Inhibitory effect of galanin on postprandial gastrointestinal motility and gut hormone release in humans

Galanin System in the Human Bile Duct and Perihilar Cholangiocarcinoma

BACKGROUND

Perihilar cholangiocarcinoma (pCCA) is characterised by poor outcomes. Early diagnosis is essential for patient survival. The peptide galanin (GAL) and its receptors GAL1-3 are expressed in various tumours. Detailed characterisation of the GAL system in pCCA is lacking. Our study sought to characterise GAL and GAL1-3 receptor (GAL1-3-R) expression in the healthy human bile duct, in cholestasis and pCCA.

METHODS

Immunohistochemical staining was performed in healthy controls (n = 5) and in the peritumoural tissues (with and without cholestasis) (n = 20) and tumour tissues of pCCA patients (n = 33) using validated antibodies. The score values of GAL and GAL1-3-R expression were calculated and statistically evaluated.

RESULTS

GAL and GAL1-R were expressed in various bile duct cell types. GAL2-R was only slightly but still expressed in almost all the examined tissues, and GAL3-R specifically in cholangiocytes and capillaries. In a small pCCA patient cohort (n = 18), high GAL expression correlated with good survival, whereas high GAL3-R correlated with poor survival.

CONCLUSIONS

Our in-depth characterisation of the GAL system in the healthy human biliary duct and pCCA in a small patient cohort revealed that GAL and GAL3-R expression in tumour cells of pCCA patients could potentially represent suitable biomarkers for survival.

Downregulation of the expression of galanin impairs erectile function in hypoandrogenic rats

Background

The relationship between galanin and erectile function under low androgen levels is still unclear.

Aim

To explore whether a low testosterone level damages the erection of a rat by regulating the expression of galanin and GalR in penile cavernous tissue.

Methods

Thirty-six male Sprague-Dawley rats, 8 weeks of age, were randomly grouped as follows (n = 6): control, castration, castration + testosterone replacement, control + transfection, castration + transfection, and castration + empty transfection. At 4 weeks after castration, rats in the transfection group were injected with lentivirus carrying the targeting galanin gene (2 × 10⁸ TU/mL, 10 μL) in the corpus cavernosum. After 1 week of injection, the intracavernosal pressure (ICP), mean arterial blood pressure (MAP), nitric oxide (NO), serum testosterone concentration, galanin, GalR1-3, ROCK1, ROCK2, and p-eNOS/eNOS in the rat penile tissues were evaluated.

Outcomes

ICPmax/MAP and the expression of galanin in the corpus cavernosum in castrated rats were obviously decreased as compared with those in the control rats.

Results

The castrated rats showed remarkably lower ICPmax/MAP, galanin, GalR1-3, p-eNOS/eNOS, and NO content and markedly higher ROCK1 and ROCK2 in penile tissues than the control group (P < .05). The transfected rats administrated with LV Gal had obviously higher ICPmax/MAP, p-eNOS/eNOS, and NO content and less ROCK1 and ROCK2 protein expression in the corpus cavernosum when compared with the castration group (P < .05).

Clinical Translation

Upregulating the expression of galanin in the penile corpus cavernosum might be a novel method of treating erectile dysfunction caused by a low androgen level.

Strengths and Limitations

The conclusions obtained in the animal experiments need to be confirmed in human data.

Conclusion

The erectile function of hypoandrogen rats might be inhibited by downregulating the level of galanin and GalR1-3, upregulating ROCK1 and ROCK2 levels, and inhibiting the eNOS/NO signaling pathway in penile corpus cavernosum.

Functions of galanin, spexin and kisspeptin in metabolism, mood and behaviour

The bioactive peptides galanin, spexin and kisspeptin have a common ancestral origin and their pathophysiological roles are increasingly the subject of investigation. Evidence suggests that these bioactive peptides play a role in the regulation of metabolism, pancreatic β-cell function, energy homeostasis, mood and behaviour in several species, including zebrafish, rodents and humans. Galanin signalling suppresses insulin secretion in animal models (but not in humans), is potently obesogenic and plays putative roles governing certain evolutionary behaviours and mood modulation. Spexin decreases insulin secretion and has potent anorectic, analgesic, anxiolytic and antidepressive-like effects in animal models. Kisspeptin modulates glucose-stimulated insulin secretion, food intake and/or energy expenditure in animal models and humans. Furthermore, kisspeptin is implicated in the control of reproductive behaviour in animals, modulation of human sexual and emotional brain processing, and has antidepressive and fear-suppressing effects. In addition, galanin-like peptide is a further member of the galaninergic family that plays emerging key roles in metabolism and behaviour. Therapeutic interventions targeting galanin, spexin and/or kisspeptin signalling pathways could therefore contribute to the treatment of conditions ranging from obesity to mood disorders. However, many gaps and controversies exist, which must be addressed before the therapeutic potential of these bioactive peptides can be established.

Inferior vagal ganglion galaninergic response to gastric ulcers

Galanin is a neuropeptide widely expressed in central and peripheral nerves and is known to be engaged in neuronal responses to pathological changes. Stomach ulcerations are one of the most common gastrointestinal disorders. Impaired stomach function in peptic ulcer disease suggests changes in autonomic nerve reflexes controlled by the inferior vagal ganglion, resulting in stomach dysfunction. In this paper, changes in the galaninergic response of inferior vagal neurons to gastric ulceration in a pig model of the disease were analyzed based on the authors' previous studies. The study was performed on 24 animals (12 control and 12 experimental). Gastric ulcers were induced by submucosal injections of 40% acetic acid solution into stomach submucosa and bilateral inferior vagal ganglia were collected one week afterwards. The number of galanin-immunoreactive perikarya in each ganglion was counted to determine fold-changes between both groups of animals and Q-PCR was applied to verify the changes in relative expression level of mRNA encoding both galanin and its receptor subtypes: GalR1, GalR2, GalR3. The results revealed a 2.72-fold increase in the number of galanin-immunoreactive perikarya compared with the controls. Q-PCR revealed that all studied genes were expressed in examined ganglia in both groups of animals. Statistical analysis revealed a 4.63-fold increase in galanin and a 1.45-fold increase in GalR3 mRNA as compared with the controls. No differences were observed between the groups for GalR1 or GalR2. The current study confirmed changes in the galaninergic inferior vagal ganglion response to stomach ulcerations and demonstrated, for the first time, the expression of mRNA encoding all galanin receptor subtypes in the porcine inferior vagal ganglia.

Insights into Potential Targets for Therapeutic Intervention in Epilepsy

Epilepsy is a chronic brain disease that affects approximately 65 million people worldwide. However, despite the continuous development of antiepileptic drugs, over 30% patients with epilepsy progress to drug-resistant epilepsy. For this reason, it is a high priority objective in preclinical research to find novel therapeutic targets and to develop effective drugs that prevent or reverse the molecular mechanisms underlying epilepsy progression. Among these potential therapeutic targets, we highlight currently available information involving signaling pathways (Wnt/β-catenin, Mammalian Target of Rapamycin (mTOR) signaling and zinc signaling), enzymes (carbonic anhydrase), proteins (erythropoietin, copine 6 and complement system), channels (Transient Receptor Potential Vanilloid Type 1 (TRPV1) channel) and receptors (galanin and melatonin receptors). All of them have demonstrated a certain degree of efficacy not only in controlling seizures but also in displaying neuroprotective activity and in modifying the progression of epilepsy. Although some research with these specific targets has been done in relation with epilepsy, they have not been fully explored as potential therapeutic targets that could help address the unsolved issue of drug-resistant epilepsy and develop new antiseizure therapies for the treatment of epilepsy.

