Ontogeny of pituitary adenylate cyclase-activating polypeptide (PACAP) receptors in the rat cerebellum: a quantitative autoradiographic study

Long-term protective effect of PACAP in a fetal alcohol syndrome (FAS) model

Prenatal ethanol exposure provokes teratogenic effects, due to oxidative stress and massive neuronal apoptosis in the developing brain that result in lifelong behavioral abnormalities. PACAP exerts anti-oxidative and neuroprotective activities on neuronal cells, and prevents ethanol neurotoxicity. The present study focused on the ability of PACAP to protect the brain of 30-day-old mice (P30) from prenatal alcohol exposure induced oxidative damage and toxicity. Pregnant mice were divided randomly into 4 groups, i.e. control group, ethanol group (1.5 g/kg ip daily injection), PACAP group (5 μg intrauterine daily injection) and an ethanol plus PACAP group. Offspring prenatally exposed to ethanol had decreased body weight and reduced cell survival. Moreover, production of ROS was sharply enhanced in the brain of prenatal ethanol-exposed animals, associated with an elevation in the activity of the antioxidant enzymes, and an increase of oxidative damages as shown by the accumulation of the lipid oxidation marker malondialdehyde and of protein carbonyl compounds. Intrauterine administration of PACAP during the gestational period restored the endogenous antioxidant system, prevented ROS overproduction and promoted the survival of dissociated cells from animals prenatally exposed to ethanol. Behavioral tests revealed that P30 animals exposed to ethanol during the prenatal period exhibited reduced motor activity, altered exploratory interest and increased anxiety. However, PACAP treatment significantly attenuated these behavioral impairments. This study demonstrates that PACAP exerts a potent neuroprotective effect against alcohol toxicity during brain development, and indicates that PACAP and/or PACAP analogs might be a useful tool for treatment of alcohol intoxication during pregnancy.

Postnatal Migration of Cerebellar Interneurons

Due to its continuing development after birth, the cerebellum represents a unique model for studying the postnatal orchestration of interneuron migration. The combination of fluorescent labeling and ex/in vivo imaging revealed a cellular highway network within cerebellar cortical layers (the external granular layer, the molecular layer, the Purkinje cell layer, and the internal granular layer). During the first two postnatal weeks, saltatory movements, transient stop phases, cell-cell interaction/contact, and degradation of the extracellular matrix mark out the route of cerebellar interneurons, notably granule cells and basket/stellate cells, to their final location. In addition, cortical-layer specific regulatory factors such as neuropeptides (pituitary adenylate cyclase-activating polypeptide (PACAP), somatostatin) or proteins (tissue-type plasminogen activator (tPA), insulin growth factor-1 (IGF-1)) have been shown to inhibit or stimulate the migratory process of interneurons. These factors show further complexity because somatostatin, PACAP, or tPA have opposite or no effect on interneuron migration depending on which layer or cell type they act upon. External factors originating from environmental conditions (light stimuli, pollutants), nutrients or drug of abuse (alcohol) also alter normal cell migration, leading to cerebellar disorders.

Activation of PAC1 Receptors in Rat Cerebellar Granule Cells Stimulates Both Calcium Mobilization from Intracellular Stores and Calcium Influx through N-Type Calcium Channels

High concentrations of pituitary adenylate cyclase-activating polypeptide (PACAP) and a high density of PACAP binding sites have been detected in the developing rat cerebellum. In particular, PACAP receptors are actively expressed in immature granule cells, where they activate both adenylyl cyclase and phospholipase C. The aim of the present study was to investigate the ability of PACAP to induce calcium mobilization in cerebellar granule neurons. Administration of PACAP-induced a transient, rapid, and monophasic rise of the cytosolic calcium concentration ([Ca(2+)]i), while vasoactive intestinal peptide was devoid of effect, indicating the involvement of the PAC1 receptor in the Ca(2+) response. Preincubation of granule cells with the Ca(2+) ATPase inhibitor, thapsigargin, or the d-myo-inositol 1,4,5-trisphosphate (IP3) receptor antagonist, 2-aminoethoxydiphenyl borate, markedly reduced the stimulatory effect of PACAP on [Ca(2+)]i. Furthermore, addition of the calcium chelator, EGTA, or exposure of cells to the non-selective Ca(2+) channel blocker, NiCl2, significantly attenuated the PACAP-evoked [Ca(2+)]i increase. Preincubation of granule neurons with the N-type Ca(2+) channel blocker, ω-conotoxin GVIA, decreased the PACAP-induced [Ca(2+)]i response, whereas the L-type Ca(2+) channel blocker, nifedipine, and the P- and Q-type Ca(2+) channel blocker, ω-conotoxin MVIIC, had no effect. Altogether, these findings indicate that PACAP, acting through PAC1 receptors, provokes an increase in [Ca(2+)]i in granule neurons, which is mediated by both mobilization of calcium from IP3-sensitive intracellular stores and activation of N-type Ca(2+) channel. Some of the activities of PACAP on proliferation, survival, migration, and differentiation of cerebellar granule cells could thus be mediated, at least in part, through these intracellular and/or extracellular calcium fluxes.

Pharmacology and functions of receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide: IUPHAR review 1

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are members of a superfamily of structurally related peptide hormones that includes glucagon, glucagon-like peptides, secretin, gastric inhibitory peptide (GIP) and growth hormone-releasing hormone (GHRH). VIP and PACAP exert their actions through three GPCRs - PAC(1) , VPAC(1) and VPAC(2) - belonging to class B (also referred to as class II, or secretin receptor-like GPCRs). This family comprises receptors for all peptides structurally related to VIP and PACAP, and also receptors for parathyroid hormone, corticotropin-releasing factor, calcitonin and related peptides. PAC(1) receptors are selective for PACAP, whereas VPAC(1) and VPAC(2) respond to both VIP and PACAP with high affinity. VIP and PACAP play diverse and important roles in the CNS, with functions in the control of circadian rhythms, learning and memory, anxiety and responses to stress and brain injury. Recent genetic studies also implicate the VPAC(2) receptor in susceptibility to schizophrenia and the PAC(1) receptor in post-traumatic stress disorder. In the periphery, VIP and PACAP play important roles in the control of immunity and inflammation, the control of pancreatic insulin secretion, the release of catecholamines from the adrenal medulla and as co-transmitters in autonomic and sensory neurons. This article, written by members of the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR) subcommittee on receptors for VIP and PACAP, confirms the existing nomenclature for these receptors and reviews our current understanding of their structure, pharmacology and functions and their likely physiological roles in health and disease. More detailed information has been incorporated into newly revised pages in the IUPHAR database (http://www.iuphar-db.org/DATABASE/FamilyMenuForward?familyId=67).

