Distribution of galanin immunoreactivity in the respiratory tract of pig, guinea pig, rat, and dog

Is Galanin a Promising Therapeutic Resource for Neural and Nonneural Diseases?

BACKGROUND

Galanin (GAL) constitutes a family of neuropeptides composed of four peptides: (i) galanin (GAL), (ii) galanin-message associated peptide (GAMP), (iii) galanin-like peptide (GALP), and (iv) alarin. GAL contains 29/30 amino acids, and its biological action occurs through the interactions with its various receptors (GALR1, GALR2, and GALR3). The neuropeptide GAL regulates several physiological and pathophysiological functions in the central nervous system, the peripheral nervous system, and the peripheral organs. GAL is secreted mainly by oligodendrocytes, astrocytes, and the gastrointestinal tract, and its effect depends on the interaction with its different receptors. These receptors are expressed mainly in the central, peripheral nervous systems and the intestines.

OBJECTIVE

The present review evaluates the role of GAL family in inflammatory diseases. An overview is given of the signaling and pharmacological effects due to the interaction between GAL and GALR in different cell types. The potential use of GAL as a therapeutic resource is critically discussed.

CONCLUSION

GAL is suggested to have an anti-inflammatory function in some situations and a proinflammatory function in others. The literature on GAL is controversial and currently not conclusive. This could be due to the complexity of the metabolic network signaling induced by the interactions between GAL and GALR. In the next future, GAL might be a promising therapeutic resource for several diseases, but its practical use for disease control is presently not advisable.

Airway Neuropeptides

Nonadrenergic and noncholinergic pathways appear to be important in regulating lung functions. The neurotransmitters intrinsic to the nonadrenergic and noncholinergic nerves are peptides. These neuropeptides probably play a significant role in the pathogenesis of asthma by influencing airway tone, pulmonary vasomotor tone, mucus production, mucosal permeability, and inflammatory cell influx and mediator release. This paper reviews the function of these lung neuropeptides and speculates on the role of these peptides in the pathophysiology of asthma.

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.

Airway Gland Structure and Function

Submucosal glands contribute to airway surface liquid (ASL), a film that protects all airway surfaces. Glandular mucus comprises electrolytes, water, the gel-forming mucin MUC5B, and hundreds of different proteins with diverse protective functions. Gland volume per unit area of mucosal surface correlates positively with impaction rate of inhaled particles. In human main bronchi, the volume of the glands is ∼ 50 times that of surface goblet cells, but the glands diminish in size and frequency distally. ASL and its trapped particles are removed from the airways by mucociliary transport. Airway glands have a tubuloacinar structure, with a single terminal duct, a nonciliated collecting duct, then branching secretory tubules lined with mucous cells and ending in serous acini. They allow for a massive increase in numbers of mucus-producing cells without replacing surface ciliated cells. Active secretion of Cl(-) and HCO3 (-) by serous cells produces most of the fluid of gland secretions. Glands are densely innervated by tonically active, mutually excitatory airway intrinsic neurons. Most gland mucus is secreted constitutively in vivo, with large, transient increases produced by emergency reflex drive from the vagus. Elevations of [cAMP]i and [Ca(2+)]i coordinate electrolyte and macromolecular secretion and probably occur together for baseline activity in vivo, with cholinergic elevation of [Ca(2+)]i being mainly responsive for transient increases in secretion. Altered submucosal gland function contributes to the pathology of all obstructive diseases, but is an early stage of pathogenesis only in cystic fibrosis.

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.

Sudomotor function and sweat gland innervation in galanin knockout mice

The presence of galanin and galanin binding sites in sweat gland has been demonstrated previously. In order to investigate whether galanin can influence sweat gland function, we compared sweating induced in footpads of wild type and galanin knockout mice by cholinergic and thermal stimulation using the silicone impression technique. Pilocarpine injections resulted in a similar number of reactive sweat glands and non-significant difference in the amount of sweat secretion in wild type and galanin knockout mice. However, thermal stimulation led to a significant increase in the number of secreting sweat glands in galanin knockout mice. To further evaluate possible differences in the innervation of sweat glands that could explain differences in their secretory activity, immunohistochemical labeling of cutaneous and sudomotor innervations against protein gene product 9.5, vasoactive intestinal polypeptide and choline acetyltransferase in plantar pads was performed. Immunohistochemical analysis revealed no significant differences in the distribution and intensity of the innervations between wild type mice and galanin knockout mice. Although our results indicate normal cholinergic responses and innervation of the sweat glands in galanin knockout mice, they also demonstrate that galanin plays a role in regulating the sudomotor activity in response to thermal stimulation.

Galanin in human pituitary adenomas: frequency and clinical significance

OBJECTIVES

Galanin (GAL) is a neuropeptide widely expressed in the central and peripheral nervous system and in neuroendocrine tissue, including the adenohypophysis where, in humans, it is expressed in corticotrophs and in ACTH-producing adenomas. Previous analyses of human tissue have used antiserum against porcine GAL for detection of GAL immunoreactivity (GAL-IR) and no pathophysiological correlates have been reported. Given significant differences between the sequence of porcine and human GAL peptides, the aim of this study was to use antiserum raised against synthetic human GAL to investigate GAL-IR in non tumorous pituitaries and in pituitary adenomas, and to correlate GAL-IR with the clinical and hormonal characteristics of patients with Cushing's disease.

