PACAP-related peptide (PRP)--molecular evolution and potential functions

From CGRP to PACAP, VIP, and Beyond: Unraveling the Next Chapters in Migraine Treatment

Migraine is a neurovascular disorder that can be debilitating for individuals and society. Current research focuses on finding effective analgesics and management strategies for migraines by targeting specific receptors and neuropeptides. Nonetheless, newly approved calcitonin gene-related peptide (CGRP) monoclonal antibodies (mAbs) have a 50% responder rate ranging from 27 to 71.0%, whereas CGRP receptor inhibitors have a 50% responder rate ranging from 56 to 71%. To address the need for novel therapeutic targets, researchers are exploring the potential of another secretin family peptide, pituitary adenylate cyclase-activating polypeptide (PACAP), as a ground-breaking treatment avenue for migraine. Preclinical models have revealed how PACAP affects the trigeminal system, which is implicated in headache disorders. Clinical studies have demonstrated the significance of PACAP in migraine pathophysiology; however, a few clinical trials remain inconclusive: the pituitary adenylate cyclase-activating peptide 1 receptor mAb, AMG 301 showed no benefit for migraine prevention, while the PACAP ligand mAb, Lu AG09222 significantly reduced the number of monthly migraine days over placebo in a phase 2 clinical trial. Meanwhile, another secretin family peptide vasoactive intestinal peptide (VIP) is gaining interest as a potential new target. In light of recent advances in PACAP research, we emphasize the potential of PACAP as a promising target for migraine treatment, highlighting the significance of exploring PACAP as a member of the antimigraine armamentarium, especially for patients who do not respond to or contraindicated to anti-CGRP therapies. By updating our knowledge of PACAP and its unique contribution to migraine pathophysiology, we can pave the way for reinforcing PACAP and other secretin peptides, including VIP, as a novel treatment option for migraines.

PACAP/GCGa Is an Important Modulator of the Amphioxus CNS-Hatschek's Pit Axis, the Homolog of the Vertebrate Hypothalamic-Pituitary Axis in the Basal Chordates

The Hatschek's pit in the cephalochordate amphioxus, an invertebrate deuterostome basal to chordates is suggested to be the functional homolog structure of the vertebrate adenohypophysis based on anatomy and expression of homologous neuroendocrine genes. However, the endocrine potential of the cephalochordate Hatschek's pit remains to be demonstrated as well as the physiological actions of the secreted neuropeptides. In this study, we have explored the distribution and characterize the potential function of the amphioxus PACAP/GCG precursor, which is the ortholog of the hypothalamic PACAP neuropeptide in vertebrates. In amphioxi, two PACAP/GCG transcripts PACAP/GCGa and PACAP/GCGbc that are alternative isoforms of a single gene with different peptide coding potentials were isolated. Immunofluorescence staining detected their expression around the nucleus of Rohde, supporting that this structure may be homologous of the neurosecretory cells of the vertebrate hypothalamus where abundant PACAP is found. PACAP/GCGa was also detected in the infundibulum-like downgrowth approaching the Hatschek's pit, indicating diffusion of PACAP/GCGa from the CNS to the pit via the infundibulum-like downgrowth. Under a high salinity challenge, PACAP/GCGa was upregulated in amphioxi head and PACAP/GCGa treatment increased expression of GHl in Hatschek's pit in a dose-dependent manner, suggesting that PACAP/GCGa may be involved in the regulation of GHl via hypothalamic-pituitary (HP)-like axis similar as in the vertebrates. Our results support that the amphioxus Hatschek's pit is likely to be the functional homolog of pituitary gland in vertebrates.

Characterization and distribution of GHRH, PACAP, TRH, SST and IGF1 mRNAs in the green iguana

