Isolation of a novel 38 residue-hypothalamic polypeptide which stimulates adenylate cyclase in pituitary cells

Pituitary Adenylate Cyclase Activating Polypeptide Has Inhibitory Effects on Melanoma Cell Proliferation and Migration In Vitro

Pituitary adenylate cyclase activating polypeptide (PACAP) is an endogenous neuropeptide which is distributed throughout the body. PACAP influences development of various tissues and exerts protective function during cellular stress and in some tumour formation. No evidence is available on its role in neural crest derived melanocytes and its malignant transformation into melanoma. Expression of PACAP receptors was examined in human skin samples, melanoma lesions and in a primary melanocyte cell culture. A2058 and WM35 melanoma cell lines, representing two different stages of melanoma progression, were used to investigate the effects of PACAP. PAC1 receptor was identified in melanocytes in vivo and in vitro and in melanoma cell lines as well as in melanoma lesions. PACAP administration did not alter viability but decreased proliferation of melanoma cells. With live imaging random motility, average speed, vectorial distance and maximum distance of migration of cells were reduced upon PACAP treatment. PACAP administration did not alter viability but decreased proliferation capacity of melanoma cells. On the other hand, PACAP administration decreased the migration of melanoma cell lines towards fibronectin chemoattractant in the Boyden chamber. Furthermore, the presence of the neuropeptide inhibited the invasion capability of melanoma cell lines in Matrigel chambers. In summary, we provide evidence that PACAP receptors are expressed in melanocytes and in melanoma cells. Our results also prove that various aspects of the cellular motility were inhibited by this neuropeptide. On the basis of these results, we propose PACAP signalling as a possible target in melanoma progression.

Targeted deletion of PAC1 receptors in retinal neurons enhances neuron loss and axonopathy in a model of multiple sclerosis and optic neuritis

Chronic inflammation drives synaptic loss in multiple sclerosis (MS) and is also commonly observed in other neurodegenerative diseases. Clinically approved treatments for MS provide symptomatic relief but fail to halt neurodegeneration and neurological decline. Studies in animal disease models have demonstrated that the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP, ADCYAP1) exhibits anti-inflammatory, neuroprotective and regenerative properties. Anti-inflammatory actions appear to be mediated primarily by two receptors, VPAC1 and VPAC2, which also bind vasoactive intestinal peptide (VIP). Pharmacological experiments indicate that another receptor, PAC1 (ADCYAP1R1), which is highly selective for PACAP, provides protection to neurons, although genetic evidence and other mechanistic information is lacking. To determine if PAC1 receptors protect neurons in a cell-autonomous manner, we used adeno-associated virus (AAV2) to deliver Cre recombinase to the retina of mice harboring floxed PAC1 alleles. Mice were then subjected to chronic experimental autoimmune encephalomyelitis (EAE), a disease model that recapitulates major clinical and pathological features of MS and associated optic neuritis. Unexpectedly, deletion of PAC1 in naïve mice resulted in a deficit of retinal ganglionic neurons (RGNs) and their dendrites, suggesting a homeostatic role of PAC1. Moreover, deletion of PAC1 resulted in increased EAE-induced loss of a subpopulation of RGNs purported to be vulnerable in animal models of glaucoma. Increased axonal pathology and increased secondary presence of microglia/macrophages was also prominently seen in the optic nerve. These findings demonstrate that neuronal PAC1 receptors play a homeostatic role in protecting RGNs and directly protects neurons and their axons against neuroinflammatory challenge. SIGNIFICANCE STATEMENT: Chronic inflammation is a major component of neurodegenerative diseases and plays a central role in multiple sclerosis (MS). Current treatments for MS do not prevent neurodegeneration and/or neurological decline. The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) has been shown to have anti-inflammatory, neuroprotective and regenerative properties but the cell type- and receptor-specific mechanisms are not clear. To test whether the protective effects of PACAP are direct on the PAC1 receptor subtype on neurons, we delete PAC1 receptors from neurons and investigate neuropathologigical changes in an animal model of MS. The findings demonstrate that PAC1 receptors on neurons play a homeostatic role in maintaining neuron health and can directly protect neurons and their axons during neuroinflammatory disease.

Correlation of Decreased Serum Pituitary Adenylate Cyclase-Activating Polypeptide and Vasoactive Intestinal Peptide Levels With Non-motor Symptoms in Patients With Parkinson's Disease

Objective: Pituitary adenylate-cyclase activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are two neuropeptides that exhibit anti-inflammatory and neuroprotective properties, modulating the production of cytokines and chemokines, and the behavior of immune cells. However, the relationship between PACAP and VIP levels and Parkinson’s disease (PD) are not clear. The aim of the current study was to evaluate serum PACAP and VIP levels in PD patients and to analysis the correlation between neuropeptide levels and non-motor symptoms.

Methods: In this cross-sectional study, we enrolled 72 patients with idiopathic PD and 71 healthy volunteers. Serum PACAP and VIP levels were measured using an enzyme-linked immunosorbent assay (ELISA) kit. Non-motor symptoms were assessed with the Non-Motor Symptoms Scale (NMSS) for PD, including total and single-item scores.

Results: The serum PACAP levels of PD patients were significantly lower than those of healthy controls [(76.02 ± 43.78) pg/ml vs. (154.96 ± 76.54) pg/ml, P < 0.001]; and the serum VIP levels of PD patients were also significantly lower than those of healthy controls [(109.56 ± 15.39) pg/ml vs. (136.46 ± 24.16) pg/ml, P < 0.001]. PACAP levels were inversely correlated only with the score on NMSS item five, assessing Attention/memory (r = −0.276, P < 0.05) and lower serum PACAP levels were detected in the cognitive dysfunction subgroup than in the cognitively intact subgroup [(61.87 ± 32.66) pg/ml vs. (84.51 ± 47.59) pg/ml, P < 0.05]; meanwhile, VIP levels were inversely correlated with the NMSS total score (r = −0.285, P < 0.05) and the single-item scores for item one, assessing Cardiovascular (r = −0.257, P < 0.05) and item three, assessing Mood/cognition (r = −0.373, P < 0.05), and lower serum VIP levels were detected in the anxiety subgroup and depression subgroup than in the non-anxiety subgroup and non-depression subgroup, respectively [(107.45 ± 15.40) pg/ml vs. (116.41 ± 13.67) pg/ml, P < 0.05]; [(104.45 ± 15.26) pg/ml vs. (113.43 ± 14.52) pg/ml, P < 0.05].

Conclusion: The serum PACAP and VIP levels of PD patients were significantly lower than those of healthy controls. The non-motor symptoms significantly negatively correlated with serum PACAP level was cognitive dysfunction, while mood disorder was significantly correlated with serum VIP level.

PAC1 Receptor Mediates Electroacupuncture-Induced Neuro and Immune Protection During Cisplatin Chemotherapy

Platinum-based chemotherapy is an effective treatment used in multiple tumor treatments, but produces severe side effects including neurotoxicity, anemia, and immunosuppression, which limits its anti-tumor efficacy and increases the risk of infections. Electroacupuncture (EA) is often used to ameliorate these side effects, but its mechanism is unknown. Here, we report that EA on ST36 and SP6 prevents cisplatin-induced neurotoxicity and immunosuppression. EA induces neuroprotection, prevents pain-related neurotoxicity, preserves bone marrow (BM) hematopoiesis, and peripheral levels of leukocytes. EA activates sympathetic BM terminals to release pituitary adenylate cyclase activating polypeptide (PACAP). PACAP-receptor PAC1-antagonists abrogate the effects of EA, whereas PAC1-agonists mimic EA, prevent neurotoxicity, immunosuppression, and preserve BM hematopoiesis during cisplatin chemotherapy. Our results indicate that PAC1-agonists may provide therapeutic advantages during chemotherapy to treat patients with advanced neurotoxicity or neuropathies limiting EA efficacy.