PATIENTS

Six nontumorous pituitaries were obtained from autopsy and 151 pituitary adenomas, comprising 62 functioning (16 corticotroph, 26 somatotroph, 19 lactotroph and one thyrotroph) and 89 nonfunctioning adenomas, were obtained by surgery.

RESULTS

All non tumorous pituitary glands showed GAL-IR in corticotrophs, in basophil cells within the neurohypophysis and in nerve fibres of the neurohypophysis. GAL-IR was found in a subset (10 of 16) of patients with ACTH-secreting tumours causing Cushing's syndrome. GAL-IR was rarely expressed in somatotroph adenomas and prolactinomas, but was expressed in approximately one-third of nonfunctioning tumours. GAL-IR was found in almost 90% of nonfunctioning tumours that were positive for ACTH. There were no significant differences in sex ratio, age at presentation or 24-h urinary free cortisol secretion in the subset of patients with Cushing's disease positive (n = 10) or negative (n = 6) for GAL-IR. However, Cushing's patients positive for GAL-IR tended to have smaller tumours and achieved a higher cure rate than those without (100 vs. 50%, P = 0.017).

CONCLUSIONS

Galanin is present in normal and tumorous human pituitaries. In addition, GAL colocalizes exclusively in corticotrophs of normal pituitaries and is coexpressed almost exclusively in corticotrophs from functioning and nonfunctioning tumours. The finding that corticotroph adenomas can function irrespective of the presence of GAL suggests that GAL may not play a pathophysiological role in Cushing's disease. However, the better surgical outcome observed in patients with Cushing's disease who had tumours positive for GAL-IR suggests that the expression of GAL confers a less aggressive tumour phenotype.

Tyrosine hydroxylase- and neuropeptides-immunoreactive nerves in canine trachea

OBJECTIVE

To determine distribution of catecholaminergic and peptidergic nerve fibers in canine tracheas by use of immunohistochemistry.

SAMPLE POPULATION

10 tracheas collected from healthy adult dogs after euthanasia.

PROCEDURE

Structure of the nerve network and distribution of tyrosine hydroxylase (TH)- and 6 types of neuropeptide-containing nerves in canine tracheas were immunohistochemically studied, using neurochemical markers.

RESULTS

Intraepithelial free nerve endings with immunoreactivity for calcitonin gene-related peptide (CGRP) and substance P (SP) were observed. Tyrosine hydroxylase-, SP-, vasoactive intestinal peptide (VIP)-, and galanin (GAL)-immunoreactive nerve fibers were observed within and around the submucosal seromucous gland. In the smooth muscle layer, numerous TH- and GAL-immunoreactive nerve fibers, a moderate number of VIP- and neuropeptide Y (NPY)-immunoreactive nerve fibers, and a few SP- and methionine enkephalin (ENK)-immunoreactive nerve fibers were observed. Numerous nerve cell bodies with VIP and GAL immunoreactivity and a few with SP ENK, and NPY immunoreactivity were observed. Many TH-immunoreactive fibers were arranged in a meshwork around blood vessels. Nerves with CGRP-, SP-, VIP-, GAL-, ENK-, and NPY-immunoreactivity were also observed around blood vessels.

CONCLUSIONS

Complex innervation, including catecholamine- and neuropeptide-containing nerves, which may be related to regulation of muscle contraction and glandular secretion, are found in canine tracheas.

Galanin-acetylcholine interactions in rodent memory tasks and Alzheimer's disease

Galanin is a 29-amino-acid neuropeptide that is widely distributed in the mammalian central nervous system. Galanin-immunoreactive cell bodies, fibres and terminals, and galanin binding sites, are located in the basal forebrain of rats, monkeys and humans. Galanin fibres hyperinnervate the surviving cholinergic cell bodies in patients with Alzheimer's disease (AD). In rats, galanin inhibits acetylcholine release and produces deficits in learning and memory. These findings suggest that overexpressed galanin may contribute to the cognitive impairments exhibited by patients with AD. This paper reviews the literature on galanin distribution and function in light of its putative role in the mnemonic deficits in patients with AD, the effects of galanin on tests of learning and memory, and preliminary experiments with galanin antagonists in animal models of AD.

Quantitative microscopical methods for the identification and localisation of nerves and neuroendocrine cell markers in mammalian lung

The lung contains a dense innervation and a population of endocrinelike cells both of which are believed to have a role in pulmonary function and to be involved in disease processes. They contain a number of regulatory peptides that affect vascular and bronchial tone, growth and repair. They can be detected and localised by immunocytochemistry, thereby allowing investigation of the normal distribution and changes in disease processes. The application of image analysis has added greatly to the amount of information that can be obtained from such morphological studies. Data can be obtained on either the overall distribution and amount of the antigen in a tissue, thereby allowing comparisons between normal and disease states, or following experimental manipulation. Furthermore, the actual intracellular level can be assessed, which adds the previously unattained dimension of comparisons between cells. Thus the density of innervation in the specific regions of the lung tissue, either total nerves or specific peptide-containing cells, may be estimated and used to show release of a peptide or to determine changes in the nerve density in disease. Image processing and image analysis have reduced the labour-intensive manual input required to perform such studies. The continuing development of digital image processing and computer technology will increase the application of these methods in lung research of normal and pathological material.

