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

Early development of chick embryo respiratory nervous system: an immunohistochemical study

The extrinsic and intrinsic respiratory nervous systems receive specific contributions from the vagal and sympathetic components. Using specific markers for vagal and sympathetic structures, we studied the distribution patterns of immunoreactivity to galanin (GAL), pituitary adenylate cyclase-activating polypeptide-27 (PACAP) and the tachykinin substance P in extrinsic and intrinsic nerve of chick embryo respiratory system, during development from the very early age to hatching. All peptides studied appeared in the intrinsic and extrinsic nervous systems early. We found substance P in both the vagal and sympathetic systems, PACAP in vagal components alone and GAL mainly in the sympathetic system. The intrinsic nervous system showed high immunoreactivity for all peptides studied. These data accord with the well known early trophic functions that peptides have on the development of nervous networks and modulatory activity on the intrinsic nervous system. The GAL again proves to be the main peptide in chick embryo sympathetic respiratory system.

Coexistence of non-adrenergic non-cholinergic inhibitory and excitatory neurotransmitters in a large neuronal subpopulation in the vaginal segment of the chicken oviduct

The presence, distribution and smooth muscle motor effects of galanin and pituitary adenylate cyclase activating peptide (PACAP) were studied in the nerves of the vaginal part of the oviduct of egg-laying hens. Galanin and PACAP immunoreactivity were found both in neuronal perikarya and nerve fibres within the wall of the vaginal segment. Both populations showed a similar distribution pattern. Particularly the circular muscle and the intramural vascular net were richly innervated. A few galanin- and PACAP-IR nerve fibres extended up to the mucosal folds. Multiple labelling showed galanin to be colocalised with PACAP as well as with vasoactive intestinal polypeptide (VIP) and nitric oxide synthase (NOS) in a large, partly intrinsic neuronal subpopulation innervating the smooth muscle wall. Pharmacological in vitro experiments showed that isolated vaginal muscle strips had a spontaneous basal activity that was not affected by the neuronal conductance blocker tetrodotoxin (TTX). Galanin induced concentration-dependent contractions that were TTX-insensitive. PACAP, VIP, nitric oxide (NO) and the NO donor nitroglycerin caused concentration-dependent relaxations that were TTX-insensitive. Electrical field stimulation of isolated muscle strips induced frequency-dependent relaxations that were blocked by TTX and reduced by the NOS blocker L-nitroarginine. These data provide evidence that the vaginal part of the oviduct contains a largely intrinsic, neuronal subpopulation, capable of releasing multiple non-adrenergic, non-cholinergic (NANC) motor agents for the control of local muscular activities. In addition, we provided pharmacological evidence that VIP, NO and PACAP exert an inhibitory and galanin an excitatory action on isolated muscle strips of the vaginal part of the chicken oviduct. Our results suggest that these NANC neurotransmitters play an important role in the regulation of neuromuscular activity in this region.

Ontogeny of galanin-immunoreactive elements in chicken embryo autonomic nervous system

To elucidate the main ontogenetic steps of galanin immunoreactivity within the extrinsic nerve supply of the alimentary tract, we undertook an immunohistochemical study of chicken embryo specimens. Fluorescence and streptavidin-biotin-peroxidase protocols were combined, using a galanin polyclonal antiserum, on transverse serial sections obtained from chicken embryos from embryonic Day 3 (E3) to hatching, and from 9-day-old newborn chicks. Galanin-immunoreactive cells were first detected at E3.5 within the pharyngeal pouch region, the nodose ganglion, the primary sympathetic chain, primitive splanchnic branches and the caudal portion of the Remak ganglion. At E5.5 galanin-immunoreactive cells and fibers appeared in the secondary (paravertebral) sympathetic chain, splanchnic nerves, peri- and preaortic plexuses, adrenal gland anlage and visceral nerves. Galanin-immunoreactive cells also lay scattered along the vagus nerve, and in the intermediate zone of the thoracolumbar spinal cord. At E18, galanin-immunoreactive cells and fibers were found along the entire Remak ganglion and around the gastrointestinal blood vessels. In post-hatching-9-day old chicks, the para- and prevertebral ganglia, but not the intermediate zone of the spinal cord, contained galanin-immunoreactive cells. Data indicate the presence of a consistent "galaninergic" nerve system supplying the chick embryonal gut wall. Whether this system has growth or differentiating role remains to be demonstrated. Its presence and distribution pattern in the later stages clearly support its well known role as a visceral neuromodulator of gut function.

Effect of galanin on isolated strips of smooth muscle from the gastrointestinal tract of chickens

The contractile effects of galanin on isolated longitudinal smooth muscle strips of pre-crop esophagus, proventriculus, duodenum, colon, and cecum of chickens were investigated. Application of galanin (5.0-100.0 nM) evoked strong contractions from the colon and cecum (hindgut), but evoked minimal responses from the pre-crop esophagus, proventriculus, and duodenum (foregut). Previous studies have demonstrated that the central administration of galanin stimulates food consumption in rats. Since galanin-like immunoreactivity is present in the chicken brain, we speculate that the central release of galanin may increase food intake and possibly be involved in a hypothalamic-colonic reflex modulating hindgut motility and generating a defecation. Thus, the results of this study demonstrate the presence of galanin receptors in the chicken gut and suggest a possible link with their functional presence in the hindgut to the chicken central nervous system.

