Galanin--10 years with a neuroendocrine peptide

Investigating the potential of GalR2 as a drug target for neuropathic pain

Neuropathic pain is a chronic and debilitating condition characterised by episodes of hyperalgesia and allodynia. It occurs following nerve damage from disease, inflammation or injury and currently impacts up to 17% of the UK population. Existing therapies lack efficacy and have deleterious side effects that can be severely limiting. Galanin receptor 2 (GalR2) is a G-protein coupled receptor (GPCR) implicated in the control and processing of painful stimuli. Within the nervous system it is expressed in key tissues involved in these actions such as dorsal root ganglia (DRG) and the dorsal horn of the spinal cord. Stimulation of GalR2 is widely reported to have a role in the attenuation of inflammatory and neuropathic pain. Several studies have indicated GalR2 as a possible drug target, highlighting the potential of specific GalR2 agonists to both provide efficacy and to address the side-effect profiles of current pain therapies in clinical use. A strong biological target for drug discovery will be well validated with regards to its role in the relevant disease pathology. Ideally there will be good translational models, sensitive probes, selective and appropriate molecular tools, translational biomarkers, a clearly defined patient population and strong opportunities for commercialisation. Before GalR2 can be considered as a drug target suitable for investment, key questions need to be asked regarding its expression profile, receptor signalling and ligand interactions. This article aims to critically review the available literature and determine the current strength of hypothesis of GalR2 as a target for the treatment of neuropathic pain.

Noradrenergic modulation of stress resilience

Resilience represents an active adaption process in the face of adversity, trauma, tragedy, threats, or significant sources of stress. Investigations of neurobiological mechanisms of resilience opens an innovative direction for preclinical research and drug development for various stress-related disorders. The locus coeruleus norepinephrine system has been implicated in mediating stress susceptibility versus resilience. It has attracted increasing attention over the past decades with the revolution of modern neuroscience technologies. In this review article, we first briefly go over resilience-related concepts and introduce rodent paradigms for segregation of susceptibility and resilience, then highlight recent literature that identifies the neuronal and molecular substrates of active resilience in the locus coeruleus, and discuss possible future directions for resilience investigations.

Successful Application of a Galanin-Coated Scaffold for Periodontal Regeneration

The nervous system exerts finely tuned control over all aspects of the life of an organism, including pain, sensation, growth, and development. Recent developments in tissue regeneration research have increasingly turned to small molecule peptides to tailor and augment the biological response following tissue loss or injury. In the present study, we have introduced the small molecule peptide galanin (GAL) as a novel scaffold-coating agent for the healing and regeneration of craniofacial tissues. Using immunohistochemistry, we detected GAL and GAL receptors in healthy periodontal tissues and in the proximity of blood vessels, while exposure to our periodontal disease regimen resulted in a downregulation of GAL. In a 3-dimensional bioreactor culture, GAL coating of collagen scaffolds promoted cell proliferation and matrix synthesis. Following subcutaneous implantation, GAL-coated scaffolds were associated with mineralized bone-like tissue deposits, which reacted positively for alizarin red and von Kossa, and demonstrated increased expression and protein levels of RUNX2, OCN, OSX, and iBSP. In contrast, the GAL receptor antagonist galantide blocked the effect of GAL on Runx2 expression and inhibited mineralization in our subcutaneous implantation model. Moreover, GAL coating promoted periodontal regeneration and a rescue of the periodontal defect generated in our periodontitis model mice. Together, these data demonstrate the efficacy of the neuropeptide GAL as a coating material for tissue regeneration. They are also suggestive of a novel role for neurogenic signaling pathways in craniofacial and periodontal regeneration.

Conformational signatures in β-arrestin2 reveal natural biased agonism at a G-protein-coupled receptor

Discovery of biased ligands and receptor mutants allows characterization of G-protein- and β-arrestin-mediated signaling mechanisms of G-protein-coupled receptors (GPCRs). However, the structural mechanisms underlying biased agonism remain unclear for many GPCRs. We show that while Galanin induces the activation of the galanin receptor 2 (Galr2) that leads to a robust stimulation toward Gαq-protein and β-arrestin1/2, an alternative ligand Spexin and its analog have biased agonism toward G-protein signaling relative to Galanin. We used intramolecular fluorescein arsenical hairpin bioluminescence resonance energy transfer-based biosensors of β-arrestin2 combined with NanoBit technology to measure β-arrestin2–Galr2 interactions in real-time living systems. We found that Spexin and Galanin induce specific active conformations of Galr2, which may lead to different internalization rates of the receptor as well as different signaling outputs. This work represents an additional pharmacological evidence of endogenous G-protein-biased agonism at a GPCR.

Arfaxad Reyes-Alcaraz et al. report that galanin induces robust signaling mediated by β-arrestin1/2 and Gαq, whereas an alternative ligand spexin prefers the Gαq-protein signaling pathway. This study provides mechanistic insights into how endogenous ligands can generate biased signaling outputs.

Short N-terminal galanin fragments are occurring naturally in vivo

The galanin family currently consists of four peptides, namely galanin, galanin-message associated peptide, galanin-like peptide and alarin. Unlike galanin that signals through three different G protein-coupled receptors; GAL₁, GAL₂, and GAL₃, binding at its N-terminal end, the cognate receptors for other members of the galanin family are currently unknown. Research using short N-terminal galanin fragments generated either by enzymatic cleavage or solid-phase synthesis has revealed differences in their receptor binding properties exerting numerous biological effects distinct from galanin(1-29) itself. Our studies on tissue extracts derived from rat small intestine and bovine gut using chromatographic techniques and sensitive galanin(1-16)-specific radioimmunoassay revealed the presence of immunoreactive compounds reacting with antiserum against galanin(1-16) distributed in distinct elution volumes. These results suggested a possible presence of short N-terminal galanin fragments also in vivo. Moreover, employing immunoaffinity chromatography and reverse-phase high performance liquid chromatography (HPLC) followed by mass spectrometry allowed specific enrichment of these immunoreactive compounds from rat tissues and identification of their molecular structure. Indeed, our study revealed presence of several distinct short N-terminal galanin sequences in rat tissue. To prove their receptor binding, four of the identified sequences were synthetized, namely, galanin(1-13), galanin(1-16), galanin(1-20), galanin(6-20), and tested on coronal rat brain sections competing with ¹²⁵I-labeled galanin(1-29). Our autoradiographs confirmed that galanin(1-13), galanin(1-16), and galanin(1-20) comprehensively displaced ¹²⁵I-galanin(1-29) but galanin(6-20) did not. Here we show, for the first time, that short N-terminal galanin fragments occur naturally in rat tissues and that similar or identical galanin sequences can be present also in tissues of other species.

BIOLOGICAL SIGNIFICANCE

This study is first to provide an evidence of the presence of short N-terminal galanin fragments in vivo in a biological system and provides further foundations for the previous studies using synthetized short N-terminal galanin fragments.

