Immunohistochemical distribution and biological activity of pituitary adenylate cyclase-activating polypeptide (PACAP) in the central nervous system of the frog Rana ridibunda

Current State of Understanding of the Role of PACAP in the Hypothalamo-Hypophyseal Gonadotropin Functions of Mammals

PACAP was discovered 30 years ago in Dr. Akira Arimura's laboratory. In the past three decades since then, it has become evident that this peptide plays numerous crucial roles in mammalian organisms. The most important functions of PACAP are the following: 1. neurotransmitter, 2. neuromodulator, 3. hypophysiotropic hormone, 4. neuroprotector. This paper reviews the accumulated data regarding the distribution of PACAP and its receptors in the mammalian hypothalamus and pituitary gland, the role of PACAP in the gonadotropin hormone secretion of females and males. The review also summarizes the interaction between PACAP, GnRH, and sex steroids as well as hypothalamic peptides including kisspeptin. The possible role of PACAP in reproductive functions through the biological clock is also discussed. Finally, the significance of PACAP in the hypothalamo-hypophysial system is considered and the facts missing, that would help better understand the function of PACAP in this system, are also highlighted.

Distribution of pituitary adenylate cyclase-activating polypeptide 2 in zebrafish brain

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multipotent neuropeptide with an amino acid sequence that is well conserved among vertebrates. In teleosts, including zebrafish, the PACAP gene (adcyap1) has been duplicated to yield adcyap1a (coding PACAP1) and adcyap1b (coding PACAP2). This study aims to determine the distribution of these PACAPs and their mRNAs in zebrafish. We generated a zebrafish PACAP2-specific antibody. Using real-time PCR, we observed that adcyap1b mRNA was primarily localized in the brain, with the highest level in the telencephalon, followed by the diencephalon. Using immunostaining of brain tissue samples, PACAP2 immunoreactivity was observed mainly in the telencephalon, hypothalamus, and cerebellum, and the immunopositive fibers formed a line to the habenula. PACAP2-immunopositive cells were observed in the ventral and dorsal regions of the telencephalon and in the hypothalamic nucleus of the diencephalon in the colchicine-injected brain. This distribution of PACAP2 suggests its involvement in higher brain functions in teleosts, such as learning and cognition, as well as instinctive behaviors such as feeding and emotional regulation.

The presence and distribution of pituitary adenylate cyclase activating polypeptide and its receptor in the snail Helix pomatia

The aim of this study was to show the presence, distribution and function of the pituitary adenylate cyclase activating polypeptide (PACAP) and its receptors in the CNS and peripheral nervous system of the mollusk, Helix pomatia. PACAP-like and pituitary adenylate cyclase activating polypeptide receptor (PAC1-R)-like immunoreactivity was abundant both in the CNS and the peripheral nervous system of the snail. In addition several non-neuronal cells also revealed PACAP-like immunoreactivity. In inactive animals labeled cell bodies were mainly found and in the neuropile of active animals dense immunostained fiber system was additionally detected suggesting that expression of PACAP-like peptide was affected by the behavioral state of the animal. RIA measurements revealed the existence of both forms of PACAP in the CNS where the 27 amino acid form was found to be dominant. The concentration of PACAP27 was significantly higher in samples from active animals supporting the data obtained by immunohistochemistry. In Western blot experiments PACAP27 and PACAP38 antibodies specifically labeled protein band at 4.5 kDa both in rat and snail brain homogenates, and additionally an approximately 14 kDa band in snail. The 4.5 kDa protein corresponds to PACAP38 and the 14 kDa protein corresponds to the preproPACAP or to a PACAP-like peptide having larger molecular weight than mammalian PACAP38. In matrix-assisted laser desorption ionization time of flight (MALDI TOF) measurements fragments of PACAP38 were identified in brain samples suggesting the presence of a large molecular weight peptide in the snail. Applying antibodies developed against the PACAP receptor PAC1-R, immunopositive stained neurons and a dense network of fibers were identified in each of the ganglia. In electrophysiological experiments, extracellular application of PACAP27 and PACAP38 transiently depolarized or increased postsynaptic activity of neurons expressing PAC1-R. In several neurons PACAP elicited a long lasting hyperpolarization which was eliminated after 1.5 h continuous washing. Taken together, these results indicate that PACAP may have significant role in a wide range of basic physiological functions in snail.

PAC1 receptor localization in a model nervous system: light and electron microscopic immunocytochemistry on the earthworm ventral nerve cord ganglia

The presence and pattern of pituitary adenylate cyclase activating polypeptide (PACAP) type I (PAC1) receptors were identified by means of pre- and post-embedding immunocytochemical methods in the ventral nerve cord ganglia (VNC) of the earthworm Eisenia fetida. Light and electron microscopic observations revealed the exact anatomical positions of labeled structures suggesting that PACAP mediates the activity of some interneurons, a few small motoneurons and certain sensory fibers that are located in ventrolateral, ventromedial and intermediomedial sensory longitudinal axon bundles of the VNC ganglia. No labeling was located on large interneuronal systems such as dorsal medial and lateral giant axon systems and ventral giant axons. At the ultrastructural level labeling was mainly restricted to endo- and plasma membranes showing characteristic unequal distribution in various neuron parts. An increasing abundance of PAC1 receptors located on both rough endoplasmic reticulum and plasma membranes was seen from perikarya to neural processes, indicating that intracellular membrane traffic might play a crucial role in the transportation of PAC1 receptors. High number of PAC1 receptors was found in both pre- and postsynaptic membranes in addition to extrasynaptic sites suggesting that PACAP acts as neurotransmitter and neuromodulator in the earthworm nervous system.

Ontogeny of PAC1-R and VPAC1-R in the frog, Rana esculenta

The distribution of pituitary adenylate cyclase-activating polypeptide (PACAP) and PACAP receptors in the brain of amphibians has been previously described. In the present study, we have investigated the ontogeny of the selective PACAP receptor, PAC1-R, and the PACAP-vasoactive intestinal polypeptide (VIP) mutual receptor, VPAC1-R, in frog embryos by whole-mount in situ hybridization histochemistry. At stage 20, expression of PAC1-R and/or VPAC1-R mRNAs was detected in the brain, the auditory vesicles, the external gills, the buds of the lateral lines and the coelomatic cavity. At stage 25, PAC1-R and/or VPAC1-R mRNAs were observed in the buds of the orbital lateral line, the pancreas and heart. At stage 30, PAC1-R and VPAC1-R mRNAs were widely distributed in the telencephalon and diencephalon as well as in the bud of the lateral line, the heart and the pancreas. The anatomical distribution of PAC1-R and VPAC1-R mRNAs, although similar, did not totally overlap, indicating that PACAP and VIP may exert differential effects in frog during development.

VIP and PACAP stimulate TSH release from the bullfrog pituitary

We have recently shown that corticotropin-releasing hormone (CRH) is a major thyrotropin (TSH)-releasing factor in amphibians, but we have also found that, besides CRH, other hypothalamic substances stimulate TSH secretion in frog. In order to characterize novel TSH secretagogues, we have investigated the effect of frog (Rana ridibunda) vasoactive intestinal polypeptide (VIP) (fVIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) (fPACAP38 and PACAP27) on TSH release from bullfrog (Rana catesbeiana) pituitary cells in primary culture. Incubation of pituitary cells for 24h with graded concentrations of fVIP, fPACAP38 and PACAP27 (10(-9) to 10(-6)M) induced a dose-dependent stimulation of TSH release with minimum effective doses of 10(-9)M for fVIP and 10(-8)M for fPACAP38 and PACAP27. The PAC1-R/VPAC2-R antagonist PACAP(6-38) (10(-7) and 10(-6)M) dose-dependently suppressed the stimulatory effects of fVIP and fPACAP38 (10(-7)M each). Likewise, this antagonist (10(-6) and 10(-5)M) dose-dependently attenuated the stimulatory effect of PACAP27 (10(-7)M). On the other hand, the VPAC1-R/VPAC2-R antagonist [d-pCl-Phe(6), Leu(17)]VIP (10(-6) and 10(-5)M) dose-dependently inhibited the stimulatory effect of fVIP (10(-9)M) and PACAP27 (10(-8)M), but did not affect the response to fPACAP38 (10(-8)M). These data indicate that, in amphibians, the activity of thyrotrophs can be regulated by VIP and PACAP acting likely through VPAC2-R and PAC1-R.