Motor Neuron Diseases and Neuroprotective Peptides: A Closer Look to Neurons

Motor neurons (MNs) are specialized neurons responsible for muscle contraction that specifically degenerate in motor neuron diseases (MNDs), such as amyotrophic lateral sclerosis (ALS), spinal and bulbar muscular atrophy (SBMA), and spinal muscular atrophy (SMA). Distinct classes of MNs degenerate at different rates in disease, with a particular class named fast-fatigable MNs (FF-MNs) degenerating first. The etiology behind the selective vulnerability of FF-MNs is still largely under investigation. Among the different strategies to target MNs, the administration of protective neuropeptides is one of the potential therapeutic interventions. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide with beneficial effects in many neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and more recently SBMA. Another neuropeptide that has a neurotrophic effect on MNs is insulin-like growth factor 1 (IGF-1), also known as somatomedin C. These two peptides are implicated in the activation of neuroprotective pathways exploitable in the amelioration of pathological outcomes related to MNDs.

The critical period: neurochemical and synaptic mechanisms shared by the visual cortex and the brain stem respiratory system

The landmark studies of Wiesel and Hubel in the 1960's initiated a surge of investigations into the critical period of visual cortical development, when abnormal visual experience can alter cortical structures and functions. Most studies focused on the visual cortex, with relatively little attention to subcortical structures. The goal of the present review is to elucidate neurochemical and synaptic mechanisms common to the critical periods of the visual cortex and the brain stem respiratory system in the normal rat. In both regions, the critical period is a time of (i) heightened inhibition; (ii) reduced expression of brain-derived neurotrophic factor (BDNF); and (iii) synaptic imbalance, with heightened inhibition and suppressed excitation. The last two mechanisms are contrary to the conventional premise. Synaptic imbalance renders developing neurons more vulnerable to external stressors. However, the critical period is necessary to enable each system to strengthen its circuitry, adapt to its environment, and transition from immaturity to maturity, when a state of relative synaptic balance is attained. Failure to achieve such a balance leads to neurological disorders.

Molecular Mechanism for PACAP 38-Induced Neurite Outgrowth in PC12 Cells

The present research investigates the molecular mechanism of neurite outgrowth (protrusion elongation) under pituitary adenylate cyclase-activating polypeptide (PACAP) 38 treatments using a rat adrenal-derived pheochromocytoma cell line-PC12. This study specifically looks into the regulation of PACAP38-induced collapsing response mediator protein 2 (CRMP2) previously identified in a mouse brain ischemia model and which could be recovered by PACAP38 treatment. Previously, DNA microarray analysis revealed that PACAP 38-mediated neuroprotection involved not only CRMP2 but also pathways related to glycogen synthase kinase-3β (GSK-3β) and other signaling components. Thus, to clarify whether CRMP2 acts directly on PACAP38 or through GSK-3β as part of the mechanism of PACAP38-induced neurite outgrowth, we observed neurite outgrowth in the presence of GSK-3β inhibitors and activators. PC12 cells were treated with PACAP38 being added to the cell culture medium at concentrations of 10^-7 M, 10^-8 M, and 10^-9 M. Post PACAP38 treatment, immunostaining was used to confirm protrusion elongation of the PC12 cells, while RT-PCR, two-dimensional gel electrophoresis in conjunction with Western blotting, and inhibition experiments were performed to confirm the expression of the PACAP gene, its receptors, and downstream signaling components. Our data show that neurite protrusion elongation by PACAP38 (10^-7 M) in PC12 cells is mediated through the PAC1-R receptor as demonstrated by its suppression by a specific inhibitor PA-8. Inhibitor experiments suggested that PACAP38-triggered neurite protrusion follows a GSK-3β-regulated pathway, where the AKT and cAMP/ERK pathways are involved and where the inhibition of Rho/Roc could enhance neurite protrusion under PACAP38 stimulation. Although we could not yet confirm the exact role and position of CRMP2 in PACAP38-mediated PC12 cell elongation, it appears that its phosphorylation and dephosphorylation have a correlation with the neurite protrusion elongation through the interplay of CDK5, which needs to be investigated further.

Retinoprotective Effects of PACAP Eye Drops in Microbead-Induced Glaucoma Model in Rats

Glaucoma is associated with increased intraocular pressure (IOP), causing the apoptosis of retinal ganglion cells (RGCs) and the loss of their axons leading to blindness. Pituitary adenylate cyclase activating polypeptide (PACAP) is neuroprotective in several neural injuries, including retinopathies. The aim of this study was to investigate the effects of PACAP1-38 eye drops in a model of glaucoma. IOP was elevated bilaterally by injections of microbeads to block the aqueous humor outflow. The control groups received the same volume of saline. Animals were treated with PACAP1-38 (1 µg/drop, 3 × 1 drop/day) or vehicle for 4 weeks starting one day after the injections. Retinal morphology by histology and optical coherence tomography, function by electroretinography, and IOP changes were analyzed. Animals were sacrificed 8 weeks after the injections. Microbeads injections induced a significant increase in the IOP, while PACAP1-38 treatment lowered it to normal levels (~10 mmHg). Significant retinal degeneration and functional impairment were observed in the microbead-injected group without PACAP1-38 treatment. In the microbeads + PACAP1-38 group, the retinal morphology and functionality were close to the normal values. In summary, our results show that PACAP1-38, given in form of eye drops, is neuroprotective in glaucoma, providing the basis for potential future therapeutic administration.

Estrogen mediates sex differences in preoptic neuropeptide and pituitary hormone production in medaka

The preoptic area (POA) is one of the most evolutionarily conserved regions of the vertebrate brain and contains subsets of neuropeptide-expressing neurons. Here we found in the teleost medaka that two neuropeptides belonging to the secretin family, pituitary adenylate cyclase-activating polypeptide (Pacap) and vasoactive intestinal peptide (Vip), exhibit opposite patterns of sexually dimorphic expression in the same population of POA neurons that project to the anterior pituitary: Pacap is male-biased, whereas Vip is female-biased. Estrogen secreted by the ovary in adulthood was found to attenuate Pacap expression and, conversely, stimulate Vip expression in the female POA, thereby establishing and maintaining their opposite sexual dimorphism. Pituitary organ culture experiments demonstrated that both Pacap and Vip can markedly alter the expression of various anterior pituitary hormones. Collectively, these findings show that males and females use alternative preoptic neuropeptides to regulate anterior pituitary hormones as a result of their different estrogen milieu.

PACAP orchestration of stress-related responses in neural circuits

Pituitary adenylate cyclase activating polypeptide (PACAP) is a pleiotropic polypeptide that can activate G protein-coupled PAC1, VPAC1, and VPAC2 receptors, and has been implicated in stress signaling. PACAP and its receptors are widely distributed throughout the nervous system and other tissues and can have a multitude of effects. Human and animal studies suggest that PACAP plays a role responding to a variety of threats and stressors. Here we review the roles of PACAP in several regions of the central nervous system (CNS) as they relate to several behavioral functions. For example, in the bed nucleus of the stria terminalis (BNST), PACAP is upregulated following chronic stress and may drive anxiety-like behavior. PACAP can also influence both the consolidation and expression of fear memories, as demonstrated by studies in several fear-related areas, such as the amygdala, hippocampus, and prefrontal cortex. PACAP can also mediate the emotional component of pain, as PACAP in the central nucleus of the amygdala (CeA) is able to decrease pain sensitivity thresholds. Outside of the central nervous system, PACAP may drive glucocorticoid release via enhanced hypothalamic-pituitary-adrenal axis activity and may participate in infection-induced stress responses. Together, this suggests that PACAP exerts effects on many stress-related systems and may be an important driver of emotional behavior.