Novel pentapeptide, PALAL, derived from a bony fish elicits contraction of the muscle in starfish Patiria pectinifera

A bioactive peptide mimicking peptide-signaling molecules has been isolated from the skin extract of fish Channa argus which caused contraction of the apical muscle of a starfish Patiria pectinifera, a deuterostomian invertebrate. The primary structure of the isolated pentapeptide comprises amino acid sequence of H-Pro-Ala-Leu-Ala-Leu-OH (PALAL) with a molecular mass of 483.7 Da. Pharmacological activity of PALAL, dosage ranging from 10^-9 to 10^-5 M, revealed concentration-dependent contraction of the apical muscles of P. pectinifera and Asterias amurensis. However, PALAL was not active on the intestinal smooth muscle of the goldfish Carassius auratus and has presumably other physiological roles in fish skin. Investigation of structure-activity relationship using truncated and substituted analogs of PALAL demonstrated that H-Ala-Leu-Ala-Leu-OH was necessary and should be sufficient to constrict apical muscle of P. pectinifera. Furthermore, the second alanine residue was required to display the activity, and the fifth leucine residue was responsible for its potency. Comparison with PALAL's primary structure with those of other known bioactive peptides from fish and starfish revealed that PALAL does not have any significant homology. Consequently, PALAL is a bioactive peptide that elicits a muscle contraction in starfish, and the isolation of PALAL may lead to develop other bioactive peptides sharing its similar sequence and/or activity. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

A 72-hour high fat diet increases transcript levels of the neuropeptide galanin in the dorsal hippocampus of the rat

Background

Recent evidence identifies the hippocampus, a brain structure commonly associated with learning and memory, as key to the regulation of food intake and the development and consequences of obesity. Intake of a high fat diet (HFD) results in altered consumptive behavior, hippocampal damage, and cognitive deficits. While many studies report the effects of HFD after chronic consumption and in the instance of obesity, few examine the events that occur following acute HFD consumption. In this study, male rats were fed either a control diet (10% fat by kcal) or HFD (45% fat by kcal) for 72 h. At the end of the 72-h period, serum and tissues were collected and weighed. Brains were rapidly frozen or formalin-fixed in preparation for qRT-PCR or immunohistochemistry, respectively.

Results

Acute intake of HFD resulted in higher serum levels of leptin and cholesterol, with no significant changes in final body weight or adipose tissue mass. In the dorsal hippocampus, transcription of the neuroprotective peptide galanin was significantly upregulated along with a trend for an increase in brain-derived neurotrophic factor and histone deacetylase 2 in the rats fed HFD. In the ventral hippocampus, there was a significant increase in histone deacetylase 4 and a decrease in galanin receptor 1 in this group. Results from immunohistochemistry validate strong presence of the galanin peptide in the CA1/CA2 region of the dorsal hippocampus.

Conclusions

These results provide evidence for a distinct response in specific functional regions of the hippocampus following acute HFD intake.

The distribution of galanin-immunoreactive nerve fibers in the rat pharynx

Galanin (GAL) consists of a chain of 29/30 amino acids which is widely distributed in the central and peripheral nervous systems. In this study, the distribution of GAL-immunoreactive (-IR) nerve fibers was examined in the rat pharynx and its adjacent regions. GAL-IR nerve fibers were located beneath the epithelium and taste bud-like structure of the pharynx, epiglottis, soft palate and larynx. These nerve fibers were abundant in the laryngeal part of the pharynx, and were rare in other regions. Mucous glands were mostly devoid of GAL-IR nerve fibers. In the musculature of pharyngeal constrictor muscles, many GAL-IR nerve fibers were also located around small blood vessels. However, intrinsic laryngeal muscles contained only a few GAL-IR nerve fibers. The double immunofluorescence method demonstrated that the distribution pattern of GAL-IR nerve fibers was partly similar to that of calcitonin gene-related peptide-IR nerve fibers in the pharyngeal mucosa and muscles. The present findings suggest that the pharynx is one of main targets of GAL-containing nerves in the upper digestive and respiratory systems. These nerves may have sensory and autonomic origins.

Anticonvulsant neuropeptides as drug leads for neurological diseases

Anticonvulsant neuropeptides are best known for their ability to suppress seizures and modulate pain pathways. Galanin, neuropeptide Y, somatostatin, neurotensin, dynorphin, among others, have been validated as potential first-in-class anti-epileptic or/and analgesic compounds in animal models of epilepsy and pain, but their therapeutic potential extends to other neurological indications, including neurodegenerative and psychatric disorders. Disease-modifying properties of neuropeptides make them even more attractive templates for developing new-generation neurotherapeutics. Arguably, efforts to transform this class of neuropeptides into drugs have been limited compared to those for other bioactive peptides. Key challenges in developing neuropeptide-based anticonvulsants are: to engineer optimal receptor-subtype selectivity, to improve metabolic stability and to enhance their bioavailability, including penetration across the blood–brain barrier (BBB). Here, we summarize advances toward developing systemically active and CNS-penetrant neuropeptide analogs. Two main objectives of this review are: (1) to provide an overview of structural and pharmacological properties for selected anticonvulsant neuropeptides and their analogs and (2) to encourage broader efforts to convert these endogenous natural products into drug leads for pain, epilepsy and other neurological diseases.

The neurobiology of anxiety disorders: brain imaging, genetics, and psychoneuroendocrinology

Anxiety disorders are highly comorbid with each other and with major depressive disorder. As syndromes, anxiety and mood disorders share many symptoms, and several treatments are effective for both. Despite this overlap, there exist many distinguishing features that support the continued classification of individual anxiety disorders that are distinct from each other and from major depression. The goal of this article is to describe the key biological similarities and differences between anxiety disorders.

The neurobiology of anxiety disorders: brain imaging, genetics, and psychoneuroendocrinology

Anxiety disorders are highly comorbid with each other and with major depressive disorder. As syndromes, anxiety and mood disorders share many symptoms, and several treatments are effective for both. Despite this overlap, there exist many distinguishing features that support the continued classification of individual anxiety disorders that are distinct from each other and from major depression. The goal of this article is to describe the key biological similarities and differences between anxiety disorders.

The galanin signaling cascade is a candidate pathway regulating oncogenesis in human squamous cell carcinoma

To identify putative biomarkers in squamous cell carcinoma (SCC), a survey of parallel chromosomal alterations and gene expression studies in 10 SCC cell lines were performed using array-comparative genomic hybridization (CGH) and oligo-microarray techniques. The most frequent changes were gains of 11q13.1-13.3 and losses of 18q12.1-23 in SCC. Furthermore, the expression levels of the sets of genes at both these loci in SCC were measured using microarray analysis. By combining the array-CGH with the microarray data, 10 genes at 11q13.1-13.3 and 6 genes at 18q12.1-23 whose expression correlated with chromosomal alterations were identified. To verify the expression levels of the identified genes, we used expression analysis data derived from our earlier study of clinical specimens. In clinical samples, six genes (GAL, GSTP1, MRPL11, MRPL21, SF3B2, and YIF1A) at 11q13.1-13.3 and one gene (GALR1) at 18q23 showed a significant difference between normal and tumor samples. GAL, coding for the neuropeptide galanin, and GALR1, a galanin receptor, were identified as candidate genes of oncogenesis in SCC. The expression levels of GAL, GALR1, GALR2, and GALR3 were confirmed by real-time PCR. The expression ratio between GAL and GALR1 showed a significant negative correlation. GALR1 is a G-protein-coupled receptor that activates GTP-binding proteins to trigger signaling cascades such as the mitogen-activated protein kinase pathway, and is a well-established mitogenic pathway. This further supports the hypothesis that the genes involved in the GAL signaling cascade are candidates for regulation of oncogenesis in SCC.