The somatotropic axis (SA) regulates numerous aspects of vertebrate physiology such as development, growth, and metabolism and has influence on several tissues including neural, immune, reproductive and gastric tract. Growth hormone (GH) is a key component of SA, it is synthesized and released mainly by pituitary somatotrophs, although now it is known that virtually all tissues can express GH, which, in addition to its well-described endocrine roles, also has autocrine/paracrine/intracrine actions. In the pituitary, GH expression is regulated by several hypothalamic neuropeptides including GHRH, PACAP, TRH and SST. GH, in turn, regulates IGF1 synthesis in several target tissues, adding complexity to the system since GH effects can be exerted either directly or mediated by IGF1. In reptiles, little is known about the SA components and their functional interactions. The aim of this work was to characterize the mRNAs of the principal SA components in the green iguana and to develop the tools that allow the study of the structural and functional evolution of this system in reptiles. By employing RT-PCR and RACE, the cDNAs encoding for GHRH, PACAP, TRH, SST and IGF1 were amplified and sequenced. Results showed that these cDNAs coded for the corresponding protein precursors of 154, 170, 243, 113, and 131 amino acids, respectively. Of these, GHRH, PACAP, SST and IGF1 precursors exhibited a high structural conservation with respect to its counterparts in other vertebrates. On the other hand, iguana's TRH precursor showed 7 functional copies of mature TRH (pyr-QHP-NH₂), as compared to 4 and 6 copies of TRH in avian and mammalian proTRH sequences, respectively. It was found that in addition to its primary production site (brain for GHRH, PACAP, TRH and SST, and liver for IGF1), they were also expressed in other peripheral tissues, i.e. testes and ovaries expressed all the studied mRNAs, whereas TRH and IGF1 mRNAs were observed ubiquitously in all tissues considered. These results show that the main SA components in reptiles of the Squamata Order maintain a good structural conservation among vertebrate phylogeny, and suggest important physiological interactions (endocrine, autocrine and/or paracrine) between them due to their wide peripheral tissue expression.

Viral and bacterial septicaemic infections modulate the expression of PACAP splicing variants and VIP/PACAP receptors in brown trout immune organs

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) and PACAP-Related Peptide (PRP) are structurally similar peptides encoded in the same transcripts. Their transcription has been detected not only in the brain but also in a wide range of peripheral tissues, even including organs of the immune system. PACAP exerts pleiotropic activities through G-protein coupled membrane receptors: the PACAP-specific PAC-1 and the VPAC-1 and VPAC-2 receptors that exhibit similar affinities for the Vasoactive Intestinal Peptide (VIP) and PACAP. Recent findings added PACAP and its receptors to the growing list of mediators that allow cross-talk between the nervous, endocrine and immune systems in fish. In this study the expression of genes encoding for PACAP and PRP, as well as VIP/PACAP receptors was studied in laboratory-reared brown trout (Salmo trutta) after septicaemic infections. Respectively Viral Haemorrhagic Septicaemia Virus (VHSV-Ia) or the Gram-negative bacterium Yersinia ruckeri (ser. O1 - biot. 2) were used in infection challenges. Kidney and spleen, the teleost main lymphopoietic organs, were sampled during the first two weeks post-infection. RT-qPCR analysis assessed specific pathogens burden and gene expression levels. PACAP and PRP transcription in each organ was positively correlated to the respective pathogen burden, assessed targeting the VHSV-glycoprotein or Y. ruckeri 16S rRNA. Results showed as the transcription of PACAP splicing variants and VIP/PACAP receptors is modulated in these organs during an acute viral and bacterial septicaemic infections in brown trout. These gene expression results provide clues as to how the PACAP system is modulated in fish, confirming an involvement during active immune responses elicited by both viral and bacterial aetiological agents. However, further experimental evidence is still required to fully elucidate and characterize the role of PACAP and PRP for an efficient immune response against pathogens.

Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates release of somatolactin (SL)-α and SL-β from cultured goldfish pituitary cells via the PAC₁ receptor-signaling pathway, and affects the expression of SL-α and SL-β mRNAs

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that stimulates the release of adenohypophyseal hormone from the pituitary in fish. In the goldfish, PACAP induces the release of somatolactin (SL), in particular, from cultured pituitary cells. SL belongs to the growth hormone and prolactin family, and comprises two molecular variants termed SL-α and SL-β in goldfish. However, there is no information about the involvement of PACAP in the regulation of SL-α and SL-β release and the expression of their mRNAs. Therefore, we examined the effect of PACAP on SL-α and SL-β release from cultured goldfish pituitary cells. Treatment with PACAP (10(-10)-10(-7)M) increased the release of both SL-α and SL-β. The stimulatory action of PACAP (10(-9)M) on SL-α and SL-β release was blocked by treatment with a PACAP-selective receptor (PAC1R) antagonist, PACAP(6-38) (10(-6)M). We also examined whether PACAP affects the expression of SL-α and SL-β mRNAs in cultured pituitary cells. Treatment with PACAP (10(-9) and 10(-8)M) for 6h decreased the expression level of SL-α mRNA but increased that of SL-β mRNA. The action of PACAP (10(-8)M) on SL-β mRNA expression was blocked by treatment with PACAP(6-38) (10(-6)M), whereas PACAP(6-38) elicited no change in the expression of SL-α mRNA. These results indicate that in cultured goldfish pituitary cells, PACAP stimulates the release of SL-α and SL-β, and expression of SL-β mRNA, via the PAC1R-signaling pathway. However, the mechanism whereby PACAP inhibits the expression of SL-α mRNA does not seem to be mediated by PAC1R signaling.

