotrophin. Development of photorefractoriness was characterized by hyper-regulation of GnIH gene transcription in the hypothalamus, in addition of upregulation of VIP and TRH gene transcription, and that of their receptors, in the pituitary gland.

Seasonal Variation in Group Size Is Related to Seasonal Variation in Neuropeptide Receptor Density

In many species, seasonal variation in grouping behavior is widespread, with shifts towards territoriality in the breeding season and grouping in the winter. Compared to the hormonal and neural mechanisms of seasonal territorial aggression, the mechanisms that promote seasonal grouping have received little attention. We collected brains in spring and winter from wild-caught males of two species of emberizid sparrows that seasonally flock (the field sparrow, Spizella pusilla, and the dark-eyed junco, Junco hyemalis) and two species that do not seasonally flock (the song sparrow, Melospiza melodia, and the eastern towhee, Pipilo erythrophthalmus). We used receptor autoradiography to quantify seasonal plasticity in available binding sites for three neuropeptides known to influence social behavior. We examined binding sites for 125I-vasoactive intestinal polypeptide (VIP), 125I-sauvagine (SG, a ligand for corticotropin-releasing hormone receptors) and 125I-ornithine vasotocin analog (OVTA, a ligand for the VT3 nonapeptide). For all species and ligands, brain areas that exhibited a seasonal pattern in binding density were characterized by a winter increase. Compared to nonflocking species, seasonally flocking species showed different binding patterns in multiple brain areas. Furthermore, we found that winter flocking was associated with elevated winter 125I-VIP binding density in the medial amygdala, as well as 125I-VIP and 125I-OVTA binding density in the rostral arcopallium. While the functional significance of the avian rostral arcopallium is unclear, it may incorporate parts of the pallial amygdala. Our results point to this previously undescribed area as a likely hot spot of social modulation.

Effects of Vasoactive Intestinal Polypeptide and Forskolin on mRNA Expression of Prolactin and Prolactin Regulatory Element-Binding Protein in the Anterior Pituitary Gland of Chicken Embryo and Laying Hens

Vasoactive intestinal peptide (VIP) treatment induced mRNA expression of Prolactin (PRL) in the chicken anterior pituitary gland. VIP responsive element (VRE) of the PRL promoter was identified in the various bird species. However, transcription factor, which binds to VRE, has not yet been identified. Prolactin regulatory element-binding protein (PREB) gene cloned as a candidate transcription factor binds to VRE. Increases of mRNA levels of PRL and PREB during embryogenesis were identified. However, whether VIP affects levels of PRL and PREB mRNA during embryogenesis remains unknown. The effects of VIP and forskolin on mRNA expression of PRL and PREB in the embryonic anterior pituitary gland were assessed. Furthermore, administration of VIP to laying hens was conducted to examine the relationship between VIP and PREB mRNA expression. At day 14 of the embryonic growth stage, VIP treatment did not affect mRNA levels of either PRL or PREB, whereas forskolin treatment induced the increase of these mRNA levels. At day 20, both VIP and forskolin induced an increase of PRL and PREB mRNA levels. The administration of VIP significantly increased mRNA levels of PRL and PREB in the anterior pituitary gland of White Leghorn and Nagoya. These results indicate that the effects of VIP on PRL and PREB mRNA expression levels of VIP receptor may in turn affect PRL and PREB mRNA levels in the chicken anterior pituitary gland.

Association of VIPR-1 gene polymorphisms and haplotypes with egg production in laying quails

The laying quail is a worldwide breed which exhibits high economic value. In our current study, the vasoactive intestinal peptide receptor-1 (VIPR-1) was selected as the candidate gene for identifying traits of egg production. A single nucleotide polymorphism (SNP) detection was performed in 443 individual quails, including 196 quails from the H line, 202 quails from the L line, and 45 wild quails. The SNPs were genotyped using a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Two mutations (G373T, A313G) were detected in all the tested quail populations. The associated analysis showed that the SNP genotypes of the VIPR-1 gene were significantly linked with the egg weight of G373T and A313G in 398 quails. The quails with the genotype GG always exhibited the largest egg weight for the two mutations in the H and L lines. Linkage disequilibrium (LD) analysis indicated that G373T and A313G loci showed the weakest LD. Seven main diplotypes from the four main reconstructed haplotypes were observed, indicating a significant association of diplotypes with egg weight. Quails with the h1h2 (GGGT) diplotype always exhibited the smallest egg weight and largest egg number at 20 weeks of age. The overall results suggest that the alterations in quails may be linked with potential major loci or genes affecting reproductive traits.