Galanin inhibition of voltage-dependent Ca(2+) influx in rat cultured myenteric neurons is mediated by galanin receptor 1

Galanin activates three receptors, the galanin receptor 1 (GalR1), GalR2, and GalR3. In the gastrointestinal tract, GalR1 mediates the galanin inhibition of cholinergic transmission to the longitudinal muscle and reduction of peristalsis efficiency in the small intestine. Galanin has also been shown to inhibit depolarization-evoked Ca2+ increases in cultured myenteric neurons. Because GalR1 immunoreactivity is localized to cholinergic myenteric neurons, we hypothesized that this inhibitory action of galanin on myenteric neurons is mediated by GalR1. We investigated the effect of galanin 1-16, which has high affinity for GalR1 and GalR2, in the presence or absence of the selective GalR1 antagonist, RWJ-57408, and of galanin 2-11, which has high affinity for GalR2 and GalR3, on Ca2+ influx through voltage-dependent Ca2+ channels in cultured myenteric neurons. Myenteric neurons were loaded with fluo-4 and depolarized by high K+ concentration to activate voltage-dependent Ca2+ channels. Intracellular Ca2+ levels were quantified with confocal microscopy. Galanin 1-16 (0.01-1 microM) inhibited the depolarization-evoked Ca2+ increase in a dose-dependent manner with an EC(50) of 0.172 microM. The selective GalR1 antagonist, RWJ-57408 (10 microM), blocked the galanin 1-16 (1 microM)-mediated inhibition of voltage-dependent Ca2+ channel. By contrast, the GalR2/GalR3 agonist, galanin 2-11 did not affect the K+-evoked Ca2+ influx in myenteric neurons. GalR1 immunoreactivity was localized solely to myenteric neurons in culture, as previously observed in intact tissue. These findings indicate that the inhibition of depolarization-evoked Ca2+ influx in myenteric neurons in culture is mediated by GalR1 and confirm the presence of functional GalR1 in the myenteric plexus. This is consonant with the hypothesis that GalR1 mediates galanin inhibition of transmitter release from myenteric neurons.

Left-asymmetric expression of Galanin in the linear heart tube of the mouse embryo is independent of the nodal co-receptor gene cryptic

Only very few left/right asymmetrically expressed genes are known in the mammalian embryo. In a screen for novel factors we identified the gene encoding the neuropeptide Galanin in mouse. At embryonic day (E) 8.5 asymmetric mRNA transcription was found in the left half of the linear heart tube. During heart looping and morphogenesis expression became restricted to the atrio-ventricular (AV) canal, followed by specific staining of the AV-node and AV-rings in the four-chambered heart. Expression was inverted in inv/inv and randomized in homozygous iv mutant embryos. Left-sided heart-specific transcription of mouse Gal thus should be controlled by the left-right pathway. The asymmetric pattern was retained in cryptic mutant embryos, in which the Nodal signaling cascade is disrupted. Surprisingly, Pitx2c was found to be expressed in 50% of cryptic mutant hearts as well, suggesting that some aspects of asymmetric gene expression in the heart are independent of cryptic.

The role of proopiomelanocortin (POMC) neurones in feeding behaviour

The precursor protein, proopiomelanocortin (POMC), produces many biologically active peptides via a series of enzymatic steps in a tissue-specific manner, yielding the melanocyte-stimulating hormones (MSHs), corticotrophin (ACTH) and β-endorphin. The MSHs and ACTH bind to the extracellular G-protein coupled melanocortin receptors (MCRs) of which there are five subtypes. The MC3R and MC4R show widespread expression in the central nervous system (CNS), whilst there is low level expression of MC1R and MC5R. In the CNS, cell bodies for POMC are mainly located in the arcuate nucleus of the hypothalamus and the nucleus tractus solitarius of the brainstem. Both of these areas have well defined functions relating to appetite and food intake. Mouse knockouts (ko) for pomc, mc4r and mc3r all show an obese phenotype, as do humans expressing mutations of POMC and MC4R. Recently, human subjects with specific mutations in β-MSH have been found to be obese too, as have mice with engineered β-endorphin deficiency. The CNS POMC system has other functions, including regulation of sexual behaviour, lactation, the reproductive cycle and possibly central cardiovascular control. However, this review will focus on feeding behaviour and link it in with the neuroanatomy of the POMC neurones in the hypothalamus and brainstem.

Alcoholism is associated withGALR3but not two other galanin receptor genes

The neuropeptide galanin is widely expressed in the periphery and the central nervous system and mediates diverse physiological processes and behaviors including alcohol abuse, depression and anxiety. Four genes encoding galanin and its receptors have been identified (GAL, GALR1, GALR2 and GALR3). Recently we found that GAL haplotypes were associated with alcoholism, raising the possibility that genetic variation in GALR1, GALR2 and GALR3 might also alter alcoholism risk. Tag single nucleotide polymorphisms (SNPs) were identified by genotyping SNP panels in controls from five populations. For the association study with alcoholism, six GALR1, four GALR2 and four GALR3 SNPs were genotyped in a large cohort of Finnish alcoholics and non-alcoholics. GALR3 showed a significant association with alcoholism that was driven by one SNP (rs3,091,367). Moreover, the combination of the GALR3 rs3,091,367 risk allele and GAL risk haplotypes led to a modestly increased odds ratio (OR) for alcoholism (2.4) as compared with the effect of either GAL (1.9) or GALR3 alone (1.4). Likewise, the combination of the GALR3 and GAL risk diplotypes led to an increased OR for alcoholism (4.6) as compared with the effect of either GAL (2.0) or GALR3 alone (1.6). There was no effect of GALR1 or GALR2 on alcoholism risk. This evidence suggests that GALR3 mediates the alcoholism-related actions of galanin.