Expansion of secretin-like G protein-coupled receptors and their peptide ligands via local duplications before and after two rounds of whole-genome duplication

In humans, the secretin-like G protein-coupled receptor (GPCR) family comprises 15 members with 18 corresponding peptide ligand genes. Although members have been identified in a large variety of vertebrate and nonvertebrate species, the origin and relationship of these proteins remain unresolved. To address this issue, we employed large-scale genome comparisons to identify genome fragments with conserved synteny and matched these fragments to linkage groups in reconstructed early gnathostome ancestral chromosomes (GAC). This genome comparison revealed that most receptor and peptide genes were clustered in three GAC linkage groups and suggested that the ancestral forms of five peptide subfamilies (corticotropin-releasing hormone-like, calcitonin-like, parathyroid hormone-like, glucagon-like, and growth hormone-releasing hormone-like) and their cognate receptor families emerged through tandem local gene duplications before two rounds (2R) of whole-genome duplication. These subfamily genes have, then, been amplified by 2R whole-genome duplication, followed by additional local duplications and gene loss prior to the divergence of land vertebrates and teleosts. This study delineates a possible evolutionary scenario for whole secretin-like peptide and receptor family members and may shed light on evolutionary mechanisms for expansion of a gene family with a large number of paralogs.

Structural and functional divergence of growth hormone-releasing hormone receptors in early sarcopterygians: lungfish and Xenopus

The evolutionary trajectories of growth hormone-releasing hormone (GHRH) receptor remain enigmatic since the discovery of physiologically functional GHRH-GHRH receptor (GHRHR) in non-mammalian vertebrates in 2007. Interestingly, subsequent studies have described the identification of a GHRHR(2) in chicken in addition to the GHRHR and the closely related paralogous receptor, PACAP-related peptide (PRP) receptor (PRPR). In this article, we provide information, for the first time, on the GHRHR in sarcopterygian fish and amphibians by the cloning and characterization of GHRHRs from lungfish (P. dolloi) and X. laevis. Sequence alignment and phylogenetic analyses demonstrated structural resemblance of lungfish GHRHR to their mammalian orthologs, while the X. laevis GHRHR showed the highest homology to GHRHR(2) in zebrafish and chicken. Functionally, lungfish GHRHR displayed high affinity towards GHRH in triggering intracellular cAMP and calcium accumulation, while X. laevis GHRHR(2) was able to react with both endogenous GHRH and PRP. Tissue distribution analyses showed that both lungfish GHRHR and X. laevis GHRHR(2) had the highest expression in brain, and interestingly, X. laevis(GHRHR2) also had high abundance in the reproductive organs. These findings, together with previous reports, suggest that early in the Sarcopterygii lineage, GHRHR and PRPR have already established diverged and specific affinities towards their cognate ligands. GHRHR(2), which has only been found in xenopus, zebrafish and chicken hitherto, accommodates both GHRH and PRP.

Structural and functional characterization of pituitary adenylyl cyclase-activating polypeptide (PACAP)/PACAP-related peptide (PRP) and its receptor in olive flounder (Paralichthys olivaceus)

