Distribution and daily variations of PACAP in the chicken brain

Investigating the potential role of the pituitary adenylate cyclase-activating polypeptide (PACAP) in regulating the ubiquitin signaling pathway in poultry

The physiological processes in animal production are regulated through biologically active molecules like peptides, proteins, and hormones identified through the development of the fundamental sciences and their application. One of the main polypeptides that plays an essential role in regulating physiological responses is the pituitary adenylate cyclase-activating polypeptide (PACAP). PACAP belongs to the glucagon/growth hormone-releasing hormone (GHRH)/vasoactive intestinal proteins (VIP) family and regulates feed intake, stress, and immune response in birds. Most of these regulations occur after PACAP stimulates the cAMP signaling pathway, which can regulate the expression of genes like MuRF1, FOXO1, Atrogin 1, and other ligases that are essential members of the ubiquitin system. On the other hand, PACAP stimulates the secretion of CRH in response to stress, activating the ubiquitin signaling pathway that plays a vital role in protein degradation and regulates oxidative stress and immune responses. Many studies conducted on rodents, mammals, and other models confirm the regulatory effects of PACAP, cAMP, and the ubiquitin pathway; however, there are no studies testing whether PACAP-induced cAMP signaling in poultry regulates the ubiquitin pathway. Besides, it would be interesting to investigate if PACAP can regulate ubiquitin signaling during stress response via CRH altered by HPA axis stimulation. Therefore, this review highlights a summary of research studies that indicate the potential interaction of the PACAP and ubiquitin signaling pathways on different molecular and physiological parameters in poultry species through the cAMP and stress signaling pathways.

Relationship between Plasma Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Level and Proteome Profile of Cows

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic and multifunctional neuropeptide; it takes part in the regulation of various physiological processes, such as feeding, reproduction, catecholamine synthesis, thermoregulation, motor activity, brain development and neuronal survival. Since PACAP plays important regulatory roles, we hypothesized that the level of PACAP in blood is associated with expression of other proteins, which are involved in different metabolic pathways. The objective of the present study was to compare plasma protein profiles of cows with high and low plasma PACAP levels. Differential proteome analyses were performed by two-dimensional gel electrophoresis (2D-PAGE) followed by tryptic digestion and protein identification by liquid chromatography−mass spectrometry (LC-MS). A total of 210 protein spots were detected, and 16 protein spots showed statistically significant differences (p < 0.05) in the expression levels between groups. Ten spots showed a higher intensity in the high-PACAP-concentration group, while six spots were more abundant in the low-PACAP-concentration group. The functions of the differentially expressed proteins indicate that the PACAP level of plasma is related to the lipid metabolism and immune status of cattle.

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.

Light-at-night exposure affects brain development through pineal allopregnanolone-dependent mechanisms

The molecular mechanisms by which environmental light conditions affect cerebellar development are incompletely understood. We showed that circadian disruption by light-at-night induced Purkinje cell death through pineal allopregnanolone (ALLO) activity during early life in chicks. Light-at-night caused the loss of diurnal variation of pineal ALLO synthesis during early life and led to cerebellar Purkinje cell death, which was suppressed by a daily injection of ALLO. The loss of diurnal variation of pineal ALLO synthesis induced not only reduction in pituitary adenylate cyclase-activating polypeptide (PACAP), a neuroprotective hormone, but also transcriptional repression of the cerebellar Adcyap1 gene that produces PACAP, with subsequent Purkinje cell death. Taken together, pineal ALLO mediated the effect of light on early cerebellar development in chicks.

Melatonin mediates monochromatic green light-induced satellite cell proliferation and muscle growth in chick embryo

Background

Green light penetrates the skull and has directly affected on the secretion of melatonin in plasma, which regulates the endocrine activities to influence the muscle growth, satellite cell mitotic activity and quality properties of meat from the embryonic period to posthatch in chick. Pituitary adenylate cyclase-activating polypeptide 6–38 (PACAP6-38) could inhibit the synthesis and secretion of pineal melatonin. Finding a new way for exploring the mechanism of light-regulated muscle growth in ovo is essential for promoting the productive performance in poultry.

Methods

Chick embryos were exposed to darkness (D-group) and green light (G-group) throughout the embryonic period, and injected with PACAP6-38 or saline at embryonic day 8. Plasma hormone, skeletal muscle fiber areas, satellite cell proliferation activity, paired domain homeobox transcription factor 7 and myogenic regulatory factors were observed.