Leptin and the regulation of the hypothalamic-pituitary-adrenal axis

Leptin, the product of the obesity gene (ob) predominantly secreted from adipocytes, plays a major role in the negative control of feeding and acts via a specific receptor (Ob-R), six isoforms of which are known at present. Evidence has been accumulated that leptin, like other peptides involved in the central regulation of food intake, controls the function of the hypothalamic-pituitary-adrenal (HPA) axis, acting on both its central and peripheral branches. Leptin, along with Ob-R, is expressed in the hypothalamus and pituitary gland, where it modulates corticotropin-releasing hormone and ACTH secretion, probably acting in an autocrine-paracrine manner. Only Ob-R is expressed in the adrenal gland, thereby making it likely that leptin affects it by acting as a circulating hormone. Although in vitro and in vivo findings could suggest a glucocorticoid secretagogue action in the rat, the bulk of evidence indicates that leptin inhibits steroid-hormone secretion from the adrenal cortex. In keeping with this, leptin was found to dampen the HPA axis response to many kinds of stress. In contrast, leptin enhances catecolamine release from the adrenal medulla. This observation suggests that leptin activates the sympathoadrenal axis and does not appear to agree with its above-mentioned antistress action. Leptin and/or Ob-R are also expressed in pituitary and adrenal tumors, but little is known about the role of this cytokine in the pathophysiology.

3-arylimino-2-indolones are potent and selective galanin GAL3 receptor antagonists

A series of 3-imino-2-indolones are the first published, high-affinity antagonists of the galanin GAL3 receptor. One example, 1,3-dihydro-1-phenyl-3-[[3-(trifluoromethyl)phenyl]imino]-2H-indol-2-one (9), was shown to have high affinity for the human GAL3 receptor (Ki=17 nM) and to be highly selective for GAL3 over a broad panel of targets, including GAL1 and GAL2. Compound 9 was also shown to be an antagonist in a human GAL3 receptor functional assay (Kb=29 nM).

Galanin receptor expression in cultured human keratinocytes and in normal human skin

Galanin (GAL) is a biologically active neuropeptide that is widely distributed in the nervous system. GAL exerts diverse action via the GAL receptors (GALR1, GALR2, and GALR3), which belong in the superfamily of G-protein-coupled transmembrane receptors. In human skin, GAL-like immunoreactivity has been reported in free nerve endings and fibers of the dermis. The extraneuronal expression of GAL has also been demonstrated. Although the GALRs are essential for biological functions, the expressions of different GALR subtypes in cultured human keratinocytes have not yet been investigated. The aim of our study was to investigate the mRNA and protein expressions of the different GALRs in the HaCaT immortalized keratinocyte cell line and in cultured human keratinocytes. When reverse transcription (RT)-polymerase chain reaction (PCR) was used with different GALR-specific primers, only GALR2 mRNA was identified in cultured HaCaT cells and keratinocytes. Sequencing of the PCR products proved the presence of GALR2 mRNA in the keratinocytes. The presence of GALR2 protein was next investigated, using a polyclonal antibody against human GALR2. Both the HaCaT cells and the cultured keratinocytes displayed specific immunohistochemical staining, with higher intensity on the surface of the keratinocytes. Immunohistochemical investigations of normal human skin specimens revealed that GALR2 was expressed with high intensity in the basal layer of the epidermis and also around the hair follicles in the dermis. GAL treatment of the keratinocytes resulted in an increase in cytosolic Ca2+ concentration, suggesting that GALR2 is a functional receptor. Further studies are necessary to clarify the biological effects of GAL in the skin.

Amino substituted analogs of 1-phenyl-3-phenylimino-2-indolones with potent galanin Gal3 receptor binding affinity and improved solubility

A series of amino analogs of 1,3-dihydro-1-phenyl-3-[[3-(trifluoromethyl)phenyl]imino]-2H-indol-2-one (1) were synthesized to improve aqueous solubility, while retaining high affinity for the human galanin Gal3 receptor. A very potent analog (9e, 1,3-dihydro-1-[3-(2-pyrrolidinylethoxy)phenyl]-3-[[3-(trifluoromethyl)phenyl]imino]-2H-indol-2-one, Ki=5 nM) shows good selectivity and solubility of 48 microg/mL at pH 7.4.

Effects of the neuropeptides substance P, calcitonin gene-related peptide, vasoactive intestinal polypeptide and galanin on the production of nerve growth factor and inflammatory cytokines in cultured human keratinocytes

Neuropeptides released from the cutaneous sensory nerve endings have neurotransmitter and immunoregulatory roles; they exert mitogenic actions and can influence the functions of different cell types in the skin. The aims of this study were a systematic investigation of the effects of the neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP) and galanin (GAL) on the inflammatory cytokine production (IL-1alpha, IL-8 and TNF-alpha) of the keratinocytes, and a study of their role in the production and secretion of nerve growth factor (NGF) and its precursor molecule (proNGF). Cultures of normal human keratinocytes were treated with 10(-8)M SP, CGRP, VIP or GAL for 30 min. After different time intervals, cells were harvested for total RNA isolation; in addition, cell lysates and supernatants were collected. The effects of the neuropeptides on the mRNA expressions of the different cytokines and NGF were investigated by Q-RT-PCR and the protein levels were studied by means of ELISA assays and Western blotting. Each of the four neuropeptides induced increases in the expressions of IL-1alpha, IL-8 and TNF-alpha mRNA. Increases appeared in the amount of the IL-1alpha protein in the supernatants of neuropeptide-treated cells, and the IL-8 secretion was mildly elevated, while secretion of TNF-alpha remained undetectable. The four neuropeptides increased the NGF mRNA expression to different extents. In the cell lysates of the keratinocytes, only proNGF could be detected, its concentration in the neuropeptide-treated cells being approximately twice that in the time-matched controls. Both control cultures and neuropeptide-treated cultures were found to secrete proNGF and mature NGF, but neuropeptide-treated cell cultures produced markedly higher (3-7-fold) amounts of NGF-like immunoreactive materials. The results demonstrated that neuropeptides released from cutaneous nerves after an injurious stimulus are able to induce an upregulation of IL-1alpha and IL-8 production; they are additionally able to influence the expressions of proNGF/NGF and their secretion from the keratinocytes. These findings may contribute toward an understanding of the neural influence on skin health and disease.

Galanin-like peptide stimulates food intake via activation of neuropeptide Y neurons in the hypothalamic dorsomedial nucleus of the rat

Galanin-like peptide (GALP), a 29-amino-acid neuropeptide, is located in the hypothalamic arcuate nucleus (ARC), binds to galanin receptor subtype 2, and induces food intake upon intracerebroventricular (icv) injection in rats. However, neural mechanisms underlying its orexigenic action remain unclear. We aimed to identify the nuclei and neuron species that mediate the food intake in response to icv GALP injection. Intracerebroventricular injection of GALP, as powerfully as that of neuropeptide Y (NYP), increased food intake for the initial 2 h. GALP injected focally into the dorsomedial nucleus (DMN), but not the ARC, lateral hypothalamus, or paraventricular nucleus (PVN), stimulated food intake for 2 h after injection. In contrast, galanin injected into the DMN had no effect. DMN-lesion rats that received icv GALP injection showed attenuated feeding compared with control rats. Intracerebroventricular GALP injection increased c-Fos expression in NPY-containing neurons in the DMN, but not the ARC. GALP increased the cytosolic calcium concentration ([Ca(2+)](i)) in NPY-immunoreactive neurons isolated from the DMN, but not the ARC. Furthermore, both anti-NPY IgG and NPY antagonists, when preinjected, counteracted the feeding induced by GALP injection. These data show that icv GALP injection induces a potent short-term stimulation of food intake mainly via activation of NPY-containing neurons in the DMN.