We identified full-length cDNAs encoding pituitary adenylyl cyclase-activating polypeptide (PACAP), PACAP-related peptide (PRP), and PACAP-specific receptor (PAC1R) from olive flounder, Paralichthys olivaceus. Two variant mRNA forms were created by alternative splicing. Comparison of genomic and cDNA sequences of the PRP-PACAP precursor revealed that skipping of exon 4 within PRP resulted in two variant transcripts: a long form encoding both PRP and PACAP and a short form encoding PACAP only. Both transcripts were constitutively observed only in the brain, whereas the short form appeared in gut tissues, such as the intestine and pyloric cecum in fish challenged with a pathogen, but not in healthy fish. Furthermore, expression of the long PRP/PACAP transcript gradually increased in the intestine of flounder challenged with bacteria, suggesting that PRP and/or PACAP may serve as a regulator(s) of the immune system, especially in the gastrointestinal tract of olive flounder. The biological functions of PACAP and PRP were investigated by exogenous treatment of flounder embryogenic cells (hirame natural embryonic cells, HINAE cells) with synthetic peptides of fPACAP-38 and/or fPRP-45. Intracellular cyclic adenosine monophosphate (cAMP) production in PAC1R-overexpressing HINAE cells was regulated by fPACAP-38 in a concentration-dependent manner, but was not regulated by fPRP-45. Results from real-time quantitative polymerase chain reaction revealed that PAC1R mRNA was specifically induced by fPACAP-38 but not by fPRP-45; PACAP significantly increased TNF-α mRNA but not growth hormone (GH) mRNA in HINAE cells; however, PRP affected GH but not TNF-α mRNA expression. These results suggest that the expression ratio of PRP and PACAP is regulated at the transcriptional level depending on the tissues and conditions, and that the unique biological roles of PRP and PACAP differ from that of mammalian PRP.

Regulation of somatic growth and gene expression of the GH-IGF system and PRP-PACAP by dietary lipid level in early juveniles of a teleost fish, the pejerrey (Odontesthes bonariensis)

Growth and mRNA levels of the pituitary adenylate cyclase-activating polypeptide (PACAP) and its related peptide (PRP), and the system controlled by the growth hormone (GH) and insulin-like growth factors (IGFs) were analyzed in pejerrey fry fed with graded levels of dietary lipids: 10% (L10), 13% (L13) and 21% (L21). First, the full sequence of pejerrey PRP-PACAP was obtained by RT-PCR, using primers based on conserved fragments of teleosts PACAP sequences. The growth of the fish at 83 days after hatching (dah) and the GH mRNA levels were not significantly affected by the dietary treatment. Conversely, PRP-PACAP expression significantly decreased with increasing dietary lipids (L10 > L21). While GH receptor (GHR)-I and IGF-I transcripts did not differ among groups, GHR-II transcripts decreased in group L21. IGF-II expression apparently followed the same trend. These results in combination with the lower expression of the anorexigenic PRP-PACAP in fish fed diet L21 and the correlation analysis evidencing a particularly fine tuning of the GH-IGF system in group L13, suggest that this diet may cover the energy demands for growing pejerrey from 27 dah onwards. Our results show for first time in fish a differential response of PRP-PACAP transcripts to dietary manipulations, and confirm the sensitivity of the pejerrey GH-IGF system to changes in diet composition despite the lack of (or in advance to) a clear response of somatic growth.

Discovery of a new reproductive hormone in teleosts: pituitary adenylate cyclase-activating polypeptide-related peptide (PRP)

Pituitary adenylate cyclase-activating polypeptide (PACAP)-related peptide (PRP) is a peptide encoded with PACAP in the same precursor protein. Non-mammalian PRPs were previously termed growth hormone-releasing hormone (GHRH)-like peptide, and was regarded as the mammalian GHRH homologue in non-mammalian vertebrates until the discovery of authentic GHRH genes in teleosts and amphibians. Although a highly specific receptor for PRP, which is lost in mammals, is present in non-mammals, a clear function of PRP in vertebrates remains unknown. Using goldfish as a model, here we show the expression of PRP and its cognate receptor in the brain-pituitary-gonadal (BPG) axis, thus suggesting a function of goldfish (gf) PRP in regulating reproduction. We found that gfPRP controls the expression of reproductive hormones in the brain, pituitary and ovary. Goldfish PRP exerts stimulatory effects on the expression of salmon gonadotropin-releasing hormone (sGnRH) in the brain, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in pituitary primary culture cells, but inhibits the expression of LH in the ovary. Using the same technique, we showed that gfPRP did not alter the mRNA level of growth hormone in the pituitary primary culture. In summary, we have discovered the first function of vertebrate PRP in regulating reproduction, which provides a new research direction in studying the neuroendocrine control of reproduction not only in teleosts, but also in other non-mammalian vertebrates.