Co-expression of caspase-3 or caspase-8 with galanin in the human stomach section affected by carcinoma

Neoplastic process may cause distinct changes in the morphology, i.e. size and number of the neurons of the neuronal plexuses forming the enteric nervous system (ENS) of the human intestine. Moreover, it was also reported that these changes were not directly associated with apoptosis. Thus, the main aim of this study was to determine the atrophic changes of myenteric plexuses (MPs) in the vicinity of cancer invasion and the potential reason which may be responsible for these changes if they occur. Tissue samples from the stomach were collected from ten patients which undergo organ resection due to cancer diagnosis. Samples were taken from the margin of cancer invasion and from a macroscopically-unchanged part of the stomach wall. Triple-immunofluorescence staining of the 10-µm-thick cryostat sections was used to visualize the co-expression of caspase-3 (CASP3) or caspase-8 (CASP8) with galanin (GAL) in the MPs of ENS. Microscopic observations of MPs located closely to gastric cancer invasion showed that they were significantly smaller than plexuses located distally. The percentage of neurons containing CASP3 within MPs located close to cancer-affected regions of the stomach was higher, while containing CASP8 was lower compared to the unchanged regions. Additionally, elevated high expression of CASP3 or CASP8 in the neurons from MPs was accompanied by a decreased expression of GAL. To our knowledge, this is the first report describing the decomposition of MPs within cancer-affected human stomach wall and the possible role of apoptosis in this process.

Alterations in Galanin-Like Immunoreactivity in the Enteric Nervous System of the Porcine Stomach Following Acrylamide Supplementation

In recent years, a significant increase in the consumption of products containing large amounts of acrylamide (e.g., chips, fries, coffee), especially among young people has been noted. The present study was created to establish the impact of acrylamide supplementation, in tolerable daily intake (TDI) dose and a dose ten times higher than TDI, on the population of galanin-like immunoreactive (GAL-LI) stomach neurons in pigs. Additionally, in the present study, the possible functional co-operation of GAL with other neuroactive substances and their role in acrylamide intoxication was investigated. Using double-labelling immunohistochemistry, alterations in the expression of GAL were examined in the porcine stomach enteric neurons after low and high doses of acrylamide supplementation. Generally, upregulation in GAL-LI immunoreactivity in both myenteric and submucous plexuses was noted in all stomach fragments studied. Additionally, the proportion of GAL-expressing cell bodies simultaneously immunoreactive to vasoactive intestinal peptide (VIP), neuronal nitric oxide synthase (nNOS) and cocaine- and amphetamine- regulated transcript peptide (CART) also increased. The results suggest neurotrophic or/and neuroprotective properties of GAL and possible co-operation of GAL with VIP, nNOS, CART in the recovery processes in the stomach enteric nervous system (ENS) neurons following acrylamide intoxication.

Role of Melatonin, Galanin, and RFamide Neuropeptides QRFP26 and QRFP43 in the Neuroendocrine Control of Pancreatic β-Cell Function

Glucose homeostasis is finely regulated by a number of hormones and peptides released mainly from the brain, gastrointestinal tract, and muscle, regulating pancreatic secretion through cellular receptors and their signal transduction cascades. The endocrine function of the pancreas is controlled by islets within the exocrine pancreatic tissue that release hormones like insulin, glucagon, somatostatin, pancreatic polypeptide, and ghrelin. Moreover, both exocrine and endocrine pancreatic functions are regulated by a variety of hormonal and neural mechanisms, such as ghrelin, glucagon-like peptide, glucose-dependent insulinotropic polypeptide, or the inhibitory peptide somatostatin. In this review, we describe the role of neurohormones that have been less characterized compared to others, on the regulation of insulin secretion. In particular, we will focus on melatonin, galanin, and RFamide neuropeptides QRFP26 and QRFP43, which display either insulinotropic or insulinostatic effects. In fact, in addition to other hormones, amino acids, cytokines, and a variety of proteins, brain-derived hormones are now considered as key regulators of glucose homeostasis, representing potential therapeutic targets for the treatment of diabetes and obesity.

Serum Galanin Levels in Young Healthy Lean and Obese Non-Diabetic Men during an Oral Glucose Tolerance Test

Galanin (GAL) is a neuropeptide involved in the homeostasis of energy metabolism. The objective of this study was to investigate the serum levels of GAL during an oral glucose tolerance test (OGTT) in lean and obese young men. This cross-sectional study included 30 obese non-diabetic young men (median 22 years; mean BMI 37 kg/m²) and 30 healthy lean men (median 23 years; mean BMI 22 kg/m²). Serum GAL was determined during OGTT. The results of this study include that serum GAL levels showed a reduction during OGTT compared with basal levels in the lean subjects group. Conversely, serum GAL levels increased significantly during OGTT in obese subjects. Serum GAL levels were also higher in obese non-diabetic men compared with lean subjects during fasting and in every period of the OGTT (p < 0.001). Serum GAL levels were positively correlated with BMI, total fat, visceral fat, HOMA–IR, total cholesterol, triglycerides and Leptin. A multiple regression analysis revealed that serum insulin levels at 30, 60 and 120 minutes during the OGTT is the most predictive variable for serum GAL levels (p < 0.001). In conclusion, serum GAL levels are significantly higher in the obese group compared with lean subjects during an OGTT.

The Influence of Gastric Antral Ulcerations on the Expression of Galanin and GalR1, GalR2, GalR3 Receptors in the Pylorus with Regard to Gastric Intrinsic Innervation of the Pyloric Sphincter

Gastric antrum ulcerations are common disorders occurring in humans and animals. Such localization of ulcers disturbs the gastric emptying process, which is precisely controlled by the pylorus. Galanin (Gal) and its receptors are commonly accepted to participate in the regulation of inflammatory processes and neuronal plasticity. Their role in the regulation of gastrointestinal motility is also widely described. However, there is lack of data considering antral ulcerations in relation to changes in the expression of Gal and GalR1, GalR2, GalR3 receptors in the pyloric wall tissue and galaninergic intramural innervation of the pylorus. Two groups of pigs were used in the study: healthy gilts and gilts with experimentally induced antral ulcers. By double immunocytochemistry percentages of myenteric and submucosal neurons expressing Gal-immunoreactivity were determined in the pyloric wall tissue and in the population of gastric descending neurons supplying the pyloric sphincter (labelled by retrograde Fast Blue neuronal tracer). The percentage of Gal-immunoreactive neurons increased only in the myenteric plexus of the pyloric wall (from 16.14±2.06% in control to 25.5±2.07% in experimental animals), while no significant differences in other neuronal populations were observed between animals of both groups. Real-Time PCR revealed the increased expression of mRNA encoding Gal and GalR1 receptor in the pyloric wall tissue of the experimental animals, while the expression(s) of GalR2 and GalR3 were not significantly changed. The results obtained suggest the involvement of Gal, GalR1 and galaninergic pyloric myenteric neurons in the response of pyloric wall structures to antral ulcerations.