Existence and co-existence of vasoactive substances in nerve fibres supplying the abdomino-pelvic arterial tree of the female pig and cow

The occurrence and co-localization of several presumed vasoactive neuropeptides, serotonin, and catecholamine-synthesising enzymes--tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (D beta H) and phenylethanolamine-N-methyltransferase (PNMT)--were investigated in perivascular nerves supplying the systemic and distributing arteries of the abdomino-pelvic arterial tree of the female pig and certain arteries supplying female reproductive organs in the cow. As revealed by single immunofluorescence, perivascular axons immunoreactive for TH, D beta H, neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP) and Leu-enkephalin (LENK) occurred in both species examined, whereas galanin-immunoreactive (GAL-IR) nerve fibres were found exclusively in the pig. PNMT-, serotonin-, dynorphin A-, alpha-neoendorphin-, bombesin- or cholecystokinin-IR nerve terminals were not observed. The following classes of perivascular nerve fibres might be distinguished in the present study: 1) noradrenergic (i.e. TH/D beta H-IR), 2) NPY-, 3) GAL- (pig only), 4) LENK-, 5) VIP-, 6) SP-, 7) VIP/NPY-, 8) SP/CGRP-, 9) SP/GAL- (pig only), 10) SP/VIP- (cow only), 11) TH/D beta H/NPY- and 12) TH/D beta H/NPY/LENK-IR. Distinct differences in the distribution of LENK- and SP-IR axons around particular parts of the studied arterial tree in individual species were also observed. The present data indicate that the abdomino-pelvic arterial tree of the pig and cow receive perivascular nerve fibres that exhibit diverse chemical codes, and that different chemical coding of perivascular nerve fibres in individual species may depend on the target organ of the particular artery.

Calcitonin gene-related peptide and substance P in the pharynx and lung of the bullfrog, Rana catesbeiana

Indirect double immunofluorescence labelling in the pharynx and lung of the bullfrog, Rana catesbeiana, demonstrated the occurrence, distribution, and coexistence of two neuropeptides. In the pharynx, immunoreactive calcitonin gene-related peptide (CGRP) and substance P (SP) were localized in nerve fibers distributed within and just beneath the ciliated epithelium. In the lung, CGRP and SP were localized in nerve fibers in five principal locations: 1) within the smooth muscle layer in the interfaveolar septa; 2) in the luminal thickened edges of the septa; 3) around the pulmonary vasculature; 4) within, and 5) under the ciliated epithelium. Within the smooth muscle layer in the septa, luminal thickened septa, and around blood vessels, almost all fibers showed coexistence of CGRP and SP. Within and just beneath the ciliated epithelium in the thickened septa, all fibers showed coexistence of CGRP and SP. No immunoreactivity for vasoactive intestinal polypeptide, neuropeptide Y, galanin, somatostatin, FMRFamide, and leucine- and methionine-enkephalins was detected in the nerve fibers within the larynx and the lung. Together with our previous data, the present findings suggest that peptidergic mechanisms are involved in the regulation of amphibian respiratory systems throughout their life.

Modulation of neurotransmission in guinea-pig airways by galanin and the effect of a new antagonist galantide

Galanin is localised to sensory nerve fibres and cholinergic nerves in airways. Galantide has been shown to be a novel high affinity antagonist to galanin, since it inhibits galanin-mediated inhibition of glucose-induced insulin secretion and the neuronal action of galanin in the brain. We investigated the effects of galanin on cholinergic and non-adrenergic, non-cholinergic (NANC) responses to electrical field stimulation in guinea-pig airways, and examined whether galantide antagonised the effect of galanin on neurotransmission. Galanin (10(-6)M) had no effect on cholinergic bronchoconstrictor responses and inhibitory NANC relaxation responses in trachea, but significantly inhibited excitatory NANC bronchoconstrictor responses in bronchi which is due to the release of tachykinins. Galantide (10(-8)-10(-6)M) had no effect on the galanin-induced inhibition of the excitatory NANC responses. Galanin may be important in the modulation of excitatory NANC responses but not cholinergic and inhibitory NANC responses in guinea-pig airways. This modulatory effect may be via a different type of galanin receptor than is present in other organs.

Origin of galanin in nerves of cat airways and colocalization with vasoactive intestinal peptide

Galanin is a 29 amino acid residue neuropeptide. In mammalian airways, galanin is found in nerve fibers associated with airway smooth muscle, bronchial glands, and blood vessels, and in nerve cell bodies of airway ganglia. The present study was conducted to determine if galanin-containing fibers in the walls of feline airways originate from the nerve cell bodies of airway ganglia. The colocalization of galanin with vasoactive intestinal peptide was also investigated. Organotypic cultures of cat airways were held in culture for 0 (nonculture control), 3, 5, and 7 days. After each culture period, the distribution of galanin and the colocalization of galanin with vasoactive intestinal peptide were determined by immunocytochemistry. Galanin-containing fibers were found in bronchial smooth muscle, around bronchial glands and in the walls of bronchial arteries and arterioles throughout the culture period. Nerve fibers and cell bodies containing both galanin and vasoactive intestinal peptide were observed after all culture periods. Nerve fibers and cells bodies that contained galanin frequently contained vasoactive intestinal peptide as well, but nerve fibers with only galanin or vasoactive intestinal peptide were also observed. Galanin- and vasoactive intestinal peptide-containing nerve fibers and cell bodies were both well maintained throughout the culture period. The findings show that galanin-containing nerve fibers associated with bronchial smooth muscle, bronchial glands, and bronchial arteries, originate from nerve cell bodies of intrinsic airway ganglia, and that galanin and vasoactive intestinal peptide are frequently colocalized in these neurons.