Vasoactive intestinal peptide promotes differentiation and clock gene expression in granulosa cells from prehierarchal follicles

Vasoactive intestinal peptide (VIP) signaling via cyclic adenosine monophosphate (cAMP) is reported to stimulate steroidogenesis in ovarian granulosa cells from a variety of vertebrate species, including the domestic hen. Prior to follicle selection in the hen ovary (i.e., cyclic recruitment) follicle-stimulating-hormone (FSH)-induced cAMP signaling is absent within the granulosa layer until immediately following follicle selection. As a consequence, granulosa cells remain in an undifferentiated state and are unable to initiate FSH-induced steroidogenesis. VIP receptors (VPAC1 and VPAC2), like the FSH receptor, are G protein-coupled receptors, so we predicted that VIP signaling in granulosa cells is also absent in follicles that have not yet been selected into the preovulatory hierarchy. Initial studies established that mRNA encoding VPAC1 and VPAC2 are expressed within the granulosa cells throughout follicle development. Nevertheless, undifferentiated granulosa cells from prehierarchal (6-8 mm) follicles do not accumulate cAMP in response to a 4-hr incubation with chicken VIP; the capacity for such receptor signaling is attained only following selection within actively differentiating granulosa cells. VIP treatment did, however, increase expression of mRNA encoding the Gallus circadian clock protein, BMAL1-but only in granulosa cells collected from selected follicles. These findings provide evidence that, at follicle selection, the acquisition of VIP-induced cAMP cell signaling helps initiate and promote the differentiation of of granulosa cells. Furthermore, we propose that VIP signaling may regulate BMAL1 expression and, thus, a daily rhythmicity within granulosa cells of preovulatory follicles. Mol. Reprod. Dev. 83: 455-463, 2016. © 2016 Wiley Periodicals, Inc.

Characterization and Expression of Turkey Prolactin Regulatory Element Binding in the Anterior Pituitary Gland and Pancreas During Embryogenesis

The PRL regulatory element-binding (PREB) protein is a transcription factor that was originally cloned from the rat anterior pituitary gland and characterized as a regulator of the PRL promoter. It is also strongly expressed in several extrapituitary tissues; however, its functional role is not well understood to date. In this study, we aimed to clone and characterize the turkey PREB gene and investigate its mRNA expression in the anterior pituitary gland and pancreas during embryogenesis. Based on the conserved sequence of chicken and mammalian PREB cDNAs, a turkey PREB cDNA fragment was obtained, and after sequencing of the fragment, the 5′-and 3′-ends of mRNA were amplified and determined. To identify the PREB gene structure, polymerase chain reaction (PCR) amplification was performed. The turkey PREB gene consists of 9 exons and 8 introns, and it encodes a 411-amino-acid protein. The expression of PREB mRNA in the anterior pituitary gland was measured during embryogenesis. Levels of PREB mRNA significantly increased at embryonic day 22, with maximum levels being detected on day 25 of ontogeny, which correlated with similar changes in levels of PRL mRNA. The highest level of PREB mRNA was detected on day 19 in the pancreas. However, the highest level of insulin mRNA was detected at embryonic day 25. These results indicate that PREB may be involved in the expression of PRL mRNA in the anterior pituitary gland, whereas insulin mRNA may be expressed independently of the expression of PREB mRNA in the pancreas during embryogenesis.