PAC1 Receptor Internalization and Endosomal MEK/ERK Activation Is Essential for PACAP-Mediated Neuronal Excitability

Pituitary adenylate cyclase activating polypeptide (PACAP, Adcyap1) activation of PAC1 receptors (Adcyap1r1) can significantly increase the excitability of diverse neurons through differential mechanisms. For guinea pig cardiac neurons, the modulation of excitability can be mediated in part by PAC1 receptor plasma membrane G protein-dependent activation of adenylyl cyclase and downstream signaling cascades. By contrast, PAC1 receptor-mediated excitability of hippocampal dentate gyrus granule cells appears independent of membrane-delimited AC/cAMP/PKA and PLC/PKC signaling. For both neuronal types, there is mechanistic convergence demonstrating that endosomal PAC1 receptor signaling has prominent roles. In these models, neuronal exposure to Pitstop2 to inhibit β-arrestin/clathrin-mediated PAC1 receptor internalization eliminates PACAP modulation of excitability. β-arrestin is a scaffold for a number of effectors especially MEK/ERK and notably, paradigms that inhibit PAC1 receptor endosome formation and ERK signaling also blunt the PACAP-induced increase in excitability. Detailed PAC1 receptor internalization and endosomal ERK signaling mechanisms have been confirmed in HEK PAC1R-EGFP cells and shown to be long lasting which appear to recapitulate the sustained electrophysiological responses. Thus, PAC1 receptor internalization/endosomal recruitment efficiently and efficaciously activates MEK/ERK signaling and appears to represent a singular and critical common denominator in regulating neuronal excitability by PACAP.

Multimodal Role of PACAP in Glioblastoma

Glioblastoma multiforme (GBM) is the deadliest form of brain tumors. To date, the GBM therapeutical approach consists of surgery, radiation-therapy and chemotherapy combined with molecules improving cancer responsiveness to treatments. In this review, we will present a brief overview of the GBM classification and pathogenesis, as well as the therapeutic approach currently used. Then, we will focus on the modulatory role exerted by pituitary adenylate cyclase-activating peptide, known as PACAP, on GBM malignancy. Specifically, we will describe PACAP ability to interfere with GBM cell proliferation, as well as the tumoral microenvironment. Considering its anti-oncogenic role in GBM, synthesis of PACAP agonist molecules may open new perspectives for combined therapy to existing gold standard treatment.

Emerging drugs for the prevention of migraine

INTRODUCTION

Migraine is a common and disabling neurological disorder. A greater understanding of the pathophysiological mechanisms underlying migraine has led to the availability of specific new drugs targeting calcitonin gene-related peptide (CGRP). The success of the CGRP inhibitors validates research efforts into migraine-specific therapies.

AREAS COVERED

There are additional promising therapeutic targets that will be covered in this paper, focusing on the pain phase. They include pituitary adenylate cyclase-activating polypeptide (PACAP), the orexinergic system, the nitric oxide signaling pathway specifically neuronal nitric oxide synthase inhibitors (nNOSi), and metabotropic glutamate receptor 5 (mGluR5).

EXPERT OPINION

Based on currently available research; the targets discussed in this paper are all on equal footing with each other in terms of their potential as effective novel migraine therapies. There is a need for more clinical trials to pinpoint which of these potential drug targets will be effective for migraine preventio.

Pituitary Adenylate Cyclase-Activating Polypeptide in Learning and Memory

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a highly conserved neuropeptide that regulates neuronal physiology and transcription through Gs/Gq-coupled receptors. Its actions within hypothalamic, limbic, and mnemonic systems underlie its roles in stress regulation, affective processing, neuroprotection, and cognition. Recently, elevated PACAP levels and genetic disruption of PAC1 receptor signaling in humans has been linked to maladaptive threat learning and pathological stress and fear in post-traumatic stress disorder (PTSD). PACAP is positioned to integrate stress and memory in PTSD for which memory of the traumatic experience is central to the disorder. However, PACAP's role in memory has received comparatively less attention than its role in stress. In this review, we consider the evidence for PACAP-PAC1 receptor signaling in learning and plasticity, discuss emerging data on sex differences in PACAP signaling, and raise key questions for further study toward elucidating the contribution of PACAP to adaptive and maladaptive fear learning.

PACAP Induces Light Aversion in Mice by an Inheritable Mechanism Independent of CGRP

The neuropeptides CGRP (calcitonin gene-related peptide) and PACAP (pituitary adenylate cyclase-activating polypeptide) have emerged as mediators of migraine, yet the potential overlap of their mechanisms remains unknown. Infusion of PACAP, like CGRP, can cause migraine in people, and both peptides share similar vasodilatory and nociceptive functions. In this study, we have used light aversion in mice as a surrogate for migraine-like photophobia to compare CGRP and PACAP and ask whether CGRP or PACAP actions were dependent on each other. Similar to CGRP, PACAP induced light aversion in outbred CD-1 mice. The light aversion was accompanied by increased resting in the dark, but not anxiety in a light-independent open field assay. Unexpectedly, about one-third of the CD-1 mice did not respond to PACAP, which was not seen with CGRP. The responder and nonresponder phenotypes were stable, inheritable, and not sex linked, although there was a trend for greater responses among male mice. RNA-sequencing analysis of trigeminal ganglia yielded hierarchical clustering of responder and nonresponder mice and revealed a number of candidate genes, including greater expression of the Trpc5 and Kcnk12 ion channels and glycoprotein hormones and receptors in a subset of male responder mice. Importantly, an anti-PACAP monoclonal antibody could block PACAP-induced light aversion but not CGRP-induced light aversion. Conversely, an anti-CGRP antibody could not block PACAP-induced light aversion. Thus, we propose that CGRP and PACAP act by independent convergent pathways that cause a migraine-like symptom in mice.SIGNIFICANCE STATEMENT The relationship between the neuropeptides CGRP (calcitonin gene-related peptide) and PACAP (pituitary adenylate cyclase-activating polypeptide) in migraine is relevant given that both peptides can induce migraine in people, yet to date only drugs that target CGRP are available. Using an outbred strain of mice, we were able to show that most, but not all, mice respond to PACAP in a preclinical photophobia assay. Our finding that CGRP and PACAP monoclonal antibodies do not cross-inhibit the other peptide indicates that CGRP and PACAP actions are independent and suggests that PACAP-targeted drugs may be effective in patients who do not respond to CGRP-based therapeutics.

Implications of VIP and PACAP in Parkinson's Disease: What do we Know So Far?

BACKGROUND

Parkinson's disease is one of the most common neurodegenerative disorders and although its aetiology is not yet fully understood, neuroinflammation has been identified as a key factor in the progression of the disease. Vasoactive intestinal peptide and pituitary adenylate-cyclase activating polypeptide are two neuropeptides that exhibit anti-inflammatory and neuroprotective properties, modulating the production of cytokines and chemokines and the behaviour of immune cells. However, the role of chemokines and cytokines modulated by the endogenous receptors of the peptides varies according to the stage of the disease.

METHODS

We present an overview of the relationship between some cytokines and chemokines with vasoactive intestinal peptide, pituitary adenylate cyclase activating polypeptide and their endogenous receptors in the context of Parkinson's disease neuroinflammation and oxidative stress, as well as the modulation of microglial cells by the peptides in this context.

RESULTS

The two peptides exhibit neuroprotective and anti-inflammatory properties in models of Parkinson's disease, as they ameliorate cognitive functions, decrease the level of neuroinflammation and promote dopaminergic neuronal survival. The peptides have been tested in a variety of in vivo and in vitro models of Parkinson's disease, demonstrating the potential for therapeutic application.