The role of galanin in cholinergically-mediated memory processes

1. Galanin, a 29 amino-acid neuroactive peptide, has been shown to affect diverse processes throughout the nervous system and to coexist with several "classical" neurotransmitters, including norepinephrine, serotonin, and acetylcholine. 2. Galanin coexists with acetylcholine in neurons of the medial septum, diagonal band, and nucleus basalis of Meynert, cells which degenerate during the course of Alzheimer's disease. 3. In the ventral hippocampus, galanin inhibits the release of acetylcholine and inhibits carbachol stimulated phosphatidyl inositol hydrolysis. 4. Galanin impairs choice accuracy in learning and memory paradigms in rats, and is therefore hypothesized to be a contributory factor in the memory and cognitive disabilities found in Alzheimer's patients. 5. Newly developed galanin antagonists, by eliminating putative inhibitory effects of endogenous galanin on cholinergic function, may serve as useful therapies for memory disorders.

Presence of galanin in rat vagal sensory neurons: evidence from immunohistochemistry and in situ hybridization

Galanin (GAL), a 29 amino acid peptide originally isolated from the porcine upper small intestine, is widely distributed in the rat central nervous system, including the area postrema (AP) and nucleus of the solitary tract (NTS). Although vagal sensory neurons terminate in the AP/NTS, it is not known whether these neurons contain GAL in the rat. Therefore, we examined the presence and distribution of GAL in the rat nodose ganglia which contain the cell bodies of vagal sensory neurons. We used avidin-biotin-peroxidase immunohistochemistry and in situ hybridization histochemistry with a 35S-labeled oligonucleotide probe. Results with both techniques revealed the presence of GAL-containing cell bodies and fibers in the nodose ganglion. GAL-like immunoreactive cell bodies, mostly between 25 and 40 microns in diameter, were unevenly scattered throughout the nodose ganglia. The distribution and cell diameter range of GAL mRNA-labeled neurons appeared similar to those of GAL-like immunoreactive cells. These findings suggest a role for GAL in the transmission of visceral sensory information by the vagus nerve in rats.

Liver releases galanin during sympathetic nerve stimulation

To determine whether the gut or liver releases galanin during sympathetic neural activation, we performed bilateral thoracic splanchnic nerve stimulation (BTSNS) in halothane-anesthetized dogs. Using experimentally determined galanin extraction rates of 60% for gut and no extraction by liver, calculations demonstrated a minor increase in gut spillover during BTSNS (delta = +4.8 +/- 1.8 pmol/min), whereas liver spillover of galanin-like immunoreactivity (GLIR) increased markedly (delta = +27.9 +/- 9.5 pmol/min). To confirm the finding of liver galanin release, GLIR was measured in femoral artery, portal vein, and hepatic vein during hepatic nerve stimulation (HNS). GLIR spillover from gut was not increased by HNS (delta = +1.9 +/- 6.3 pmol/min). In contrast, liver GLIR spillover was greatly increased during HNS (delta = +53.3 +/- 16.4 pmol/min). Extracts of canine liver contained 2.7 +/- 0.4 pmol GLIR/g tissue. We conclude that, despite the known significant galanin content of the gut, little galanin is released from this organ during sympathetic activation. In contrast, the liver, heretofore not described to contain galanin, contains and releases significant amounts of the peptide during sympathetic activation.

Effects of vasoactive intestinal peptide, helodermin and galanin on responses of guinea-pig lung parenchyma to histamine, acetylcholine and leukotriene D4

1. The effect of vasoactive intestinal peptide (VIP) was studied on the contractile response of guinea-pig lung parenchymal strips (GPP) induced by bronchoconstrictor agonists, such as leukotriene D4 (LTD4), histamine and acetylcholine (ACh). This effect of VIP was compared with helodermin, a peptide that is structurally related to VIP, and galanin, another neuropeptide that is thought to co-exist with VIP. 2. VIP (10 nM) induced a potent and reversible inhibition of the contractions of GPP induced by LTD4 (1-30 pmol) but did not affect those due to ACh (1-100 nmol) or histamine (1-30 nmol). A ten fold higher concentration of VIP (100 nM) did not further inhibit LTD4-induced responses or reduce those induced by histamine or ACh. 3. Helodermin (10 nM) had a similar inhibitory effect on contractions of GPP induced by LTD4 (3-30 pmol) but did not affect contractions induced by histamine (1-10 nmol). 4. Indomethacin (2.8 microM) and salbutamol (10 nM) significantly reduced responses elicited by LTD4 and histamine but not those due to ACh. A ten fold higher concentration of salbutamol (100 nM) further inhibited the contractions due to LTD4 and histamine and at this concentration responses induced by ACh were inhibited. 5. VIP (10 nM) and helodermin (10 nM) significantly reduced the LTD4-induced release of thromboxane A2 (TXA2), measured as TxB2 by radioimmunoassay, from GPP. The smaller release of TxA2 induced by histamine was not significantly reduced in the presence of VIP. 6. In comparative studies, galanin (10-100 nM) did not affect contractions of GPP induced by either LTD4, histamine or ACh. In contrast to VIP and helodermin, both at 0.1-3 nmol, which induced doserelated relaxations of guinea-pig trachea, galanin was inactive on this preparation in doses of up to 3 nmol.7. In conclusion, our results show that contractions of GPP induced by LTD4 are more sensitive to inhibition by VIP and helodermin than are contractions due to histamine or ACh. This inhibition appears to be associated with the different contribution of released TxA2 to contractions evoked by the agonists. VIP and helodermin inhibit the cyclo-oxygenase-dependent component of the LTD4-induced response, as in the case of indomethacin.