Transcriptome profiling identifies differentially expressed genes in Huoyan goose ovaries between the laying period and ceased period

The Huoyan goose is famous for its high egg-laying performance and is listed as a nationally protected domestic animal by the Chinese government. To elucidate the key regulatory genes involved in Huoyan goose egg laying, RNA from ovarian tissue during the ceased and laying periods was sequenced using the Illumina HiSeq 2000 sequencing platform. More than 12 million reads were produced in ceased and laying libraries that included 11,896,423 and 12,534,799 clean reads, respectively. More than 20% of the reads were matched to the reference genome, and 23% of the reads were matched to reference genes. Genes with a false discovery rate (FDR) ≤0.001 and log₂ratio ≧1 or ≤−1 were characterized as differentially expressed, and 344 up-regulated and 344 down-regulated genes were classified into functional categories. Twelve genes that are mainly involved in pathways for reproduction regulation, such as steroid hormone biosynthesis, GnRH signaling pathways, oocyte meiosis, progesterone-mediated oocyte maturation, steroid biosynthesis, calcium signaling pathways, and G-protein coupled receptor signaling pathway were selected for validation by a quantitative real-time polymerase chain reaction (qRT-PCR) analysis, the qRT-PCR results are consistent with the general expression patterns of those genes from the Illumina sequencing. These data provide comprehensive gene expression information at the transcriptional level that might increase our understanding of the Huoyan goose's reproductive biology.

Feeding response following central administration of chicken vasoactive intestinal peptide in chicks

Vasoactive intestinal peptide (VIP) is expressed in central nervous systems and peripheral tissues across lower and higher vertebrates and is involved in many physiological functions. One of these functions is appetite regulation; however the mechanisms mediating this response are poorly understood. Therefore, the purpose of this study was to investigate central mechanisms of VIP induction of satiety using chicks as models. Intracerebroventricular (ICV) injection of VIP (0.1 and 0.5 nmol) significantly decreased food intake under both ad libitum and food deprivation conditions and chicken VIP (cVIP) was more potent than mammalian VIP. The mechanisms involved with the VIP-induced anorexigenic effect were investigated by studying the involvement of the central corticotrophin-releasing hormone (CRH) systems. ICV injection of cVIP caused increased plasma corticosterone concentration and decreased diencephalic mRNA expression of CRH, CRH receptor-2 (CRH-R2) and urocortin 3 (UCN-3, which has high affinity for CRH-R2). This simultaneous decrease in the expression of ligands and their receptor, with the increase in plasma corticosterone concentration suggests that the anorexigenic effect of cVIP might be related to CRH systems. The cVIP-induced anorexigenic effect was partly attenuated by co-injection of astressin, a CRH-R2 antagonist, supporting this thesis. The present study demonstrated that VIP inhibits feeding behavior via CRH systems in the brain of chicks.

Characterization of the receptors for chicken GHRH and GHRH-related peptides: identification of a novel receptor for GHRH and the receptor for GHRH-LP (PRP)

Growth hormone-releasing hormone and its structurally related peptides, GHRH-like peptide (GHRH-LP) (also called PRP), peptide histidine-isoleucine (PHI), vasoactive intestinal polypeptide (VIP), and pituitary adenylate cyclase-activating polypeptide (PACAP), have been reported to play important physiological roles in pituitary and extrapituitary tissues of vertebrates; however, little is known about the identity of these GHRH-related peptide receptors in birds. In this study, 6 receptors for GHRH and GHRH-related peptides (cGHRHR(1), cGHRHR(2), cGHRH-LPR, cPAC(1), cVPAC(1), and cVPAC(2)) were cloned from chicken brain or pituitary, and their functionalities were examined in Chinese hamster ovary (CHO) cells using a pGL3-CRE-luciferase reporter system. Results showed that: (1) all receptors are G protein-coupled receptors functionally coupled to the intracellular PKA signaling pathway; (2) 2 GHRH receptors (cGHRHR(1) and cGHRHR(2)) were identified, and both receptors could be potently activated by cGHRH; (3) cGHRH-LP could activate its specific receptor cGHRH-LPR (cPRP-R), and it also activated cGHRHR(1) and cGHRHR(2); and (4) PACAP could potently activate its receptors cPAC(1), cVPAC(1) and cVPAC(2); however, cVPAC(1) and cVPAC(2) could also be effectively activated by cVIP and tPHI, indicating that they can serve as VIP receptors and potential PHI receptors. Using a reverse transcription polymerase chain reaction assay, we further examined the mRNA expression of these receptors in adult chicken tissues. The expressions of cGHRHR(1), cGHRHR(2), and cGHRH-LPR are restricted mainly to the pituitary and/or brain, whereas cPAC(1), cVPAC(1), and cVPAC(2) are expressed in most of the tissues examined. Collectively, our study identified the receptors for chicken GHRH and GHRH-related peptides, including a novel GHRH receptor (cGHRHR(2)), and established a basis to elucidate the roles of these peptides in target tissues.