Galanin inhibits GLP-1 and GIP secretion via the GAL1 receptor in enteroendocrine L and K cells

Background and Purpose

Galanin is a widely expressed neuropeptide, which in the gut is thought to modulate gastrointestinal motility and secretion. We aimed to elucidate the poorly characterised mechanisms underlying the inhibitory effect of galanin and the potential involvement of G‐protein coupled inwardly rectifying potassium, K_ir3, (GIRK) channels in glucagon‐like peptide 1 (GLP‐1) and glucose‐dependent insulinotropic polypeptide (GIP) secretion.

Experimental Approach

Purified murine L and K cells were analysed for expression of galanin receptors and GIRK subunits. Hormone secretion was measured from primary murine intestinal cultures. Intracellular cAMP was monitored in primary L cells derived from mice expressing the Epac2camps sensor under the control of the proglucagon promoter.

Key Results

Galanin receptor 1 (GAL₁, Galr1) and GIRK channel 1 (K_ir3.1, Kcnj3) and 4 (K_ir3.4, Kcnj5) mRNA expression was highly enriched in K and L cells. Galanin and a selective GAL₁ receptor agonist (M617) potently inhibited GLP‐1 and GIP secretion from primary small intestinal cultures. In L cells, galanin significantly inhibited the forskolin‐induced cAMP response. The GIRK1/4 activator ML297 significantly reduced glucose‐stimulated and IBMX‐stimulated GLP‐1 secretion but had no effect on GIP. The GIRK blocker tertiapin‐Q did not impair galanin‐mediated GLP‐1 inhibition.

Conclusions and Implications

Galanin, acting via the GAL₁ receptor and G_i‐coupled signalling in L and K cells, is a potent inhibitor of GLP‐1 and GIP secretion. Although GIRK1/4 channels are expressed in these cells, their activation does not appear to play a major role in galanin‐mediated inhibition of incretin secretion.

Pharmacology and physiology of gastrointestinal enteroendocrine cells

Gastrointestinal (GI) polypeptides are secreted from enteroendocrine cells (EECs). Recent technical advances and the identification of endogenous and synthetic ligands have enabled exploration of the pharmacology and physiology of EECs. Enteroendocrine signaling pathways stimulating hormone secretion involve multiple nutrient transporters and G protein-coupled receptors (GPCRs), which are activated simultaneously under prevailing nutrient conditions in the intestine following a meal. The majority of studies investigate hormone secretion from EECs in response to single ligands and although the mechanisms behind how individual signaling pathways generate a hormonal output have been well characterized, our understanding of how these signaling pathways converge to generate a single hormone secretory response is still in its infancy. However, a picture is beginning to emerge of how nutrients and full, partial, or allosteric GPCR ligands differentially regulate the enteroendocrine system and its interaction with the enteric and central nervous system. So far, activation of multiple pathways underlies drug discovery efforts to harness the therapeutic potential of the enteroendocrine system to mimic the phenotypic changes observed in patients who have undergone Roux-en-Y gastric surgery. Typically obese patients exhibit ∼30% weight loss and greater than 80% of obese diabetics show remission of diabetes. Targeting combinations of enteroendocrine signaling pathways that work synergistically may manifest with significant, differentiated EEC secretory efficacy. Furthermore, allosteric modulators with their increased selectivity, self-limiting activity, and structural novelty may translate into more promising enteroendocrine drugs. Together with the potential to bias enteroendocrine GPCR signaling and/or to activate multiple divergent signaling pathways highlights the considerable range of therapeutic possibilities available. Here, we review the pharmacology and physiology of the EEC system.

Physiology, signaling, and pharmacology of galanin peptides and receptors: three decades of emerging diversity

Galanin was first identified 30 years ago as a "classic neuropeptide," with actions primarily as a modulator of neurotransmission in the brain and peripheral nervous system. Other structurally-related peptides-galanin-like peptide and alarin-with diverse biologic actions in brain and other tissues have since been identified, although, unlike galanin, their cognate receptors are currently unknown. Over the last two decades, in addition to many neuronal actions, a number of nonneuronal actions of galanin and other galanin family peptides have been described. These include actions associated with neural stem cells, nonneuronal cells in the brain such as glia, endocrine functions, effects on metabolism, energy homeostasis, and paracrine effects in bone. Substantial new data also indicate an emerging role for galanin in innate immunity, inflammation, and cancer. Galanin has been shown to regulate its numerous physiologic and pathophysiological processes through interactions with three G protein-coupled receptors, GAL1, GAL2, and GAL3, and signaling via multiple transduction pathways, including inhibition of cAMP/PKA (GAL1, GAL3) and stimulation of phospholipase C (GAL2). In this review, we emphasize the importance of novel galanin receptor-specific agonists and antagonists. Also, other approaches, including new transgenic mouse lines (such as a recently characterized GAL3 knockout mouse) represent, in combination with viral-based techniques, critical tools required to better evaluate galanin system physiology. These in turn will help identify potential targets of the galanin/galanin-receptor systems in a diverse range of human diseases, including pain, mood disorders, epilepsy, neurodegenerative conditions, diabetes, and cancer.

Gut chemosensing mechanisms

The enteroendocrine system is the primary sensor of ingested nutrients and is responsible for secreting an array of gut hormones, which modulate multiple physiological responses including gastrointestinal motility and secretion, glucose homeostasis, and appetite. This Review provides an up-to-date synopsis of the molecular mechanisms underlying enteroendocrine nutrient sensing and highlights our current understanding of the neuro-hormonal regulation of gut hormone secretion, including the interaction between the enteroendocrine system and the enteric nervous system. It is hoped that a deeper understanding of how these systems collectively regulate postprandial physiology will further facilitate the development of novel therapeutic strategies.

Galanin and its receptors: a novel strategy for appetite control and obesity therapy

The rapid increase in the prevalence of overweight and obesity is becoming an important health problem. Overweight and obesity may cause several metabolic complications, including type 2 diabetes mellitus, hyperlipidemia, high cholesterol, coronary artery disease as well as hypertension. Prevention and treatment of obesity will benefit the treatment of these related diseases. Current strategies for treatment of obesity are not adequately effective and are frequently companied with many side effects. Thus, new ways to treat obesity are urgently needed. Galanin is undoubtedly involved in the regulation of food intake and body weight. The aim of this review is to provide up-to-date knowledge concerning the roles of central and peripheral galanin as well as its receptors in the regulation of metabolism, obesity and appetite. We also highlight the mechanisms of galanin and its receptors in experimental obesity, trying to establish a novel anti-obesity strategy.