Recombinant adeno-associated viral vectors as therapeutic agents to treat neurological disorders

Recombinant adeno-associated virus (rAAV) is derived from a small human parvovirus with an excellent safety profile. In addition, this viral vector efficiently transduces and supports long-term transgene expression in the nervous system. These properties make rAAV a reasonable candidate vector for treating neurological disorders. Indeed, rAAV is currently being used in five early stage clinical trials for various neurodegenerative disorders. Therefore, we will review the currently available preclinical data using rAAV in animal models of central nervous system (CNS) disorders. Moreover, potential caveats for rAAV-based gene therapy in the CNS are also presented.

Galanin attenuates cyclic AMP regulatory element-binding protein (CREB) phosphorylation induced by chronic morphine and naloxone challenge in Cath.a cells and primary striatal cultures

Repeated morphine administration leads to molecular alterations of the neural circuitry in the locus coeruleus and nucleus accumbens. These changes include increased activity of several components of the cAMP signaling pathway that are thought to be associated with psychological and somatic signs of opiate withdrawal. The neuropeptide galanin has been shown to attenuate cAMP signaling in multiple cell types. The current study demonstrates that acute galanin treatment blocks the consequences of increased cAMP signaling following chronic opiate administration and withdrawal in Cath.a cells and primary cultures of striatal neurons as measured by phosphorylation of the transcription factor cAMP regulatory element-binding protein (CREB). In addition, galanin-mediated attenuation of CREB phosphorylation is independent of galanin-induced extracellular signal-regulated kinase (ERK) 1/2 phosphorylation in Cath.a cells. These data suggest that galanin receptors may serve as an additional potential therapeutic target for the treatment of opiate withdrawal.

The contractile effects of several substituted short analogues of porcine galanin in isolated rat jejunal and colonic smooth muscle strips

The activity of short porcine galanin (Gal) analogues was tested in vitro using rat jejunal and colonic smooth muscle strips. Peptides evoked concentration-dependent tissue contractions yielding typical response curves in concentration range from 0.3 nM to 300 microM, with a characteristic fall-down effect at the supramaximal concentrations. Gal(1-15) was less potent than Gal(1-29). Furthermore, [D-Trp(2)]Gal(1-15), [endo-Trp(2),Cle(4)]Gal(1-15), [D-Leu(4)]Gal(1-15), [des-Leu(4)]Gal(1-15), [Hse(6)]Gal(1-15), [Dab(14)]Gal(1-15), [Dpr(14)]Gal(1-15) or [Arg(14)]Gal(1-15) showed a considerable decrease in potency compared to Gal(1-15) in jejunal and/or colonic smooth muscle cells. Functional evidence confirmed that the integrity of both N- and C-terminals must be preserved in order to preserve a full excitatory myogenic potential of the peptide in rat jejunum and colon. Besides, amino acids located in positions 2, 4, 6 and 14 play a crucial role in recognition and activation of molecular domains responsible for Gal action in the intestinal smooth muscle.

Phenotypic analysis of mice deficient in the type 2 galanin receptor (GALR2)

Galanin is a neuropeptide implicated in the regulation of feeding, reproduction, cognition, nociception, and seizure susceptibility. There are three known galanin receptor (GALR) subtypes (GALR1, GALR2, and GALR3), which bind to galanin with different affinities and have their own unique distributions, signaling mechanisms, and putative functions in the brain and peripheral nervous system. To gain further insight into the possible physiological significance of GALR2, we created mutant mice that were deficient in GALR2 and compared their phenotype to that of wild-type (WT) littermate or age-matched controls, with respect to basic motor and sensory function, feeding behavior, reproduction, mood, learning and memory, and seizure susceptibility. Phenotypic analysis revealed that animals bearing a deletion of GALR2 did not differ significantly from their WT controls in any of the measured variables. We conclude that either GALR2 plays no role in these physiological functions or through redundancy or compensation these mutant animals can adapt to the congenital absence of GALR2. It is also conceivable that GALR2 plays only a subtle role in some of these functions and that the impact of its loss could not be detected by the analytical procedures used here.

GalR1, but not GalR2 or GalR3, levels are regulated by galanin signaling in the locus coeruleus through a cyclic AMP-dependent mechanism

The galanin receptors GalR1, GalR2 and GalR3 are widely expressed throughout the mouse brain and are enriched in catecholaminergic nuclei. Here, we show that GalR1 protein levels are regulated by neuronal activity and changes in cAMP levels. GalR1, but not GalR2 or GalR3, is specifically up-regulated in the LC-like Cath.a cell line in a cAMP-dependent manner. GalR1 protein and mRNA levels are also up-regulated in the LC of galanin knockout mice, whereas GalR2 and GalR3 are not. Lack of galanin-maintained cAMP tone in the galanin knockout mouse appears to result in a loss of negative feedback resulting in increased levels of CREB phosphorylation and increased GalR1 expression. These findings suggest that changes in levels of GalR1 may play an important role in modulating signaling events and neuroplasticity underlying physiological functions of the LC.

Galanin-like peptide and ghrelin increase cytosolic Ca2+ in neurons containing growth hormone-releasing hormone in the arcuate nucleus

Galanin-like peptide (GALP), discovered in the porcine hypothalamus, is expressed predominantly in the arcuate nucleus (ARC), a feeding-controlling center. Intracerebroventricular injection of GALP has been shown to stimulate food intake in the rats. However, the mechanisms underlying the orexigenic effect of GALP are unknown. The present study aimed to determine the target neurons of GALP in the ARC. We investigated the effects of GALP on cytosolic free Ca2+ concentration ([Ca2+]i) in the neurons isolated from the rat ARC, followed by neurochemical identification of these neurons by immunocytochemistry using antisera against growth hormone-releasing hormone (GHRH), neuropeptide Y (NPY) and proopiomelanocortin (POMC), the peptides localized in the ARC. GALP at 10(-10) M increased [Ca2+]i in 11% of single neurons of the ARC, while ghrelin, an orexigenic and GH-releasing peptide, at 10(-10) M increased [Ca2+]i in 35% of the ARC neurons. Some of these GALP- and/or ghrelin-responsive neurons were proved to contain GHRH. In contrast, NPY- and POMC-containing neurons did not respond to GALP. These results indicate that GALP directly targets GHRH neurons, but not NPY and POMC neurons, and that ghrelin directly targets GHRH neurons in the ARC. The former action may be involved in the orexigenic effect of GALP and the latter in the GH-releasing and/or orexigenic effects ghrelin.