A possible neural cascade involving the photoneuroendocrine system (PNES) responsible for regulating gonadal development in an avian species, Gallus gallus

Neurons located in the lateral septal organ (LSO) and medial basal hypothalamus (MBH) have been proposed to be encephalic photoreceptors (EPRs), which sense photoperiodic time and initiate avian gonadal development. Controversy continues regarding the location of EPRs serving the PNES and their signal transduction pathway. Using quantitative real-time RT-PCR we determined activation of key genes following prolonged light periods and sulfamethethazine (compound known to advance light-induced testes development) in 21-day old chicks. Earliest activation occurred in genes of vasoactive intestinal polypeptide (VIP) and type 6 phosphodiesterase beta subunit (PDE-6 beta) in the LSO at 4 and 6h, respectively, after onset of light and sulfamethazine intake. In contrast, no change was detected in the MBH during the first 8h of that treatment. Thereafter, significant increases in gonadotropin releasing hormone (GnRH-1) and VIP receptor (VIPR) mRNA transcripts were detected in the bed nucleus of the pallial commissure (NCPa). Hours later, activation of all four genes (VIP, PDE-6 beta, GnRH-1, VIPR) were induced solely by photostimulation. Deiodinase 2 and tyrosine hydroxylase in the MBH did not show increased gene expression until 12h of photostimulation. Prolactin mRNA transcripts showed significant increases at 4h due to SMZ intake and at 24, 36 and 48 h due to long-day photoperiodic effects. Data suggest that VIP neurons in the LSO may serve as EPRs and utilize PDE, present in the phototransduction cascade of known photoreceptors. Additionally, VIP released from the LSO may modulate GnRH-1 neurons in the NCPa via VIP receptors by increasing GnRH-1 gene expression.

Functional analysis of neuropeptides in avian thymocyte development

The function of lymphoid organs and immune cells is often modulated by peptides and hormones produced by the neuroendocrine and immune systems. We have previously reported the intrathymic expression of neuropeptides in the thymus of different species and that neuropeptides can influence murine thymocyte development in vitro. To further explore the evolutionary nature of neuroendocrine interactions in the thymus, we identified the expression of calcitonin-gene-related peptide, neuropeptide Y, somatostatin (SOM), substance P and vasointestinal polypeptide, as well as their receptors on chicken thymic epithelial cells (TEC) and thymocytes by immunofluorescence and reverse transcription polymerase chain reaction (RT-PCR). All the studied neuropeptides and their receptors were found to be expressed in both TEC and thymocytes, suggesting that intrathymic neuroendocrine interactions may take place within the avian thymus. In order to elucidate whether such interactions play a role in avian thymocyte development, neuropeptides and their antagonists were added to embryonic thymus organ cultures and found to influence chicken thymopoiesis. In particular, an antagonist of SOM increased the proportion of double-positive thymocytes, while SOM itself appeared to inhibit the early stages of thymocyte development. Taken together, these data provide further evidence to suggest that neuropeptides play a conserved role in vertebrate thymocyte development.

PACAP, VIP and their receptors in the metazoa: insights about the origin and evolution of the ligand-receptor pair

The evolution, function and interaction of ligand-receptor pairs are of major pharmaceutical interest. Comparative sequence analysis approaches using data from phylogenetically distant organisms can provide insights into their origin and possible physiological roles. The present review focuses on the pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal polypeptide (VIP) and their receptors in the metazoa. A PACAP-like peptide is present in tunicates and chordates while VIP- and PACAP/VIP-specific receptors have only been isolated in the latter phyla. The apparently disparate evolution of the ligands and their specific receptors raises questions about their evolution during the metazoan radiation and also about how the ligands may have acquired new functions.