Immunohistochemical localization and biological activity of the steroidogenic enzyme cytochrome P450 17α-hydroxylase/C17, 20-lyase (P450C17) in the frog brain and pituitary

It is now clearly established that the brain has the capability of synthesizing various biologically active steroids including 17-hydroxypregnenolone (17OH-Delta(5)P), 17-hydroxyprogesterone (17OH-P), dehydroepiandrosterone (DHEA) and androstenedione (Delta(4)). However, the presence, distribution and activity of cytochrome P450 17alpha-hydroxylase/C17, 20-lyase (P450(C17)), a key enzyme required for the conversion of pregnenolone (Delta(5)P) and progesterone (P) into these steroids, are poorly documented. Here, we show that P450(C17)-like immunoreactivity is widely distributed in the frog brain and pituitary. Prominent populations of P450(C17)-containing cells were observed in a number nuclei of the telencephalon, diencephalon, mesencephalon and metencephalon, as well as in the pars distalis and pars intermedia of the pituitary. In the brain, P450(C17)-like immunoreactivity was almost exclusively located in neurons. In several hypothalamic nuclei, P450(C17)-positive cell bodies also contained 3beta-hydroxysteroid dehydrogenase-like immunoreactivity. Incubation of telencephalon, diencephalon, mesencephalon, metencephalon or pituitary explants with [(3)H]Delta(5)P resulted in the formation of several tritiated steroids including 17OH-Delta(5)P, 17OH-P, DHEA and Delta(4). De novo synthesis of C(21) 17-hydroxysteroids and C(19) ketosteroids was reduced in a concentration-dependent manner by ketoconazole, a P450(C17) inhibitor. This is the first detailed immunohistochemical mapping of P450(C17) in the brain and pituitary of any vertebrate. Altogether, the present data provide evidence that CNS neurons and pituitary cells can synthesize androgens.

The common organization of the amygdaloid complex in tetrapods: new concepts based on developmental, hodological and neurochemical data in anuran amphibians

Research over the last few years has demonstrated that the amygdaloid complex in amniotes shares basic developmental, hodological and neurochemical features. Furthermore, homolog territories of all main amygdaloid subdivisions have been recognized among amniotes, primarily highlighted by the common expression patterns for numerous developmental genes. With the achievement of new technical approaches, the study of the precise neuroanatomy of the telencephalon of the anuran amphibians has been possible, revealing that most of the structures present in amniotes are recognizable in these anamniotes. Thus, recent investigations have yielded enough results to support the notion that the organization of the anuran amygdaloid complex includes subdivisions with origin in ventral pallial and subpallial territories, a strong relationship with the vomeronasal and olfactory systems, abundant intra-amygdaloid connections, a main output center involved in the autonomic system, profuse amygdaloid fiber systems, and distinct chemoarchitecture. When all these new data about the development, connectivity and neurochemistry of the amygdaloid complex in anurans are taken into account, it becomes patent that a basic organization pattern is shared by both amniotic and anamniotic tetrapods.

Pituitary adenylate cyclase-activating polypeptide inhibits caspase-3 activity but does not protect cerebellar granule neurons against β-amyloid (25–35)-induced apoptosis

The beta-amyloid (Abeta) peptide Abeta25-35 provokes apoptosis of cerebellar granule cells through activation of caspase-3 while the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) promotes granule cell survival by inhibiting caspase-3 activation through the intrinsic apoptotic pathway. The aim of the present study was to determine whether PACAP could prevent Abeta25-35 neurotoxicity by inhibiting caspase-3 activity. A 24-h exposure of cultured cerebellar granule cells to Abeta25-35 induced shrinkage of cell bodies, neurite retraction and alteration of mitochondrial activity. Administration of graded concentrations (10-80 microM) of Abeta25-35 induced a dose-related decrease of the number of living cells, and the neurotoxic effect was highly significant after a 24-h exposure to 80 microM Abeta25-35. Exposure of cerebellar granule cells to Abeta25-35 markedly enhanced caspase-3 but not caspase-9 activity. Co-incubation with 1 microM PACAP significantly reduced Abeta25-35-evoked caspase-3 activation. In contrast, PACAP did not prevent the deleterious effects of Abeta25-35 on mitochondrial potential and granule cell survival. Taken together, these data suggest that caspase-3 activation is not the main pathway activated by Abeta25-35 that leads to granule cell death. The results also demonstrate that PACAP cannot be considered as a potent neuroprotective factor against Abeta25-35-induced apoptosis in cerebellar granule neurons.

Pituitary adenylate cyclase-activating polypeptide in the brain, spinal cord and sensory organs of the zebrafish, Danio rerio, during development

The distribution of Pituitary adenylate cyclase-activating polypeptide (PACAP) was investigated in the brain, pituitary and sensory organs of the zebrafish, Danio rerio, during development, in juvenile and adult specimens, using the immunofluorescence method. In 24 h post fertilization (hpf) embryos, PACAP immunoreactive cells appeared in the rostral telencephalon, dorsal diencephalon, caudal and medial rhombencephalon, spinal cord and retina. At 48 hpf stage, positive cells were present in the dorsal diencephalon, medial rhombencephalon, spinal cord, retina and olfactory placode (Op). At 72 hpf stage, additional immunoreactive elements appeared in the medial telencephalon, hypothalamus, mesencephalic tegmentum, retina and otic sensory epithelium (Ose). At day 5, new immunoreactive cells were found in the anterior rhombencephalon and pituitary pars distalis. At day 13, positive cells were mainly concentrated in the mesencephalic tegmentum and spinal cord. In the telencephalon, diencephalon, rhombencephalon and pituitary, the distribution of positive cells was similar to that previously reported. At 1 month stage, positive cells were detected in the hypothalamus, nucleus of the medial longitudinal fascicle (nMlf), rhombencephalic griseum centrale (Gc) and pituitary pars distalis. At 2-3 month stages, immunoreactive elements were found in several hypothalamic nuclei, in the mesencephalic nucleus isthmi, cerebellum and pituitary. In adults, PACAP immunoreactivity was confined to a few brain regions and the pituitary. PACAP immunoreactivity was transiently expressed in several regions suggesting that the peptide may have a role in the control of cells differentiation and proliferation during zebrafish ontogeny. The finding of positive fibers in the pituitary from day 5 onward indicates that PACAP may function from this stage as a hypophysiotropic peptide.

Hodological characterization of the medial amygdala in anuran amphibians

Early studies in anuran amphibians defined the amygdala as a single unit that only later could be subdivided into medial and lateral parts with the achievement of sensitive immunohistochemical and tracing techniques. However, the terminology used was often misleading when comparing with "homologous" amygdaloid nuclei in amniotes. Recently, the basal telencephalon of anurans has been demonstrated to be more complex than previously thought, and distinct amygdaloid nuclei were proposed on the basis of immunohistochemistry. Moreover, developmental data are increasing that support this notion. In the present study, we analyzed the patterns of afferent and efferent connections of the medial amygdala (MeA; formerly amygdala pars lateralis), considered as the main target of the vomeronasal information from the accessory olfactory bulb, as in other vertebrates. By means of axonal transport of dextran amines, the afferent and efferent connections of the MeA were traced in Rana perezi and Xenopus laevis under in vivo and in vitro conditions. Largely similar results were found in both species. The results showed abundant intratelencephalic and extratelencephalic connections that were readily comparable to those of other tetrapods. Most of these connections were reciprocal and, in particular, the strong relation of the MeA with the hypothalamus, via the stria terminalis, was demonstrated. Immunohistochemical techniques showed staining patterns that revealed abundant peptidergic afferents to the MeA, as well as minor inputs containing other neurotransmitters such as catecholamines. Double-labeling experiments demonstrated that the peptidergic fibers that reach the MeA originate in the ventral hypothalamus, whereas the catecholaminergic innervation of the MeA arises in the caudal extent of the posterior tubercle. Taken together, the results about connectivity in our study support the comparison of the MeA in anurans with its counterparts (and similarly named) amygdaloid nuclei in amniotes. Most of the hodological features of the medial amygdala seem to be shared by those tetrapods with well-developed vomeronasal systems.