Identification of galanin receptor 1 on excitatory motor neurons in the guinea pig ileum

Exogenously administered galanin inhibits cholinergic transmission to the longitudinal muscle and reduces peristaltic efficiency in the guinea pig ileum with a mechanism partially mediated by galanin receptor 1 (GAL-R1). We investigated the effect of exogenous galanin 1-16, which has high affinity for GAL-R1, on the ascending excitatory reflex of the circular muscle elicited by radial distension in isolated segments of guinea pig ileum. We used a three-compartment bath that allows dissecting the ascending pathway into the oral (site of excitatory motor neurons), intermediate (site of ascending interneurons) and caudal compartment (site of intrinsic primary afferent neurons). Galanin 1-16 (0.3-3 micromol L(-1)) applied to the oral compartment inhibited in a concentration-dependent manner the ascending excitatory reflex elicited by the wall distension in the caudal compartment. This effect was antagonized by the GAL-R1 antagonist, RWJ-57408 (1 and 10 micromol L(-1)). By contrast, galanin 1-16 was ineffective when added to the intermediate or caudal compartment up to 3 micromol L(-1). GAL-R1 immunoreactive neurons did not contain neuron-specific nuclear protein, a marker for intrinsic primary afferent neurons. These findings indicate that GAL-R1s are present on motor neurons responsible for the ascending excitatory reflex, but not on ascending interneurons and intrinsic primary afferent neurons.

Galanin receptor 1 has anti-proliferative effects in oral squamous cell carcinoma

In the United States, oral cancer accounts for more deaths annually than cervical cancer, leukemias, or Hodgkin's lymphoma. Studies have shown that aberrations of chromosome 18q develop with tumor progression and are associated with significantly decreased survival in head and neck cancer patients. The G-protein-coupled receptor, galanin receptor 1 (GALR1), maps to this region of chromosome 18q. Although the role of GALR1 has been well characterized in neuronal cells, little is known regarding this receptor in non-neuronal cells. In this study, the expression, mitogenic function, and signaling mechanism of GALR1 are investigated in normal and malignant oral epithelial cells. mRNA expression was determined via reverse transcriptase-PCR. Protein quantification was done via immunoblot analysis and enzyme-linked immunosorbent assay. For functional and signaling studies, an inhibitory antibody was generated to the N-terminal ligand binding domain of GALR1. GALR1 protein and mRNA expression and GAL secretion were detected at variable levels in immortalized human oral keratinocytes and human oropharyngeal squamous cell carcinoma cell lines. Upon competitive inhibition of GALR1, proliferation was up-regulated in immortalized and malignant keratinocytes. Furthermore, studies with the inhibitory antibody and U0126, the MAPK inhibitor, show that GALR1 inhibits proliferation in immortalized and malignant keratinocytes by inactivating the MAPK pathway. GALR1s inhibitory effects on proliferation in epithelial cells raises the possibility that inactivation or disregulation of this receptor can lead to uncontrolled proliferation and neoplastic transformation.

Effects of galnon, a non-peptide galanin-receptor agonist, on insulin release from rat pancreatic islets

Galanin is a neurotransmitter peptide that suppresses insulin secretion. The present study aimed at investigating how a non-peptide galanin receptor agonist, galnon, affects insulin secretion from isolated pancreatic islets of healthy Wistar and diabetic Goto-Kakizaki (GK) rats. Galnon stimulated insulin release potently in isolated Wistar rat islets; 100 microM of the compound increased the release 8.5 times (p<0.001) at 3.3 mM and 3.7 times (p<0.001) at 16.7 mM glucose. Also in islet perifusions, galnon augmented several-fold both acute and late phases of insulin response to glucose. Furthermore, galnon stimulated insulin release in GK rat islets. These effects were not inhibited by the presence of galanin or the galanin receptor antagonist M35. The stimulatory effects of galnon were partly inhibited by the PKA and PKC inhibitors, H-89 and calphostin C, respectively, at 16.7 but not 3.3 mM glucose. In both Wistar and GK rat islets, insulin release was stimulated by depolarization of 30 mM KCl, and 100 microM galnon further enhanced insulin release 1.5-2 times (p<0.05). Cytosolic calcium levels, determined by fura-2, were increased in parallel with insulin release, and the L-type Ca2+-channel blocker nimodipine suppressed insulin response to glucose and galnon. In conclusion, galnon stimulates insulin release in islets of healthy rats and diabetic GK rats. The mechanism of this stimulatory effect does not involve galanin receptors. Galnon-induced insulin release is not glucose-dependent and appears to involve opening of L-type Ca2+-channels, but the main effect of galnon seems to be exerted at a step distal to these channels, i.e., at B-cell exocytosis.

Development of neurotransmitter systems during critical periods

Neurotransmitters are released from neurons and mediate neuronal communication. Neuromodulators can also be released from other cells and influence the neuronal signaling. Both neurotransmitters and neuromodulators play an important role in the shaping and the wiring of the nervous system possibly during critical windows of the development. Monoamines are expressed in the very early embryo, at which stage the notochord already contains high noradrenaline levels. Purines and neuropeptides are probably also expressed at an early stage, in a similar way as they occur during early phylogenesis. The levels of most neurotransmitters and neuromodulators increase concomitantly with synapse formation. Some of them surge during the perinatal period (such as glutamate, catecholamines, and some neuropeptides) and then level off. The interesting question is to what extent the expression of neuroactive agents is related to the functional state of the fetus and the newborn. Monoamines are expressed in the very early embryo, at which stage the notochord already contains high noradrenaline levels. They may have an important role for neurotransmission in the fetus. In the adult mammal, the fast switching excitatory amino acids dominate. However, they also seem to be important for the wiring of the brain and the plasticity before birth. NMDA receptors that are supposed to mediate these effects dominate and are then substituted by AMPA receptors. The main inhibitory amino acids gamma-aminobutyric acid (GABA) and glycine are excitatory in the developing brain by depolarizing developing neurons that have high Cl- concentrations. This seems to be of major importance for the wiring of neuronal circuits. Prenatal or neonatal stress, for example, hypoxia, can affect the programming of neurotransmitter and receptor expression, which can lead to long-term behavioral effects.

Relationship between growth hormone (GH) pulses in the peripheral circulation and GH-releasing hormone and somatostatin profiles in the cerebrospinal fluid of goats

Growth hormone (GH) is secreted in a pulsatile manner, but the underlying mechanisms of GH pulse generation remain to be resolved. In the present study, we investigated the relationship between GH pulses in the peripheral circulation and GH-releasing hormone (GHRH) and somatostatin (SRIF) profiles in the cerebrospinal fluid (CSF) of male goats. The effects of an intracerebroventricular (icv) injection of neuropeptide Y (NPY), galanin and ghrelin were also analyzed. Blood and CSF samples were collected every 15 min for 8 hr from the jugular vein and third ventricle, respectively. GH pulsatility in the goat was found to consist of distinct large pulses of 5 hr periodicity and small pulses of 1 hr periodicity. GHRH and SRIF in the CSF fluctuated in a pulsatile manner with 1 hr periodicity, and most of the descending phase of SRIF pulses were associated with the initiation of GH pulses. Icv injections of NPY, galanin and ghrelin stimulated GHRH release without affecting SRIF release. In addition, NPY suppressed, and galanin and ghrelin induced large GH pulses, although ghrelin was much more effective than galanin. These results suggest that an hourly fall in SRIF is involved in generating intrinsic circhoral rhythm of GH pulsatility. The mechanisms underlying the generation of large GH pulses of 5 hr periodicity remain unknown, while direct action of NPY and/or ghrelin on the pituitary might be involved.