CONCLUSION

More studies are needed to establish the clinical use of vasoactive intestinal peptide and pituitary adenylate cyclase activating polypeptide as safe candidates for treating Parkinson's disease, as the use of the peptides in different stages of the disease could produce different results concerning effectiveness.

Comparative Neurology of Circadian Photoreception: The Retinohypothalamic Tract (RHT) in Sighted and Naturally Blind Mammals

The mammalian eye contains two systems for light perception: an image detecting system constituted primarily of the classical photoreceptors, rods and cones, and a non-image forming system (NIF) constituted of a small group of intrinsically photosensitive retinal ganglion cells driven by melanopsin (mRGCs). The mRGCs receive input from the outer retina and NIF mediates light entrainment of circadian rhythms, masking behavior, light induced inhibition of nocturnal melatonin secretion, pupillary reflex (PLR), and affect the sleep/wake cycle. This review focuses on the mammalian NIF and its anatomy in the eye as well as its neuronal projection to the brain. This pathway is known as the retinohypothalamic tract (RHT). The development and functions of the NIF as well as the knowledge gained from studying gene modified mice is highlighted. Furthermore, the similarities of the NIF between sighted (nocturnal and diurnal rodent species, monkeys, humans) and naturally blind mammals (blind mole rats Spalax ehrenbergi and the Iberian mole, Talpa occidentalis) are discussed in relation to a changing world where increasing exposure to artificial light at night (ALAN) is becoming a challenge for humans and animals in the modern society.

Effects of pituitary adenylate cyclase-activating polypeptide isoforms in nucleus accumbens subregions on ethanol drinking

While limited research has implicated the neuropeptide, pituitary adenylate cyclase-activating polypeptide (PACAP), in problematic alcohol use, the brain regions and isoforms involved in this effect remain to be determined. One region that has been found both to exhibit PACAP binding and, separately, to be involved in ethanol drinking is the nucleus accumbens (NAc). Thus, this study sought to characterize the effect of the PACAP isoforms in the NAc on ethanol drinking under the intermittent-access two-bottle-choice paradigm, in male and female Long-Evans rats. With microinjection into the medial NAc shell, PACAP-27 but not PACAP-38 was found to dose-dependently reduce binge-like ethanol drinking. In contrast, the PACAP receptor antagonist, PACAP (6-27), but not PACAP (6-38), enhanced ethanol drinking. This effect of PACAP was substance specific, as neither isoform in the NAc shell affected binge-like sucrose drinking. It was also anatomically specific, as PACAP-38 rather than PACAP-27 suppressed ethanol drinking when injected into the NAc core, and PACAP-27 instead enhanced drinking when injected into the caudal third of the medial NAc shell. Finally, while PACAP-38 in the NAc shell affected stress-related exploratory behavior, reducing time spent in the light chamber of a light-dark box, PACAP-27 did not significantly affect behavior in a light-dark box or open field. Together, these results, showing that PACAP-27 in the NAc shell attenuates binge-like ethanol drinking without affecting select stress-related behaviors, suggest that compounds related to this PACAP isoform should be investigated as potential novel therapeutics for the treatment of alcohol use disorder.

Cluster headache pathophysiology - insights from current and emerging treatments

Cluster headache is a debilitating primary headache disorder that affects approximately 0.1% of the population worldwide. Cluster headache attacks involve severe unilateral pain in the trigeminal distribution together with ipsilateral cranial autonomic features and a sense of agitation. Acute treatments are available and are effective in just over half of the patients. Until recently, preventive medications were borrowed from non-headache indications, so management of cluster headache is challenging. However, as our understanding of cluster headache pathophysiology has evolved on the basis of key bench and neuroimaging studies, crucial neuropeptides and brain structures have been identified as emerging treatment targets. In this Review, we provide an overview of what is known about the pathophysiology of cluster headache and discuss the existing treatment options and their mechanisms of action. Existing acute treatments include triptans and high-flow oxygen, interim treatment options include corticosteroids in oral form or for greater occipital nerve block, and preventive treatments include verapamil, lithium, melatonin and topiramate. We also consider emerging treatment options, including calcitonin gene-related peptide antibodies, non-invasive vagus nerve stimulation, sphenopalatine ganglion stimulation and somatostatin receptor agonists, discuss how evidence from trials of these emerging treatments provides insights into the pathophysiology of cluster headache and highlight areas for future research.

Advances in the Regulation of Mammalian Follicle-Stimulating Hormone Secretion

Simple Summary

The reproduction of mammals is regulated by the hypothalamic-pituitary-gonadal axis. Follicle stimulating hormone, as one of the gonadotropins secreted by the pituitary gland, plays an immeasurable role. This article mainly reviews the molecular basis and classical signaling pathways that regulate the synthesis and secretion of follicle stimulating hormone, and summarizes its internal molecular mechanism, which provides a certain theoretical basis for the research of mammalian reproduction regulation and the application of follicle stimulating hormone in production practice.

Abstract

Mammalian reproduction is mainly driven and regulated by the hypothalamic-pituitary-gonadal (HPG) axis. Follicle-stimulating hormone (FSH), which is synthesized and secreted by the anterior pituitary gland, is a key regulator that ultimately affects animal fertility. As a dimeric glycoprotein hormone, the biological specificity of FSH is mainly determined by the β subunit. As research techniques are being continuously innovated, studies are exploring the underlying molecular mechanism regulating the secretion of mammalian FSH. This article will review the current knowledge on the molecular mechanisms and signaling pathways systematically regulating FSH synthesis and will present the latest hypothesis about the nuclear cross-talk among the various endocrine-induced pathways for transcriptional regulation of the FSH β subunit. This article will provide novel ideas and potential targets for the improved use of FSH in livestock breeding and therapeutic development.

The pivotal role of pituitary adenylate cyclase-activating polypeptide for lactate production and secretion in astrocytes during fear memory

BACKGROUND

Pituitary adenylate cyclase-activating polypeptide (PACAP) plays an essential role in the modulation of astrocyte functions. Although lactate secretion from astrocytes contributes to many forms of neuronal plasticity in the central nervous system, including fear learning and memory, the role of PACAP in lactate secretion from astrocytes is unclear.

METHODS

The amygdala and hippocampus of PACAP (+ / +) and PACAP (-/-) mice were acquired 1 h after memory acquisition and recall in the passive avoidance test. The concentration of glycogen and lactate in these regions was measured. The concentration of lactate in the hippocampus's extracellular fluid was also measured by microdialysis during memory acquisition or intracerebroventricular administration of PACAP.

RESULTS

We observed that memory acquisition caused a significant decrease in glycogen concentration and increased lactate concentration in the PACAP (+ / +) mice's hippocampus. However, memory acquisition did not increase in the lactate concentration in PACAP (-/-) mice's hippocampus. Further, memory retrieval evoked lactate production in the amygdala and the hippocampus of PACAP (+ / +) mice. Still, there was no significant increase in lactate concentration in the same regions of PACAP (-/-) mice. In vivo microdialysis in rats revealed that the hippocampus's extracellular lactate concentration increased after a single PACAP intracerebroventricular injection. Additionally, the hippocampus's extracellular lactate concentration increased with the memory acquisition in PACAP (+ / +) mice, but not in PACAP (-/-) mice.

CONCLUSIONS

PACAP may enhance lactate production and secretion in astrocytes during the acquisition and recall of fear memories.