Molecular characterization of the cDNA and localization of the mRNA encoding the prohormone convertase PC5-A in the European green frog

The structure and distribution of PC5-A, a prohormone convertase that is thought to be involved in post-translational processing of peptide hormone and neuropeptide precursors, have not been investigated in submammalian vertebrates. In the present study, we characterized the cDNA encoding PC5-A in the European green frog Rana esculenta. The frog PC5-A cDNA encodes a 913-amino acid protein that encompasses a 28-amino acid signal peptide, the Asp/His/Ser catalytic triad found in all serine proteinases of the subtilisin family, and two potential N-linked glycosylation sites located in a C-terminal cysteine-rich domain. Reverse transcriptase polymerase chain reaction amplification showed that PC5-A mRNA is expressed in various organs including the brain, spinal cord, pituitary, lung, liver, intestine, and testis, but not in the stomach and pancreas. The distribution of PC5-A mRNA in the frog brain was studied by in situ hybridization histochemistry. Intense expression was observed in the mitral cellular layer of the olfactory bulb, the nucleus of the diagonal band of Broca, the anterior preoptic area, and the suprachiasmatic and ventral hypothalamic nuclei. The expression pattern of PC5-A mRNA in the central nervous system of anuran amphibians was consistent with the implication of this prohormone convertase in the processing of various neuropeptide precursors.

Comparative distributions of pituitary adenylyl cyclase-activating polypeptide and its selective type I receptor mRNA in the frog (Xenopus laevis) brain

The detailed mRNA distributions of pituitary adenylyl cyclase-activating polypeptide (PACAP) and its selective type I receptor (PAC(1)) were systematically compared in the brain of the frog Xenopus laevis. PACAP mRNA expression overlapped with that of PAC(1) in many brain areas such as the pallium, hypothalamic preoptic area, ventral hypothalamic nuclei, habenular nucleus, most thalamic nuclei, the cerebellular nucleus, and nuclei of isthmi. In some structures, PACAP and PAC(1) gene transcripts were present in anatomically distinct cell layers. For example, in the olfactory bulb, PACAP mRNA was present in the mitral cell layer, whereas gene transcripts for the receptor were observed in the granule layer. In a number of regions, expression showed no obvious overlap. PAC(1) but not PACAP mRNA was present at moderate levels in the Purkinje cell layer of the cerebellum and distal lobe of the pituitary. Conversely, PAC(1) gene expression was absent in the spinal cord while PACAP mRNA signals were observed in the medial portion of the ventral horn and deep portion of the dorsal horn. The granule and molecular cell layer of the cerebellum, alpha-motor neurons in the spinal cord, and reticular nucleus of isthmi showed neither PACAP nor PAC(1) gene transcripts. These localized patterns of ligand and receptor gene expression suggest possible PACAP projection and target fields in the frog brain.

Immunohistochemical localization and biochemical characterization of ghrelin in the brain and stomach of the frog Rana esculenta

Ghrelin is a 28-amino acid n-octanoylated peptide recently isolated from the rat stomach as an endogenous ligand of the growth hormone secretagogue receptor. So far, the occurrence of ghrelin has not been investigated in submammalian vertebrates. In the present work, we have studied the anatomic distribution and biochemical characterization of ghrelin-like immunoreactivity in the brain and stomach of the frog Rana esculenta by using two distinct antisera directed against rat ghrelin. In the brain, sparse ghrelin-positive cells were detected in three nuclei of the diencephalon, namely the suprachiasmatic nucleus and the posterior tuberculum in the hypothalamus, and the posterodorsal aspect of the lateral nucleus in the thalamus. A few ghrelin-immunoreactive neurons were also found in the mesencephalon, i.e., in the pretoral gray and the anterodorsal tegmental nucleus. Ghrelin-containing fibers were widely distributed in the frog brain. In particular, diffuse networks of immunoreactive processes were observed in various regions of the telencephalon, including the medial pallium, the striatum, the nucleus of the diagonal band of Broca, the nucleus accumbens, and the amygdala. In the diencephalon, the magnocellular nucleus, the suprachiasmatic nucleus, the posterior tuberculum, and the ventrolateral and lateral thalamic nuclei were moderately to densely innervated with ghrelin-containing fibers. A moderate density of positive fibers was also found in different areas of the mesencephalon such as the nucleus of the medial longitudinal fasciculus, the pretoral gray, and the tegmentum. In the stomach, a few brightly immunofluorescent cells were detected in the mucosa. The distribution pattern and morphologic characteristics of ghrelin-containing cells in the stomach suggest that they correspond to endocrine cells. Reversed-phase high performance liquid chromatography analysis of frog brain and stomach extracts, combined with RIA detection, revealed that ghrelin-immunoreactive material eluted as a single peak with a retention time slightly shorter than that of synthetic rat ghrelin. The present data provide the first evidence that a ghrelin-related peptide is present in submammalian vertebrates. The occurrence of ghrelin-containing cells in the hypothalamus and the stomach mucosa suggests that, in amphibians, ghrelin may exert both neuroendocrine and endocrine activities.

Novel splice variants of type I pituitary adenylate cyclase-activating polypeptide receptor in frog exhibit altered adenylate cyclase stimulation and differential relative abundance

Pituitary adenylate cyclase-activating polypeptide (PACAP) exerts its various effects through activation of two types of G protein-coupled receptors, a receptor with high affinity for PACAP named PAC1-R and two receptors exhibiting similar affinity for both PACAP and vasoactive intestinal polypeptide named VPAC1-R and VPAC2-R. Here, we report the characterization of PAC1-R and novel splice variants in the frog Rana ridibunda. The frog PAC1-R has 78% homology with human PAC1-R and is highly expressed in the central nervous system. Two splice variants of the frog receptor that display additional amino acid cassettes in the third intracellular loop were characterized. PAC1-R25 carries a 25-amino acid insertion that matches the hop cassette of the mammalian receptor, whereas PAC1-R41 carries a cassette with no homology to any mammalian PAC1-R variant. A third splice variant of PAC1-R, exhibiting a completely different intracellular C-terminal domain, named PAC1-Rmc has also been identified. Determination of cAMP formation in cells transfected with the cloned receptors showed that PACAP activated PAC1-R, PAC1-R25, and PAC1-R41 with similar potency. In contrast, PACAP failed to stimulate adenylate cyclase in cells transfected with PAC1-Rmc. Fusion of PAC1-R or PAC1-Rmc with the green fluorescent protein revealed that both receptors are expressed and targeted to the plasma membrane in transfected cells. The different PAC1-R variants are highly expressed in the frog brain and spinal cord and to a lesser extent in peripheral tissues, where only certain isoforms could be detected. The present data indicate that in frog, PACAP may act through different PAC1-R splice variants that differ in their G(s) protein coupling and their abundance in various tissues.