Pituitary adenylate cyclase-activating polypeptide (PACAP)/PAC1HOP1 receptor activation coordinates multiple neurotrophic signaling pathways: Akt activation through phosphatidylinositol 3-kinase gamma and vesicle endocytosis for neuronal survival

MAPK and Akt pathways are predominant mediators of trophic signaling for many neuronal systems. Among the vasoactive intestinal peptide/secretin/glucagon family of related peptides, pituitary adenylate cyclase-activating polypeptide (PACAP) binding to specific PAC(1) receptor isoforms can engage multiple signaling pathways and promote neuroprotection through mechanisms that are not well understood. Using a primary sympathetic neuronal system, the current studies demonstrate that PACAP activation of PAC(1)HOP1 receptors engages both MAPK and Akt neurotrophic pathways in an integrated program to facilitate neuronal survival after growth factor withdrawal. PACAP not only stimulated prosurvival ERK1/2 and ERK5 activation but also abrogated SAPK/JNK and p38 MAPK signaling in parallel. In contrast to the potent and rapid effects of PACAP in ERK1/2 phosphorylation, PACAP stimulated Akt phosphorylation in a late phase of PAC(1)HOP1 receptor signaling. From inhibitor and immunoprecipitation analyses, the PACAP/PAC(1)HOP1 receptor-mediated Akt responses did not represent transactivation mechanisms but appeared to depend on G alpha(q)/phosphatidylinositol 3-kinase gamma activity and vesicular internalization pathways. Phosphatidylinositol 3-kinase gamma-selective inhibitors blocked PACAP-stimulated Akt phosphorylation in primary neuronal cultures and in PAC(1)HOP1-overexpressing cell lines; RNA interference-mediated knockdown of the receptor effectors attenuated PACAP-mediated Akt activation. Similarly, perturbation of endocytic pathways also blocked Akt phosphorylation. Between ERK and Akt pathways, PACAP-stimulated Akt signaling was the primary cascade that attenuated cultured neuron apoptosis after growth factor withdrawal. The partitioning of PACAP-mediated Akt signaling in endosomes may be a key mechanism contributing to the high spatial and temporal specificity in signal transduction necessary for survival pathways.

Changes in the expression of PACAP-like compounds during the embryonic development of the earthworm Eisenia fetida

Pituitary adenylate cyclase-activating polypeptide (PACAP) is expressed at very early stages in the vertebrate nervous system, and its functions in the embryonic development have been shown by various studies. PACAP is an extremely conserved molecule in phylogeny; however, little is known about its presence and functions in invertebrates. Our previous studies have shown the occurrence of PACAP-like immunoreactivity in the invertebrate nervous system. The aim of this study was to investigate the presence and localization of PACAP-like compounds during the embryonic development of earthworms from cocoon deposition to hatching using immunological methods (radioimmunoassay, dot blot, immunohistochemistry). PACAP-like immunoreactive compounds were detected at very early stages of the embryonic development of the earthworm Eisenia fetida. No significant changes were observed during the early stages in the developing embryo, but a marked increase occurred before hatching. In contrast, during the embryonic development, the level of PACAP-like compounds gradually decreased in cocoon fluids. Immunohistochemistry revealed the presence of PACAP-like immunoreactive cell bodies and processes in the developing body wall, prostomium, pharyngeal wall, and central nervous system. Cells located in the body wall correspond to putative progenitor cells of primary sensory cells. In the present study, we also showed that the clitellum (reproductive organ) of sexually mature worms contained significantly higher levels of PACAP-like immunoreactivity than other regions of the same animals or the clitellar region of a non-reproducing animal. In summary, these observations provide a morphological basis and suggest a role of PACAP(-like peptides) in the reproductive and developmental functions of invertebrates.

Inhibitory effect of PACAP on caspase activity in neuronal apoptosis: a better understanding towards therapeutic applications in neurodegenerative diseases

Programmed cell death, which is part of the normal development of the central nervous system, is also implicated in various neurodegenerative disorders. Cysteine-dependent aspartate-specific proteases (caspases) play a pivotal role in the cascade of events leading to apoptosis. Many factors that inhibit cell death have now been identified, but the underlying mechanisms are not fully understood. Pituitary adenylate cyclase-activating polypeptide (PACAP) has been shown to exert neurotrophic activities during development and to prevent neuronal apoptosis induced by various insults such as ischemia. Most of the neuroprotective effects of PACAP are mediated through the PAC1 receptor. This receptor activates a transduction cascade of second messengers to stimulate Bcl-2 expression, which inhibits cytochrome c release and blocks the activation of caspases. The inhibitory effect of PACAP on the apoptotic cascade suggests that selective, stable, and potent PACAP derivatives could potentially be of therapeutic value for the treatment of post-traumatic and/or chronic neurodegenerative processes.

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.