Distribution of galanin in bone and joint tissues

The article describes the distribution of galanin in normal bone and joint tissues. Periosteum, cortical bone, bone marrow, and synovial membrane of normal rats were analyzed. Immunoelectron microscopy (iEM) was used to analyze the distribution of galanin, and radioimmunoassay (RIA) was used to determine its concentration. Immunoelectron microscopy showed that galanin is abundant in nerve fibers and endothelial cells in the periosteum and also in macrophage-like-cells and nerve fibers of the synovial membrane. The concentration of galanin measured by RIA showed the highest concentration in bone marrow, followed by periosteum and cortical bone. This study demonstrates that galanin is present and can be quantified in different compartments of bone and joint tissues and illustrates the possible role of galanin under physiological conditions.

Increased galanin receptor occupancy in Alzheimer's disease

Increased galanin (GAL) may be associated with the cognitive deficits characteristic of Alzheimer's disease (AD). However, both increased and decreased GAL receptor density has been reported in AD brain. Previous studies indicate pre-treatment with guanine nucleotides displaces endogenous GAL from GAL receptors (GALR), providing an indirect measurement of GALR occupancy. In addition, pre-treatment with guanine nucleotides may provide a more accurate measurement of GALR density since it would avoid the masking of GALRs by residual binding of endogenous GAL. Thus, in the present study, we examined the influence of pre-treatment with guanine nucleotides on 125I-GAL binding in multiple regions of normal and AD brain. Our results indicate that GTP pre-treatment enhances GAL binding in specific regions in normal and AD brain. In addition, our results suggest an increase in the number of GALRs occupied by endogenous GAL in the deep layers of the frontal cortex and the lateral hypothalamus of AD subjects compared to normal subjects. The regional differences in GALR density and receptor occupancy between normal and AD subjects may play a role in the cognitive disturbances associated with the disease.

Role of galanin receptor 1 in gastric motility in rat

Galanin actions are mediated by distinct galanin receptors (GAL-R), GAL-R1, -R2 and -R3. We investigated the role of GAL-R1 in gastric motility and the expression of GAL-R1 in the rat stomach. In vivo, in urethane-anaesthetized rats, galanin (equipotent for all GAL-Rs) induced a short inhibition of gastric motility, followed by increase in tonic and phasic gastric motility; the latter was significantly reduced by the GAL-R1 antagonist, RWJ-57408. Galanin 1-16 (high affinity for GAL-R1 and -R2) induced a long-lasting decrease of intragastric pressure, which was not modified by RWJ-57408. In vitro, galanin and galanin 1-16 induced increase of intragastric pressure that was not affected by RWJ-57408. Tetrodotoxin (TTX) did not suppress the galanin excitatory effect, whereas the effect of galanin 1-16 on gastric contraction was increased by TTX- or N-nitro-L-arginine, an inhibitor of nitric oxide synthase. GAL-R1 immunoreactivity was localized to cholinergic and tachykinergic neurons and to neurons immunoreactive for nitric oxide synthase or vasoactive intestinal polypeptide. This study suggests that an extrinsic GAL-R1 pathway mediates the galanin excitatory action, whereas an extrinsic, non GAL-R1 pathway is likely to mediate the galanin inhibitory effect in vivo. GAL-R1 intrinsic neurons do not appear to play a major role in the control of gastric motility.

Galanin-like peptide as a link in the integration of metabolism and reproduction

The arcuate nucleus is a hypothalamic center that couples energetics and reproduction. Peptide-releasing neurons in the arcuate nucleus receive and process humoral signals from the periphery and relay this information to other nuclei in the hypothalamus and preoptic area. Galanin-like peptide (GALP) is expressed in the arcuate nucleus, and GALP-containing neurons are targets for the action of leptin. GALP-containing neurons are closely apposed to gonadotropin-releasing hormone (GnRH) neurons in the preoptic area, and CNS injections of GALP stimulate GnRH-mediated secretion of luteinizing hormone. These observations indicate that GALP is a molecular signal that couples circulating indices of metabolism to the neuroendocrine reproductive system and, thus, regulates reproductive activity as a function of the energy state. In this article, we describe the involvement of GALP in metabolism and reproduction, and in the coupling between these two processes.

Role of galanin receptor 1 in peristaltic activity in the guinea pig ileum

Galanin effects are mediated by distinct receptors, galanin receptor 1 (GAL-R1), GAL-R2 and GAL-R3. Here, we analyzed 1) the role of GAL-R1 in cholinergic transmission and peristalsis in the guinea-pig ileum using longitudinal muscle-myenteric plexus preparations and intact segments of the ileum in organ bath, and 2) the distribution of GAL-R1 immunoreactivity in the myenteric plexus with immunohistochemistry and confocal microscopy. Galanin inhibited electrically stimulated contractions of longitudinal muscle-myenteric plexus preparations with a biphasic curve. Desensitization with 1 microM galanin suppressed the high potency phase of the curve, whereas the GAL-R1 antagonist, RWJ-57408 (1 microM), inhibited the low potency phase. Galanin (3 microM) reduced the longitudinal muscle contraction and the peak pressure, and decreased the compliance of the circular muscle. All these effects were antagonized by RWJ-57408 (1 or 10 microM). RWJ-57408 (10 microM) per se did not affect peristalsis parameters in normal conditions, nor when peristalsis efficiency was reduced by partial nicotinic transmission blockade with hexamethonium. In the myenteric plexus, GAL-R1 immunoreactivity was localized to neurons and to fibers projecting within the plexus and to the muscle. GAL-R1 was expressed mostly by cholinergic neurons and by some neurons containing vasoactive intestinal polypeptide or nitric oxide synthase. This study indicates that galanin inhibits cholinergic transmission to the longitudinal muscle via two separate receptors; GAL-R1 mediates the low potency phase. The reduced peristalsis efficiency could be explained by inhibition of the cholinergic drive, whereas the decreased compliance is probably due to inhibition of descending neurons and/or to the activation of an excitatory muscular receptor. Endogenous galanin does not appear to affect neuronal pathways subserving peristalsis in physiologic conditions via GAL-R1.