Isolation, characterization, and distribution of a novel neuropeptide, Rana RFamide (R-RFa), in the brain of the European green frog Rana esculenta

A novel neuropeptide of the RFamide peptide family was isolated in pure form from a frog (Rana esculenta) brain extract by using reversed-phase high performance liquid chromatography in combination with a radioimmunoassay for mammalian neuropeptide FF (NPFF). The primary structure of the peptide was established as Ser-Leu-Lys- Pro-Ala-Ala-Asn-Leu-Pro-Leu- Arg-Phe-NH(2). The sequence of this neuropeptide, designated Rana RFamide (R-RFa), exhibits substantial similarities with those of avian LPLRFamide, gonadotropin-inhibitory hormone, and human RFRP-1. The distribution of R-RFa was investigated in the frog central nervous system by using an antiserum directed against bovine NPFF. In the brain, immunoreactive cell bodies were primarily located in the hypothalamus, i.e., the anterior preoptic area, the suprachiasmatic nucleus, and the dorsal and ventral hypothalamic nuclei. The most abundant population of R-RFa-containing neurons was found in the periependymal region of the suprachiasmatic nucleus. R-RFa- containing fibers were widely distributed throughout the brain from the olfactory bulb to the brainstem, and were particularly abundant in the external layer of the median eminence. In the spinal cord, scattered immunoreactive neurons were found in the gray matter. R-RFa-positive processes were found in all regions of the spinal cord, but they were more abundant in the dorsal horn. This study provides the first characterization of a member of the RFamide peptide family in amphibians. The occurrence of this novel neuropeptide in the hypothalamus and median eminence and in the dorsal region of the spinal cord suggests that, in frog, R-RFa may exert neuroendocrine activities and/or may be involved in the transmission of nociceptive stimuli.

Pituitary adenylate cyclase-activating polypeptide induces testicular testosterone synthesis through PGE(2) mediation in crested newt, Triturus carnifex

The aim of the present work was to study the possible role of adenylate cyclase-activating polypeptide (PACAP) 38 in the testicular intracellular mechanism regulating steroidogenesis of crested newt, Triturus carnifex. Gonads were incubated in vitro with PACAP 38 and prostaglandin (PG) E(2) alone or with inhibitors of cyclooxygenase (COX), adenylate cyclase (AC), and phospholipase C (PLC) for 30 min and 60 min. PGE(2), PGF(2 alpha), testosterone, and estradiol-17 beta were measured in the culture medium; aromatase (AR) activity and cAMP were assessed in the tissue. PACAP 38 increased PGE(2) (30 min and 60 min), estradiol-17 beta (60 min), cAMP (60 min), and AR (60 min) but decreased testosterone (60 min). PGE(2) increased estradiol-17 beta, cAMP, and AR and decreased testosterone at 30 and 60 min.PLC inhibitor counteracted the effects of PACAP 38, while AC inhibitor counteracted these effects except for PGE(2) increase. AC inhibitor counteracted the effects of PGE(2), while PLC did not. COX inhibitor decreased PGF(2 alpha) (30 min and 60 min), PGE(2) (30 min and 60 min), estradiol-17 beta (60 min), cAMP (60 min), and AR (60 min), but increased testosterone (60 min). These in vitro results suggest that, in newt testis, PACAP 38 acts on PLC, inducing the increase of PGE(2) which, in turn, acting on AC, increases AR activity with the consequent estradiol-17 beta increase and testosterone decrease.

Immunocytochemical localization of growth hormone-releasing hormone-like peptide in the brain of the tiger frog, Rana tigrina

Using antisera directed against carp growth hormone-releasing hormone (cGHRH), we found more extensive brain distribution of GHRH-like immunoreactive (ir) neurons in the tiger frog, Rana tigrina, than reported in previous studies, which employed mammalian GHRH antibodies. In the telencephalon, GHRH-ir perikarya were present in the pallium dorsale, pallium laterale (pars dorsalis and pars ventralis), pallium mediale, nucleus entopeduncularis, amygdala pars medialis, and in the ventral portion of the lateral preoptic area. Most GHRH somata were present in the nucleus infundibularis ventralis located around the third ventricle, extending from the region posterior to the optic chiasma to the caudal end of infundibulum. In the thalamic region, GHRH-ir perikarya occurred in the area ventrolateralis thalami, the nuclei posterocentralis thalami, and the posterolateralis thalami. The ir cell bodies in the nucleus posteroventralis tegmenti mesencephali represented the caudal-most brain GHRH perikarya. Extensive GHRH-ir fibers occurred around the nonreactive cells in the ventral preoptic area and ventral area of the infundibulum. GHRH-ir fibers were present in the outer layers of the median eminence, but not in the neural lobe or pars distalis of the pituitary gland. This wider neuroanatomical distribution of GHRH-like peptide in the brain of R. tigrina should, provide the basis for future studies to establish the exact role of GHRH-like peptides in anuran brain.

Pituitary adenylate cyclase-activating polypeptide and vasoactive intestinal peptide-stimulated cyclic AMP synthesis in rat cerebral cortical slices: interaction with noradrenaline, adrenaline, and forskolin

Pituitary adenylate cyclase-activating polypeptide (PACAP; 0.001-1 microM) and vasoactive intestinal peptide (VIP; 0.01-1 microM) produced a concentration-dependent stimulation of cyclic AMP (cAMP) formation in rat cerebral cortical slices prelabeled with [3H]adenine. The effects of PACAP38 and PACAP27 were similar, and more efficacious (at 0.1 and 1 microM) than those of VIP. Adrenaline and noradrenaline (each at 100 microM) also stimulated cAMP formation, with the latter compound being more effective. Combination of PACAP38, PACAP27 (each at 0.1 microM) and VIP (1 microM) with adrenaline or noradrenaline resulted in most cases in additive effects, with some supraadditive (PACAP27 plus adrenaline) or subadditive (PACAP38 or VIP plus noradrenaline) fluctuations. In contrast, combination of each of the three peptides with 3 microM forskolin resulted in synergistic effects. These results indicate that in rat cerebral cortex there is no synergism between PACAP or VIP with noradrenaline or adrenaline; however, based on the forskolin data, it seems likely that synergistic effects may take place with VIP or PACAP and other cAMP-stimulating neuroregulators.

Peptides in frog brain areas processing visual information

Vision is the most important sensory modality to anurans and a great deal of work in terms of hodological, physiological, and behavioral studies has been devoted to the visual system. The aim of this account is to survey data about the distribution of peptides in primary (lateral geniculate complex, pretectum, tectum) and secondary (striatum, anterodorsal and anteroventral tegmental nuclei, isthmic nucleus) visual relay centers. The emphasis is on general traits but interspecies variations are also noted. The smallest amount of peptide-containing neuronal elements was found in the lateral geniculate complex, where primarily nerve fibers showed immunostaining. All peptides found in the lateral geniculate complex, except two, occurred in the pretectum together with four other peptides. A large number of neurons showing intense neuropeptide thyrosine-like immunoreactivity was characteristic here. The mesencephalic tectum was the richest in peptide-like immunoreactive neuronal elements. Almost all peptides investigated were present mainly in fibers, but 9 peptides were found also in cells. The immunoreactive fibers show a complicated overlapping laminar arrangement. Cholecystokinin octapeptide, enkephalins, neuropeptide tyrosine, and substance P (not discussed here) gave the most prominent immunoreactivity. Several peptides also occur in the tectum of fishes, reptiles, birds, and mammals. Peptides in various combinations were found in the striatum, the anterodorsal- and anteroventral tegmental nucleus, and the isthmic nucleus that receive projections from the primary visual centers. The functional significance of peptides in visual information processing is not known. The only exception is neuropeptide tyrosine, which was found to be inhibitory on retinotectal synapses.

Pituitary adenylate cyclase-activating polypeptide and its receptors in amphibians

Pituitary adenylate cyclase-activating polypeptide (PACAP), a novel peptide of the secretin/glucagon/vasoactive intestinal polypeptide superfamily, has been initially characterized in mammals in 1989 and, only 2 years later, its counterpart has been isolated in amphibians. A number of studies conducted in the frog Rana ridibunda have demonstrated that PACAP is widely distributed in the central nervous system (particularly in the hypothalamus and the median eminence) and in peripheral organs including the adrenal gland. The cDNAs encoding the PACAP precursor and 3 types of PACAP receptors have been cloned in amphibians and their distribution has been determined by in situ hybridization histochemistry. Ontogenetic studies have revealed that PACAP is expressed early in the brain of tadpoles, soon after hatching. In the frog Rana ridibunda, PACAP exerts a large array of biological effects in the brain, pituitary, adrenal gland, and ovary, suggesting that, in amphibians as in mammals, PACAP may act as neurotrophic factor, a neurotransmitter and a neurohormone.