Neurotrophic effects of PACAP in the cerebellar cortex

In the rodent cerebellum, PACAP is expressed by Purkinje neurons and PAC1 receptors are present on granule cells during both the development period and in adulthood. Treatment of granule neurons with PACAP inhibits proliferation, slows migration, promotes survival and induces differentiation. PACAP also protects cerebellar granule cells against the deleterious effects of neurotoxic agents. Most of the neurotrophic effects of PACAP are mediated through the cAMP/PKA signaling pathway and often involve the ERK MAPkinase. Caspase-3 is one of the key enzymes implicated in the neuroprotective action of PACAP but PACAP also inhibits caspase-9 activity and increases Bcl-2 expression. PACAP and functional PAC1 receptors are expressed in the monkey and human cerebellar cortex with a pattern of expression very similar to that described in rodents, suggesting that PACAP could also exert neurodevelopmental and neuroprotective functions in the cerebellum of primates including human.

Molecular, cellular, and functional characterizations of pituitary adenylate cyclase-activating polypeptide and its receptors in the cerebellum of New and Old World monkeys

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) exerts trophic activities during cerebellar development, and a neuroprotective effect of PACAP has been demonstrated in pathological conditions such as stroke. However, all these data have been obtained in rodents, and neuroprotective effects of PACAP in primates remain unknown. Because of their evolutionary relationships with humans, monkeys represent powerful models for validating the therapeutic interest in PACAP. The objective of the present study was to characterize PACAP and its receptors in the cerebellum of two nonhuman primates. RT-PCR and in situ hybridization experiments revealed that PACAP is expressed in the cerebellum by Purkinje cells. Via immunohistochemistry, PACAP was detected in Purkinje cells and radial glial fibers. With regard to PACAP receptors, PAC1-R and VPAC1-R were detected by RT-PCR. In situ hybridization revealed a strong expression of PAC1-R and VPAC1-R in the granule cell layer (GCL), and VPAC1-R was also expressed in the Purkinje cell layer. A high density of PACAP binding sites was visualized in the GCL and the Purkinje cell layer. Competition studies indicated that, in the GCL, PACAP induced complete displacement of [(125)I]PACAP27 binding, whereas vasoactive intestinal polypeptide (VIP) was a weak competitor. In contrast, in the Purkinje cell layer, both PACAP and VIP displaced [(125)I]PACAP27 binding. Measurement of cAMP levels showed that PACAP is a powerful activator of adenylyl cyclase, whereas VIP is about 100-fold less potent. Altogether, these observations constitute the first demonstration of a functional PACAPergic system in monkey cerebellum. They strongly suggest that neuroprotective effects of PACAP can be transposed to primates, including human.

Altered cerebellar development in mice lacking pituitary adenylate cyclase-activating polypeptide

Previous studies have demonstrated that pituitary adenylate cyclase-activating polypeptide (PACAP) exerts trophic effects during neurodevelopment. In particular, the occurrence of PACAP and its receptors in the cerebellum during pre- and postnatal periods suggests that it could play a crucial role in ontogenesis of this structure. To test this hypothesis, we compared the histogenesis of cerebellar cortex in wild-type and PACAP-knockout (PACAP-/-) mice at postnatal days (P)4 and 7. Morphometric analysis of PACAP-/- mice revealed a significant reduction in the thickness of the external granule cell layer at P4 and of the internal granule cell layer at P7. Expression of nestin, a neural precursor marker, and synaptophysin, a mature neuronal marker, was quantified by real-time PCR and Western blot. No modification of nestin expression was noticed between wild-type and PACAP-/- mice, but a substantial decrease in synaptophysin expression was observed in PACAP-/- mice at P4 and P7. Immunohistochemistry revealed a reduction in synaptophysin labelling in the molecular and internal granule cell layers of PACAP-/- mice at P7. Caspase-3 activation was significantly increased in PACAP-/- mice at P4 and P7. Autoradiographic studies revealed no difference in PACAP binding site distributions and PACAP was effective at stimulating cAMP production in both wild-type and PACAP-/- cultured granule cells. This study demonstrates that disruption of the PACAP gene induces alteration of the immature cerebellum. Neuronal differentiation of granule cells was delayed whereas cell death that naturally occurs during ontogeny was increased in PACAP-/- mice. These data provide the first evidence of a physiological role for PACAP during cerebellar development.

The neuropeptide pituitary adenylate cyclase-activating polypeptide exerts anti-apoptotic and differentiating effects during neurogenesis: focus on cerebellar granule neurones and embryonic stem cells

Pituitary adenylate cyclase-activating polypeptide (PACAP) was originally isolated from ovine hypothalamus on the basis of its hypophysiotrophic activity. It has subsequently been shown that PACAP and its receptors are widely distributed in the central nervous system of adult mammals, indicating that PACAP may act as a neurotransmitter and/or neuromodulator. It has also been found that PACAP and its receptors are expressed in germinative neuroepithelia, suggesting that PACAP could be involved in neurogenesis. There is now compelling evidence that PACAP exerts neurotrophic activities in the developing cerebellum and in embryonic stem (ES) cells. In particular, the presence of PACAP receptors has been demonstrated in the granule layer of the immature cerebellar cortex, and PACAP has been shown to promote survival, inhibit migration and activate neurite outgrowth of granule cell precursors. In cerebellar neuroblasts, PACAP is a potent inhibitor of the mitochondrial apoptotic pathway through activation of the MAPkinase extracellular regulated kinase. ES cells and embryoid bodies (EB) also express PACAP receptors and PACAP facilitates neuronal orientation and induces the appearance of an electrophysiological activity. Taken together, the anti-apoptotic and pro-differentiating effects of PACAP characterised in cerebellar neuroblasts as well as ES and EB cells indicate that PACAP acts not only as a neurohormone and a neurotransmitter, but also as a growth factor.