Localization and neurochemical characteristics of the extrinsic sympathetic neurons projecting to the pylorus in the domestic pig

The pylorus, an important part of the digestive tract controlling the flow of chyme between the stomach and the duodenum, is widely innervated by intrinsic and extrinsic nerves. To determine the locations of postganglionic sympathetic perikarya that innervate the pylorus of the domestic pig, a retrograde tracing method with application of Fast Blue tracer was used. All positive neuronal cell bodies (ca. 1750) were found in the celiac-cranial mesenteric ganglion complex (CSMG), however, the coeliac poles of this complex provided the major input to the pylorus. Afterwards, the immunohistochemical staining procedure was applied to determine biologically active substances expressed in the FB-labeled perikarya. Approximately 77% of the FB-positive cell bodies contained tyrosine hydroxylase (TH), 87% dopamine β-hydroxylase (DβH), 40% neuropeptide Y (NPY), 12% somatostatin (SOM) and 7% galanin (GAL). The presence of all these substances in the ganglion tissue was confirmed by RT-PCR technique. Double immunocytochemistry revealed that all of the TH-positive perikarya contained DβH, about 40% NPY, 12% SOM and 8% GAL. Additionally, all above-cited immunohistochemical markers as well as VIP, PACAP, ChAT, LEU, MET, SP and nNOS were observed within nerve fibers associated with the FB-positive perikarya. Immunocytochemical labeling of the pyloric wall tissue disclosed that TH+, DβH+ and NPY+ nerve fibers innervated ganglia of the myenteric and submucosal plexuses, blood vessels, both muscular layers and the muscularis mucosae; nerve fibers immunoreactive to GAL mostly innervated both muscular layers, while SOM+ nerve fibers were observed within the myenteric plexus. Presented study revealed sources of origin and immunohistochemical characteristics of the sympathetic postganglionic perikarya innervating the porcine pylorus.

Characterization of the chicken galanin type I receptor (GalR1) and a novel GalR1-like receptor (GalR1-L)

Galanin is a multi-functional neuropeptide that is widely distributed in the mammalian central nervous system and peripheral tissues. It exerts multiple physiological functions through interaction with 3 known G protein-coupled receptors (GPCR), namely, galanin type I, II and III (GalR1, 2 and 3) receptors, which have only been identified in mammals. In this study, we reported the cloning and characterization of chicken galanin type I receptor (GalR1) and a novel galanin receptor with considerable homology to chicken GalR1, which herein is designated as galanin type I-like receptor (GalR1-L). Chicken GalR1 and GalR1-L full-length cDNAs were cloned from chicken brain and small intestine tissue, respectively. The former encodes a protein of 357 amino acids that shares 84-86% amino acid sequence identities with its mammalian counterparts, whereas the latter encodes a 363-amino acid protein with comparatively lower identities (55-56%) to the mammalian GalR1. Using reverse transcription (RT)-PCR assays, we examined the expression of both receptors in adult chicken tissues. Both receptors were found to be widely distributed in the tissues examined, including brain, small intestine, kidney, ovary, pancreas, pituitary and spleen. Interestingly, cGalR1 expression was detected in different regions of chicken oviduct, while cGalR1-L expression was restricted to the vagina. Using a pGL3-CRE luciferase reporter system, chicken galanin peptide (1-29) was demonstrated to inhibit both basal and forskolin-stimulated luciferase activities, in dose-dependent manners, through the cAMP-mediated signaling pathway in Chinese hamster ovary (CHO) cells expressing either cGalR1 or cGalR1-L, thus suggesting the functional couplings of both receptors to G(i) proteins. Together, the characterization of chicken GalR1 and GalR1-L provides a better understanding of the physiological roles of galanin in avian species.

Quantitative estimation and chemical coding of spiny type I neurons in human intestines

Previous studies have shown that most human myenteric neurons co-staining for vasoactive intestinal peptide (VIP), neuronal nitric oxide synthase (nNOS) and neurofilaments (NF) display the morphology of spiny type I neurons displaying a descending projection pattern. Here, we estimated the proportions of spiny neurons in human intestines, the amount of congruence of VIP/nNOS-immunoreactive with spiny neurons and whether galanin (GAL) is co-localized with VIP. Three sets of colchicine-pretreated and fixed whole mounts of 21 patients or body donors (median age 65 years; 10 female, 11 male) were stained for VIP, nNOS and NF, for VIP, nNOS and the human neuronal protein Hu C/D (HU) as well as for VIP, nNOS and GAL. The majority of VIP/nNOS-co-reactive neurons were spiny neurons (79/80% in small/large intestine, respectively) and the majority of spiny neurons co-stained for VIP and nNOS (82/69%). Neurons co-immunoreactive for VIP/nNOS/HU amounted to 7 and 4%, respectively. GAL/VIP-co-immunoreactivity was demonstrated in 69 and 27% of spiny neurons, respectively. We conclude that the number of neurons displaying co-reactivity for VIP and nNOS is a quantitative indicator of spiny neurons in both small and large intestine and that the proportion of spiny neurons is about 7% in small and 4% in large intestines. Since nerve fibres co-staining for NF/VIP/nNOS were found mainly in the circular muscle layer but not the surrounding perikarya of spiny neurons, we suggest that they may represent inhibitory motor neurons rather than descending interneurons.

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.

Sensory-nerve-derived neuropeptides: possible therapeutic targets

This review examines our developing understanding of the families and activities of some of the best known sensory-nerve-derived inflammatory neuropeptides, namely substance P, calcitonin gene-related peptide and galanin. Evidence to date shows involvement of these transmitters in a wide range of systems that includes roles as inflammatory modulators. There is an increasing understanding of the mechanisms involved in the release of the peptides from sensory nerves and these are key in understanding the potential of neuropeptides in modulating inflammatory responses and may also provide novel targets for anti-inflammatory therapy. The neuropeptides released act via specific G protein coupled receptors, most of which have now been cloned. There is knowledge of selective agonists and antagonists for many subtypes within these families. The study of neuropeptides in animal models has additionally revealed pathophysiological roles that in turn have led to the development of new drugs, based on selective receptor antagonism.

The distribution and chemical coding of intramural neurons supplying the porcine stomach - the study on normal pigs and on animals suffering from swine dysentery

The present study was designed to investigate the expression of biologically active substances by intramural neurons supplying the stomach in normal (control) pigs and in pigs suffering from dysentery. Eight juvenile female pigs were used. Both dysenteric (n = 4; inoculated with Brachyspira hyodysenteriae) and control (n = 4) animals were deeply anaesthetized, transcardially perfused with buffered paraformalehyde, and tissue samples comprising all layers of the wall of the ventricular fundus were collected. The cryostat sections were processed for double-labelling immunofluorescence to study the distribution of the intramural nerve structures (visualized with antibodies against protein gene-product 9.5) and their chemical coding using antibodies against vesicular acetylcholine (ACh) transporter (VAChT), nitric oxide synthase (NOS), galanin (GAL), vasoactive intestinal polypeptide (VIP), somatostatin (SOM), Leu(5)-enkephalin (LENK), substance P (SP) and calcitonin gene-related peptide (CGRP). In both inner and outer submucosal plexuses of the control pigs, the majority of neurons were SP (55% and 58%, respectively)- or VAChT (54%)-positive. Many neurons stained also for CGRP (43 and 45%) or GAL (20% and 18%) and solitary perikarya were NOS-, SOM- or VIP-positive. The myenteric plexus neurons stained for NOS (20%), VAChT (15%), GAL (10%), VIP (7%), SP (6%) or CGRP (solitary neurons), but they were SOM-negative. No intramural neurons immunoreactive to LENK were found. The most remarkable difference in the chemical coding of enteric neurons between the control and dysenteric pigs was a very increased number of GAL- and VAChT-positive nerve cells (up to 61% and 85%, respectively) in submucosal plexuses of the infected animals. The present results suggest that GAL and ACh have a specific role in local neural circuits of the inflamed porcine stomach in the course of swine dysentery.