Galanin inhibits pancreatic amylase secretion in the pentobarbital-anesthetized rat

The potent inhibitory effect of galanin on basal and pentagastrin-stimulated gastric acid secretion in vivo, and the presence of galanin-containing nerves in gastrointestinal tract and pancreas, suggested that this peptide may regulate the exocrine secretion of the GI system. Male rats were anesthetized with pentobarbital and the dose-dependent inhibitory effects of galanin on basal and stimulated pancreatic protein and amylase secretions were investigated in separate experiments. Galanin was administered intravenously in the following doses: 3, 6, 10, 15 and 20 micrograms/kg/h (0.93, 1.86, 3.1, 4.65 and 6.2 nmol/kg/h), and pancreatic secretions measured. The maximal effective dose of galanin (3.1 nmol/kg/h) on basal pancreatic secretions was found, and was used for evaluating the inhibitory effect of galanin on pancreatic protein and amylase secretions stimulated by bombesin, secretin and cholecystokinin. Galanin potently inhibited basal, bombesin-, secretin- and cholecystokinin-stimulated pancreatic protein and amylase secretion. Inhibitory effect of galanin was dose-dependent and biphasic.

Pulmonary calcitonin gene-related peptide immunoreactivity: nerve-endocrine cell interrelationships

Respiratory epithelium has been reported to be supplied with sensory nerves and to contain irritant and other receptors. In this immunohistochemical study, we examined the incidence, morphology, and distribution of calcitonin gene-related peptide (CGRP) immunoreactivity in epithelial cells the rat respiratory tract, using peroxidase anti-peroxidase (PAP) techniques. CGRP immunoreactivity was localized in capsaicin-sensitive nerve fibers and in capsaicin-nonsensitive endocrine cells occurring singly or in groups. These CGRP-immunoreactive structures reached close to or actually touched the airway lumen, were widely and abundantly present in the respiratory epithelium, and were arranged in distinct and characteristic patterns. CGRP-immunoreactive nerves innervated not only grouped cells but also single cells, and the innervation of these cells differed depending on whether they were in extrapulmonary or intrapulmonary epithelium. The specificity of the immunoreactivity was confirmed by absorption tests that excluded cross-reactivity with other peptides. The results suggest that epithelial nerve fibers and endocrine-like cells exhibiting CGRP immunoreactivity form a morphologic, and probably also a functional, complex throughout the respiratory epithelium. CGRP innervation may be related to receptor functions of respiratory epithelium.

Immunoreactive nerve fibers in the nasal mucosa. An experimental study on neuropeptides Y, calcitonin gene-related peptide and galanin

The presence of immunoreactive nervous fibers in the respiratory nasal mucosa of rats and guinea pigs was studied by means of a modified peroxidase antiperoxidase technique for whole mounting. The fibers with neuropeptide Y (NPY) always appeared in the walls of blood vessels, while the fibers immunoreactive to calcitonin gene-related peptide (CGRP) were found in nerve tracts near the vessels and the acini of seromucous glands as thick networks located in the subepithelial layers. Immunoreactivity (IR) for galanin was found in the mucosa studied. The findings after surgical and chemical denervation of the trigeminal and superior cervical ganglia may support the theory that the fibers with NPY are of a sympathetic nature with the superior cervical ganglion their site of origin, while the CGRP-IR fibers may have a sensory nature.

Regulatory peptides and general neuroendocrine markers in human nasal mucosa, soft palate and larynx

Various peptide immunoreactivities in the respiratory system have been reported, indicating complex physiological mechanisms. There is only little information on the upper respiratory system of man. The present study was carried out to demonstrate regulatory peptides in the nasal mucosa, larynx (vocal cords and ventricular folds) and soft palate of man using highly efficient immunocytochemical methods. In addition, some peptide immunoreactivities were measured by use of radioimmunoassay (RIA). Using indirect immunofluorescence and immunogold-silver staining (IGSS) with silver acetate autometallography, a series of peptides could be detected, including vasoactive intestinal polypeptide (VIP), peptide histidine methionine (PHM), galanin, calcitonin gene-related peptide (CGRP), substance P, neuropeptide tyrosine (NPY), C-flanking peptide of NPY (CPON) and somatostatin. In addition, antibodies to protein gene-product (PGP) 9.5, neuron-specific enolase (NSE), S-100, PHE-5 and neurofilament proteins gave positive reactions in tissue sections. Using RIA, CGRP, substance P, and neurokinin A were measured. Our results demonstrate a complex network of regulatory peptide-containing nerve fibers and the possible existence of endocrine cells regulating various functions of the upper respiratory system, which need to be further investigated.

Distribution of galanin-immunoreactive nerve fibers in the rat nasal mucosa

Galanin-like immunoreactivity was found in nerve fibers beneath and within the epithelium of the rat mucosa by the use of immunohistochemical techniques. Immunoreactive fibers were also noted close to blood vessels and seromucous glands in the lamina propria. Fast blue applied to the nasal mucosa underwent retrograde transport to some immunoreactive neurons of the trigeminal ganglion. Thus, the rat nasal mucosa was shown to be innervated by galanin-containing sensory nerves.