Cerebellar cortical-layer-specific control of neuronal migration by pituitary adenylate cyclase-activating polypeptide

Migration of immature neurons is essential for forming the cortical layers and nuclei. Impairment of migration results in aberrant neuronal cytoarchitecture, which leads to various neurological disorders. Neurons alter the mode, tempo and rate of migration when they translocate through different cortical layers, but little is known about the mechanisms underlying this process. Here we show that endogenous pituitary adenylate cyclase-activating polypeptide (PACAP) has short-term and cortical-layer-specific effects on granule cell migration in the early postnatal mouse cerebellum. Application of exogenous PACAP significantly slowed the migration of isolated granule cells and shortened the leading process in the microexplant cultures of the postnatal day (P)0-3 cerebella. Interestingly, in the cerebellar slices of P10 mice, application of exogenous PACAP significantly inhibited granule cell migration in the external granular layer (EGL) and molecular layer (ML), but failed to alter the movement in the Purkinje cell layer (PCL) and internal granular layer (IGL). In contrast, application of PACAP antagonist accelerated granule cell migration in the PCL, but did not change the movement in the EGL, ML and IGL. Inhibition of the cAMP signaling and the activity of phospholipase C significantly reduced the effects of exogenous PACAP on granule cell migration. The PACAP action on granule cell migration was transient, and lasted for approximately 2 h. The duration of PACAP action on granule cell migration was determined by the desensitization of its receptors and prolonged by inhibiting the protein kinase C. Endogenous PACAP was present sporadically in the bottom of the ML, intensively in the PCL, and throughout the IGL. Collectively, these results indicated that PACAP acts on granule cell migration as "a brake (stop signal) for cell movement." Furthermore, these results suggest that endogenous PACAP slows granule cell migration when the cells enter the PACAP-rich PCL, and 2 h later the desensitization of PACAP receptors allows the cells to accelerate the rate of migration and to actively move within the PACAP-rich IGL. Therefore, endogenous PACAP may provide a cue that regulates granule cell migration in a cerebellar cortical-layer-specific manner.

Ontogeny of PACAP receptors in the human cerebellum: Perspectives of therapeutic applications

It is now well established that pituitary adenylate cyclase-activating polypeptide (PACAP) exerts anti-apoptotic and pro-differentiating actions during development of the rodent cerebellum. Cell signaling involved in the neurotrophic effects of PACAP has been precisely investigated. In particular, PACAP is a potent inhibitor of the mitochondrial apoptotic pathway through an ERK- and PKA-dependent mechanism. However, transposition of the neurodevelopmental activities of PACAP to the human cerebellum remains speculative, essentially because of the lack of data concerning the PACAP-ergic system. The present review is based on recent results that provide the first molecular, pharmacological and anatomical characterizations of PACAP receptors in the developing human cerebellum. It is now clearly established that the distribution pattern of PAC1-R and VPAC1-R mRNA in the human cerebellum is very similar to that already described in rodents. [(125)I]PACAP27 binding sites are closely associated with germinative neuroepithelia in fetal stages and with mature granule cells in infants and adults. Pharmacological characterization revealed that, in fetuses, PACAP binding sites exhibit a PAC1-R profile while, in adult patients, they correspond to a heterogeneous population of PAC1-R and VPAC(1/2)-R. Altogether, these data provide the first evidence that PACAP may exert neurodevelopmental functions in the human cerebellum.

Localization and characterization of pituitary adenylate cyclase-activating polypeptide receptors in the human cerebellum during development

Pituitary adenylate cyclase-activating polypeptide (PACAP) receptors are actively expressed in the cortical layers of the cerebellum of rodents and contribute to cerebellar development. The present report provides the first anatomical localization and characterization of PACAP receptors in the developing human cerebellum. RT-PCR analysis from 15-week-old fetuses to 22-year-old subject showed that PAC1-R and VPAC1-R are expressed in the cerebellum at all stages, whereas VPAC2-R mRNA was barely detectable. In situ hybridization labeling indicated that, in human fetuses, PAC1-R mRNA is associated with the external granule cell layer (EGL), a germinative neuroepithelium, and with the internal granule cell layer (IGL). The distribution pattern of VPAC1-R mRNA was very similar to that of PAC1-R mRNA, whereas VPAC2-R mRNA was visualized only in 7-22-year-old subjects. The localization of [(125)I]PACAP27 binding sites was fully consistent with the distribution of PAC1-R and VPAC1-R mRNA. Pharmacological characterization revealed that, in the EGL and IGL from 15-24-week-old fetuses and in the granule cell layer from 7-22-year-old patients, binding sites exhibit a PAC1-R profile. In contrast, PACAP binding sites observed in the molecular layer and medulla of the adult cerebellum consisted of a heterogeneous population of PAC1-R and VPAC(1/2)-R. Altogether, these data provide the first evidence that PACAP receptors are expressed in the human cerebellar cortex. PAC1-R is the predominant PACAP receptor found in fetuses, and both PAC1-R and VPAC1-R are expressed in the mature cerebellum. These observations suggest that PACAP has neurodevelopmental functions in the human cerebellum.

Induction of galanin receptor-1 (GalR1) expression in external granule cell layer of post-natal mouse cerebellum

Galanin is a modulator of fast transmission in adult brain and recent evidence suggests that it also acts as a trophic factor during neurogenesis and neural injury and repair. Previous studies in our laboratory have identified galanin mRNA in Purkinje cells of adult and developing rat (but not adult mouse) cerebellum; and galanin-binding sites in adult mouse (but not rat) cerebellum. The post-natal development of the cerebellum provides a unique and convenient model for the investigation of developmental processes and to learn more about putative cerebellar galanin systems, the current study examined the presence and distribution of galanin-like-immunoreactivity (- LI), [(125)I]-galanin binding sites and galanin receptor-1 (GalR1) mRNA in post-natal mouse cerebellum. Using autoradiography and in situ hybridization, [(125)I]-galanin binding sites and GalR1 mRNA were first detected on post-natal day 10 (P10) in the external germinal layer of all lobes and high levels were maintained until P14. Quantitative real-time PCR assays detected GalR1 mRNA in whole cerebellum across the post-natal period, with a strong induction and peak of expression at P10. Assessment of galanin levels in whole cerebellum by radioimmunoassay revealed relatively similar concentrations from P5 to P20 and in adult mice (80-170 pg/mg protein), with a significantly higher concentration (250 pg/mg, p < 0.01) detected at P3. These concentrations were some four- to six-fold lower than those in adult forebrain samples. Using immunohistochemistry, galanin-like-immuno-reactivity was observed in prominent fibrous elements within the white matter tracts of the cerebellum at P3-5 and in more punctate elements in the internal granule cell layer and associated with the Purkinje cell layer at P12 and P20. Increased levels of GalR1 mRNA and galanin binding (attributed to GalR1) in the external granule cell layer at P10-12/(14) coincide with granule cell migration from the external to the inner granule cell layer and together with demonstrated effects of other neuropeptide-receptor systems suggest a role for GalR1 signalling in regulating this or related developmental processes.