Growth differences and differential expression analysis of pituitary adenylate cyclase activating polypeptide (PACAP) and growth hormone-releasing hormone (GHRH) between the sexes in half-smooth tongue sole Cynoglossus semilaevis

Pituitary adenylate cyclase activating polypeptide (PACAP) and growth hormone-releasing hormone (GHRH) are regulators of growth hormone secretion. In this article, we examined the difference in growth and mRNA expression of PACAP and GHRH between the sexes in half-smooth tongue sole, an important cultured fish species indicating sexually growth dimorphism in China. Firstly, a significant body weight difference between females and males was first observed at 7 months (P<0.05) and at 18 onths the mean body weight of the females (771.0±44.3 g) was as much as 4.9 times higher than that of males (130.6±6.0 g). As a result, half-smooth tongue sole, Cynoglossus semilaevis, is a good model to investigate the effects of growth-related genes expression on sexual growth dimorphism. Secondly, the cDNAs encoding PRP/PACAP and GHRH were isolated. Two differently processed mRNA transcripts of PRP/PACAP (PRP-encoding and PRP splice variant) were found. PACAP and GHRH mRNA was highly abundant in brain and less abundant in other tissues. However, PACAP mRNA was expressed in most brain regions, and was lower in the cerebellum. GHRH mRNA was predominantly expressed in the hypothalamus and weakly expressed in all areas of the brain examined. Ontogenetic expression analysis indicated that PACAP and GHRH mRNA was detected in the early stages of embryogenesis. Finally, differential expression showed that there was no significant difference of the expression level of PACAP or GHRH between the sexes before 8 months of age. However, between 9 and 12 months of age, the GHRH mRNA expression level in males was significantly higher than in females (P<0.05), which might be associated with GH deficiency in males. In contrast, the male PACAP mRNA expression level was not significantly higher than that in females even at 9 and 12 months of age. The present results provide important clues for understanding the sexual growth dimorphism mechanisms in half-smooth tongue sole.

The serendipitous origin of chordate secretin peptide family members

Background

The secretin family is a pleotropic group of brain-gut peptides with affinity for class 2 G-protein coupled receptors (secretin family GPCRs) proposed to have emerged early in the metazoan radiation via gene or genome duplications. In human, 10 members exist and sequence and functional homologues and ligand-receptor pairs have been characterised in representatives of most vertebrate classes. Secretin-like family GPCR homologues have also been isolated in non-vertebrate genomes however their corresponding ligands have not been convincingly identified and their evolution remains enigmatic.

Results

In silico sequence comparisons failed to retrieve a non-vertebrate (porifera, cnidaria, protostome and early deuterostome) secretin family homologue. In contrast, secretin family members were identified in lamprey, several teleosts and tetrapods and comparative studies revealed that sequence and structure is in general maintained. Sequence comparisons and phylogenetic analysis revealed that PACAP, VIP and GCG are the most highly conserved members and two major peptide subfamilies exist; i) PACAP-like which includes PACAP, PRP, VIP, PH, GHRH, SCT and ii) GCG-like which includes GCG, GLP1, GLP2 and GIP. Conserved regions flanking secretin family members were established by comparative analysis of the Takifugu, Xenopus, chicken and human genomes and gene homologues were identified in nematode, Drosophila and Ciona genomes but no gene linkage occurred. However, in Drosophila and nematode genes which flank vertebrate secretin family members were identified in the same chromosome.

Conclusions

Receptors of the secretin-like family GPCRs are present in protostomes but no sequence homologues of the vertebrate cognate ligands have been identified. It has not been possible to determine when the ligands evolved but it seems likely that it was after the protostome-deuterostome divergence from an exon that was part of an existing gene or gene fragment by rounds of gene/genome duplication. The duplicate exon under different evolutionary pressures originated the chordate PACAP-like and GCG-like subfamily groups. This event occurred after the emergence of the metazoan secretin GPCRs and led to the establishment of novel peptide-receptor interactions that contributed to the generation of novel physiological functions in the chordate lineage.

Association between pituitary adenylate cyclase-activating polypeptide and reproduction in the blue gourami