Galanin in porcine vagal sensory nerves: immunohistochemical and immunochemical study

In this work, the presence of galanin was examined by immunohistochemistry, radioimmunoassay and high performance liquid chromatography (HPLC) in porcine nodose ganglia, mainly constituted of cell bodies from the vagal sensory neurons. Galanin-like immunoreactivity (Gal-LI) was revealed in 10 to 15% of the total cell bodies by the indirect immunofluorescent technique of Coons. For comparison, a positive staining was revealed in a few cell bodies of the submucous plexus and in fibers located in the different layers of the ileum. The extractable Gal-LI content in nodose ganglia was 7.2 +/- 0.8 pmol/g wet tissue, which represents a concentration about nine times lower than that found in the ileum. HPLC of extractable material revealed a predominant peak which coeluted with the synthetic peptide. We propose that, in pigs, galanin may play a role in the transmission of visceral information through the vagal afferences.

Autoradiographic visualization of muscarinic receptors on rat paratracheal neurons in dissociated cell culture

An autoradiographic method was used to determine the distribution of muscarinic receptors on cells cultured from the trachealis muscle of 12-13-day-old rats. Cells identified in these culture preparations included neurones, fibroblasts, smooth muscle, and glial and epithelial cells. The cultured cells were incubated with the specific, irreversible ligand [3H]propylbenzylylcholine mustard, and the autoradiographs generated showed that most, if not all, of the paratracheal neurones observed in these cultures were specifically labelled. Both the neuronal cell body and associated neurites were evenly labelled over their entire surface. Neither the pattern nor the density of neuronal labelling appeared to be influenced by close association with other cultured cell types. Autoradiographic grains for muscarinic receptors also appeared to be uniformly distributed over smooth muscle cells and epithelial cell groups in culture. In contrast, no specific labelling was associated with cultured fibroblasts, glial cells and other non-neuronal supporting cells. The precise localization of muscarinic receptors on different cell types in culture may prove to be useful knowledge in the design of an effective and specific antimuscarinic bronchodilator.

[Met]enkephalin-Arg6-Gly7-Leu8-immunoreactive nerves in guinea-pig and rat lungs: distribution, origin, and co-existence with vasoactive intestinal polypeptide immunoreactivity

[Met]Enkephalin-Arg6-Gly7-Leu8 is an endogenous opioid peptide, first isolated from the bovine adrenal medulla. Because this octapeptide is specifically contained in the amino acid sequence of preproenkephalin A but not in other opioid precursors like preproopiomelanocortin or preproenkephalin B, [Met]enkephalin-Arg6-Gly7-Leu8 has been regarded as a specific marker for preproenkephalin A and its derivatives. In this study, we examined the occurrence and origin of [Met]enkephalin-Arg6-Gly7-Leu8-immunoreactive nerves in the guinea-pig and rat lung by immunohistochemical techniques, using a specific antiserum against this peptide. In addition, we investigated the possible co-existence of [Met]enkephalin-Arg6-Gly7-Leu8 and vasoactive intestinal peptide immunoreactivity in neuronal elements of the respiratory tract. In both species, [Met]enkephalin-Arg6-Gly7-Leu8 immunoreactivity was localized in nerve fibers chiefly distributed to the trachea and major bronchi, where they were prevalent in smooth muscle bundles, in the lamina propria, around airway glands, and in the walls of pulmonary vessels, but were absent in airway epithelium. Slight differences in the distribution pattern of immunoreactive nerve fibers were noted between the two species: immunoreactive nerve fibers in the smooth muscle bundles were much more abundant in guinea-pigs than in rats, while those in the mucous glands were richer in rats than in guinea-pigs. Neither chemical sympathectomy by 6-hydroxydopamine, nor chemical sensory denervation by capsaicin, changed the density or distribution of [Met]enkephalin-Arg6-Gly7-Leu8-immunoreactive nerve fibers in the airway, suggesting an intrinsic source for these nerve fibers. Colchicine injection into the tracheal wall, to promote the accumulation of neuropeptides in nerve cell bodies, led to the visualization of [Met]enkephalin-Arg6-Gly7-Leu8 immunoreactivity in some neuronal cell bodies within airway ganglia. Immunostaining for [Met]enkephalin-Arg6-Gly7-Leu8 and for vasoactive intestinal polypeptide on serial adjacent sections of airway ganglia obtained from colchicine-treated tracheae, demonstrated the co-existence of these immunoreactivities in a population of nerve cell bodies in these ganglia. The immunohistochemical localization of immunoreactive [Met]enkephalin-Arg6-Gly7-Leu8 in nerve elements in guinea-pig and rat lungs provides a morphological basis for the possibility that preproenkephalin A-related opioid peptides may have a neuromodulatory role in mammalian airways and pulmonary vessels.

Peptides and vasomotor mechanisms

The multiple and diverse roles played by neuropeptide Y, vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide and other biologically active peptides in the cardiovascular system are considered. A model of the vascular neuroeffector junction is described, which illustrates the interactions of peptidergic and nonpeptidergic transmitters that are possible at pre- and postjunctional sites. The effects of peptides on specific endothelial receptors are also described, which highlights the ability of these agents to act as dual regulators of vascular tone at both adventitial and intimal surfaces, following local release from nerves, or from endothelial cells themselves. Changes in expression of vascular neuropeptides that occur during development and aging in some disease situations and following nerve lesion are discussed.