Effects of in ovo treatment with PACAP antagonist on general activity, motor and social behavior of chickens

Pituitary adenylate cyclase activating polypeptide (PACAP) has been shown to influence nervous system development. The aim of the present study was to investigate the effects of in ovo treatment with the PACAP antagonist PACAP6-38 during embryonic life (E8 and E16) on motor activity and social behavior in chicken. Our results showed that a single injection of PACAP6-38 during the first half of embryonic life caused subtle transient changes in general behavior and motor control when compared to saline-treated controls. Increased activity and reduced anxiety were observed also in a novel environment at 2 days after hatching. However, most of these behavioral differences disappeared by 2 weeks. PACAP6-38-treatment during the first half of embryonic life resulted in markedly reduced social behavior, which was still present at 2 weeks of age. Treatment during the second half of embryonic life resulted in no behavioral differences between control and PACAP6-38-treated chicken. PACAP content in different brain areas was not different between control and PACAP6-38-treated chicken at 5 days or 3 weeks of age, but it decreased significantly with age in both groups. In summary, our results show that PACAP6-38 treatment at E8 caused transient changes in motor behavior, and long-lasting reduction in social behavior.

Developmental expression, alternative splicing and gene copy number for the pituitary adenylate cyclase-activating polypeptide (PACAP) and growth hormone-releasing hormone (GRF) gene in rainbow trout

Both growth hormone-releasing hormone (GRF) and pituitary adenylate cyclase-activating polypeptide (PACAP) are encoded on the same gene in fish, but not in mammals. Our objective was to examine the onset and pattern of expression for the grf/pacap gene and to determine whether there is more than one gene in rainbow trout. The results show that grf/pacap mRNA is first expressed at 4 days after fertilization and continues through to hatching. Alternative splicing at all developmental stages produces a full-length transcript and one lacking exon four, which encodes GRF. Thus, independent regulation of the hormones occurs throughout development. Southern analysis shows that two grf/pacap genes exist in trout, but only one gene is responsible for the two identified transcripts. Overexpression of the grf/pacap gene in transgenic fish was attempted, but did not succeed. We conclude that the early and continued expression of grf/pacap mRNA in trout embryos and regulation of the neuropeptide ratio suggests they have a role in early brain development apart from their later role in releasing pituitary hormones.

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.

PACAP acts as a neurotrophic factor during histogenesis of the rat cerebellar cortex

During development of the rat cerebellum, PAC1 receptors are transiently expressed by neuroblasts of the external granule cell layer (EGL). We have previously shown that PACAP is a potent stimulator of granule cell survival in vitro. In the study reported in this paper, we have investigated the effect of PACAP on the development of the rat cerebellar cortex in vivo. PACAP induces a transient increase in the volume of the cerebellar cortex, with a maximum effect at postnatal day 12, which can be accounted for by an increase in the number of granule cells in the EGL, the molecular layer, and the internal granule cell layer (IGL). The effect of PACAP on the number of granule cells is blocked by the antagonist PACAP(6-38), which, by itself, produces a slight inhibition of the number of granule cells in the IGL. These data indicate that PACAP activates proliferation and/or inhibits programmed cell death of granule cells in the developing rat cerebellum. PACAP also stimulates neuronal migration from the EGL to the IGL. Thus, it appears that PACAP can act in vivo as a neurotrophic factor controlling histogenesis of the cerebellar cortex.

Maxadilan specifically interacts with PAC1 receptor, which is a dominant form of PACAP/VIP family receptors in cultured rat cortical neurons

Maxadilan is a potent vasodilator peptide isolated from salivary gland extracts of the hematophagous sand fly. Recently, the possibility was demonstrated that maxadilan binds to PAC1 receptor (PACAP, pituitary adenylate cyclase activating polypeptide type I receptor) in mammals. In the present study, we demonstrated that: (1) maxadilan specifically binds to PAC1 receptor and stimulates cyclic AMP accumulation in a dose-dependent manner in CHO cells stably expressing PAC1 receptor, not VIP (vasoactive intestinal polypeptide) receptors; that (2) the deleted peptide (amino acid #24-42) of maxadilan (termed max.d.4) also specifically binds to PAC1 receptor although max.d.4 inhibits cyclic AMP accumulation stimulated by both maxadilan and PACAP; and that (3) max.d.4 completely blocks the cyclic AMP accumulation induced by VIP in cultured rat cortical neurons. The expression of specific PACAP receptors in cultured rat cortical neurons was further investigated by the reverse transcription-polymerase chain reaction technique, which showed the presence of mRNA coding for PAC1 receptor among PACAP/VIP family receptors. These data indicate that maxadilan and max.d.4 represent important tools for clarifying the physiological role of PAC1 receptor, and that PAC1 receptor plays an important role in the regulation of the functions induced by PACAP in rat cultured cortical neurons.

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.