Analysis of the contribution of galanin receptors 1 and 2 to the central actions of galanin-like peptide

Galanin-like peptide (GALP) shares partial sequence identity with galanin and exhibits agonistic activity at two of the galanin receptor subtypes (GALR1 and GALR2) in vitro. The goal of these experiments was to determine whether galanin receptors mediate the effects of central GALP administration on food intake, body weight, and luteinizing hormone (LH) secretion in the mouse. We first evaluated the effects of intracerebroventricular injections of GALP or its vehicle alone in GALR1 knockout mice, GALR2 knockout mice, and their respective wild-type controls. GALP reduced food intake and body weight after 24 h to a similar degree in wild-type, GALR1 knockout, and GALR2 knockout mice. The wild-type, GALR1 knockout, and GALR2 knockout mice also exhibited significant increases in serum levels of LH following the GALP injections. To help delineate the biologically active moiety of the GALP molecule, we injected wild-type mice with shorter fragments of the full-length GALP peptide. Neither GALP((1-21)) (the fragment containing the galanin-homologous sequence) nor GALP((22-60)) (the C-terminal portion of the GALP molecule lacking sequence identity with galanin) had any discernable effect on food intake, body weight or circulating LH. These observations demonstrate that neither GALR1 nor GALR2 are essential for mediating the effects of GALP on feeding, body weight or LH secretion. Furthermore, the galanin-homologous region of the GALP molecule is not sufficient to mimic the effects of full-length GALP. Together, these findings argue against the hypothesis that GALP signals solely through galanin receptors in vivoand suggest the existence of a yet-to-be-identified GALP-specific receptor.

An antinociceptive role of galanin in the arcuate nucleus of hypothalamus in intact rats and rats with inflammation

In the arcuate nucleus of hypothalamus (ARC), galaninergic fibers form synaptic contacts with proopiomelanocortin neurons, which are involved in pain modulation. The present study assessed the role of exogenous and endogenous galanin in the modulation of nociception in the ARC of rats. The hindpaw withdrawal latency (HWL) to thermal and mechanical stimulation was assessed by the hot-plate test and the Randall Selitto Test. Intra-ARC injection of galanin dose-dependently increased the HWLs in intact rats, indicating an antinociceptive role of exogenous galanin in the ARC. The antinociceptive effect of galanin was blocked by following intra-ARC injection of galantide, a putative galanin receptor antagonist, suggesting that the antinociceptive effect of galanin is mediated by galanin receptors. Moreover, intra-ARC injection of galanin increased the HWL in rats with inflammation. Intra-ARC administration of galantide alone reduced the HWLs in rats with inflammation, while there were no influences of galantide on the HWL in intact rats. Taken together, the results show that galanin has an antinociceptive role in the ARC of intact rats and rats with inflammation.

Galanin immunoreactivity in paragangliomas but not in carcinoid tumors

Galanin is a 29 to 30-amino acid neuropeptide involved in diverse regulatory effects in the central and peripheral nervous systems. Although galanin has been found in paragangliomas and other tumors, its expression has not been studied in carcinoid tumors arising in various locations. Galanin was detected in 62% (15/24) of adrenal pheochromocytomas, 40% (2/5) of jugulotympanic paragangliomas, and 18% (2/11) of carotid body paragangliomas, but was absent in 4 extra-adrenal pheochromocytomas and 3 metastatic or recurrent paragangliomas. All 26 carcinoid tumors were negative. Galanin may have limited utility as a diagnostic marker alone but would be most useful in conjunction with other immunohistochemical markers for the differential diagnosis of neuroendocrine tumors.

Inter- and intra-nuclear differences in galanin expression between the hypothalamic paraventricular and supraoptic nuclei in colchicine-untreated rats

Not much is known of the topography of galanin expression in the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei neurons in colchicine (an axoplasmic inhibitor)-untreated animals. Insight into the biological implication(s) of galanin expression in the PVN and SON will depend, at least in part, on the nature of its distribution in colchicine-untreated animals. In this study therefore, the topographical distribution of galaninergic profiles was examined in the PVN and SON of colchicine-untreated rats. Staining in the parvocellular PVN (PVN(p)) was predominantly as varicose thin galanin fiber processes while the magnocellular PVN (PVN(m)) contained large cell soma and fiber processes. The relative fiber density was higher in the anterior, periventricular and medial PVN(p) than in the dorsal, lateral and posterior subdivisions. Large-sized cells and thick fibers were limited to the posterior PVN(m) while the anterior and medial PVN(m) contained varicose profiles. Light- and intensely-stained galanin-positive cells as well as large- and small-diameter (varicose or non-varicose) fibers were observed in the SON. The large and thin fibers exhibit preferential ventral and dorsal distribution, respectively. Together with the complexity of specific afferent and efferent connections within the PVN and SON, these observations underscore heterogeneous galanin expression and raise potential implications for understanding the biological role of galanin by physiologically challenging stimuli.

A role for galanin-like peptide in the integration of feeding, body weight regulation, and reproduction in the mouse

Galanin-like peptide (GALP) shares sequence homology with galanin and binds to galanin receptors in vitro. GALP neurons in the arcuate nucleus coexpress leptin receptors, and GALP mRNA expression is up-regulated by leptin. Based on these observations, we postulated that GALP plays a role in mediating leptin's inhibitory effects on food intake (FI) and body weight (BW), as well as its stimulatory effect on the reproductive axis. To test these hypotheses, we performed several studies in which mice received intracerebroventricular injections of either GALP or vehicle. Acute GALP treatment elicited a dose-dependent suppression of FI and BW. Long-term treatment with GALP caused only transient reductions in FI and BW, demonstrating that the mice became refractory to continued exposure to GALP. GALP inhibited FI as early as 1 h post injection. Central injection of GALP suppressed locomotor activity and elicited the formation of a conditioned taste aversion. In male mice, serum levels of LH and testosterone were increased by GALP administration. Although we cannot rule out possible nonspecific effects of GALP on FI, the present observations are consistent with the argument that GALP is a downstream effector of leptin's actions within the central nervous system.

Restricted distribution of galanin receptor 3 (GalR3) mRNA in the adult rat central nervous system

Recent molecular cloning studies have established the existence of a third rat galanin receptor subtype, GalR3, however its precise distribution in the mammalian central nervous system (CNS) is not well established. In the present study, we examined the regional and cellular distribution of GalR3 mRNA in the CNS of the rat by in situ hybridization. Our findings indicate that GALR3 mRNA expression in the rat brain is discrete and highly restricted, concentrated mainly in the preoptic/hypothalamic area. Within the hypothalamus, GalR3 expression was confined to the paraventricular, ventromedial and dorsomedial hypothalamic nuclei. In addition to these hypothalamic nuclei, GalR3 mRNA-expressing cells were observed in the medial septum/diagonal band of Broca complex, the bed nucleus of the stria terminalis, the medial amygdaloid nucleus, the periaqueductal gray, the lateral parabrachial nucleus, the dorsal raphe nucleus, the locus coeruleus, the medial medullary reticular formation and in one of the circumventricular organs, the subfornical organ. In the spinal cord, a faint but specific ISH signal was observed over the laminae I-II with a few moderately labeled cells distributed in laminae V and X. The neuroanatomical distribution of GalR3 suggests it might be involved in mediating documented effects of galanin on food intake, fluid homeostasis, cardiovascular function and nociception.