Distribution of adrenomedullin-like immunoreactivity in the central nervous system of the frog

Adrenomedullin (AM) is a recently discovered peptide widely distributed in the mammalian brain. By using an antiserum specific for human AM, we have analyzed the localization of AM-like immunoreactivity in the brain and spinal cord of the anuran amphibian Rana perezi. Cell bodies immunoreactive (AMi) for AM were located in the dorsal, lateral and medial pallial regions, diagonal band of Broca, medial septum, and above and rostral to the anterior commissure. A large population of AMi neurons was located in the anterior preoptic area, suprachiasmatic nucleus and in the infundibular hypothalamus. The processes of these latter cells are part of the hypothalamo-hypophysial pathway to the neural and intermediate lobes. Labeled cells were observed in the pretectal region, posterior tubercle and the mesencephalic anteroventral tegmental nucleus. Strikingly, Purkinje cells in the cerebellum also showed AM immunoreactivity, albeit not all of these cells were equally stained. Additional cells were located in the parabrachial region, principal trigeminal sensory nucleus, reticular nuclei medius and inferior, and the intermediolateral gray of the spinal cord. Immunolabeled fibers were widespread throughout the brain and spinal cord of the frog. They were particularly abundant in the medial amygdala, hypothalamus, mesencephalic tectum, periventricular gray and spinal cord. The distribution pattern of AM-like immunoreactivity in the brain of the frog is very selective and does not correspond with the pattern observed for any other transmitter or neuroactive molecule. The wide distribution of this peptide strongly suggests that it may play a significant role in the multiple neuronal functions in the amphibian brain.

Ontogeny of pituitary adenylate cyclase-activating polypeptide (PACAP) in the frog (Rana ridibunda) tadpole brain: immunohistochemical localization and biochemical characterization

The anatomic distribution and biochemical characteristics of the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) were investigated in the central nervous system of the frog, Rana ridibunda, during development. Three to four days after hatching, at stages IV-VII, PACAP-immunoreactive perikarya were detected in the dorsal thalamus within the anterior ventral area, and a few fibers were found in the medial pallium. Positive cell bodies were first observed in the hypothalamus at stages VIII-IX, at the level of the dorsal and ventral infundibular nuclei. In these regions, the number of positive perikarya increased during ontogeny. In tadpoles, during the mid- and late premetamorphosis, a more complex organization of the PACAP-immunoreactive system was found in the thalamus with the appearance, at stages IX-XII, of two additional groups of positive neurons in the ventrolateral area and posterocentral nucleus. At stages XIII-XVIII of larval development and subsequent larval stages, PACAP-immunoreactive fibers were found in the median eminence. In newly metamorphosed animals, several additional groups of positive perikarya appeared in the medial pallium, the preoptic nucleus, the torus semicircularis, the tegmentum of the mesencephalon, and the cerebellum. The immunoreactive peptide contained in the tadpole brain was characterized by high performance liquid chromatography analysis combined with radioimmunoassay quantification. At all stages investigated, the predominant form of PACAP-immunoreactive material coeluted with synthetic frog PACAP38. The occurrence of PACAP soon after hatching indicates that the peptide may exert neurotrophic activities. The existence of immunoreactive elements in several thalamic regions at mid- and late premetamorphic stages suggests that PACAP may act as a neurotransmitter, neuromodulator, or both, during ontogenesis. Finally, the presence of PACAP-immunoreactive perikarya in hypothalamic nuclei and nerve fibers in the median eminence supports the view that PACAP may play a role in the control of pituitary hormone secretion during larval development.

Immunohistochemical localization and biochemical characterization of hypocretin/orexin-related peptides in the central nervous system of the frog Rana ridibunda

In the present study, we have investigated the distribution and biochemical characteristics of hypocretin (hcrt) -like immunoreactivity in the central nervous system (CNS) of the frog Rana ridibunda by using an antiserum directed against rat hcrt2. Immunoreactive cell bodies were only detected in four diencephalic nuclei, including the anterior preoptic area and the suprachiasmatic, magnocellular, and ventral hypothalamic nuclei. In contrast, hcrt2-immunoreactive fibers were widely distributed throughout the frog CNS. In particular, a high density of hcrt-positive fibers was detected in several areas of the telencephalon, including the olfactory bulb, the nucleus of the diagonal band of Broca, and the amygdala. A dense network of hcrt-containing fibers was observed in all thalamic and hypothalamic nuclei. A low to moderate density of immunoreactive fibers was also found in the mesencephalon, rhombencephalon, and spinal cord. Reversed-phase high performance liquid chromatography analysis of frog brain extracts revealed that hcrt2-immunoreactive material eluted as two peaks, the major one exhibiting the same retention time as synthetic rat hcrt2. The present data provide the first detailed mapping of the hcrt neuronal system in the CNS of a nonmammalian vertebrate. The occurrence of hcrt-containing cell bodies in the hypothalamus and the widespread distribution of hcrt-immunoreactive fibers throughout the brain and spinal cord suggest that, in amphibians, hcrts may exert neuroendocrine, neurotransmitter, and/or neuromodulator activities.

The origin and function of the pituitary adenylate cyclase-activating polypeptide (PACAP)/glucagon superfamily

The pituitary adenylate cyclase-activating polypeptide (PACAP)/ glucagon superfamily includes nine hormones in humans that are related by structure, distribution (especially the brain and gut), function (often by activation of cAMP), and receptors (a subset of seven-transmembrane receptors). The nine hormones include glucagon, glucagon-like peptide-1 (GLP-1), GLP-2, glucose-dependent insulinotropic polypeptide (GIP), GH-releasing hormone (GRF), peptide histidine-methionine (PHM), PACAP, secretin, and vasoactive intestinal polypeptide (VIP). The origin of the ancestral superfamily members is at least as old as the invertebrates; the most ancient and tightly conserved members are PACAP and glucagon. Evidence to date suggests the superfamily began with a gene or exon duplication and then continued to diverge with some gene duplications in vertebrates. The function of PACAP is considered in detail because it is newly (1989) discovered; it is tightly conserved (96% over 700 million years); and it is probably the ancestral molecule. The diverse functions of PACAP include regulation of proliferation, differentiation, and apoptosis in some cell populations. In addition, PACAP regulates metabolism and the cardiovascular, endocrine, and immune systems, although the physiological event(s) that coordinates PACAP responses remains to be identified.

Pituitary adenylate cyclase-activating polypeptide innervation of the mudpuppy cardiac ganglion

The presence and potential origin of the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) was determined in cardiac ganglia of the mudpuppy, Necturus maculosus. Although PACAP has been implicated in the regulation of cardiac function in several mammalian species, the presence of this peptide in the autonomic nervous system (ANS) of other species is unclear. Thus, this study is the first to characterize this highly conserved peptide in the ANS of a non-mammalian species. PACAP-immunoreactivity was observed in nerve fibers throughout the mudpuppy cardiac ganglia and often was co-localized with the sensory neuropeptides substance P and calcitonin gene-related peptide. Removal of all extrinsic inputs to the ganglia by organ culture eliminated PACAP-immunoreactivity in the cardiac ganglia, whereas bilateral vagotomies only partially reduced PACAP-labeling. PACAP-immunoreactive neurons were observed in both high thoracic dorsal root ganglia and in vagal sensory ganglia. While no PACAP-positive neurons were observed in caudal medulla brainstem regions, PACAP-containing nerve fibers were found in the region of the nucleus solitarius. These results suggest that, in the mudpuppy, PACAP is found primarily in visceral afferent fibers, originating from cells in either the dorsal root ganglia or vagal sensory ganglia. Based on their anatomic localization, these afferent fibers may function to transmit important sensory information to cardiovascular centers in the brain as well as serving as local reflex inputs to modulate postganglionic parasympathetic output within the cardiac ganglion itself.