In order to gain a better understanding of the roles of pituitary adenylate cyclase-activating polypeptide (PACAP) in reproduction and growth, the expression of the PACAP gene during the reproduction cycle and its potential role in regulating gonadotropin and growth hormone (GH) gene transcription in blue gourami were investigated. The cDNA sequences of the full-length blue gourami brain PACAP and that of its related peptide (PRP) were acquired. PACAP cDNA had two variants, obtainable by alternative splicing: a long form encoding for both PRP and PACAP and a short form encoding only for PACAP. In females, mRNA levels of PACAP were very high only in individuals with oocytes in the maturation stage, as compared to levels in unpaired vitellogenic and non-vitellogenic fish. The PACAP mRNA levels in males were high only in nest builders, as opposed to in non-nest building males and juveniles. In pituitary culture cells from high vitellogenic females, PACAP38 (the 38 amino acid form) only brought about an increase in betaFSH levels, without altering GH and betaLH mRNA levels. On the other hand, in adult non-reproductive male pituitary cells, PACAP38 decreased the GH mRNA level. Based on these results, we propose that in the blue gourami, PACAP is involved in the final oocyte maturation stage in females, whereas in males, it is associated with sexual behavior. In addition, the effect of PACAP38 on pituitary hormone gene expression is different in females and males, indicating that PACAP38 is potentially a hypophysiotropic regulator of reproduction, which mediates pituitary hormone expression.

Evolution of genes for incretin hormones and their receptors

The incretin hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are essential components in the regulation of blood glucose levels in mammals. These two incretins are produced by evolutionarily related genes and these hormones show similarity in sequence as both are glucagon-like sequences. Genes for these hormones have been identified in a number of diverse vertebrate species indicating that they originated prior to the earliest divergences of vertebrate species. However, analysis of functional and sequence data suggest that each of these hormones acquired incretin activity independently, and only since the divergence of tetrapods from fish. Not only are the hormones related, but so are their receptors. Like the hormones, the incretin action of the receptors is not a product of a shared common ancestral history, as the receptors for GLP-1 and GIP are not most closely related. Further study of the physiological functions of GLP-1 and GIP in additional vertebrates is required to better understand the origin of incretin action.

Pituitary adenylate cyclase-activating polypeptide and its receptors: 20 years after the discovery

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid C-terminally alpha-amidated peptide that was first isolated 20 years ago from an ovine hypothalamic extract on the basis of its ability to stimulate cAMP formation in anterior pituitary cells (Miyata et al., 1989. PACAP belongs to the vasoactive intestinal polypeptide (VIP)-secretin-growth hormone-releasing hormone-glucagon superfamily. The sequence of PACAP has been remarkably well conserved during evolution from protochordates to mammals, suggesting that PACAP is involved in the regulation of important biological functions. PACAP is widely distributed in the brain and peripheral organs, notably in the endocrine pancreas, gonads, respiratory and urogenital tracts. Characterization of the PACAP precursor has revealed the existence of a PACAP-related peptide, the activity of which remains unknown. Two types of PACAP binding sites have been characterized: type I binding sites exhibit a high affinity for PACAP and a much lower affinity for VIP, whereas type II binding sites have similar affinity for PACAP and VIP. Molecular cloning of PACAP receptors has shown the existence of three distinct receptor subtypes: the PACAP-specific PAC1-R, which is coupled to several transduction systems, and the PACAP/VIP-indifferent VPAC1-R and VPAC2-R, which are primarily coupled to adenylyl cyclase. PAC1-Rs are particularly abundant in the brain, the pituitary and the adrenal gland, whereas VPAC receptors are expressed mainly in lung, liver, and testis. The development of transgenic animal models and specific PACAP receptor ligands has strongly contributed to deciphering the various actions of PACAP. Consistent with the wide distribution of PACAP and its receptors, the peptide has now been shown to exert a large array of pharmacological effects and biological functions. The present report reviews the current knowledge concerning the pleiotropic actions of PACAP and discusses its possible use for future therapeutic applications.

Pituitary adenylate cyclase-activating polypeptide induces somatolactin release from cultured goldfish pituitary cells