Central administration of vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide differentially regulates energy metabolism in chicks

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are the members of the glucagon superfamily and bind to common receptors while PACAP also acts via the PACAP-specific receptor, PAC1. The aim of the present study was to investigate whether intracerebroventricular (i.c.v.) injection of VIP and PACAP acts in a similar or different manner to affect body temperature and energy expenditure in the domestic chick. I.c.v. injection of VIP did not significantly affect rectal temperature, but decreased energy expenditure. On the other hand, i.c.v. injection of PACAP significantly increased both body temperature and energy expenditure. These specific actions of PACAP could be explained by an interaction with the PAC1 receptor, since they were partly, but not entirely, attenuated by PACAP (6-38), a PAC1 receptor antagonist. In addition, it was observed that central administration of both VIP and PACAP induced a reduction in respiratory quotient and increased plasma non-esterified fatty acid concentrations. This suggests that both peptides act centrally to regulate a catabolic response. In summary, brain VIP and PACAP both appear to exert generally catabolic effects on energy metabolism in the chick, but their influence on body temperature and glucose metabolism differs and their central effects do not appear to be mediated by the same receptors.

Development of a real-time (Q) PCR assay to measure variation in expression of prolactin receptor mRNA in the hypothalamus and pituitary gland during late embryogenesis in turkeys and chickens

Changes in levels of PRLR mRNA in the pituitary gland and hypothalamus of chickens and turkeys from embryonic day (ED) 15 and ED21 to 1 day post-hatch, respectively, were measured by real-time PCR. In both species, PRLR mRNA increased from low levels during the last week of ED to reach maxima at the peri-hatch period. Similarly, circulating levels of PRL also increased during this interval and were highly correlated with levels of the PRLR mRNA in both the pituitary gland and hypothalamus. This suggests that PRL was up-regulating its receptor. In support of this, stimulation of the turkey pituitary gland with VIP on ED24 resulted in a 4- and 3-fold increase in PRL and PRLR, respectively. Since VIP had no direct effect on the levels of PRLR transcript in the hypothalamus, it is likely that VIP is acting indirectly through increased PRL to up-regulate the number of receptors.

Neuropeptide binding reflects convergent and divergent evolution in species-typical group sizes

Neuroendocrine factors that produce species differences in aggregation behavior ("sociality") are largely unknown, although relevant studies should yield important insights into mechanisms of affiliation and social evolution. We here focused on five species in the avian family Estrildidae that differ selectively in their species-typical group sizes (all species are monogamous and occupy similar habitats). These include two highly gregarious species that independently evolved coloniality; two territorial species that independently evolved territoriality; and an intermediate, modestly gregarious species that is a sympatric congener of one of the territorial species. Using males and females of each species, we examined binding sites for (125)I-vasoactive intestinal polypeptide (VIP), (125)I-sauvagine (SG; a ligand for corticotropin releasing factor, CRF, receptors) and a linear (125)I-V(1a) vasopressin antagonist (to localize receptors for vasotocin, VT). VIP, CRF and VT are neuropeptides that influence stress, anxiety and/or various social behaviors. For numerous areas (particularly within the septal complex), binding densities in the territorial species differed significantly from binding in the more gregarious species, and in most of these cases, binding densities for the moderately gregarious species were either comparable to the two colonial species or were intermediate to the territorial and colonial species. Such patterns were observed for (125)I-VIP binding in the medial bed nucleus of the stria terminalis, medial septum, septohippocampal septum, and subpallial zones of the lateral septum; for (125)I-SG binding in the infundibular hypothalamus, and lateral and medial divisions of the ventromedial hypothalamus; and for the linear (125)I-V(1a) antagonist in the medial septum, and the pallial and subpallial zones of the caudal lateral septum. With the exception of (125)I-SG binding in the infundibular hypothalamus, binding densitites are positively related to sociality.

Pituitary adenylate cyclase-activating polypeptide (PACAP) can act as determinant of the tyrosine hydroxylase phenotype of dopaminergic cells during retina development