Chemoarchitecture of the anuran auditory midbrain

The anuran torus semicircularis consists of several subnuclei that are part of the ascending auditory pathway as well as audiomotor interface structures. Additionally, recent anatomical studies suggest that the midbrain tegmentum is an integral part of the audiomotor network. To describe the chemoarchitecture of these nuclei, taking into account the toral subdivisions, we investigated the distribution of serotonin, leucine-enkephalin, substance P, tyrosine-hydroxylase, dopamine D2-receptor, parvalbumin, aspartate, GABA, and estrogen-binding protein-immunoreactivity in the midbrain of Bombina orientalis, Discoglossus pictus and Xenopus laevis. In the torus semicircularis, the highest density of immunoreactive fibers and terminals for all transmitters was found in the laminar nucleus. Parvalbumin-like immunoreactivity was highest in the principal nucleus, and D2-receptor-like immunoreactivity was uniformly distributed throughout the torus. In the tegmentum, axons and/or dendrites were stained with all antibodies except estrogen-binding protein. Additionally, heavily stained enkephalin and substance P-immunopositive fiber plexus were found in the lateral and dorsal tegmentum. The immunostainings revealed no qualitative differences between the three species. Immunopositive cell bodies were labeled in several brain areas, the connectivity of which with torus and tegmentum is discussed on the background of functional questions. The putative neuromodulatory innervation of both the laminar nucleus of the torus semicircularis and the tegmentum may be the anatomical basis for the influence of the animal's endogenous state on the behavioral reaction to sensory stimuli. These data corroborate earlier anatomical and physiological findings that the neurons of these nuclei are key elements in the audio-motor interface.

Molecular cloning of growth hormone-releasing hormone/pituitary adenylyl cyclase-activating polypeptide in the frog Xenopus laevis: brain distribution and regulation after castration

Pituitary adenylyl cyclase-activating peptide (PACAP) appears to regulate several neuroendocrine functions in the frog, but its messenger RNA (mRNA) structure and brain distribution are unknown. To understand the potential role of PACAP in the male frog hypothalamic-pituitary-gonadal axis, we cloned the frog Xenopus laevis PACAP mRNA and determined its distribution in the brain. We then analyzed the castration-induced alterations of mRNA expression for PACAP and its selective type I receptor (PAC1) in the hypothalamic anterior preoptic area, a region known to regulate reproductive function. The PACAP mRNA encodes a peptide precursor predicted to give rise to both GH-releasing hormone and PACAP. The deduced peptide sequence of PACAP-38 was nearly identical to that of human PACAP with one amino acid substitution. Abundant PACAP mRNA was detected in the brain, but not several other tissues, including the testis. In situ hybridization revealed strong expression of the PACAP gene in the dorsal pallium, ventral hypothalamus, and nuclei of cerebellum. PACAP mRNA signals were weak to moderate in the hypothalamic anterior preoptic area and were absent in the pituitary. Castration induced an increase in the expression of PACAP and PAC1 receptor mRNAs in the hypothalamic anterior preoptic area after 3 days. Replacement with testosterone prevented the castration-induced changes. These results provide a molecular basis for studying the physiological functions of PACAP in frog brain and suggest that PACAP may be involved in the feedback regulation of hypothalamic-pituitary-gonadal axis.

Structure and distribution of the mRNAs encoding pituitary adenylate cyclase-activating polypeptide and growth hormone-releasing hormone-like peptide in the frog, Rana ridibunda

The structure of the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) has been characterized in several species including protochordates, fish, amphibians, birds, and mammals. Although PACAP has been shown to stimulate frog pituitary and adrenal cell activity, the structure of the PACAP precursor and the expression of its gene have not yet been reported in any amphibian species. In this study, we have characterized two cDNA variants encoding PACAP of the frog Rana ridibunda, one of which encodes a second peptide exhibiting strong homologies to growth hormone-releasing hormone (GHRH) of fish and mammals. Northern blot and reverse transcriptase-polymerase chain reaction (RT-PCR) analyses revealed that PACAP/GHRH-like peptide mRNAs are predominantly expressed in the brain and spinal cord and, to a lesser extent, in the neurointermediate lobe of the pituitary. Other tissues including the testis and the distal lobe of the pituitary do not express the PACAP precursor gene. The distribution of PACAP/GHRH-like peptide mRNAs in the frog brain has been determined by in situ hybridization histochemistry. High levels of expression were found in the accessory olfactory bulb, the distal pallium, the ventral part of the magnocellular preoptic nucleus, the ventral hypothalamic nucleus, the posterior tuberculum, and the ventral habenular nucleus. These data contribute to the understanding of the evolution of the PACAP and GHRH genes in vertebrates and provide the anatomical bases to elucidate the roles of PACAP and the GHRH-like peptide in amphibians.

Characterization and localization of pituitary adenylate cyclase-activating polypeptide (PACAP) binding sites in the brain of the frog Rana ridibunda

The biochemical characteristics and the distribution of pituitary adenylate cyclase-activating polypeptide (PACAP) binding sites have been investigated in the brain of the frog Rana ridibunda by using [(125)I]PACAP27 as a radioligand. Membrane-binding studies revealed the existence of high-affinity receptors for frog PACAP38 and PACAP27. In contrast, the [Des-His(1)]PACAP38 analogue had a much lower affinity and vasoactive intestinal polypeptide did not produce any displacement of the binding. Autoradiographic labeling of frozen brain sections revealed that the highest concentrations of PACAP receptors were located in the olfactory bulb, pallium, striatum, habenular nuclei, ventromedial thalamic nucleus, corpus geniculatum, posterior tubercle, dorsal part of the magnocellular preoptic nucleus, tectum, and the molecular cell layer of the cerebellum. Moderate binding was observed in the septum, in most parts of the thalamus, the dorsal hypothalamic nucleus, the median eminence, the ventral nuclei of the tegmentum, the torus semicircularis, and the interpeduncular and isthmi nuclei. The present data provide the first biochemical characterization and anatomic distribution of PACAP binding sites in the brain of a nonmammalian vertebrate species. The widespread distribution of specific PACAP receptors in the frog brain suggests that the peptide does not act solely as a hypophysiotropic factor, but likely fulfills neurotransmitter functions, neuromodulator functions, or both.

Molecular cloning and expression of a chicken pituitary adenylate cyclase-activating polypeptide receptor

Although, since the isolation of pituitary adenylate cyclase-activating polypeptide (PACAP), a wealth of literature has been published describing its localization, binding sites, and biological activities in a variety of mammalian tissues, only very little is known about PACAP in avian species. Therefore, in order to find out the sites of actions of PACAP and to elucidate its physiological significance in birds, we identified a chicken PACAP receptor homologue of the mammalian type I receptors (PAC(1)-Rs). The chicken PACAP type I cDNA sequence was obtained using reverse transcriptase-polymerase chain reaction (RT-PCR) in combination with 3'- and 5'-RACE PCR. This cDNA encodes a 471 amino acid precursor protein, sharing 81-83% sequence identity with mammalian analogs and 76% amino acid identity with the goldfish type I PACAP receptor. Northern blot analysis of chicken brain poly(A)(+)-rich RNA revealed the presence of a 5.5 kb and 7.5 kb PAC(1) receptor transcript. RT-PCR revealed that the chicken PACAP receptor is mainly expressed in the brain and gonads. A smaller amount of the receptor mRNA was found in pituitary, adrenal gland, kidney, intestine, pancreas, lung, and heart tissue. In situ hybridization with specific antisense oligodeoxynucleotide probes showed a widespread distribution of PAC(1) receptor mRNA in the chicken brain, with the highest expression being found in the dorsal telencephalon, olfactory bulb, hypothalamus, optic tectum, and cerebellar cortex. These findings suggest that PACAP affect a variety of functions both in the brain and peripheral tissues of the chicken.