Chronic administration of galanin attenuates the TNBS-induced colitis in rats

Inflammatory bowel disease (IBD) is a chronic intestinal inflammatory disorder considered as a consequence of an aberrant response of the immune system to luminal antigens. Numerous groups of agents are being evaluated as novel therapeutic approaches for its treatment; in this way, different peptides have emerged as potential candidates. Galanin is an active neuropeptide distributed in the central and periphery nervous systems although it has been also described having important autocrine and paracrine regulatory capacities with interesting inflammatory and immune properties. In this line, we have observed that galanin treatment has a significant preventive effect in the experimental trinitrobenzensulfonic acid (TNBS) acute model of inflammatory colitis. The aim of the present study was to investigate intensively the role played by the peptide in the evolution of the inflammatory pathology associated to IBD. Galanin (5 and 10 microg/kg/day) was administered i.p., daily, starting 24 h after TNBS instillation, and continuing for 14 and 21 days. The lesions were blindly scored according to macroscopic and histological analyses and quantified as ulcer index. The results demonstrated that chronic administration of galanin improved the colon injury than the TNBS induced. The study by Western-blotting of the expression of nitric oxide inducible enzyme (iNOS), as well as the total nitrite production (NO) assayed by Griess-reaction, showed significant reduction associated with peptide administration. The number of mast cells was also identified in histological preparations stained with toluidine blue and the results showed that samples from galanin treatment, mostly at 21 days, had increased the number of these cells and many of them had a degranulated feature. In conclusion, chronic administration of galanin is able to exert a beneficial effect in the animal model of IBD assayed improving the reparative process. Participation of nitric oxide pathways and mucosal mast cells can not be discarded.

Expression of galanin receptor messenger RNAs in different regions of the rat gastrointestinal tract

Galanin effects are mediated by three G-protein-coupled receptors: galanin receptor 1 (GalR1), GalR2 and GalR3. We quantified mRNA levels of GalR1, GalR2 and GalR3 in the rat stomach, small and large intestine using real-time RT-PCR. All three GalR mRNAs were detected throughout the gut at different levels. GalR1 and GalR2 mRNA levels were higher in the large than in the small intestine. GalR2 mRNA was most abundant in the stomach. GalR3 mRNA levels were generally quite low. The differential regional distribution of GalRs suggests that the complex effects of galanin in the gut are the result of activating multiple receptor subtypes, whose density, subtype and signaling vary along the gastrointestinal tract.

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 contributes to the excess colonic fluid secretion observed in dextran sulfate sodium murine colitis

Galanin is present in enteric nerves lining the gastrointestinal (GI) tract where it is normally involved in regulating intestinal motility by binding to the galanin-1 receptor (Gal1R) subtype expressed by smooth muscle cells. In contrast, although epithelial cells lining the colon do not normally express Gal1R, this protein is up-regulated by the inflammation-associated transcription factor NF-kappaB. We previously showed that the murine colitis induced by dextran sulfate sodium (DSS) was associated with increased Gal1R expression as well as by increased colonic fluid secretion. Although Gal1R up-regulation by colonic epithelial cells results in increased intestinal Cl- secretion, the relative contributions of galanin to this excess colonic fluid secretion could not be determined. We therefore created a mouse genetically incapable of synthesizing Gal1R (GAL1R-/- mice). We herein demonstrate that both wild-type and GAL1R-/- mice developed identical histologic lesions in response to DSS. This was characterized by a marked inflammatory infiltrate, activation of NF-kappaB in both enterocytes and enteric nerves, and a threefold increase in neuronal galanin. Colonic fluid secretion, while increased, was approximately half that in GAL1R-/- mice as compared with their wild-type littermates. Overall, then, these findings strongly suggest that approximately half of the increase in colonic fluid secretion in DSS colitis is due to up-regulation of the Gal1R.

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.

Central orexin facilitates gastric relaxation and contractility in rats

The effects of the intracisternal administration of synthetic orexin-A (3 nmol) on gastric motility were examined in rats. The administration of orexin but not a vehicle induced relaxation of the proximal stomach lasting for more than 30 min. Phasic contractions in the distal stomach were facilitated in response to the administration of orexin but not a vehicle. Facilitation in the distal stomach was not observed in the animals which underwent the sectioning of the bilateral vagi at the subdiaphragmatic level. Relaxation of the proximal stomach was observed in vagotomized animals but the magnitude of relaxation was significantly smaller than that in intact animals. These results suggest that central orexin facilitates distal stomach motility and relaxation of the proximal stomach via vagi.

Regulation of feeding behavior, gastric emptying, and sympathetic nerve activity to interscapular brown adipose tissue by galanin and enterostatin: the involvement of vagal-central nervous system interactions

Galanin and enterostatin, which are distributed in both the central nervous system and the gastrointestinal tract, regulate the feeding behavior. In the first set of experiments, we investigated the effects of galanin and enterostatin, injected into the third ventricle, on food intake, gastric emptying, and the sympathetic activity of nerves innervating interscapular brown adipose tissue in rats. Galanin dose-dependently increased the intake of a high-fat diet after overnight starvation, but it did not affect low-fat diet intake. In contrast, enterostatin suppressed the intake of the high-fat diet, while intake of the low-fat diet was not affected. Galanin significantly and dose-dependently suppressed gastric emptying rate. However, gastric emptying showed no response to enterostatin. Galanin produced a dose-dependent suppression of sympathetic firing rate. In rats fed a high-fat diet, the injection of enterostatin showed a dose-dependent increase in firing rate. In contrast, animals fed a chow diet showed almost no response. In the second set of experiments, we investigated the role of the hepatic vagus nerve in modulating the peripheral response to enterostatin in rats. Intraperitoneal (i.p.) enterostatin reduced the intake of a high-fat diet. Immunohistochemical identification indicated that the Fos protein was present in the nucleus tractus solitarius, and parabrachial, paraventricular, and supraoptic nuclei after IP enterostatin. These responses to i.p. enterostatin were blocked by hepatic vagotomy. These results suggest that galanin and enterostatin coordinate to regulate feeding behavior, gastric emptying, and sympathetic activity to interscapular brown adipose tissue via central and peripheral sites of action, one of which was the interaction which was found to exist through the vagal system.

Distribution of galanin receptor 1 immunoreactivity in the rat stomach and small intestine

Galanin affects gastrointestinal functions by activating different G protein-coupled receptors. Here, we identified the sites of expression of the galanin receptor 1 (GAL-R1) subtype in the rat stomach and small intestine by using immunohistochemistry with an antibody raised to the third intracellular loop of rat GAL-R1 (GAL-R1(Y225-238)) and confocal microscopy. Antibody specificity was confirmed by (1) the detection of a band at approximately 70 kDa in Western blot of membranes from GAL-R1 transfected cells, (2) the cell surface staining of GAL-R1 transfected cells, which was not detected in control cells, and (3) the abolition of Western signal and tissue immunostaining by preadsorbing the antibody with the peptide used for immunization. GAL-R1 immunoreactivity was localized to the cell surface of enterochromaffin-like cells, and of myenteric and submucous neurons, and to fibers distributed to the plexuses, interconnecting strands, muscle layers, vasculature, and mucosa. A dense network of GAL-R1 immunoreactivity was observed in the deep muscular plexus in very close association with interstitial cells of Cajal visualized by c-kit immunostaining. In the ileum, 81.6% of GAL-R1 myenteric neurons and 70.7% of GAL-R1 submucosal neurons were substance P immunoreactive. Vasoactive intestinal polypeptide immunoreactivity was found in 48.3% of GAL-R1 submucosal neurons, but not in GAL-R1 myenteric neurons. These findings support the hypothesis that GAL-R1 mediates galanin actions on gastrointestinal motility and secretion by modulating the release of other neurotransmitters and contributes to galanin-induced inhibition of gastric acid secretion by means of the suppression of endogenous histamine release.