In the goldfish pituitary, nerve fibers containing pituitary adenylate cyclase-activating polypeptide (PACAP) are located in close proximity to somatolactin (SL)-producing cells, and PACAP enhances SL release from cultured pituitary cells. However, there is little information about the mechanism of PACAP-induced SL release. In order to elucidate this issue, we used the cell immunoblot method. Treatment with PACAP at 10(-8) and 10(-7)M, but not with vasoactive intestinal polypeptide (VIP) at the same concentrations, increased the immunoblot area for SL-like immunoreactivity from dispersed pituitary cells, and PACAP-induced SL release was blocked by treatment with the PACAP selective receptor (PAC(1)R) antagonist, PACAP(6-38), at 10(-6)M, but not with the PACAP/VIP receptor antagonist, VIP(6-28). PACAP-induced SL release was also attenuated by treatment with the calmodulin inhibitor, calmidazolium at 10(-6)M. This led us to explore the signal transduction mechanism up to SL release, and we examined whether PACAP-induced SL release is mediated by the adenylate cyclase (AC)/cAMP/protein kinase A (PKA)- or the phospholipase C (PLC)/inositol 1,4,5-trisphosphate (IP(3))/protein kinase C (PKC)-signaling pathway. PACAP-induced SL release was attenuated by treatment with the AC inhibitor, MDL-12330A, at 10(-5)M or with the PKA inhibitor, H-89, at 10(-5)M. PACAP-induced SL release was suppressed by treatment with the PLC inhibitor, U-73122, at 3 x 10(-6)M or with the PKC inhibitor, GF109203X, at 10(-6)M. These results suggest that PACAP can potentially function as a hypophysiotropic factor mediating SL release via the PAC(1)R and subsequently through perhaps the AC/cAMP/PKA- and the PLC/IP(3)/PKC-signaling pathways in goldfish pituitary cells.

Distribution of growth hormone-releasing hormone-like peptide: Immunoreactivity in the central nervous system of the adult zebrafish (Danio rerio)

The distribution of growth hormone-releasing hormone-like peptides (GHRH-LP) in the central nervous system of the zebrafish was investigated by using immunohistochemical techniques with polyclonal antibodies. ELISAs showed that the antiserum raised against salmon (s)GHRH-LP recognized both zebrafish GHRH-LP1 and -2, whereas the antiserum raised against carp (c)GHRH-LP was more sensitive but detected only zebrafish GHRH-LP1. Neither antiserum detected the true GHRH. Large cells in the nucleus lateralis tuberis were immunoreactive with both antisera, which suggests that they contained zebrafish GHRH-LP1, but not excluding GHRH-LP2. Also, immunoreactive fibers, which putatively originated from these hypothalamic neurons, were present in the hypophysis; both antisera detected fibers, although only sGHRH-LP antiserum stained fibers in the neurointermediate lobe. These fibers may have a neuroendocrine role. Candidates for a role in feeding include several areas in which both antisera labeled cells and fibers, implying a strong reaction for GHRH-LP1 and possibly GHRH-LP2. These areas include the isthmus with cells in the secondary gustatory/visceral nucleus, which were also calretinin immunoreactive. Numerous GHRH-LP-immunoreactive fibers (also labeled by both antisera) probably originate from the gustatory/visceral nucleus to innervate the ventral area of the telencephalon, preglomerular nuclei, torus lateralis and hypothalamic diffuse nucleus, habenula, torus semicircularis, and dorsolateral funiculus of the spinal cord. Present results in the zebrafish brain suggest involvement of GHRH-LP in both neuroendocrine and feeding-associated nervous circuits. The present data on the location of the two GHRH-LPs are the first clue to the possible functions of these two hormones.

Cloning, tissue distribution and effects of food deprivation on pituitary adenylate cyclase activating polypeptide (PACAP)/PACAP-related peptide (PRP) and preprosomatostatin 1 (PPSS 1) in Atlantic cod (Gadus morhua)

Full-length complementary deoxyribonucleic acid sequences encoding pituitary adenylate cyclase activating polypeptide (PACAP)/PACAP-related peptide (PRP) and preprosomatostatin 1 (PPSS 1) were cloned from Atlantic cod (Gadus morhua) hypothalamus using reverse transcription and rapid amplification of complementary deoxyribonucleic acid ends. Semi-quantitative reverse transcriptase polymerase chain reaction shows that PRP/PACAP mRNA and PPSS 1 mRNA are widely distributed throughout cod brain. During development, PRP/PACAP and PPSS 1 were detected at the 30-somite stage and pre-hatching stage, respectively, and expression levels gradually increased up to the hatched larvae. PPSS 1, but not PRP/PACAP, appeared to be affected by food availability during early development. In juvenile cod, PPSS 1 expression levels increased and remained significantly higher than that of control fed fish throughout 30 days of starvation and during a subsequent 10 days refeeding period. In contrast, PRP/PACAP expression levels were not affected by 30 days of food deprivation, but a significant increase in expression levels was observed during the 10 days refeeding period in the experimental food-deprived group as compared to the control fed group. Our results suggest that PRP/PACAP and PPSS 1 may be involved in the complex regulation of growth, feeding and metabolism during food deprivation and refeeding in Atlantic cod.