Galanin: hydrokinetic action on salivary glands in man

Galanin was infused intravenously into eight healthy volunteers at a dose of 40 pmol kg-1 min-1 for 1 h to investigate the pharmacological effects of this peptide on the postprandial sialagogical response in man. Galanin significantly increased the salivary volume and the saliva output of sodium, chloride and bicarbonate compared to control saline infusion, but had no effect on the output of potassium and alpha-amylase. An increase in salivary pH was also observed. The increase in salivary volume may indicate a physiological role of galanin in the control of salivary secretion.

Peptide-containing nerve fibers in the respiratory tract of the ferret

The ferret is widely used in functional and neuromorphological studies on the respiratory tract. We have examined the occurrence and distribution of peptide-containing and adrenergic nerve fibers (using dopamine-beta-hydroxylase as a marker). Adrenergic nerve fibers and fibers storing vasoactive intestinal peptide have a widespread distribution along the entire respiratory tract. Adrenergic nerve fibers were found in the lamina propria, as well as around blood vessels and glands and in smooth muscle. Nerve fibers storing vasoactive intestinal peptide occurred in the epithelium, the lamina propria, around blood vessels and glands, and among muscle bundles. Substance P-, neurokinin A- and calcitonin gene-related peptide-containing nerve fibers predominated beneath and within the epithelium along the entire respiratory tract. Neuropeptide Y-containing nerve fibers were prominent among smooth muscle bundles and around glands. The blood vessels in the wall of the airways were richly supplied with peptide-containing nerve fibers and adrenergic fibers. Ganglia located over the outer or dorsal surface of the tracheal wall harbored vasoactive intestinal peptide-containing nerve cell bodies. Substance P and neurokinin A invariably coexisted in the same nerve fibers. Further, coexistence of substance P/neurokinin A and calcitonin gene-related peptide was observed in the nerve fibers associated with the epithelium. Vasoactive intestinal peptide, neuropeptide Y and occasionally also substance P coexisted in the population of nerve fibers associated with blood vessels and smooth muscle. Many adrenergic nerve fibers contained neuropeptide Y.

Neuronal galanin is widely distributed in the chicken respiratory tract and coexists with multiple neuropeptides

The mammalian airways are known to be richly innervated by several types of peptide-containing nerve fibers. Galanin-containing fibers are, however, comparatively few. The results of the present immunocytochemical study indicate that the chicken airways receive a notably dense supply of galanin-storing fibers. Other major neuropeptides were neuropeptide Y, vasoactive intestinal peptide and substance P. Nerve fibers containing these peptides were distributed in the trachea, main bronchi, and the lungs. Minor nerve fiber populations contained calcitonin gene-related peptide, enkephalin and gastrin-releasing peptide. In the trachea and main bronchi the majority of peptide-containing nerve fibers was distributed beneath and sometimes also within the epithelium; fibers were fewer in the lamina propria. In the lungs they occurred both in association with the epithelium of small bronchi and in the septa. Adrenergic nerves (using tyrosine hydroxylase as marker) were predominantly distributed in the lamina propria among bundles of smooth muscle and blood vessels. In the nerve fibers associated with the epithelium and in nerve cell bodies in local ganglia of the tracheal wall, galanin was found to coexist with several other neuropeptides (neuropeptide Y, vasoactive intestinal peptide and substance P) suggesting co-expression of multiple neuropeptide genes in the same population of neurons.

Regulatory peptides in the respiratory system

Many regulatory peptides have been described in the respiratory tract of animals and humans. Some peptides (bombesin, calcitonin, calcitonin gene-related peptide) are localised to neuroendocrine cells and may have a trophic or transmitter role. Others are localised to motor nerves. Vasoactive intestinal peptide and peptide histidine isoleucine are candidates for neurotransmitters of non-adrenergic inhibitory fibres and may be cotransmitters in cholinergic nerves. These peptides may regulate airway smooth muscle tone, bronchial blood flow and airway secretions. Sensory neuropeptides (substance P, neurokinin A and B, calcitonin gene-related peptide) may contract airway smooth muscle, stimulate mucus secretion and regulate bronchial blood flow and microvascular permeability. If released by an axon reflex mechanism these peptides may be involved in the pathogenesis of asthma. Other peptides, such as galanin and neuropeptide Y, are also present but their function is not yet known.

Regulatory peptides in the respiratory tract of Macaca fascicularis

The quantitative distribution and localisation of seven regulatory peptides (vasoactive intestinal peptide (VIP), peptide histidine methionine (PHM), calcitonin gene related peptide (CGRP), galanin, substance P, neuropeptide tyrosine (Y), and bombesin like peptides) were determined by radioimmunoassay and immunocytochemistry in six different regions of the respiratory tract of the cynomolgus monkey, Macaca fascicularis. In general, peptide concentrations were higher in the airways than in lung tissue itself. VIP and PHM were found in greatest abundance and in equimolar concentrations. Concentrations of substance P, neuropeptide Y, and bombesin were substantially lower. Immunocytochemistry localised all the peptides to nerve fibres, whose density generally paralleled the tissue concentrations by radioimmunoassay except in the case of bombesin, which was not detected. VIP, PHM, and galanin were mostly associated with glands of trachea and bronchus and with blood vessels and smooth muscle; CGRP and substance P were found principally beneath airway epithelium and around smooth muscle fibres and blood vessels; neuropeptide Y was found around blood vessels and seromucous glands only. The pattern of peptide distribution in the Macaca fascicularis respiratory tract is similar to that previously reported in human postmortem material, suggesting that the cynomolgus monkey may be a useful model for examining the pathophysiological role of peptides in human respiratory disease.