Results

By saline treatment, the percentage of proliferating cell nuclear antigen immunoreactive cells and mitotic activity of satellite cells in skeletal muscle were higher in G-group than those of in D-group at post-hatching day 0. With the increase of plasma melatonin, green light promoted the secretion of growth hormone (GH) and insulin like factor 1 (IGF-1) in plasma, the satellite cell proliferation, the size of muscle fiber, as well as the mRNA expressions of Pax7, myogenic regulatory factors and IGF-1R. After PACAP6-38 treatment to inhibit the secretion of melatonin in ovo, aforementioned parameters were remarkably decreased and the difference of these parameters was disappeared between D-group and G-group.

Conclusion

These data indicated that stimulation with monochromatic green light during incubation enhanced the secretion of melatonin and up-regulation of GH-IGF-1 axis to activate the satellite cells proliferation and myofiber formation, involving the expression of Pax7 and myogenic regulatory factors.

Pituitary adenylate cyclase-activating polypeptide in the testis of the quail Coturnix coturnix: Expression, localization, and phylogenetic analysis

To evaluate the involvement of pituitary adenylate cyclase-activating polypeptide (PACAP)/receptors system in the control of testis activity, we have investigated the expression and localization of PACAP and the distribution of its receptors in the testis of mature samples of quail Coturnix coturnix, and we have performed a phylogenetic analysis of PACAP in birds. Using histological, molecular, and bioinformatics tools, we demonstrated that (a) PACAP messenger RNA shows a high sequence identity with that reported in other birds studied so far and in other vertebrates. Furthermore, we showed that purifying selection acts on PACAP; (b) the PACAP peptide is present only in Leydig cells, whereas its receptors are localized within both Leydig and germ cells; (c) the synthesis of PACAP does not take place in seminiferous tubules. The role of PACAP in the control of spermatogenesis and steroidogenesis in birds is discussed. Finally, we talk about the phylogenetic and evolutionary relationships between PACAP in birds and in other vertebrates.

PACAP deficiency as a model of aging

Dysregulation of neuropeptides may play an important role in aging-induced impairments. In the long list of neuropeptides, pituitary adenylate cyclase-activating polypeptide (PACAP) represents a highly effective cytoprotective peptide that provides an endogenous control against a variety of tissue-damaging stimuli. PACAP has neuro- and general cytoprotective effects due to anti-apoptotic, anti-inflammatory, and antioxidant actions. As PACAP is also a part of the endogenous protective machinery, it can be hypothesized that the decreased protective effects in lack of endogenous PACAP would accelerate age-related degeneration and PACAP knockout mice would display age-related degenerative signs earlier. Recent results support this hypothesis showing that PACAP deficiency mimics aspects of age-related pathophysiological changes including increased neuronal vulnerability and systemic degeneration accompanied by increased apoptosis, oxidative stress, and inflammation. Decrease in PACAP expression has been shown in different species from invertebrates to humans. PACAP-deficient mice display numerous pathological alterations mimicking early aging, such as retinal changes, corneal keratinization and blurring, and systemic amyloidosis. In the present review, we summarize these findings and propose that PACAP deficiency could be a good model of premature aging.

Effects of PACAP on Dry Eye Symptoms, and Possible Use for Therapeutic Application

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 27- or 38-amino acid neuropeptide, which belongs to the vasoactive intestinal polypeptide/glucagon/secretin family of peptides. PACAP and its three receptor subtypes are expressed in neural tissues and in the eye, including the retina, cornea, and lacrimal gland. PACAP is known to exert pleiotropic effects on the central nervous system and in eye tissues where it plays important roles in protecting against dry eye. This review provides an overview of current knowledge regarding dry eye symptoms in aged animals and humans and the protective effects, mechanisms of action. In addition, we also refer to the development of a new preventive/therapeutic method by PACAP of dry eye patients.

Pleiotropic and retinoprotective functions of PACAP

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 27- or 38-amino acid neuropeptide, which belongs to the vasoactive intestinal polypeptide/glucagon/secretin family. PACAP and its three receptor subtypes are expressed in neural tissues of the eye, including the retina, cornea and lacrimal gland, and PACAP is known to exert pleiotropic effects throughout the central nervous system. This review provides an overview of current knowledge regarding the cell protective effects, mechanisms of action and therapeutic potential of PACAP in response to several types of eye injury.