PACAP and PAC1 Receptor Expression in Human Insulinomas

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide with widespread occurrence and diverse functions. PACAP binds to specific PAC1 and non-specific VPAC1/2 receptors. PACAP is considered as a growth factor, as it plays important roles during development and participates in reparative processes. Highest concentrations are found in the nervous system and endocrine glands, where several functions are known, including actions in tissue growth, differentiation and tumour development. Therefore, we have investigated expression of PACAP and its receptors in different tumours, including those of endocrine glands. We showed earlier that PACAP and PAC1 receptor staining intensity decreased in pancreatic ductal adenocarcinoma. In the present study we aimed to investigate alterations of PACAP and PAC1 receptor in human insulinoma and compared the immunostaining pattern with samples from chronic pancreatitis patients. We collected perioperative and histological data of patients who underwent operation because of insulinoma or chronic pancreatitis over a five-year-long period. Histology showed chronic pancreatitis with severe scar formation in pancreatitis patients, while tumour samples evidenced Grade 1 or 2 insulinoma. PACAP and PAC1 receptor expression was studied using immunohistochemistry. Staining intensity was very strong in the Langerhans islets of normal tissue and discernible staining was also observed in the exocrine pancreas. Immunostaining intensity for both PACAP and PAC1 receptor was markedly weaker in insulinoma samples, and disappeared from chronic pancreatitis samples except for intact islets. These findings show that PAC1 receptor/PACAP signalling is altered in insulinoma and this suggests a possible involvement of this system in tumour growth or differentiation.

Exosome-Mediated Delivery of the Neuroprotective Peptide PACAP38 Promotes Retinal Ganglion Cell Survival and Axon Regeneration in Rats With Traumatic Optic Neuropathy

Traumatic optic neuropathy (TON) refers to optic nerve damage caused by trauma, leading to partial or complete loss of vision. The primary treatment options, such as hormonal therapy and surgery, have limited efficacy. Pituitary adenylate cyclase-activating polypeptide 38 (PACAP38), a functional endogenous neuroprotective peptide, has emerged as a promising therapeutic agent. In this study, we used rat retinal ganglion cell (RGC) exosomes as nanosized vesicles for the delivery of PACAP38 loaded via the exosomal anchor peptide CP05 (EXO PACAP38 ). EXO PACAP38 showed greater uptake efficiency in vitro and in vivo than PACAP38. The results showed that EXO PACAP38 significantly enhanced the RGC survival rate and retinal nerve fiber layer thickness in a rat TON model. Moreover, EXO PACAP38 significantly promoted axon regeneration and optic nerve function after injury. These findings indicate that EXO PACAP38 can be used as a treatment option and may have therapeutic implications for patients with TON.

Pituitary adenylate cyclase-activating polypeptide/vasoactive intestinal peptide (Part 2): biology and clinical importance in central nervous system and inflammatory disorders

PURPOSE OF REVIEW

To discuss recent advances of vasoactive intestinal peptide/pituitary adenylate cyclase-activating polypeptide (VIP/PACAP) receptors in the selected central nervous system (CNS) and inflammatory disorders.

RECENT FINDINGS

Recent studies provide evidence that PACAP plays an important role in a number of CNS disorders, particularly the pathogenesis of headaches (migraine, etc.) as well as posttraumatic stress disorder and drug/alcohol/smoking addiction. VIP has important therapeutic effects in a number of autoimmune/inflammatory disorder such as rheumatoid arthritis. In some cases, these insights have advanced to therapeutic trials.

SUMMARY

Recent insights from studies of VIP/PACAP and their receptors in both CNS disorders (migraine, posttraumatic stress disorder, addiction [drugs, alcohol, smoking]) and inflammatory disorders [such as rheumatoid arthritis] are suggesting new treatment approaches. The elucidation of the importance of VIP/PACAP system in these disorders combined recent development of specific drugs acting on this system (i.e., monoclonal VIP/PACAP antibodies) will likely lead to importance novel treatment approaches in these diseases.

Pituitary adenylate cyclase-activating polypeptide/vasoactive intestinal peptide [Part 1]: biology, pharmacology, and new insights into their cellular basis of action/signaling which are providing new therapeutic targets

PURPOSE OF REVIEW

To discuss recent advances of vasoactive intestinal peptide (VIP)/pituitary adenylate cyclase-activating polypeptide (PACAP) receptors in pharmacology, cell biology, and intracellular signaling in cancer.

RECENT FINDINGS

Recent studies provide new insights into the pharmacology, cell biology of the VIP/PACAP system and show they play important roles in a number of human cancers, as well as in tumor growth/differentiation and are providing an increased understanding of their signaling cascade that is suggesting new treatment targets/approaches.

SUMMARY

Recent insights from studies of VIP/PACAP and their receptors in both central nervous system disorders and inflammatory disorders suggest possible new treatment approaches. Elucidation of the exact roles of VIP/PACAP in these disorders and development of new therapeutic approaches involving these peptides have been limited by lack of specific pharmacological tools, and exact signaling mechanisms involved, mediating their effects. Reviewed here are recent insights from the elucidation of structural basis for VIP/PACAP receptor activation as well as the signaling cascades mediating their cellular effects (using results primarily from the study of their effects in cancer) that will likely lead to novel targets and treatment approaches in these diseases.

Pituitary adenylate cyclase activating polypeptide concentrations in the sheep mammary gland, milk, and in the lamb blood plasma after suckling

Pituitary adenylate cyclase activating polypeptide (PACAP) is involved in development and reproduction. We previously described elevated PACAP levels in the milk compared to the plasma, and the presence of its specific PAC1 receptor in the mammary gland. This study aimed to determine PACAP and vasoactive intestinal peptide (VIP) levels in female suckling lambs compared to ewe plasma and mammary gland, as well as their age-dependent alterations. mRNA expressions of PACAP, VIP, PAC1 receptor and brain-derived neurotrophic factor (BDNF) were quantified in the milk whey and mammary gland. PACAP38-like immunoreactivity (PACAP38-LI) was measured in plasma, milk whey and mammary gland by radioimmunoassay, VIP-LI by enzyme-linked immunoassay. PACAP38-LI was 5, 6 times higher in the milk compared to the plasma of lactating sheep. It significantly increased in the lamb plasma 1 h, but returned to basal level 2 h after suckling. However, VIP mRNA was not present in the mammary gland, we detected the VIP protein in the milk whey. BDNF mRNA significantly decreased with age to approximately 60% and 25% in the 3- and 10-year-old sheep respectively, compared to the 3-month-old lambs. No differences were found between mammary and jugular vein plasma PACAP and VIP concentrations, or during the daily cycle. We propose a rapid absorption of PACAP38 from the milk and/or its release in suckling lambs. PACAP accumulated in the milk might be synthesized in the mammary gland or secreted from the plasma of the mothers. PACAP is suggested to have differentiation/proliferation promoting and immunomodulatory effects in the newborns and/or a local function in the mammary gland.

PACAP-38 in Acute ST-Segment Elevation Myocardial Infarction in Humans and Pigs: A Translational Study

Acute myocardial infarction (MI) is one of the most common causes of death worldwide. Pituitary adenylate cyclase activating polypeptide (PACAP) is a cardioprotective neuropeptide expressing its receptors in the cardiovascular system. The aim of our study was to examine tissue PACAP-38 in a translational porcine MI model and plasma PACAP-38 levels in patients with ST-segment elevation myocardial infarction (STEMI). Significantly lower PACAP-38 levels were detected in the non-ischemic region of the left ventricle (LV) in MI heart compared to the ischemic region of MI-LV and also to the Sham-operated LV in porcine MI model. In STEMI patients, plasma PACAP-38 level was significantly higher before percutaneous coronary intervention (PCI) compared to controls, and decreased after PCI. Significant negative correlation was found between plasma PACAP-38 and troponin levels. Furthermore, a significant effect was revealed between plasma PACAP-38, hypertension and HbA1c levels. This was the first study showing significant changes in cardiac tissue PACAP levels in a porcine MI model and plasma PACAP levels in STEMI patients. These results suggest that PACAP, due to its cardioprotective effects, may play a regulatory role in MI and could be a potential biomarker or drug target in MI.