Identification and molecular characterization of galanin receptor sites in rat brain

Receptors for galanin are identified and characterized in rat brain membranes. Interaction of [125I]-galanin with its receptors is saturable, time, pH, and ionic strength-dependent. It is reversible and highly peptide specific. Scatchard analysis of binding data reveals the existence of one single class of high affinity binding sites with a KD of 0.9 nM and a capacity of 101 fmoles/mg membranes protein. Chemical cross-linking of [125I]-galanin to its brain receptor followed by SDS-PAGE analysis leads to the identification of one major protein of 56 kD corresponding to the galanin-receptor complex. Our findings provide the first biochemical characterization of galanin receptors in the central nervous system supporting a role for galanin in the control of brain functions.

Occurrence, distribution and ontogeny of CGRP immunoreactivity in the rat lower respiratory tract: effect of capsaicin treatment and surgical denervations

The occurrence and distribution of calcitonin gene-related peptide (CGRP) immunoreactivity in the rat respiratory tract were investigated by means of immunocytochemistry and radioimmunoassay using antibodies raised in rabbits to synthetic rat CGRP. Substantial amounts of CGRP immunoreactivity (range 5-37 pmol/g) were detected in all parts of the respiratory tract, the highest being in the stem bronchus. Gel filtration chromatography of extractable CGRP immunoreactivity revealed one single peak, eluting at the position of synthetic rat CGRP. CGRP immunoreactivity was localized both in mucosal endocrine cells and nerve fibres from the larynx down to the peripheral lung. CGRP-immunoreactive endocrine cells were found singly in trachea and stem bronchi and in groups in intrapulmonary airways. They appeared at a late stage of gestation (17 days), reached a maximum number near term and decreased after birth to maintain a population similar to that of the adult animals by postnatal day 21. Similarly, CGRP-immunoreactive nerve fibres were first identified by day 18 of the gestation period and reached the adult distribution by postnatal day 21. CGRP-immunoreactive nerve fibres were localized among smooth muscle, seromucous glands, beneath and within the epithelium of the airways and around blood vessels. CGRP was also found in sensory ganglia and in motor end plates of the larynx musculature. Neonatal pretreatment with capsaicin caused a marked reduction in CGRP immunoreactivity of nerve fibres in the respiratory tracts as well as a less marked decrease in the population of CGRP-containing endocrine cells of the lung. No change was seen in motor end plates immunostaining. Vagal ligation experiments revealed that CGRP-immunoreactive nerve fibres travelling in the vagus originate mainly from neurons located in the jugular ganglion. Infranodosal right vagal ligation induced a marked loss in CGRP-immunoreactive nerves of the trachea, and of the ipsilateral stem bronchus, but no changes were observed in peripheral lung. By contrast infranodosal left side vagal ligation caused a decrease in CGRP-immunoreactive nerves of the ipsilateral lung and bronchus without affecting the peptide content in the trachea. Left vagal ligation also induced a marked increase in both the intensity of staining and number of CGRP-immunoreactive endocrine cells in the lung. We conclude that CGRP immunoreactivity is localized in both nerve fibres and endocrine cells and is associated principally with the afferent (sensory) innervation of the respiratory tract.(ABSTRACT TRUNCATED AT 400 WORDS)

Growth hormone release in man induced by galanin, a new hypothalamic peptide

Galanin, a 29-aminoacid neuropeptide, was infused for 60 min into healthy volunteers at 7.8 pmol/kg/min (n = 4) or 33.2 pmol/kg/min (n = 6). During the infusion there was no change in heart rate or blood pressure and the only symptoms were a transitory bitter taste and slight hypersalivation. Plasma growth hormone levels rose during the high-dose galanin infusion from 2.8 +/- 0.8 mU/l to a mean peak of 48.5 +/- 19.8 mU/l; prolactin levels rose from 176 +/- 33 mU/l to 274 +/- 33 mU/l. A significant rise in growth hormone also occurred with the low-dose infusion (2.5 +/- 1.1 mU/l to a mean peak of 23.5 +/- 6.6 mU/l). There was no change in cortisol, thyroid-stimulating hormone, follicle-stimulating hormone, or luteinising hormone at either dose. 20 min after the start of the infusion a 25 g glucose bolus was given intravenously. Galanin reduced glucose clearance without significantly affecting plasma insulin concentrations. Pancreatic polypeptide levels were suppressed by the galanin infusion but levels of glucagon and gastric inhibitory peptide were unchanged.

Chromatographic evidence for high-molecular-mass galanin immunoreactivity in pig and cat adrenal glands

Galanin was measured by radioimmunoassay in extracts of pig, cat and rat adrenals using non-C- and mid to C-terminally directed antibodies. The extracts were fractioned by gel chromatography and HPLC. The non-C-terminal galanin immunoreactivity in pig was 92.8 +/- 11.7 pmol/g, in cat 9.1 +/- 0.9 pmol/g and in rat less than 1 pmol/g. Two higher molecular forms of galanin have been identified in both pig and cat adrenal. One major large form behaves as if it was N-terminally extended (Kav pig 0.58, cat 0.48) and the other, a very high-molecular-mass form (Kav pig 0.10, 0.24, cat 0.10), as if it had both N- and C-terminal extensions.