Pituitary adenylate cyclase-activating polypeptide receptors during development: expression in the rat embryo at primitive streak stage

The distribution and localization of the pituitary adenylate cyclase-activating polypeptide (PACAP) receptor the PAC1 receptor (previously called the type 1 PACAP receptor or PVR1), which binds PACAP, but not vasoactive intestinal peptide, with high affinity] were first investigated in rats with in situ hybridization for its messenger RNA, and with immunohistochemical methods during prenatal and postnatal development. The expression of PACAP receptor messenger RNA was first detected in the rat embryo at the primitive streak stage as early as embryonic day 9, and it was intensely expressed in the neural plate. PACAP receptor messenger RNA was also intensely expressed in the neuroepithelia of the mesencephalon and rhombencephalon at embryonic day 11, and expressed in the basal telencephalon, hippocampal formation neuroepithelium, cortical neuroepithelium and cerebellar neuroepithelium after embryonic day 13. It was also expressed in the olfactory bulb neuroepithelium after embryonic day 16, and in mature regions of the older embryos. In postnatal developing brains, PACAP receptor messenger RNA was intensely expressed in the olfactory bulb, hippocampal formation, cerebellum and other scattered regions. The localization of PACAP receptor-like immunoreactivity coincided well with that of the gene transcripts. We also used reverse transcription-polymerase chain reaction methods to determine the expression of the splice variants of the PACAP receptor gene. At each ontogenetic stage of the rat from embryonic day 9 to postnatal day 60, two major products were detected with reverse transcription-polymerase chain reaction, a thick band (303 base pairs) corresponding to the short splice variant of the receptor that lacks both the "hip" and "hop" cassettes, and a thin band (387 base pairs) corresponding to the splice variant that contains one cassette of "hop" or "hip". There was no evidence for the other larger splice variants. Some of the amplified products were sequenced and found to have the exact sequences of "PACAP receptor" and "PACAP receptor-hopl", which are coupled to different signal transduction pathways. These results indicate that the PACAP receptor is actively expressed in different neuroepithelia from early developmental stages and expressed in various brain regions during prenatal and postnatal development, and that the major splice variants are "PACAP receptor" and "PACAP receptor-hopl". The initial mapping of ontogenetic localization of the PACAP receptor provides the basis for a better understanding of the functions of PACAP and its receptors during the development of the brain.

Characterization of the cDNA encoding the prohormone convertase PC2 and localization of the mRNA in the brain of the frog Rana ridibunda

A number of precursors for neuropeptides have recently been cloned in amphibians, but little is known concerning the endoproteases responsible for the processing of these precursors. Here we report on the molecular cloning of the cDNA encoding the proprotein convertase PC2 and the distribution of the corresponding mRNA in the European green frog Rana ridibunda. The full cDNA structure (2125 bp) was obtained from the analysis of the PCR products combined with the sequence from a clone isolated from a frog pituitary cDNA library. The deduced amino acid sequence revealed that frog PC2 comprises 636 amino acid residues including a 22-residue signal peptide. RT-PCR analysis showed that PC2 is expressed not only in the brain and pituitary but also in various peripheral organs including the pancreas, stomach, intestine, liver, kidney and testis. In situ hybridization histochemistry revealed that, in the central nervous system, PC2 mRNA is widely distributed, the highest concentrations being found in the pallium, the anterior preoptic area, the hypothalamus and the medial amygdala. High levels of PC2 mRNA were also detected in the intermediate lobe of the pituitary. The overall distribution of PC2 mRNA in the frog brain is consistent with its involvement in the processing of a number of neuropeptide and hormone precursors.

Perspectives on pituitary adenylate cyclase activating polypeptide (PACAP) in the neuroendocrine, endocrine, and nervous systems

PACAP is a pleiotropic neuropeptide that belongs to the secretin/glucagon/VIP family. PACAP functions as a hypothalamic hormone, neurotransmitter, neuromodulator, vasodilator, and neurotrophic factor. Its structure has been remarkably conserved during evolution. The PACAP receptor is G protein-coupled with seven transmembrane domains and also belongs to the VIP receptor family. PACAP, but not VIP, binds to PAC1-R, whereas PACAP and VIP bind to VPAC1-R and VPAC2-R with a similar affinity. Despite the sizable homology of the structures of PACAP and VIP and their receptors, the distribution of these peptides and receptors is quite different. At least eight subtypes of PACAP specific, or PAC1-R, result from alternate splicing. Each subtype is coupled with specific signaling pathways, and its expression is tissue or cell specific. Although PACAP fulfills most requirements for a physiological hypothalamic hypophysiotropic hormone, it does not consistently stimulate secretion of the adenohypophysial hormones, except for stimulation of IL-6 release from the FS cells of the pituitary. The major regulatory role of PACAP in pituitary cells appears to be the regulation of gene expression of pituitary hormones and/or regulatory proteins that control growth and differentiation of the pituitary glandular cells. These effects appear to be exhibited directly and indirectly through a paracrine or autocrine action. Although PACAP stimulates the release of AVP, the physiological role of neurohypophysial PACAP remains unknown. One important action of PACAP in the endocrine system is its role as a potent secretagogue for adrenaline from the adrenal medulla through activation of TH. PACAP also stimulates the release of insulin and increases [Ca2+]i from pancreatic beta-cells at an extremely small concentration. The stage-specific expression of PACAP in testicular germ cells during spermatogenesis suggests its regulatory role in the maturation of germ cells. In the ovary, PACAP is transiently expressed in the granulosa cells of the preovulatory follicles and appears to be involved in the LH-induced cellular events in the ovary, including prevention of follicular apoptosis. In the central nervous system, PACAP acts as a neurotransmitter or neuromodulator, which has been supported by IHC and electrophysiological methods. More important, PACAP is a neurotrophic factor that may play an important role during the development of the brain. In the adult brain, PACAP appears to function as a neuroprotective factor that attenuates the neuronal damage resulting from various insults.

Distribution, characterization, and growth hormone-releasing activity of pituitary adenylate cyclase-activating polypeptide in the European eel, Anguilla anguilla

The complementary DNA encoding pituitary adenylate cyclase-activating polypeptide (PACAP) has been cloned from two species of teleost fishes, the Sockeye salmon and the Thai catfish, and the amino acid sequence of PACAP has been determined in another teleost, the stargazer. However, to date, the detailed distribution of PACAP immunoreactivity has never been investigated in the fish brain. In the present study, we have determined the localization of PACAP-immunoreactive neurons in the central nervous system of a primitive teleost fish, the European eel Anguilla anguilla, using an antiserum raised against PACAP27. PACAP-positive perikarya were exclusively observed in the diencephalon, i.e. in the preoptic nucleus of the hypothalamus and in the dorsal and ventral nuclei of the thalamus. PACAP-immunoreactive fibers were detected in various areas of the brain, notably in the ventral telencephalon, the diencephalon, the mesencephalon, the cerebellar valvula, and the medulla oblongata. In addition, a dense accumulation of PACAP-containing nerve terminals was found in the pars distalis of the pituitary. The PACAP-like immunoreactivity contained in the eel brain was characterized by HPLC analysis combined with RIA quantification. The major form of PACAP-immunoreactive material coeluted with mammalian PACAP38. Molecular cloning of the PACAP precursor has previously shown that in fish, PACAP and GH-releasing hormone (GHRH) originate from the same precursor. We have thus investigated the effects of PACAP and GHRH on GH secretion from eel pituitary cells in primary culture. Dose-response experiments revealed that PACAP27 and PACAP38 possessed the same efficacy, but PACAP38 was 12 times more potent than PACAP27 in stimulating GH release (ED50 = 4.3 x 10(-10) and 3.5 x 10(-9) M, respectively). In contrast, GHRH, even at a high concentration (10(-6) M), had no effect on GH release. Taken together, these data indicate that in the eel, PACAP may play a significant role in the regulation of somatotrope cells: 1) PACAP-immunoreactive neurons are exclusively located in the diencephalon and send numerous projections in the pars distalis; and 2) PACAP, but not GHRH, dose dependently stimulates GH secretion from cultured eel pituitary cells.