Galanin-like immunoreactive neural elements in domestic ruminant pancreas

The distribution and ontogeny of the galanin-like immunoreactive (Gal-IR) neural structures in the pancreas of cattle, sheep and goat were investigated immunohistochemically. The present study confirmed the previous findings on the immunolocalization of galanin both in the neural elements and endocrine cells of cattle, and reported for the first time its exclusive localization in the neural elements of sheep and goat. The frequency of Gal-IR nerve fibers and nerve cell bodies was high in cattle and low in sheep and goat. Their first detection was at the first fetal trimester in cattle and third trimester in sheep and goat. In cattle, a marked increase in the frequency of Gal-IR nerve fibers was observed from the third trimester to early neonatal stage followed by a decrease after three months postnatal. In contrast to the non-preferential distribution pattem in sheep, the Gal-IR nerve fibers in cattle and goat pancreas were predominantly associated with the acini, excretory ducts and blood vessels, but rarely detected in the pancreatic islets. The Gal-IR nerve cell bodies were observed as isolated bodies in the intra- and interlobular connective tissues and as a group within the intrapancreatic ganglia. At the vicinity of the nerve cell bodies, Gal-IR nerve fibers were observed. The present findings may suggest that: (1) galanin regulates pancreatic function as neurotransmitter/neuromodulator in ruminants; (2) galanin plays a more important role in large than in small ruminants; and (3) particularly in cattle, it exerts its most dramatic effect during perinatal development.

Functional and immunocytochemical evidence that galanin is a physiological regulator of human jejunal motility

The neuropeptide galanin has species-dependent effects on intestinal motility. It has a contractile effect on rat jejunal muscle while it relaxes guinea-pig ileum by inhibiting cholinergic transmission. Its effect on human gut motility has been unknown. Extensive work led to the discovery of selective galanin analogues such as M15 [galanin(1-12)-Pro-substance-P(5-11)], M35 [galanin(1-12)-Pro-bradykinin(2-9)-amide] that competitively inhibit various actions of galanin in the central nervous system. The present study was designed to examine the effect of galanin, M15 and M35 on longitudinal jejunal smooth muscle strips isolated from humans and rats, and to localize galanin-immunoreactivity in human jejunum. Galanin and ACh were equally effective in stimulating contractions of the isolated jejunal muscle: sigmoid curve fitting showed that maximal contractile response to galanin and ACh were 25.7+/-11.1 mN and 23.7+/-9.7 in humans, while 8.0+/-0.6 and 8.1+/-0.3 mN in rats, respectively. These effects of galanin were not inhibited by either atropine (5 x 10(-6) M) or tetrodotoxin (3 x 10(-6) M). The potency of galanin inducing the contractile actions were similar in humans and rats. Interestingly, neither M15 nor M35 (up to 10(-7) M) were able to inhibit the responses of the smooth muscle to galanin. However, both putative galanin receptor antagonists showed agonist effects in our experimental models. In accordance with the functional studies, both the longitudinal and the circular muscle layers were abundant in nerve fibers and varicosities showing galanin immunoreactivity. Our data suggest that galanin is a potent physiological regulator of jejunal contractions in humans. Its action on the jejunum, however, is mediated by galanin receptors that are different from those located in the central nervous system.

Nitric oxide-containing neurons in the bovine gut, with special reference to their relationship with VIP and galanin

The presence and distribution of nicotinamide dinucleotide phosphate diaphorase (NADPH-d)-containing neurons have been studied by means of NADPH-d histochemistry in different regions of the adult cow gut, from the esophagus to the rectum. NADPH-d and nitric oxide synthase (NOS) were constantly recognized to be colocalized in the same neuron. The colocalization of vasoactive intestinal polypeptide (VIP) and galanin in such nitrergic neurons was also studied by means of combined histochemical and immunofluorescence techniques. NADPH-d-positive neurons were present along the myenteric plexus of the entire gut, and in the submucous plexus from the abomasum to the rectum. Notably, they formed two types of nerve networks in the submucous connective tissue of the jejunum-ileum. NADPH-d-positive innervation of the muscle layers occurred throughout the tract, and sometimes a clear correspondence was noted between the number of reactive fibres and the thickness of the muscle. Nitrergic fibres also occurred in the mucosa and often were in relation to glands and blood vessels. The nitrergic neurons varied in size, shape, and intensity of staining, and often their terminals were seen to surround unstained perikarya. Various types of neurons were recognized on the basis of their chemical content; one of them contained galanin, VIP and NOS simultaneously. The present results suggest that the nitrergic neurons of the bovine gastrointestinal tract play roles presumably for controlling the motility of the gut and the conduction of interneuronal impulses.

Effects of galanin(1-16) on pancreatic secretion in anesthetized and conscious rats

Galanin, a 29-amino acid peptide, has been demonstrated in pancreatic nerve endings and found to inhibit insulin release in the rat. However, the data available concerning its effects on exocrine pancreatic secretion are contradictory. The aim of the present study was to evaluate the effects of a synthetic porcine galanin sequence, Gal(1-16), on stimulated pancreatic secretion in hyperglycemic anesthetized and conscious rats. Male Wistar rats were anesthetized and surgically prepared with pancreatic and femoral vein catheters. In anesthetized animals, the pancreatic secretion was continuously stimulated with 150 ng cholecystokinin octapeptide (CCK-8)/kg body weight per 30 min, dissolved in saline or 10% glucose. Synthetic Gal(1-16) (0.3 or 1 nmol/kg per h) was infused over a 60-min period. In conscious rats, 1, 3, or 10 nmol Gal(1-16)/kg per h was administered in a continuous saline or 10% glucose infusion over a 30-min period. The pancreatic secretory volume and protein output were determined in 30-min samples in both models. In anesthetized rats, 0.3 nmol Gal(1-16)/kg per h did not modify pancreatic secretion during CCK-8 stimulation. However, both the pancreatic secretory volume and the protein output were significantly inhibited compared with the basal levels by 1 nmol Gal(1-16)/kg per h. The inhibitory effect of Gal(1-16) on pancreatic secretion was more marked with CCK-8/glucose (53.9%) than with CCK-8/saline stimulation (20.1%). In conscious rats, significant inhibitory effects of 1 nmol Gal(1-16)/kg per h in saline were observed (18%). During glucose infusion, a dose-dependent inhibition of 1, 3, and 10 nmol Gal(1-16)/kg per h on pancreatic secretory volume and protein output (35% inhibition at 1 nmol/kg per h) was observed. In conclusion, the inhibitory effect of Gal(1-16) on exogenous and endogenous CCK-stimulated pancreatic secretion was found to be more potent in the presence of glucose both in anesthetized and in conscious rats. These results may suggest an indirect (insulin-mediated) inhibitory effect of porcine Gal(1-16) on pancreatic secretion in the rat.