Pituitary adenylate cyclase activating polypeptide in the retina: focus on the retinoprotective effects

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neurotrophic and neuroprotective peptide that has been shown to exert protective effects against different neuronal injuries, such as traumatic brain and spinal cord injury, models of neurodegenerative diseases, and cerebral ischemia. PACAP and its receptors are present in the retina. In this study, we summarize the current knowledge on retinal PACAP with focus on the retinoprotective effects. Results of histological, immunohistochemical, and molecular biological analysis are reviewed. In vitro, PACAP shows protection against glutamate, thapsigargin, anisomycin, and anoxia. In vivo, the protective effects of intravitreal PACAP treatment have been shown in the following models of retinal degeneration in rats: excitotoxic injury induced by glutamate and kainate, ischemic injury, degeneration caused by UV-A light, optic nerve transection, and streptozotocin-induced diabetic retinopathy. Studying the molecular mechanism has revealed that PACAP acts by activating antiapoptotic and inhibiting proapoptotic signaling pathways in the retina in vivo. These studies strongly suggest that PACAP is an excellent candidate retinoprotective agent that could be a potential therapeutic substance in various retinal diseases.

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.

Investigation of the effects of PACAP on the composition of tear and endolymph proteins

Pituitary adenylate cyclase activating polypeptide (PACAP) is widely distributed in ocular tissues, including the lacrimal gland. PACAP has been shown to influence the activity of several exocrine glands, but its effects on the composition of the tear film are not known yet. Similarly, the presence of PACAP has already been shown in the inner ear, but it is not known whether PACAP influences the composition of the endolymph. The aim of the present study was to investigate whether systemic injection of PACAP has any modulatory effects on the protein composition of the tear film and endolymph using chip electrophoresis and mass spectrometry analysis. Tear and endolymph samples were collected from rats and chickens, respectively, at various time points after systemic injection of PACAP. Fluid samples were further processed for chip electrophoretic studies. No difference was found in the protein composition of the endolymph between control and PACAP-treated animals. In contrast, tear samples showed a marked difference after PACAP treatment. Proteins in the molecular range 50-70 kDa, which showed a different chip electropherogram profile in every PACAP-treated sample, were further analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. PACAP treatment induced a repression in certain keratins, while others were induced after PACAP injection. Furthermore, PACAP treatment decreased aldehyde dehydrogenase expression. The present study provides a base for further studies on the in vivo effects of PACAP on the composition of tear film. These investigations may have important clinical relevance because of the noninvasive sample collection, the correlation between tear proteins and ocular diseases, and the possible presence of biomarkers for both ophthalmological and systemic pathological conditions.

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.

The role of PACAP in the control of circadian expression of clock genes in the chicken pineal gland

Several features of the molecular circadian oscillator of the chicken pineal gland show homology with those in the mammalian SCN. Studies have shown the effects of PACAP on the mammalian SCN, but its effects on the expression of clock genes in the avian pineal gland have not yet been demonstrated. Clock and Cry1 expression was analyzed in pineal glands of chicken embryos after exposure to PACAP-38 in vitro. PACAP reduced expression of both clock genes within 2h. Ten hours after exposure, mRNA contents exceeded that of the controls. Our results support the hypothesis that the molecular clock machinery in the chicken pineal gland is also sensitive to PACAP.

The neuroprotective effects of PACAP in monosodium glutamate-induced retinal lesion involve inhibition of proapoptotic signaling pathways

Pituitary adenylate cyclase activating polypeptide (PACAP) and its receptors are present in the retina and exert several distinct functions. PACAP has well-known neuroprotective effects in neuronal cultures in vitro and against different insults in vivo. Recently we have shown that PACAP is neuroprotective against monosodium glutamate (MSG)-induced retinal degeneration. In the present study we investigated the possible signal transduction pathways involved in the protective effect of intravitreal PACAP administration against apoptotic retinal degeneration induced by neonatal MSG treatment. MSG induced activation of proapoptotic signaling proteins and reduced the levels of antiapoptotic molecules in neonatal retinas. Co-treatment with PACAP attenuated the MSG-induced activation of caspase-3 and JNK, inhibited the MSG-induced cytosolic translocation of apoptosis inducing factor (AIF) and cytochrome c, and increased the level of phospho-Bad. Furthermore, PACAP treatment alone decreased cytosolic AIF and cytochrome c levels, while PACAP6-38 increased cytochrome c release, caspase-3 and JNK activity and decreased phospho-Bad activity. In summary, our results show that PACAP treatment attenuated the MSG-induced changes in apoptotic signaling molecules in vivo and suggest that also endogenously present PACAP has neuroprotective effects. These results may have further clinical implications in reducing glutamate-induced excitotoxicity in several ophthalmic diseases.