Developmental regulation of pituitary adenylate cyclase-activating polypeptide and PAC(1) receptor mRNA expression in the rat central nervous system

As the brain develops, a homogeneous population of mitotically active progenitors generates the molecularly heterogeneous post-mitotic cells of the mature brain. The balance between cell division, growth arrest and differentiation of these progenitors undoubtedly requires the activation of a vast array of genes. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a member of the vasoactive intestinal polypeptide (VIP)/secretin/glucagon family. Within the nervous system, PACAP has been shown to stimulate neurite outgrowth, regulate neurotransmitter production and neuronal survival. These diverse biological actions are mediated through interaction with two types of receptors, a PACAP-selective receptor (PAC(1)-R) and receptors which interact almost equally with both VIP and PACAP. Since several lines of evidence suggest that PACAP acts as a neurotrophic factor, we sought to characterize PACAP and PAC(1)-R expression in the developing rat nervous system. The PAC(1)-R is expressed at very high levels in ventricular zones throughout the neuraxis. In addition to the embryonic enrichment in proliferative zones, PAC(1)-R expression is maintained in areas of neurogenesis in the adult central nervous system (CNS), namely, the subventricular zone of the olfactory bulb and hippocampal dentate gyrus. In contrast, PACAP is expressed primarily in the post-mitotic parenchyma. This temporal regulation and cellular distribution suggests that PACAP, through its interaction with the PAC(1)-R, may play a role in mammalian neurogenesis.

Long-term enhancement of REM sleep by the pituitary adenylyl cyclase-activating polypeptide (PACAP) in the pontine reticular formation of the rat

In rats, rapid eye movement (REM) sleep can be elicited by microinjection of vasoactive intestinal polypeptide (VIP) into the oral pontine reticular nucleus (PnO). In the present study, we investigated whether this area could also be a REM-promoting target for a peptide closely related to VIP: the pituitary adenylyl cyclase-activating polypeptide (PACAP). When administered into the posterior part of the PnO, but not in nearby areas, of freely moving chronically implanted rats, PACAP-27 and PACAP-38 (0.3 and 3 pmol) induced a marked enhancement (60-85% over baseline) of REM sleep for 8 h that could be prevented by prior infusion of the antagonist PACAP-(6-27) (3 pmol) into the same site. Moreover, injections of PACAP into the centre of the posterior PnO resulted in REM sleep enhancement which could last for up to 11 consecutive days. Quantitative autoradiography using [125I]PACAP-27 revealed the presence in the PnO of specific binding sites with high affinity for PACAP-27 and PACAP-38 (IC50 = 2.4 and 3.2 nM, respectively), but very low affinity for VIP (IC50 > 1 microM). These data suggest that PACAP within the PnO may play a key role in REM sleep regulation, and provide evidence for long-term (several days) mechanisms involved in such a control. PAC1 receptors which have a much higher affinity for PACAP than for VIP might mediate this long-term action of PACAP on REM sleep.

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.

Neurotrophic activity of pituitary adenylate cyclase-activating polypeptide on rat cerebellar cortex during development

High concentrations of pituitary adenylate cyclase-activating polypeptide (PACAP) receptors are present in the external granule cell layer of the rat cerebellum during postnatal development. In vitro studies have shown that PACAP promotes cell survival and neurite outgrowth on immature cerebellar granule cells in primary culture. In the present study, we have investigated the effect of PACAP on the development of the cerebellar cortex of 8-day-old rats. Incubation of cultured granule cells for 12 or 18 h with PACAP provoked a significant increase in the rate of incorporation of [(3)H]thymidine in cultured granule cells, suggesting that PACAP could stimulate the proliferation of granule cells. After 96 h of treatment, in vivo administration of PACAP provoked a transient increase in the number of granule cells in the molecular layer and in the internal granule cell layer. In contrast, PACAP did not affect the number of Purkinje cells. The augmentation of the number of granule cells evoked by PACAP was significantly inhibited by the PACAP receptor antagonist PACAP(6-38). Administration of PACAP also caused a significant increase in the volume of the cerebellar cortex. The present study provides evidence that PACAP can act in vivo as a trophic factor during rat brain development. Our data indicate that PACAP increases proliferation and/or inhibits programmed cell death of granule cells, as well as stimulating neuronal migration from the external granule cell layer toward the internal granule cell layer.

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.

Control of neuronal precursor proliferation in the cerebellum by Sonic Hedgehog

Cerebellar granule cells are the most abundant type of neuron in the brain, but the molecular mechanisms that control their generation are incompletely understood. We show that Sonic hedgehog (Shh), which is made by Purkinje cells, regulates the division of granule cell precursors (GCPs). Treatment of GCPs with Shh prevents differentiation and induces a potent, long-lasting proliferative response. This response can be inhibited by basic fibroblast growth factor or by activation of protein kinase A. Blocking Shh function in vivo dramatically reduces GCP proliferation. These findings provide insight into the mechanisms of normal growth and tumorigenesis in the cerebellum.

The neurotrophic activity of PACAP on rat cerebellar granule cells is associated with activation of the protein kinase A pathway and c-fos gene expression

In vitro studies have shown that PACAP promotes cell survival and neurite outgrowth in immature cerebellar granule cells. In the present study, we have examined the transduction pathways involved in the neurotrophic activity of PACAP. Incubation of cultured granule cells with graded concentrations of PACAP produced a dose-dependent increase in c-fos mRNA level. The effects of PACAP on c-fos gene expression and granule cell survival were both mimicked by dbcAMP but not by PMA. The maximum effect of PACAP on c-fos gene expression was observed after 1 h of treatment. Similar effects of the peptide on granule cell survival were observed whether the cells were continuously incubated with PACAP for 48 h or only exposed to PACAP during 1 h. The PKA inhibitor H89 significantly reduced the effect of PACAP on c-fos mRNA level, whereas the specific PKC inhibitor chelerytrine had no effect. These data indicate that the action of PACAP on cerebellar granule cell survival and c-fos gene expression are both mediated through the adenylyl cyclase/PKA pathway.