In the chick retina, dopaminergic cells are generated between embryonic days 3 and 7 (E3/E7). However, the expression of tyrosine hydroxylase (TH), the first enzyme in the catecholamine synthetic pathway, is only detected after E11/E12. During the interval comprising E7 to E12, signals conveyed by cAMP are important to determine the TH phenotype. The present study shows that pituitary adenylyl cyclase-activating polypeptide (PACAP), via cAMP, is a major endogenous component in defining the TH phenotype of retina dopaminergic cells during development. PACAP type 1 receptor and its mRNA were detected in retinas since E6. PACAP was also immunodetected in cells localized in the inner nuclear layer of retinas since E8. This peptide promoted greater than 10-fold increase in cAMP accumulation of retinas obtained from embryos since E8, an effect that was blocked by PACAP6-38 (PAC1 receptor antagonist). In cultured retina cells from E8 and E9, maintained for 6 days in vitro with 10 nM PACAP (for 5 days), the number of dopaminergic cells expressing tyrosine hydroxylase increased 2.4-fold. The cAMP analog, 8-Br-cAMP and 3-isobutyl-1-methylxanthine (IBMX, a phosphodiesterase inhibitor) also increased the number of tyrosine hydroxylase-positive cells by 4- to 6-fold. IBMX plus PACAP treatment resulted in 17-fold increase in the number of cells positive for tyrosine hydroxylase. Under this condition the amount of tyrosine hydroxylase expression, as detected by western blot analysis, was also increased. The protein kinase-A inhibitor, rp-cAMPS, significantly reduced the effect of PACAP. Our data show that this peptide is an important factor influencing the definition of the tyrosine hydroxylase phenotype of retina dopaminergic cells within a narrow window of development.

Anorexigenic effects of pituitary adenylate cyclase-activating polypeptide and vasoactive intestinal peptide in the chick brain are mediated by corticotrophin-releasing factor

Intracerebroventricular (ICV) injection of pituitary adenylate cyclase-activating polypeptide-38 (PACAP) or vasoactive intestinal peptide (VIP) inhibits feeding in chicks. However, the underlying anorexigenic mechanism(s) has not yet been investigated. The present study investigated whether these peptides influence the activity of corticotrophin-releasing factor (CRF) neural pathways in the brain of chicks. Firstly, we found that ICV injections of PACAP and VIP increased plasma corticosterone concentrations. The corticosterone-releasing effect of PACAP was completely attenuated by co-injection of astressin, a CRF receptor antagonist, but this effect was only partial for VIP. These results demonstrated that CRF neurons mediate the actions of PACAP and, to a lesser extent, VIP, and suggest that the signaling mechanisms differ between the two peptides. This difference may arise from the two peptides interacting with different receptors because the corticosterone-releasing effect of PACAP, but not VIP, was completely attenuated by co-injection of PACAP (6-38), a PACAP receptor antagonist. Finally, we examined the effect of ICV co-injection of astressin on the anorexigenic effects of PACAP and VIP and found that the effects of both peptides were attenuated by astressin. Overall, the present study suggests that the anorexigenic effects of PACAP and VIP are mediated by the activation of CRF neurons.

Receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide in turkey cerebral cortex: characterization by [125I]-VIP binding and effects on cyclic AMP synthesis

Receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) in turkey cerebral cortex were characterized using two approaches: (1) in vitro radioreceptor binding of [125I]-VIP, and (2) effects of peptides from the PACAP/VIP/secretin family on cyclic AMP formation. The binding of [125I]-VIP to turkey cortical membranes was rapid, stable, and reversible. Saturation analysis resulted in a linear Scatchard plot, suggesting binding to a single class of high affinity receptor binding sites with a Kd of 0.70 nM and a Bmax of 52 fmol/mg protein. Various peptides displaced the specific binding of 0.12 nM [125I]-VIP to turkey cerebral cortical membranes in a concentration-dependent manner. The relative rank order of potency of the tested peptides to inhibit [125I]-VIP binding to turkey cerebrum was: PACAP38 approximately PACAP27 approximately chicken VIP approximately mammalian VIP >>> PHI >> secretin, chicken VIP16-28 (inactive). About 65% of specific [125I]-VIP binding sites in turkey cerebral cortex was sensitive to Gpp(NH)p, a nonhydrolysable analogue of GTP. PACAP38, PACAP27, chicken VIP and, to a lesser extent, mammalian VIP potently stimulated cyclic AMP formation in turkey cerebral cortical slices in a concentration-dependent manner, displaying EC50 values of 8.7 nM (PACAP38), 21.3 nM (PACAP27), 67.4 nM (chicken VIP), and 202 nM (mammalian VIP). On the other hand, PHI and secretin very weakly affected the nucleotide production. The obtained results indicate that cerebral cortex of turkey contains VPAC type receptors that are positively linked to cyclic AMP-generating system and are labeled with [125I]-VIP.