Degree of damage compensation by various PACAP treatments in monosodium glutamate-induced retinal degeneration

Pituitary adenylate cyclase activating polypeptide (PACAP) has been shown to be neuroprotective in retinal ischemia and monosodium L-glutamate (MSG)-induced retinal degeneration. Here we describe how different MSG treatments (1x and 3x application) cause retinal damage and finally lead to the destruction of the entire inner retina and how PACAP attenuates this effect. Newborn rats from both sexes were injected subcutaneously with 2 mg/g bodyweight MSG on postnatal days 1, 5 and 9. The left eye was left intact while we injected 5 microl PACAP38 solution (100 pmol) into the vitreous of the right eye with a Hamilton syringe at the time of (i) the first, (ii) the first two or (iii) all three MSG injections. Histological analysis has shown that the above described MSG treatment caused the entire inner plexiform layer (IPL) to degenerate, and the inner nuclear (INL) and ganglion cell layers (GCL) seemed fused. One time PACAP38 treatment at the first MSG application did not change the degenerative capacity of MSG. However, if animals received PACAP38 into the vitreous of the eye at the first 2 or all 3 times, a substantial protective effect could be observed. The IPL remained well discernible, the INL retained 2-3 cell rows and the number of cells in the GCL was substantially higher than in the MSG-treated retinas, and was not significantly different from that observed in the control tissue. We conclude that (i) 2 or 3 times PACAP treatment attenuates retinal degeneration; (ii) one PACAP treatment does not provide protection against repeated excitotoxic insults, and (iii) repeated application of PACAP under these experimental conditions may lead to a primed state in which further neurotoxic insults are ineffective.

Pituitary adenylate cyclase activating polypeptide plays a role in olfactory memory formation in chicken

PACAP plays an important role during development of the nervous system and is also involved in memory processing. The aim of the present study was to investigate the function of PACAP in chicken embryonic olfactory memory formation by blocking PACAP at a sensitive period in ovo. Chicken were exposed daily to strawberry scent in ovo from embryonic day 15. Control eggs were treated only with saline, while other eggs received a single injection of the PACAP antagonist PACAP6-38 at day 15. The consumption of scented and unscented water was measured daily after hatching. Animals exposed to strawberry scent in ovo showed no preference. However, chickens exposed to PACAP6-38, showed a clear preference for plain water, similarly to unexposed chicken. Our present study points to PACAP's possible importance in embryonic olfactory memory formation.

Development of the circadian melatonin rhythm and the effect of PACAP on melatonin release in the embryonic chicken pineal gland. An in vitro study

Pituitary adenylate cyclase activating polypeptide (PACAP) has been shown to participate in modulation of circadian rhythm and to stimulate melatonin (MT) secretion in both the rat and chicken pineal glands. In contrast to mammals, the main regulator of circadian rhythm in birds is the pineal gland, which begins its rhythmic MT production already during embryonic life. In the present study, we investigated the development of MT secretion in explanted embryonic chicken pineals and their responsiveness to PACAP in a perifusion system. Our results show that: (1) the circadian clock and/or the intracellular signal transduction system connecting the clock to MT synthesizing apparatus develop between the embryonic days 16-18 (E16-18), even in vitro. (2) Exposure of the embryonic chicken pineal gland to PACAP induces transitory increase in MT secretion but does not induce visible phase shift in the circadian rhythm. (3) Cyclic AMP (cAMP) efflux also responds to PACAP at or before day E13 in embryonic chicken pineal gland in vitro.

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.

Effects of pituitary adenylate cyclase activating polypeptide in retinal degeneration induced by monosodium-glutamate

Pituitary adenylate cyclase activating polypeptide (PACAP) is a pleiotropic neuropeptide with a wide range of effects in the central and peripheral nervous systems. PACAP has well-documented neurotrophic and neuroprotective actions in both in vitro and in vivo models of different neuronal injuries. The aim of the present study was to investigate the possible neuroprotective effect of PACAP in retinal degeneration induced by monosodium-glutamate (MSG) in neonatal rats. Preceding the MSG treatment, PACAP (1 or 100pmol/5mul) was injected unilaterally into the vitreous body on postnatal days 1, 5 and 9. Immediately after the PACAP treatment, pups were treated with 2mg/g body weight MSG subcutaneously. At 3 weeks of age, rats were sacrificed and retinas were removed and processed for histological examination. Our results show that MSG treatment caused severe degeneration, primarily of the inner retinal layers. The thickness of the entire retina was only approximately half of that of the normal retinas, and the inner nuclear layer seemed to be fused with the ganglionic cell layer, with no discernible inner plexiform layer. Retinas of animals treated with 1pmol PACAP showed a similar degree of degeneration. However, retinas of rats treated with 100pmol PACAP showed significantly less damage, with clearly distinguishable inner retinal layers. In summary, our present study shows that local PACAP treatment could attenuate the retinal degeneration induced by the excitotoxic effects of glutamate.