Inhibition of PACAP/PAC1/VPAC2 signaling impairs the consolidation of social recognition memory and nitric oxide prevents this deficit

Social recognition memory (SRM) forms the basis of social relationships of animals. It is essential for social interaction and adaptive behavior, reproduction and species survival. Evidence demonstrates that social deficits of psychiatric disorders such as autism and schizophrenia are caused by alterations in SRM processing by the hippocampus and amygdala. Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) and its receptors PAC1, VPAC1 and VPAC2 are highly expressed in these regions. PACAP is a pleiotropic neuropeptide that modulates synaptic function and plasticity and is thought to be involved in social behavior. PACAP signaling also stimulates the nitric oxide (NO) production and targets outcomes to synapses. In the present work, we investigate the effect of the infusion of PACAP-38 (endogenous neuropeptide and potent stimulator of adenylyl cyclase), PACAP 6-38 (PAC1/VPAC2 receptors antagonist) and S-Nitroso-N-acetyl-DL-penicillamine (SNAP, NO donor) in the CA1 region of the hippocampus and in the basolateral amygdala (BLA) on the consolidation of SRM. For this, male Wistar rats with cannulae implanted in CA1 or in BLA were subjected to a social discrimination paradigm, which is based on the natural ability of rodents to investigate unfamiliar conspecifics more than familiar one. In the sample phase (acquisition), animals were exposed to a juvenile conspecific for 1 h. Immediately, 60 or 150 min after, animals received one of different pharmacological treatments. Twenty-four hours later, they were submitted to a 5 min retention test in the presence of the previously presented juvenile (familiar) and a novel juvenile. Animals that received infusions of PACAP 6-38 (40 pg/side) into CA1 immediately after the sample phase or into BLA immediately or 60 min after the sample phase were unable to recognize the familiar juvenile during the retention test. This impairment was abolished by the coinfusion of PACAP 6-38 plus SNAP (5 μg/side). These results show that the blockade of PACAP/PAC1/VPAC2 signaling in the CA1 and BLA during a restricted post-acquisition time window impairs the consolidation of SRM and that the SNAP is able to abolish this deficit. Findings like this could potentially be used in the future to influence studies of psychiatric disorders involving social behavior.

The Emerging Role of Neuropeptides in Parkinson's Disease

Parkinson’s disease (PD), the second most common age-related neurodegenerative disease, results from the loss of dopamine neurons in the substantia nigra. This disease is characterized by cardinal non-motor and motor symptoms. Several studies have demonstrated that neuropeptides, such as ghrelin, neuropeptide Y, pituitary adenylate cyclase-activating polypeptide, substance P, and neurotensin, are related to the onset of PD. This review mainly describes the changes in these neuropeptides and their receptors in the substantia nigra-striatum system as well as the other PD-related brain regions. Based on several in vitro and in vivo studies, most neuropeptides play a significant neuroprotective role in PD by preventing caspase-3 activation, decreasing mitochondrial-related oxidative stress, increasing mitochondrial biogenesis, inhibiting microglial activation, and anti-autophagic activity. Thus, neuropeptides may provide a new strategy for PD therapy.

Contribution of thermogenic mechanisms by male and female mice lacking pituitary adenylate cyclase-activating polypeptide in response to cold acclimation

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide critical to the regulation of the stress response, including having a role in energy homeostasis. Mice lacking PACAP are cold-sensitive and have impaired adrenergic-induced thermogenesis. Interestingly, Pacap null mice can survive cold housing if acclimated slowly, similar to observations in uncoupling protein 1 (UCP1)-deficient mice. We hypothesized that Pacap null mice use alternate thermogenic pathways to compensate for impaired adaptive thermogenesis when acclimated to cold. Observations of behavior and assessment of fiber type in skeletal muscles did not show evidence of prolonged burst shivering or changes in oxidative metabolism in male or female Pacap^-/- mice during cold acclimation compared with Pacap^+/+ mice. Despite previous work that has established impaired capacity for adaptive thermogenesis in Pacap null mice, adaptive thermogenesis can be induced in mice lacking PACAP to support survival with cold housing. Interestingly, sex-specific morphological and molecular differences in adipose tissue remodeling were observed in Pacap null mice compared with controls. Thus, sexual dimorphisms are highlighted in adipose tissue remodeling and thermogenesis with cold acclimation in the absence of PACAP.NEW & NOTEWORTHY This manuscript adds to the literature of endocrine regulation of adaptive thermogenesis and energy balance. It specifically describes the role of pituitary adenylate cyclase-activating polypeptide on the regulation of brown adipose tissue via the sympathetic nervous system with a focus on compensatory mechanisms of thermogenesis. We highlight sex-specific differences in energy metabolism.

Bombesin, endothelin, neurotensin and pituitary adenylate cyclase activating polypeptide cause tyrosine phosphorylation of receptor tyrosine kinases

Numerous peptides including bombesin (BB), endothelin (ET), neurotensin (NTS) and pituitary adenylate cyclase-activating polypeptide (PACAP) are growth factors for lung cancer cells. The peptides bind to G protein-coupled receptors (GPCRs) resulting in elevated cAMP and/or phosphatidylinositol (PI) turnover. In contrast, growth factors such as epidermal growth factor (EGF) or neuregulin (NRG)-1 bind to receptor tyrosine kinases (RTKs) such as the EGFR or HER3, increasing tyrosine kinase activity, resulting in the phosphorylation of protein substrates such as PI3K or phospholipase (PL)C. Peptide GPCRs can transactivate numerous RTKs, especially members of the EGFR/HER family resulting in increased phosphorylation of ERK, leading to cellular proliferation or increased phosphorylation of AKT, leading to cellular survival. GRCR antagonists and tyrosine kinase inhibitors are useful agents to prevent RTK transactivation and inhibit proliferation of cancer cells.

Pituitary Adenylate Cyclase-Activating Polypeptide: A Potent Therapeutic Agent in Oxidative Stress

Stroke is a life-threatening condition that is characterized by secondary cell death processes that occur after the initial disruption of blood flow to the brain. The inability of endogenous repair mechanisms to sufficiently support functional recovery in stroke patients and the inadequate treatment options available are cause for concern. The pathology behind oxidative stress in stroke is of particular interest due to its detrimental effects on the brain. The oxidative stress caused by ischemic stroke overwhelms the neutralization capacity of the body's endogenous antioxidant system, which leads to an overproduction of reactive oxygen species (ROS) and reactive nitrogen species (RNS) and eventually results in cell death. The overproduction of ROS compromises the functional and structural integrity of brain tissue. Therefore, it is essential to investigate the mechanisms involved in oxidative stress to help obtain adequate treatment options for stroke. Here, we focus on the latest preclinical research that details the mechanisms behind secondary cell death processes that cause many central nervous system (CNS) disorders, as well as research that relates to how the neuroprotective molecular mechanisms of pituitary adenylate cyclase-activating polypeptides (PACAPs) could make these molecules an ideal candidate for the treatment of stroke.

Behavioral role of PACAP signaling reflects its selective distribution in glutamatergic and GABAergic neuronal subpopulations

The neuropeptide PACAP, acting as a co-transmitter, increases neuronal excitability, which may enhance anxiety and arousal associated with threat conveyed by multiple sensory modalities. The distribution of neurons expressing PACAP and its receptor, PAC1, throughout the mouse nervous system was determined, in register with expression of glutamatergic and GABAergic neuronal markers, to develop a coherent chemoanatomical picture of PACAP role in brain motor responses to sensory input. A circuit role for PACAP was tested by observing Fos activation of brain neurons after olfactory threat cue in wild-type and PACAP knockout mice. Neuronal activation and behavioral response, were blunted in PACAP knock-out mice, accompanied by sharply downregulated vesicular transporter expression in both GABAergic and glutamatergic neurons expressing PACAP and its receptor. This report signals a new perspective on the role of neuropeptide signaling in supporting excitatory and inhibitory neurotransmission in the nervous system within functionally coherent polysynaptic circuits.