Expression of vasoactive intestinal peptide receptor messenger RNA in the hypothalamus and pituitary throughout the turkey reproductive cycle

Vasoactive intestinal peptide (VIP) has been implicated in the regulation of avian reproductive activity and appears to act at the level of the hypothalamus and pituitary. This in situ hybridization histochemistry study describes the distribution of VIP receptor mRNA expression in the hypothalamus and the pituitary of reproductively active (laying) and quiescent (nonphotostimulated, incubating, and photorefractory) female turkeys and characterizes the differences observed in VIP receptor gene expression. VIP receptor mRNA, while expressed throughout the hypothalamus, was specifically expressed in areas known to contain GnRH-I neurons in the chicken, i.e., the lateral septum, medial preoptic area, anterior hypothalamus, and paraventricular nucleus. Significant differences in VIP receptor mRNA expression between different reproductive states was observed only within the infundibular nuclear complex. VIP receptor mRNA was markedly less in nonphotostimulated and photorefractory hens as compared with laying and incubating hens. The most dense VIP receptor mRNA was found in the anterior pituitary, where it was 2.4- and 3.0-fold greater in laying and incubating hens, respectively, as compared with that in nonphotostimulated ones. Hens that stopped incubating and became photorefractory displayed pituitary VIP receptor mRNA levels similar to those of nonphotostimulated birds. The changes in pituitary VIP receptor mRNA expression were positively correlated with known changes in pituitary prolactin (PRL) mRNA expression and PRL content and release. These findings indicate that the variations in PRL secretion observed across the turkey reproductive cycle are, in part, regulated by changes in VIP receptors at the pituitary level.

Pituitary adenylate cyclase activating polypeptide and vasoactive intestinal peptide inhibit feeding in the chick brain by different mechanisms

Intracerebroventricular (ICV) injections of pituitary adenylate cyclase-activating polypeptide-38 (PACAP) and vasoactive intestinal peptide (VIP) inhibit feeding in chicks. However, the precise anorexigenic mechanisms have not been investigated, since both peptides activate the VPAC receptor in mammals. We investigated which receptor mediates the anorexigenic effects of these peptides in chicks. ICV co-injection of PACAP (6-38), a PAC1 receptor antagonist, attenuated the anorexigenic effect of PACAP but not VIP. On the other hand, ICV co-injection of [D-p-Cl-Phe6, Leu17]-VIP, a VPAC receptor antagonist, did not affect the effects of both peptides. Although these results imply that the effect of VIP was not specific, a subsequent experiment demonstrated that ICV injection of anti-chicken VIP antiserum stimulated feeding and suggested that endogenous VIP inhibits feeding in the chick brain. Collectively, the data suggest that the anorexigenic mechanism of PACAP is different from that of VIP and that an undiscovered VIP receptor may be present in the chicken brain.

Characterization of vasoactive intestinal peptide/pituitary adenylate cyclase-activating polypeptide receptors in chick cerebral cortex

In this study receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) were characterized in chick cerebral cortex by an in vitro binding technique, using 125I-labeled VIP ([125I]-VIP) as a ligand. The specific binding of [125I]-VIP to chick cerebral cortical membranes was found to be rapid, stable, saturable, reversible, and of high affinity. Saturation analysis resulted in a linear Scatchard plot, suggesting binding to a single class of receptor binding sites with high affinity (Kd = 0.21 nM) and low capacity (Bmax = 19.5 fmol/mg protein). The relative rank order of potency of the tested peptides to inhibit [125I]-VIP binding to chick cerebrum was VIP (chicken) > or = VIP (mammalian) > or = PACAP27 > or = PACAP38 >> VIP6-28 (mammalian) > PHI (porcine) >> neurotensin6-11-chicken VIP7-28 > neurotensin6-11-mammalian VIP7-28 >>> VIP16-28 (chicken; inactive) approximately secretin (inactive). About 60% of [125I]-VIP-binding sites in chick cerebral cortex were sensitive to Gpp(NH)p, a nonhydrolyzable analog of GTP. It has been concluded that the cerebral cortex of chick, in addition to PAC1 receptors, contains a population of VPAC-type receptors.