Expression of PACAP, and PACAP type 1 (PAC1) receptor mRNA during development of the mouse embryo

Pituitary adenylate cyclase activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) have been reported to have a number of neurotrophic effects. We have examined the expression of mRNA for PACAP and PACAP type 1 (PAC1) receptor in the mouse embryo by in situ hybridization and the effects of PACAP and VIP on the growth of mouse embryos in vitro. Although we were unable to detect gross effects of either peptide on the growth rates of embryos maintained in culture, mRNAs for both PAC1 receptor and PACAP peptide were present in the nervous system from day 9.5 of embryonic development. PAC1 receptor mRNA was most abundant in the neural tube and the rhombencephalon and was present also in the dorsal root and trigeminal ganglia and the sympathetic chain. The distribution of mRNA for the PACAP peptide overlapped in part with that of the receptor, but was more extensively distributed in the rhombencephalon and in the developing hypothalamus. Within the neural tube, PAC1 receptor mRNA was located in the roof and floor plates, while the distribution of PACAP peptide mRNA was more complex, being located in two columns of cells in the ventromedial neural tube (consistent with the position of developing autonomic motor neurons) and in cells in the dorsolateral neural tube. These data are concordant with a role for PACAP or a related peptide in neural development.

Pharmacological, molecular and functional characterization of vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating polypeptide receptors in the rat pineal gland

Melatonin secretion from the mammalian pineal gland is strongly stimulated by noradrenaline and also by vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP). Three types of receptors for VIP and PACAP have been characterized so far: VIP1/PACAP receptors and VIP2/PACAP receptors, which possess similar high affinities for VIP and PACAP, and PACAP1 receptors which exhibit a 100-1000-fold higher affinity for PACAP. The aim of the present study was to characterize the receptor subtype(s) mediating the stimulatory effects of VIP and PACAP on melatonin synthesis in the rat pineal gland. Autoradiographic studies showed that PACAP and VIP were equally potent in displacing binding of radioiodinated PACAP27 from pineal sections. Amplification of pineal complementary DNAs by polymerase chain reaction using specific primers for the different receptor subtypes revealed that all three receptor messenger RNAs are expressed and that VIP1/PACAP receptor messenger RNA was predominant over VIP2/PACAP receptor messenger RNA. In vitro, VIP and PACAP stimulated melatonin synthesis with similar high potency and the effect of the two peptides were not additive. The selective VIP1/PACAP receptor agonists [R16]chicken secretin (1-25) and [K15, R16, L27]VIP(1-7)/growth hormone releasing factor(8-27) were significantly more potent than the selective VIP2/PACAP receptor agonist RO 25-1553 in stimulating melatonin secretion. The stimulatory effects of VIP and PACAP were similarly inhibited by the VIP1/PACAP antagonist [acetyl-His1, D-Phe2, K15, R16, L27]VIP(3-7)/growth hormone releasing factor(8-27). These data strongly suggest that VIP and PACAP exert a stimulatory effect on melatonin synthesis mainly through activation of a pineal VIP1/PACAP receptor subtype.

Pituitary adenylate cyclase-activating polypeptide stimulates both c-fos gene expression and cell survival in rat cerebellar granule neurons through activation of the protein kinase A pathway

A high density of pituitary adenylate cyclase-activating polypeptide (PACAP) receptors coupled to both adenylyl cyclase and phospholipase C is found in the external granule cell layer of the rat cerebellum during postnatal development. It has recently been reported that synthetic PACAP promotes cell survival and neurite outgrowth in immature granule cells. In the present study, we have investigated the transduction pathways that mediate the neurotrophic activity of PACAP in cultured granule cells from eight-day-old rat cerebellum. The effect of PACAP on cell survival was mimicked by dibutyryladenosine 3',5'-cyclic-monophosphate but not phorbol 12-myristate 13-acetate suggesting that only the adenylyl cyclase pathway is involved in the neurotrophic activity of PACAP. PACAP also induced a transient increase in c-fos messenger RNA level. The ability of PACAP to stimulate c-fos gene expression was mimicked by dibutyryladenosine 3',5'-cyclic-monophosphate but not phorbol 12-myristate 13-acetate. Similar effects of PACAP on granule cell survival were observed whether the cells were continuously incubated with PACAP for 48 h or only exposed to PACAP during 1 h. The protein kinase A inhibitor H89 significantly reduced the effect of PACAP on c-fos messenger RNA level whereas the specific protein kinase C inhibitor chelerythrine did not modify c-fos gene expression. These data indicate that the action of PACAP on cerebellar granule cell survival and c-fos gene expression are both mediated through the adenylyl cyclase/protein kinase A pathway. The observation that a short-term stimulation by PACAP can be converted into a long-lasting response indicates that the effect of the peptide on cell survival must involve immediate-early gene activation. The fact that a brief exposure to PACAP causes both c-fos gene expression and promotes cell survival strongly suggests that c-fos is involved in the trophic effect of PACAP on immature cerebellar granule cells.

Embryonic expression of pituitary adenylate cyclase-activating polypeptide in sensory and autonomic ganglia and in spinal cord of the rat

Pituitary adenylate cyclase-activating polypeptide (PACAP), a neuropeptide that is related structurally to vasoactive intestinal polypeptide (VIP), has been shown to stimulate neuronal growth and differentiation, indicating a possible function in the development of the nervous system. Studies have indicated that the PACAP receptor is expressed during development, but data on PACAP expression are limited mainly to postnatal development. In the present study, we used immunohistochemistry and in situ hybridization histochemistry to examine the expression of PACAP in autonomic and sensory ganglia and spinal cord of rat fetuses at embryonic days 12-21 (E12-E21). PACAP immunoreactivity was visualized by using a specific monoclonal anti-PACAP antibody to detect both PACAP-38 and PACAP-27, and PACAP mRNA was visualized by using a [33P]-labeled cRNA-probe. PACAP- nerve fibers were observed in the spinal cord as early as E13. At E14, PACAP-immunoreactive nerve fibers projected to the sympathetic trunk, where few PACAP- nerve cell bodies were seen from E15. On the same embryonic day, PACAP-immunoreactive nerve cell bodies appeared in the intermediolateral column of the spinal cord. From E15 to E16, PACAP-immunoreactive nerve cell bodies were visible within sensory and autonomic ganglia, such as the dorsal root, the trigeminal, the sphenopalatine, the otic, the submandibular, and the nodose ganglia. At E16, PACAP+ nerve fibers were innervating the adrenal medulla, and immunoreactive fibers could also be observed in the superior cervical ganglion, in which PACAP-immunoreactive cell bodies were detected occasionally from E18. The synthesis of PACAP in neuronal cell bodies was confirmed by the demonstration of PACAP mRNA with in situ hybridization histochemistry. Thus, in all of the structures examined, PACAP appeared at roughly the same embryonic stage and, thereafter, increased to the adult level before birth. Because PACAP occurred with the same distribution pattern as that described in the adult rat, there is no evidence for transient expression. The early expression of PACAP suggests a possible role for the peptide in the developing nervous system.