PACAP for Retinal Health: Model for Cellular Aging and Rescue

Retinal aging is the result of accumulating molecular and cellular damage with a manifest decline in visual functions. Somatostatin (SST) and pituitary adenylate cyclase-activating polypeptide (PACAP) have been implicated in neuroprotection through regulating disparate aspects of neuronal activity (survival, proliferation and renewal). The aim of the present study was to validate a transgenic model for SST-expressing amacrine cells and to investigate the chronic effect of PACAP on the aging of SSTergic and dopaminergic cells of the retina. SST-tdTomato transgenic mice that were 6, 12 and 18 months old were treated intravitreally with 100 pmol of PACAP every 3 months. The density of SST and dopaminergic amacrine cells was assessed in whole-mounted retinas. Cells displaying the transgenic red fluorescence were identified as SST-immunopositive amacrine cells. By comparing the three age groups. PACAP treatment was shown to induce a moderate elevation of cell densities in both the SST and dopaminergic cell populations in the 12- and 18-month-old animals. By contrast, the control untreated and saline-treated retinas showed a minor cell loss. In conclusion, we report a reliable transgenic model for examining SSTergic amacrine cells. The fundamental novelty of this study is that PACAP could increase the cell density in matured retinal tissue, anticipating new therapeutic potential in age-related pathological processes.

Melanotan II, a melanocortin agonist, partially rescues the impaired thermogenic capacity of pituitary adenylate cyclase-activating polypeptide deficient mice

NEW FINDINGS

What is the central question of this study? Can chronic treatment of pituitary adenylate cyclase-activating polypeptide (PACAP) deficient mice with the melanocortin agonist melanotan II during cold acclimation rescue the impaired thermogenic capacity previously observed in PACAP deficient mice? What is the main finding and its importance? Using a genetic model of PACAP deficiency, this study provides evidence that PACAP acts upstream of the melanocortin system in regulating sympathetic nerve activity to brown adipose tissue in mice.

ABSTRACT

Impaired adipose tissue function in obesity, including reduced thermogenic potential, has detrimental consequences for metabolic health. Hormonal regulation of adaptive thermogenesis is being explored as a potential therapeutic target for human obesity. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide expressed in nuclei of the hypothalamus known to regulate energy expenditure, and functional studies reveal a role for PACAP in the central regulation of thermogenesis, although mechanisms are not well understood. We hypothesized that PACAP acts upstream of the melanocortin system to regulate sympathetic nerve activity to stimulate thermogenesis. To assess this, female PACAP^-/- and PACAP^+/+ mice were given daily peripheral injections of a melanocortin receptor agonist, melanotan II (MTII), for 3 weeks during cold acclimation, and the effect of MTII on thermogenic capacity and adipose tissue remodelling was examined by physiological and histological analyses. MTII partially rescued the impaired thermogenic capacity in PACAP^-/- mice as compared to PACAP^+/+ mice as determined by measuring noradrenaline-induced metabolic rate. In addition, MTII treatment during cold acclimation corrected the previously identified deficit in lipid utilization in response to adrenergic stimulation in PACAP^-/- null mice, suggesting impaired lipid mobilization may contribute to the impaired thermogenic capacity of PACAP^-/- mice. Results presented here provide physiological evidence to suggest that PACAP acts upstream of melanocortin receptors to facilitate sympathetically induced mechanisms of adaptive thermogenesis in response to cold acclimation.

PACAP: A regulator of mammalian reproductive function

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an ancestral molecule that was isolated from sheep hypothalamic extracts based on its action to stimulate cAMP production by pituitary cell cultures. PACAP is one of a number of ligands that coordinate with GnRH to control reproduction. While initially viewed as a hypothalamic releasing factor, PACAP and its receptors are widely distributed, and there is growing evidence that PACAP functions as a paracrine/autocrine regulator in the CNS, pituitary, gonads and placenta, among other tissues. This review will summarize current knowledge concerning the expression and function of PACAP in the hypothalamic-pituitary-gonadal axis with special emphasis on its role in pituitary function in the fetus and newborn.

Pituitary Adenylate Cyclase-Activating Polypeptide: A Promising Neuroprotective Peptide in Stroke

The search for viable, effective treatments for acute stroke continues to be a global priority due to the high mortality and morbidity. Current therapeutic treatments have limited effects, making the search for new treatments imperative. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a well-established cytoprotective neuropeptide that participates in diverse neural physiological and pathological activities, such as neuronal proliferation, differentiation, and migration, as well as neuroprotection. It is considered a promising treatment in numerous neurological diseases. Thus, PACAP bears potential as a new therapeutic strategy for stroke treatment. Herein, we provide an overview pertaining to the current knowledge of PACAP, its receptors, and its potential neuroprotective role in the setting of stroke, as well as various mechanisms of neuroprotection involving ionic homeostasis, excitotoxicity, cell edema, oxidative stress, inflammation, and cell death, as well as the route of PACAP administration.

Effects of Pacap on Schwann Cells: Focus on Nerve Injury

Schwann cells, the most abundant glial cells of the peripheral nervous system, represent the key players able to supply extracellular microenvironment for axonal regrowth and restoration of myelin sheaths on regenerating axons. Following nerve injury, Schwann cells respond adaptively to damage by acquiring a new phenotype. In particular, some of them localize in the distal stump to form the Bungner band, a regeneration track in the distal site of the injured nerve, whereas others produce cytokines involved in recruitment of macrophages infiltrating into the nerve damaged area for axonal and myelin debris clearance. Several neurotrophic factors, including pituitary adenylyl cyclase-activating peptide (PACAP), promote survival and axonal elongation of injured neurons. The present review summarizes the evidence existing in the literature demonstrating the autocrine and/or paracrine action exerted by PACAP to promote remyelination and ameliorate the peripheral nerve inflammatory response following nerve injury.

Spermatogenesis and regulatory factors in the wall lizard Podarcis sicula

Spermatogenesis is an extraordinarily complex process, regulated by several factors, which leads to the differentiation of spermatogonia into spermatozoa. Among vertebrates, several reports have been focused on the lizard Podarcis sicula, a seasonal breeder and a good model for the study of reproductive processes. The goal of this review is to resume all the available data about systemic and above all local control factors involved in the control of P. sicula testicular activity. During the seasonal reproductive cycle, the variation of the expression levels of these factors determines significant variations that induce the activation or blocking of spermatogenesis. The data supplied in this review, in addition to analyze the current literature regarding the main actors of Podarcis sicula spermatogenesis, will hopefully provide a basic model that can be used for further studies on the intratesticular interaction between molecular factors that control spermatogenesis.

Pituitary adenylate cyclase-activating peptide: Potential roles in the pathophysiology and complications of cirrhosis

Pituitary adenylate cyclase-activating peptide (PACAP) is a ubiquitous neuropeptide with diverse functions throughout the organism. Most abundantly investigated for its role in several neurological disorders as well as in circadian rhythms, other fields of medicine, including cardiology, have recently shown interest in the role of PACAP and its potential as a biomarker. Timely diagnosis and treatment of cirrhosis and its complications is a considerable challenge for health services world-wide and development of new areas of research is warranted. Direct and indirect evidence exists of PACAP involvement in the cascade of pathological events and processes ultimately leading to cirrhosis and its complications, but its exact role remains to be determined. Studies have documented PACAP involvement in immune function, metabolism, local vasoconstriction and dilatation and systemic vascular decompensation and there is ongoing research of a possible role in liver reperfusion injury. Considering these reports, PACAP could theoretically exude influence on the disease course of cirrhosis through the hypothalamus-pituitary-adrenal axis, chronic inflammation, fibrogenesis, vasodilation and reduced vascular resistance. The paucity of literature on the specific topic of PACAP and cirrhosis reflects complex mechanisms and difficulty in accurate measurements and sample taking. This does not detract from the need to further characterize and elucidate the role PACAP plays in the underdiagnosed and undertreated condition of cirrhosis.