Antagonism of VIP-stimulated cyclic AMP formation in chick brain

Of eight peptides tested (0.01-5 microM), only two, that is, pituitary adenylate cyclase-activating polypeptide (PACAP27) and chicken vasoactive intestinal peptide (cVIP), potently stimulated cyclic AMP (cAMP) production in cerebral cortical slices of the chick. Mammalian VIP (mVIP) showed some activity only at the highest dose tested, whereas truncated forms of PACAP or VIP, that is, PACAP6-27, cVIP6-28, and mVIP6-28, or hybrid compounds, that is, neurotensin6-11-cVIP7-28 (NT-cVIP) and neurotensin6-11-mVIP7-28 (NT-mVIP), were inactive. Thirty-minute preincubation of chick cortical slices with 5 microM PACAP6-27, NT-cVIP, or NT-mVIP competitively antagonized the cAMP effects of cVIP (0.03-1 microM), with the truncated form of PACAP being the best antagonist. Preincubation of slices with 5 microM mVIP6-28 also produced a significant inhibition of the cVIP (0.1-1 microM)-induced increase in cAMP production; however its action was independent of the concentration of cVIP. In contrast to mVIP6-28, cVIP6-28 showed no antagonistic activity against the full-length peptide. In parallel experiments, 30-min pretreatment of cortical slices with 5 microM PACAP6-27 significantly antagonized the PACAP38-evoked increase in cAMP formation, whereas mVIP6-28 or the NT-mVIP hybrid was ineffective. It has been concluded that in the chick brain, PACAP and cVIP stimulate cAMP biosynthesis via PAC1 and VPAC-type receptors, respectively, and PACAP6-27 seems to be the most potent, yet PACAP/VIP receptor-nonselective antagonist. Unlike truncated PACAP, the NT-VIP hybrid peptides tested may represent VPACtype receptor-selective blocking activity.

Intracerebroventricular injection of vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide inhibits feeding in chicks

Previous research has indicated an involvement of glucagon superfamily peptides in the regulation of feeding in the domestic chick brain. However the possible roles of vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide-38 (PACAP) have not yet been investigated. We therefore examined the effect of intracerebroventricular (ICV) injections of VIP or PACAP on food intake in chicks. ICV injection of both VIP and PACAP significantly inhibited food intake over 4 h at doses ranging from 12 to 188 pmol. Subsequently, we compared the anorexic effect the glucagon superfamily peptides VIP, PACAP, growth hormone-releasing factor (GRF) and glucagon-like peptide-1 (GLP-1) after ICV injection at an equimolar dose (12 pmol). All four peptides significantly inhibited food intake, although the anorexic effects of VIP and PACAP were weaker than those of GRF and GLP-1. These findings support the hypothesis that glucagon superfamily peptides play an important role in the regulation of appetite in the chick brain.

Stimulatory effects of pituitary adenylate cyclase-activating polypeptide on inositol phosphates accumulation in avian cerebral cortex and hypothalamus

This study has demonstrated that the short and long form of the pituitary adenylate cyclase-activating polypeptide (PACAP), i.e. PACAP(27) and PACAP(38), moderately but significantly, and in a concentration (0.5-5 microM)-dependent manner, stimulated inositol phosphates (IPs) accumulation in myo-[(3)H]inositol-prelabeled cerebral cortical and hypothalamal slices of chick and duck, and in slices of rat cerebral cortex; both peptides had no effect on IPs formation in rat hypothalamus. Vasoactive intestinal peptide (VIP; 0.5-5 microM) weakly enhanced IPs accumulation in chick hypothalamus, had no significant action in chick cerebral cortex (in fact there was a tendency to attenuate the IPs response in this tissue), and slightly, but significantly, inhibited the IPs accumulation in rat cerebral cortex. VIP showed no activity in rat hypothalamus. It is concluded that the stimulatory action of PACAP on phosphoinositide metabolism in avian cerebral cortex, similar to rat cerebral cortex, is mediated via phospholipase C-linked PAC(1) type receptors. In chick hypothalamus, however, there may be a component of VPAC type receptors stimulating IPs formation.