The localization of pituitary adenylate cyclase-activating polypeptide (PACAP)-like immunoreactivity in the hypothalamo-pituitary region of an elasmobranch, stingray, Dasyatis akajei

Pituitary adenylate cyclase activating polypeptide (PACAP), a member of the secretin/glucagon/vasoactive intestinal polypeptide family of peptides, exists as 38-residue (PACAP 38) and truncated 27-residue (PACAP 27) forms, which play various roles in mammals. Recently, we isolated and characterized PACAPs with sequences very similar to that of tetrapod PACAP from the brains of two teleosts, the blue-spotted stargazer Gnathagnus elongatus and the stargazer Uranoscopus japonicus, and located PACAP-like immunoreactivities in the preoptic area, neurohypophysis and medulla oblongata of both species. In this study, PACAP-like immunoreactivity in the brain of an elasmobranch, the stingray Dasyatis akajei, was examined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) and Western blotting analysis and its distribution in the hypothalamo-pituitary region was studied immunohistochemically using the peroxidase-antiperoxidase method. The anti-PACAP 27 serum reacted with a single band of whole brain extract with a molecular weight of ca 5000. PACAP-like immunoreactive (LI) neuronal cell bodies were found in the nucleus medius hypothalami and PACAP-LI nerve fibers and terminals were seen from the nucleus to the caudal floor of the infundibular region. These results suggest that PACAP-like peptide may be present and function as a regulatory factor in the hypothalamo-pituitary region of the elasmobranch brain.

Purification and primary structure of pituitary adenylate cyclase activating polypeptide (PACAP) from the brain of an elasmobranch, stingray, Dasyatis akajei

Pituitary adenylate cyclase activating polypeptide (PACAP) was isolated from ovine hypothalami and found to exist as two amidated forms with 38 (PACAP 38) and 27 (PACAP 27) residues. The amino acid sequences of PACAPs isolated from the vertebrates, such as a bird, a frog and teleost fish, appear to be well conserved. In the present study, we attempted to isolate PACAP from the brain of an elasmobranch fish, Dasyatis akajei (stingray), which belongs to the Chondrichthyes (cartilaginous fish), by extraction of the acetone-dried powder with acetic acid, followed by successive high-performance liquid chromatography (HPLC) on a gel-filtration, a cation-exchange and two reverse-phase columns. Purification was monitored by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) and Western blotting analysis using an anti-PACAP 27 serum. The PACAP thus obtained consisted of 44 residues. The amino acid sequence of the comparable portion of its N-terminal 38 residues showed 92%, 89%, 89%, and 82% identity with those of mammalian, chicken, frog and teleost PACAPs with 38 residues, respectively. The extra six C-terminal residues of the stingray resembled those of tetrapod and teleost PACAP precursors which were deduced from the respective cDNAs. These results indicate that PACAP, which has an amino acid sequence showing high similarity with those of tetrapod and teleost PACAPs, is present in the elasmobranch brain.

Role of VIP, PACAP, and related peptides in the regulation of the hypothalamo-pituitary-adrenal axis

Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are members of a family of regulatory peptides that are widely distributed in the body and share numerous biologic actions. The two peptides display a remarkable amino acid-sequence homology, and bind to a class of G protein-coupled receptors, named PACAP/VIP receptors (PVRs), whose signaling mechanism mainly involves the activation of adenylate-cyclase and phospholipase-C cascades. A large body of evidence suggests that VIP and PACAP play a role in the control of the hypothalamo--pituitary-adrenal (HPA) axis, almost exclusively acting in a paracrine manner, since their blood concentration is very low. VIP and PACAP are contained in both nerve fibers and neurons of the hypothalamus, and VIP, but not PACAP, is also synthesized in the pituitary gland. Both peptides are expressed in the adrenal gland, and especially in medullary chromaffin cells. All the components of the HPA axis are provided with PVRs. VIP and PACAP enhance pituitary ACTH secretion, VIP by eliciting the hypothalamic release of CRH and potentiating its secretagogue action, and PACAP by directly stimulating pituitary corticotropes. Through this central mechanism, VIP and PACAP may increase mineralo- and glucocorticoid secretion of the adrenal cortex. VIP but not PACAP also exerts a weak direct secretagogue action on adrenocortical cells by activating both PVRs and probably a subtype of ACTH receptors. VIP and PACAP raise aldosterone production via a paracrine indirect mechanism involving the stimulation of medullary chromaffin cells to release catecholamines, which in turn enhance the secretion of zona glomerulosa cells via a beta-adrenoceptor-mediated mechanism. PACAP appears to be able to evoke a glucocorticoid response through the activation, at least in the rat, of the intramedullary CRH/ACTH system. The relevance of these effects of VIP and PACAP under basal conditions is questionable, although there are indications that endogenous VIP is involved in the maintenance of the normal growth and steroidogenic capacity of rat adrenal cortex. However, indirect evidence suggests that these peptides might play a relevant role under paraphysiological conditions (e.g., in the mediation of HPA axis responses to cold and inflammatory stresses) or may be somehow involved in the pathogenesis of Cushing disease or some case of hyperaldosteronism associated with secreting pheochromocytomas.

Specific antibody recognition of rat pituitary adenylate cyclase activating polypeptide receptors

Pituitary adenylate cyclase activating polypeptide (PACAP) is a new member of the secretin/VIP family of peptides. The specific receptor for PACAP has been cloned in rat, human, and bovine tissues. The distribution of the transcripts of PACAP receptor genes has been studied in various tissues using in situ hybridization. However, the unavailability of a specific antibody against the PACAP receptor has hampered further study of the expression of receptor proteins. In the present study, rabbit antisera were generated against a synthetic 25-residue peptide corresponding to the C-terminal intracellular domain of the rat PACAP receptor. To validate the specificity of the antisera, CHO cells and cells stably transfected with rat PACAP receptor cDNA were prepared. Using one of these antisera, the membrane and soluble fractions of the transformants were examined by Western blot analysis. Three bands were observed in subcellular fractions from the transfected CHO cells, but no bands were found in similar preparations from the nontransfected cells. A distinct 57-kDa band, which corresponds to the size of cloned rat PACAP receptor, was detected. In addition, a less intense band, larger than 57 kDa, and a very weakly stained band, smaller than 57 kDa, were demonstrated. All of these bands disappeared or were considerably diminished when the antiserum was preabsorbed with the synthetic immunogen peptide. This suggests that these bands are PACAP receptor-related proteins. The membranes from the transfected CHO cells bound to [125I]PACAP27. The size of the ligand/protein crosslinked product approximated 60 kDa, corresponding to the combined size of the PACAP receptor and PACAP27. No additional bands were observed, indicating that the immunopositive proteins larger or smaller than 57 kDa do not bind to the ligand and are not functional. Unlabeled PACAP27 and PACAP38, but not VIP, displaced the binding, suggesting that the receptors expressed in CHO cells are specific for PACAP. Solubilized membrane fractions prepared from rat brains were used for an immunoprecipitation study with [125I]PACAP27 and [125I]VIP. The PACAP receptor antiserum recognized [125I]PACAP-, but not [125I]VIP-bound proteins in the solubilized brain membrane fractions. Immunohistochemistry using this antiserum showed a distribution of PACAP receptor-like immunoreactivities similar to the distribution of the mRNA of PACAP receptor in the rat brain. Thus, the PACAP receptor antiserum is sufficiently specific to be used as a tool for studying the expression of PACAP receptors and related proteins.

Isolation and structural characterization of pituitary adenylate cyclase activating polypeptide (PACAP)-like peptide from the brain of a teleost, stargazer, Uranoscopus japonicus

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a novel neuropeptide consisting of 38-residue (PACAP 1-38) and a truncated form with 27 residues (PACAP 1-27) that plays several roles in tetrapods. We isolated a highly purified PACAP-like peptide from the brain of a teleost, the stargazer, by extracting of acetone-dried powder with acetic acid followed by high-performance liquid chromatography (HPLC) on gel-filtration, cation-exchange, and reverse-phase columns. Purification was monitored by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting analysis using an anti-PACAP 1-27 antiserum. The PACAP-like peptide thus obtained had a molecular mass of 4,623, determined by mass spectrometry, and its amino acid sequence showed 89 and 87% identity with those of ovine and frog PACAPs, respectively. These results indicate that a PACAP-like peptide, which is a highly homologous with tetrapod PACAP, is present in the teleost brain.