Salmonid Antibacterial Immunity: An Aquaculture Perspective

The aquaculture industry is continuously threatened by infectious diseases, including those of bacterial origin. Regardless of the disease burden, aquaculture is already the main method for producing fish protein, having displaced capture fisheries. One attractive sector within this industry is the culture of salmonids, which are (a) uniquely under pressure due to overfishing and (b) the most valuable finfish per unit of weight. There are still knowledge gaps in the understanding of fish immunity, leading to vaccines that are not as effective as in terrestrial species, thus a common method to combat bacterial disease outbreaks is the use of antibiotics. Though effective, this method increases both the prevalence and risk of generating antibiotic-resistant bacteria. To facilitate vaccine design and/or alternative treatment efforts, a deeper understanding of the teleost immune system is essential. This review highlights the current state of teleost antibacterial immunity in the context of salmonid aquaculture. Additionally, the success of current techniques/methods used to combat bacterial diseases in salmonid aquaculture will be addressed. Filling the immunology knowledge gaps highlighted here will assist in reducing aquaculture losses in the future.

Pituitary Adenylate Cyclase-Activating Polypeptide Alleviates Intestinal, Extra-Intestinal and Systemic Inflammatory Responses during Acute Campylobacter jejuni-induced Enterocolitis in Mice

Human Campylobacter jejuni infections are emerging, and constitute a significant health burden worldwide. The ubiquitously expressed pituitary adenylate cyclase-activating polypeptide (PACAP) is well-known for its cell-protective and immunomodulatory effects. In our actual intervention study, we used an acute campylobacteriosis model and assessed the potential disease-alleviating effects of exogenous PACAP. Therefore, secondary abiotic IL-10^-/- mice were perorally infected with C. jejuni and treated with synthetic PACAP38 intraperitoneally from day 2 until day 5 post-infection. Whereas PACAP did not interfere with the gastrointestinal colonization of the pathogen, mice from the PACAP group exhibited less severe clinical signs of C. jejuni-induced disease, as compared to mock controls, which were paralleled by alleviated apoptotic, but enhanced cell proliferative responses in colonic epithelia on day 6 post-infection. Furthermore, PACAP dampened the accumulation of macrophages and monocytes, but enhanced regulatory T cell responses in the colon, which were accompanied by less IFN-γ secretion in intestinal compartments in PACAP versus mock-treated mice. Remarkably, the inflammation-dampening properties of PACAP could also be observed in extra-intestinal organs, and strikingly, even the systemic circulation on day 6 post-infection. For the first time, we provide evidence that synthetic PACAP might be a promising candidate to combat acute campylobacteriosis and post-infectious sequelae.

Investigation of pituitary adenylate cyclase activating polypeptide (PACAP) in human amniotic fluid samples

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide acting as a hormone, a neuromodulator, a neurotransmitter, a trophic factor and is involved in a variety of developmental and regenerative processes. PACAP is present in several human tissues and biological fluids. In many pathological conditions, changes in PACAP levels have been described to reflect disease progression, therefore PACAP has diagnostic value as a potential biomarker. Since PACAP has been shown to play an important role in reproductive physiology and development, it was of interest to examine whether this neuropeptide occurs in the human amniotic fluid. Amniotic fluid samples were collected between the 15-19^th weeks of gestation from volunteering pregnant women undergoing amniocentesis as a prenatal diagnostic tool due to maternal age. Pathological cases were excluded after prenatal karyotype analysis. PACAP-like immunoreactivity was measured by radioimmunoassay and could be detected in all samples. The present study provides evidence for the presence of PACAP in human amniotic fluid, but determination of the exact physiological or pathological significance awaits further investigation.

Physical Activity Protects the Pathological Alterations of Alzheimer's Disease Kidneys via the Activation of PACAP and BMP Signaling Pathways

Alzheimer's disease (AD) is a neurodegenerative disorder with typical amyloid beta (Aβ) aggregations. Elimination of the Aβ precursors via the kidneys makes the organ a potential factor in the systemic degeneration leading to AD. Pituitary adenylate cyclase-activating polypeptide (PACAP) exerts neuroprotective effects in AD and plays a protective role in kidney pathologies. Increased physical activity is preventive of the formation of AD, but its detailed mechanism and possible connections with PACAP have not been clarified. In the kidneys of AD mice, the effects of physical activity were investigated by comparing wild-type and AD organs. Aβ plaque formation was reduced in AD kidneys after increased training (TAD). Mechanotransduction elevated PACAP receptor expression in TAD mice and normalized the protein kinase A (PKA)-mediated pathways. BMP4/BMPR1 elevation activated Smad1 expression and normalized collagen type IV in TAD animals. In conclusion, our data suggest that elevated physical activity can prevent the AD-induced pathological changes in the kidneys via, at least in part, the activation of PACAP-BMP signaling crosstalk.

Pituitary adenylate cyclase-activating polypeptide: Protective effects in stroke and dementia

Evidence shows that pituitary adenylate cyclase-activating polypeptide (PACAP) improves stroke outcomes and dementia. The blood-brain barrier (BBB) controls the peptide and regulatory protein exchange between the central nervous system and the blood; the transport of these regulatory substances across the BBB has been altered in animal models of stroke and Alzheimer's disease (AD). PACAP is a powerful neurotrophin that can cross the BBB, which may aid in the therapy of neurodegenerative diseases, including stroke and AD. PACAP may function as a potential drug in the treatment, prevention, or management of stroke and AD and other neurodegenerative conditions. Here, we review the effects of PACAP in studies on stroke and dementias.

First in vivo evidence of pituitary adenylate cyclase-activating polypeptide antiviral activity in teleost

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a multifunctional neuropeptide belonging to the glucagon/secretin superfamily. In teleost fish, PACAP has been demonstrated to have an immunomodulatory role. Although previous studies have shown that viral/bacterial infections can influence the transcription of PACAP splicing variants and associated receptors in salmonids, the antiviral activity of PACAP has never been studied in teleost. Thus, in the present work, we investigated in vitro the influence of synthetic Clarias gariepinus PACAP-38 on the transcription of genes related to viral immunity using the rainbow trout monocyte/macrophage-like cell line RTS11 as a model. Positive transcriptional modulation of interferon gamma (IFNγ), interferon alpha (FNα1,2), interleukin 8 (IL-8), Mx and Toll-like receptor 3 (TLR3) genes was found in a dose and time dependent manner. We also explored how a pre-treatment with PACAP could enhance antiviral immune response using poly (I:C) as viral mimic. Interferons and IL-8 transcription levels were enhanced when PACAP was added 24 h previous to poly (I:C) exposure. With these evidences, we tested in vivo how PACAP administration by immersion bath affected the survival of rainbow trout fry to a challenge with viral hemorrhagic septicemia virus (VHSV). After challenge, PACAP-treated fish had increased survival compared to non-treated/challenge fish. Furthermore, PACAP was able to decrease the viral load in spleen/kidney and stimulate the transcription of IFNs and Mx when compared to untreated infected fish. Altogether, the results of this work provide valuable insights regarding the role of teleost PACAP in antiviral immunity and point to a potential application of this peptide to reduce the impact of viral infections in aquaculture.