Pituitary adenylate cyclase-activating polypeptide promotes cell survival and neurite outgrowth in rat cerebellar neuroblasts

High concentrations of pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors have been detected in the rat cerebellum during ontogenesis. In particular, PACAP receptors are actively expressed in immature granule cells, suggesting that PACAP may act as a neurotrophic factor in the developing rat cerebellum. In the present study, we have investigated the effect of PACAP on cell survival and neurite outgrowth in cultured immature cerebellar granule cells. In control conditions, cultured granule cells undergo programmed cell death. Exposure of cultured cells to PACAP for 24 and 48 h provoked a significant increase in the number of living cells. The effect of PACAP on cell survival was inhibited by the PACAP antagonist PACAP(6-38). Vasoactive intestinal polypeptide was approximately 1000 times less potent than PACAP in promoting cell survival. PACAP also induced a significant increase in the number of processes and in the cumulated length of neurites borne by cultured neuroblasts. The present results demonstrate that PACAP promotes cell survival and neurite outgrowth in cultured immature granule cells. Since PACAP and its receptors are expressed in situ in the rat cerebellar cortex, these data strongly suggest that PACAP plays a physiological role in the survival and differentiation of cerebellar granule cells.

PACAP type I receptor activation promotes cerebellar neuron survival through the cAMP/PKA signaling pathway

The molecular nature, transduction pathways, and neurotrophic functions of pituitary adenylate cyclase activating peptide (PACAP) receptors were studied in primary culture of rat cerebellar granule cells. We show that cerebellar neurons express several PACAP type I receptor (PVR I) isoforms, including the short (PVR Is) and the Hop (PVR I-Hop) splice variants, the latter being restricted to neurons and not found in cerebellar glial cell cultures. In vitro, cerebellar granule cells die rapidly in the absence of a high concentration of K+ (25 mM), as demonstrated by TUNEL histochemistry, which shows that K+ deprivation induces massive neuronal apoptosis within 12 hr. This effect was reversed by PACAP 27 and 38. Both forms of PACAP prevent DNA fragmentation and allow long-term neuronal survival in the absence of high K+ (as shown by MAP2 immunostaining) and stimulate a reporter gene driven by the full-length c-fos promoter. These effects of PACAP are fully abolished upon transient transfection of cells with a dominant inhibitory mutant of the cAMP-dependent protein kinase (PKA). Taken together, these results show that in cerebellar granule neurons, PACAP type I receptors regulate gene expression and promote neuronal survival through the cAMP/PKA pathway.

Expression of pituitary adenylate cyclase activating polypeptide receptors in the early mouse embryo as assessed by reverse transcription polymerase chain reaction and in situ hybridisation

We have examined the expression of mRNA for the pituitary adenylate cyclase activating polypeptide (PACAP) receptor in the mouse from day 9.5 of embryonic development onwards by reverse transcription polymerase chain reaction (RT-PCR) and by in situ hybridisation. PACAP receptor mRNAs were detected by PCR in the earliest developmental stage examined and thereafter the levels of mRNA for all receptors increased during development. Wholemount in situ hybridisation first showed the expression of the PACAP receptor in the neural tube of 9.5 day old embryos, in later embryos heaviest expression of the PACAP receptor was found in the developing rhombencephalon (day 10.5 and 11.5). These results are consistent with a role for PACAP or a related peptide in the early development of the central nervous system.

Tissue-specific and developmental expression of pituitary adenylate cyclase-activating polypeptide (PACAP) receptors in rat brain

The two forms of pituitary adenylate cyclase-activating polypeptide, PACAP27,and PACAP38, are novel members of the vasoactive intestinal peptide (VIP)/secretin/glucagon family of peptides. PACAP receptors that are positively coupled to adenylate cyclase and phospholipase C have been recently identified. We examined the expression of PACAP receptors in the rat cortex, hippocampus, cerebellum and hypothalamus during postnatal development. Functional studies revealed PACAP stimulation of cAMP formation in all the brain areas examined and [3H]inositol monophosphate ([3H]InsP) accumulation only in the cerebellum and hypothalamus. Throughout development, the efficacy or PACAP in stimulating cAMP formation slightly increased in the cortex and hypothalamus and decreased in the hippocampus and cerebellum; PACAP stimulation of [3H]InsP formation decreased in the cerebellum and remained steady in the hypothalamus. The effects of PACAP27 and PACAP38 on cAMP levels and inositol phospholipid hydrolysis were dose-dependent between 1 and 100 nM. In the same brain areas, treatment with VIP increased cAMP formation at doses greater than 100nM and failed to affect [3H]InsP content, thus suggesting the existence of type-1 PACAP receptors. The reverse transcription polymerase chain reaction (RT-PCR) was used to analyse the mRNA expression of type-1 PACAP receptor splice variants. PACAP receptor gene expression in the central nervous system was regulated in a developmental- and tissue-specific manner. The PACAP-R transcript was detected in all the brain areas examined whereas PACAP-R-hop mRNA ocurred only in the cerebellum and hypothalamus. The different expression profiles and functional properties of PACAP receptors in the developing rat brain suggest an involvement of PACAP in histogenesis, maturation and neurotransmission.