Galanin-like immunoreactive endocrine cells in bovine pancreas

Pancreata of fetal, neonatal and adult cattle were studied immunohistochemically for galanin. The results revealed galanin-like immunoreactivity both in the endocrine cells and in the neural elements. The galanin-like immunoreactive endocrine cells (Gal-LIEC) were confined to the large islets, and were not observed in the islets of Langerhans and exocrine pancreas. They were first detected at the third prenatal month. Their developmental profile showed an increase from fetal to early neonatal stage with a subsequent decrease towards adulthood. The considerable number of Gal-LIEC from late prepartum to early postpartum stage may imply functional significance of galanin during the perinatal development of cattle. Coexistence of galanin and insulin was also observed which may suggest autocrine interaction between the 2 hormones.

Antisecretory effects of galanin and its putative antagonists M15, M35 and C7 in the rat stomach

The neuropeptide galanin has been reported to have a wide range of biological actions both in the central nervous system and in the gastrointestinal tract. Recent works led to the discovery of selective galanin receptor antagonists including M15 (galanin(1-12)-Pro-substanceP(5-11)-amide), M35 (galanin(1-12)-Pro-bradykinin(2-9)-amide) and C7 (galanin(1-12)-Pro-spantide-amide). These antagonists were shown to competitively inhibit actions of galanin in the central nervous system. The present study was designed to investigate the effect of galanin, M15, M35 and C7 on gastric acid secretion and gastric emptying. Pentagastrin-stimulated gastric acid secretion was inhibited by galanin (0.1-9 nmol x kg(-1) x h(-1), i.v.) in a dose-dependent manner (ID50 = 1.8 +/- 0.3 nmol x kg(-1) x h(-1)). When 9 nmol x kg(-1) x h(-1) galanin infusion was given, inhibition became almost complete. M15, M35 and C7 (1-9 nmol x kg(-1) x h(-1)) did not modify responses of the stomach to galanin, but acted as agonists of galanin on acid secretion. Neither galanin nor its putative antagonists affected the emptying of non-caloric liquids from the stomach. In conclusion, galanin may play an antisecretory role in the regulation of gastric acid secretion but not in the control of gastric emptying of liquids in rats. Its antisecretory action on the stomach is mediated by galanin receptors that are distinct from those in the central nervous system.

The role of galanin in feeding behavior

Galanin inhibits food consumption in satiated rats. Discovered relatively recently, galanin is a 29-amino-acid neuropeptide, not homologous with any other known peptide. Three G-protein-linked galanin receptor subtypes have been cloned. This review summarizes the mechanisms by which exogenously administered galanin may stimulate ingestion, discusses pharmacological and genetic investigations of the role of endogenous galanin on feeding and body weight, and speculates on the therapeutic potential of non-peptide galanin receptor antagonists for the treatment of appetite disorders.

Pathogenic Escherichia coli increase Cl- secretion from intestinal epithelia by upregulating galanin-1 receptor expression

Galanin is widely distributed in enteric nerve terminals lining the human gastrointestinal (GI) tract. We have shown previously that galanin-1 receptors (Gal1-R) are expressed by epithelial cells lining the human GI tract, and upon activation cause Cl- secretion. Because expression of this receptor is transcriptionally regulated by nuclear factor-kappa B (NF-kappa B), which is activated by enteric pathogens as a part of the host epithelial response to infection, we investigated whether such bacterial pathogens could directly increase Gal1-R expression in the T84-cell model system. Pathogenic Escherichia coli, but not nonpathogenic E. coli, activate a p50/p65 NF-kappa B complex that binds to oligonucleotides corresponding to a recognition site located within the 5' flanking region of the human GAL1R gene. Pathogenic E. coli, but not normal commensal organisms, increase Gal1-R mRNA synthesis and [(125)I]galanin binding sites. Whereas galanin increases short-circuit current (Isc) approximately 5-fold in uninfected T84 cells, exposure to pathogenic, but not nonpathogenic, E. coli results in galanin increasing Isc approximately 20-fold. To confirm the validity of these in vitro observations, we also studied C57BL/6J mice infected with enterohemorrhagic E. coli (EHEC) by gavage. Infection caused a progressive increase in both NF-kappa B activation and Gal1-R expression, with maximal levels of both observed 3 days after gavage. Ussing chamber studies revealed that colons infected with EHEC, but not those exposed to normal colonic flora, markedly increased Isc in response to galanin. These data indicate that pathogen-induced increases in Gal1-R expression by epithelial cells lining the colon may represent a novel unifying pathway responsible for at least a portion of the excessive fluid secretion observed during infectious diarrhea.

Ontogeny of galanin-immunoreactive elements in the intrinsic nervous system of the chicken gut

Galanin is a brain-gut peptide that is present in the central and peripheral nervous systems. In the gut, it is contained exclusively in intrinsic and extrinsic nerve supplies, and it is involved overall in the regulation of gut motility. To obtain information about the ontogeny of galanin, we undertook an immunohistochemical study of chicken embryos. The time of first appearance and the distribution patterns of galanin were investigated with fluorescence and streptavidin-biotin-peroxidase (ABC) immunohistochemical protocols by using a galanin polyclonal antiserum. The various regions of the gut and the pancreas were obtained from chicken embryos aged from 3 days of incubation to hatching. All specimens were fixed in buffered picric acid-paraformaldehyde, frozen, and cut with a cryostat. Galanin-immunoreactive neuroblasts were first detected at 4 days in the mesenchyme of the proventriculus/gizzard primordium and within the Remak ganglion. They then extended cranially and caudally, reaching all of the other gut regions at 6.5 days. Galanin-immunoreactive nerve elements mainly occupied the sites of myenteric and submucous plexuses. From day 15, galanin-immunoreactive nerve fibers tended to invade the circular muscular layer and part of the lamina propria of the mucosa. In the pancreas, weak galanin-immunoreactive nerve elements were detected at 5.5 days. They tended to be distributed among the glandular lobules according to the organ differentiation. The widespread distribution during the earlier embryonic stages represents evidence indicating that the neuropeptide galanin may have a role as a differentiating or growth factor. From late embryonic life, its predominant presence in sympathetic nerves and in muscular layers fits with the functions demonstrated previously in adults of other vertebrates for galanin as a modulator of intestinal motility.

Role of galanin in the gastrointestinal sphincters

Galanin was present and exerted potent effects in all the gastrointestinal sphincters examined. Galanin-immunoreactive nerve fibers and neurons are present in both the myenteric and submucosal plexuses of sphincters. The neuropeptide exerts diverse effects in different sphincteric smooth muscles that may be species specific. For example, in the lower esophageal sphincter, it may cause an increase in basal tone and suppression of nonadrenergic noncholinergic (NANC) nerve-mediated relaxation. On the contrary, in the internal anal sphincter (IAS), the predominant effect of galanin is to cause smooth muscle relaxation and augmentation of NANC nerve-mediated relaxation. In other sphincters, galanin may either have no effect or cause either an increase or a decrease in basal tone. Most of the actions of galanin on basal smooth muscle sphincteric tone are due to its actions directly on smooth muscle cells. However, some of the relaxant actions of the peptide may also be due to activation of NANC inhibitory neurons. The basic mechanism/s responsible for sphincteric smooth muscle contraction or relaxation in response to galanin have not been investigated. The suppressive as well as the augmentatory effects of galanin on NANC nerve-mediated sphincteric smooth muscle relaxation may be due to inhibition or facilitation, respectively, of the release of NANC inhibitory neurotransmitters such as nitric oxide and vasoactive intestinal polypeptide. Diverse effects in different gastrointestinal sphincters suggest a neuromodulatory rather than a neurotransmitter role of galanin and a significant role of the neuropeptide and putative antagonists in the pathophysiology and potential therapy of gastrointestinal motility disorders especially those affecting sphincteric function.