Distribution of PACAP-38 in the central nervous system of various species determined by a novel radioimmunoassay

Pituitary adenylate cyclase activating polypeptide (PACAP) occurs in two molecular forms: PACAP-38 and PACAP-27. Soon after the isolation and chemical characterization of PACAP, the first radioimmunoassay (RIA) methods have been developed, but it is a still rarely used laboratory technique in the field of PACAP research. The aim of the present study was to develop a novel, highly specific PACAP-38 assay to investigate the quantitative distribution of PACAP-38 in the central nervous system of various vertebrate species under the same technical and experimental conditions. Different areas of the brain and the spinal cord were removed from rats, chickens and fishes and the tissue samples were processed for PACAP-38 RIA. Our results indicate that the antiserum used in the RIA is C-terminal specific, without affinity for other members of the vasoactive intestinal polypeptide (VIP)/secretin/glucagon peptide family. The average ID50 value was 48.6+/-3.4 fmol/ml determined in 10 consecutive assays. Detection limit for PACAP-38 proved to be 2 fmol/ml. PACAP-38 immunoreactivity was present in the examined brain areas of each species studied, with highest concentration in the rat diencephalons. High levels of PACAP-38 were also detected in the rat telencephalon, followed by spinal cord and brainstem. The central nervous system of the fish also contained considerable concentrations of PACAP-38, whereas lowest concentrations were measured in the central nervous system of the chicken.

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

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

PAC1 receptors in chick cerebral cortex: characterization by binding of pituitary adenylate cyclase-activating polypeptide, [125I]-PACAP27

In this study we characterized receptors for pituitary adenylate cyclase-activating polypeptide (PACAP) in chick cerebral cortex by in vitro binding technique, using [125I]-PACAP27 as a ligand. The specific binding of [125I]-PACAP27 to chick cerebral cortical membranes was found to be rapid, stable, saturable, and of high affinity. Scatchard analysis suggested binding to a single class of receptor binding sites with high affinity (K(d)=0.41+/-0.08 nM) and high capacity (B(max)=457+/-35 fmol/mg protein). The relative rank order of potency of the tested peptides to inhibit [125I]-PACAP27 binding to chick cerebrum was: PACAP38 approximately PACAP27>PACAP6-27 approximately PACAP6-38 >> chicken VIP >> mammalian VIP >> secretin (inactive). It is concluded that the cerebral cortex of chick, in addition to VPAC recognition sites, contains a large population of PAC(1)-type receptor binding sites.

Influence of pinealectomy on levels of PACAP and cAMP in the chicken brain

One of the recently found functions of pituitary adenylate cyclase activating polypeptide (PACAP) is the modulation of circadian rhythms. Widespread distribution of PACAP-containing neurons and receptors has been shown in the chicken. Recently, we have demonstrated that PACAP levels oscillate in a circadian manner in the chicken brain. Daily variation in PACAP levels might be influenced by several regulatory mechanisms. Among the structures that may regulate PACAP levels, one candidate is the pineal gland. Therefore, in the present study, we investigated the effect of pinealectomy on the levels of PACAP in the chicken brain. Animals were kept under 12:12-h light-dark schedule. Pinealectomy was performed at 3 weeks of age; sham-operated animals were used as controls. The animals were sacrificed at 15 and 24 h 1 week after pinealectomy. The brainstem and diencephalon were removed, and tissue samples were processed for PACAP and cAMP radioimmunoassay (RIA).PACAP and cAMP levels showed nighttime elevations in both the sham-operated and pinealectomized animals, except for the PACAP content in the diencephalon of pinealectomized chicken. PACAP levels of pinealectomized animals were significantly higher in the diencephalon and brainstem as compared to the control animals at both time-points. Levels of cAMP correlated well with levels of PACAP. The present results provide evidence that the pineal gland has an inhibitory impact on PACAP-neurons in the chicken brainstem and diencephalon.