Galanin inhibition of enterochromaffin-like cell function

BACKGROUND & AIMS

Galanin, a 29-amino acid neuropeptide found in the gastric mucosa, inhibits basal and pentagastrin-stimulated acid secretion. Its cellular target is unknown. The aim of this study was to determine whether galanin inhibits Ca2+ signaling and histamine release in enterochromaffin-like (ECL) cells.

METHODS

Isolated rat ECL cells were purified to 85% homogeneity by a combination of elutriation, density gradient centrifugation, and 48-hour culture. Intracellular calcium concentration ([Ca2+]i) was determined using video imaging with Fura-2 in a 37 degreesC superfusion chamber. Histamine was measured by radioimmunoassay.

RESULTS

Reverse-transciption polymerase chain reaction of the ECL cell RNA showed a galanin type I receptor subtype. Galanin inhibited gastrin, Bay K8644, and K+ depolarization-induced calcium mobilization and entry as well as reduced basal calcium levels. Pretreatment with pertussis toxin decreased the effect of galanin. Galanin inhibited basal and gastrin-stimulated histamine release by approximately 60% with a median effective concentration of 1.10(-10) mol/L. The inhibitory actions of galanin on histamine release and Ca2+ influx could be reduced by a galanin antagonist, galantide.

CONCLUSIONS

Galanin's inhibition of acid secretion can be explained in part by inhibition of calcium signaling and histamine release from the ECL cells due to activation of a Gi,o protein-coupled receptor.

Actions of galanin and some of its analogues on rat isolated gastric fundus

The study was undertaken to characterize the effects of porcine galanin (pGal) and some of its analogues on rat gastric fundus muscle strips. pGal, galantide (M15) and pGal(1-14)-[Abu8]SCY-I evoked reproducible concentration-dependent contractions in concentrations of 1-300, 3-1,000 and 100-3,000 nM, respectively, with EC50 values of 13, 70 and 187 nM. Hill's coefficient for pGal is 1.03, indicating an interaction of one pGal molecule with one receptor, fulfilling criteria of classical receptor theory. For M15 and pGal(1-14)-[Abu8]SCY-I, Hill's coefficients are significantly different from 1, namely 0.73 and 1.56, so that one drug molecule may not interact with one receptor. The stimulatory effects of pGal were not modified by dibenamine 10 microM or glybenclamide 1 or 10 microM. Diltiazem 0.1, 1 and 10 microM, papaverine 0.1, 10 microM or dibutyryl cAMP (dib cAMP) 100 and 300 microM, blocked the contraction to pGal in a concentration-dependent manner, indicating an important role for the influx of extracellular calcium ions and regulation by cAMP the pGal-evoked contraction. Diltiazem, dibutyryl cAMP and papaverine were not competitive antagonists of pGal in the stomach smooth muscle.

Galanin is a potent inhibitor of glucagon-like peptide-1 secretion from rat ileum

The insulinotropic glucagon-like peptide 1 (GLP-1) originates from the lower intestines. Surprisingly, food ingestion induces a rapid increase of GLP-1 plasma levels. Therefore, a complex regulation for postprandial GLP-1 secretion must exist, which cannot be solely explained by direct contact of nutrients in the gut lumen with the GLP-1-releasing L cells. This was addressed in the present study utilizing an isolated vascularly perfused rat ileum preparation. Cholinergic (methacholine) as well as peptidergic stimulation by glucose-dependent insulin-releasing polypeptide (synonym: gastric inhibitory polypeptide) (GIP) strongly enhanced GLP-1 secretion from the rat ileum. The stimulation of GLP-1 secretion by methacholine was abolished by addition of atropine and partly reduced by galanin. Galanin dose-dependently antagonized the stimulatory effect of GIP on GLP-1 release. Atropine was without effect. Furthermore, employing double immunohistochemistry labeling techniques galanin-immunoreactive nerves were detected in the vicinity of GLP-1-immunostained cells. Our data indicate that stimulatory and inhibitory mediators regulate GLP-1 secretion and that galanin is a likely inhibitor.

Site of action of galanin in the cholinergic transmission of guinea pig small intestine

The mode and site of action of galanin were examined in the guinea pig small intestine. Galanin (3 x 10(-9)-10(-7) M) inhibited the twitch contractions of longitudinally and circularly oriented muscle strips mediated by the stimulation of cholinergic neurons, but not the contractions mediated by direct stimulation of smooth muscle cells with carbachol. Galanin (3 x 10(-9)-10(-7) M) inhibited both the electrically stimulated and the tetrodotoxin-resistant high K+ (40 mM)-induced increase of [3H]acetylcholine outflow from the ileal strips preloaded with [3H]choline, in a concentration dependent fashion. The inhibitory effect of galanin was antagonized by galantide and produced self-desensitization. The spontaneous and stimulated outflow of [3H]noradrenaline and [3H]gamma-aminobutyric acid were not affected by galanin even at 10(-7) M. Thus, galanin inhibits the motility of guinea pig ileum by inhibition of acetylcholine release from the enteric cholinergic neurons. Galanin may act on the specific receptor located on soma-dendritic regions and nerve terminals of cholinergic neurons.

Galanin contracts and relaxes guinea pig and canine intestinal smooth muscle cells through distinct receptors

BACKGROUND/AIMS

Galanin induces a contraction or a relaxation of digestive smooth muscle. Receptors mediating these effects have not been pharmacologically characterized. The aim of the study was to evaluate properties of two specific galanin antagonists M15 and M35 on galanin effects on muscle cells.

METHODS

Isolated muscle cells were obtained separately from circular and longitudinal layers of guinea pig and dog ileums. Contraction was expressed as percentage decrease in cell length from control.

RESULTS

Galanin induced a contraction of cells from guinea pig circular layer (50% effective concentration [EC50], 80 pmol/L) and dog longitudinal layer (EC50, 100 pmol/L). The antagonists inhibited galanin-induced contraction. The most potent was M15 (50% inhibitory concentration [IC50], 80 pmol/L in guinea pig; 90 pmol/L in dog) which was > M35 (IC50, 4 nmol/L in guinea pig; 1 nmol/L in dog). In dog circular layer, galanin inhibited cholecystokinin-induced contraction by relaxing the cells (EC50, 3 pmol/L). The antagonists inhibited this relaxation. The most potent was M35 (IC50, 60 pmol/L) which was > M15 (IC50, 900 pmol/L).

CONCLUSIONS

Galanin antagonists M15 and M35 inhibit the contraction and the relaxation induced by galanin with different potency, suggesting the presence of distinct galanin receptors in gastrointestinal tract that each mediates a specific effect.