Vasoconstrictor effects of galanin and distribution of galanin containing fibres in three species of elasmobranch fish

Galanin is found in perivascular sympathetic neurons in a wide range of vertebrate species. In placental mammals, galanin has either no effect on blood pressure, or weak depressor effects, but in other vertebrates it has been shown to be a potent pressor agent. To investigate how extensive the vasoconstrictor effects of galanin may be in the vertebrates, the vascular effects of galanin were tested in two species of shark, Heterodontus portusjacksoni, and Hemiscyllium ocellatum, and a ray, Rhinobatos typus. Nerve fibres showing immunoreactivity to galanin were located surrounding gut blood vessels, but were absent from branchial efferent arteries in all three species. Intravenous injection of galanin caused a significant rise in caudal arterial blood pressure in H. portusjacksoni and H. ocellatum, but no change in R. typus. Contraction of segments of pancreatico-mesenteric artery were measured in an organ bath also. Galanin (10(-6) M) caused 21-38% of the maximum K+ induced contraction in all species, but no response in efferent branchial arteries from R. typus. In conclusion, in three elasmobranchs, a galanin-like peptide is present in perivascular nerve fibres, and galanin causes differential vasoconstriction in vascular beds. These data extend the number of vertebrate groups in which galanin has been shown to be a vasoconstrictor peptide.

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.

Distribution and chromatographic analysis of galanin message-associated peptide (GMAP)-like immunoreactivity in the rat

Galanin message-associated peptide (GMAP) constitutes the C-terminal part of the precursor protein encoding also the biologically active neuropeptide galanin (GAL). We have raised antisera against a species-conserved portion of GMAP, and investigated the localization of GMAP-like immunoreactivity (-LI) in relation to that of GAL-LI in the rat central and peripheral nervous system using the indirect immunofluorescence technique. In the central nervous system, GMAP-immunoreactive (-IR) cell bodies were observed in the hypothalamus, while GMAP-IR nerve fibers were demonstrated in the septum, hypothalamus, pons and spinal cord. In the posterior pituitary and in the connecting infundibular stalk, weakly fluorescent GMAP-IR nerve fibers were observed. GMAP-IR nerve fibers were also observed throughout the gastrointestinal tract, i.e., from the stomach down to the colon, and in all layers, except in the epithelium, of the wall. In general, the staining of consecutive tissue sections suggested that GMAP-IR was co-distributed with that of GAL-IR. A sensitive radioimmunoassay (RIA) for characterization of GMAP-IR in the rat central and peripheral nervous system was also developed. Characterization of GMAP-LI in acid extracts of rat brain and small intestine, using reverse phase high pressure liquid chromatography (rpHPLC), revealed multiple GMAP-IR forms that co-eluted with a synthetic porcine GMAP(19-41)-amide fragment, or were less or more polar than this fragment. The corresponding chromatographic analysis of GAL-LI revealed only one major form corresponding to rat GAL. The immunohistochemical data indicate that a GMAP-like peptide(s) probably is axonally transported and may possibly have pre- and/or post-synaptic functions. The nature of the multiple GMAP-IR components remains to be investigated, but may tentatively represent differently processed and/or chemically modified forms of rat GMAP(1-60).

Purification and primary structure of galanin from the alligator stomach

Galanin-like immunoreactivity (6 pmol/g tissue) was detected by radioimmunoassay in an extract of the stomach of the alligator, Alligator mississipiensis, but the peptide was present only in low concentration (< 0.5 pmol/g) in extracts of the brain and small intestine. Alligator galanin comprises 29 amino acid residues and contains an alpha-amidated C-terminal residue. Residues 1-22 of alligator galanin are identical to the corresponding sequence in pig/sheep/rat galanins, demonstrating that strong evolutionary pressure has acted to conserve the receptor-binding domain of the peptide. Unexpectedly, in view of the close phylogenetic relationship between crocodilians and birds, alligator galanin is structurally more similar to sheep galanin (three amino acid substitutions) than to chicken galanin (four amino acid substitutions).

Galanin-like immunoreactivity in the chicken brain

The anatomical distribution of neurons containing galanin has been studied in the central nervous system of the chicken by means of immunocytochemistry using antisera against rat galanin. Major populations of immunostained perikarya were detected in several brain areas. The majority of galanin-immunoreactive cell bodies was present in the hypothalamus and in the caudal brainstem. Extensive groups of labeled perikarya were found in the paraventricular, periventricular, dorsomedial and tuberal hypothalamic nuclei, and in the nucleus of the solitary tract in the medulla oblongata. In the telencephalon, immunoreactive perikarya were observed in the preoptic area, in the lateral septal nucleus and in the hippocampus. The mesencephalon contained only a few galanin-positive perikarya located in the interpeduncular nucleus. Immunoreactive nerve fibers of varying density were detected in all subdivisions of the brain. Dense accumulations of galanin-positive fibers were seen in the preoptic area, periventricular region of the diencephalon, the ventral hypothalamus, the median eminence, the central gray of the brainstem, and the dorsomedial caudal medulla. The distributional pattern of galanin-immunoreactive neurons suggests a possible involvement of a galanin-like peptide in several neuroregulatory mechanisms.

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.

Galanin receptors in the brain of a teleost: autoradiographic distribution of binding sites in the Atlantic salmon

The distribution of galanin (GAL) binding sites in the brain of the Atlantic salmon (Salmo salar) was investigated by means of radioligand binding in conjunction with autoradiography by using high-performance liquid chromatography (HPLC) characterized radio-iodinated porcine galanin ([125I]GAL). On slide-mounted sections of frozen salmon brain homogenate, [125I]GAL (4 nM) bound rapidly and reversibly to a single population of sites with a Kd of 1.0 +/- 0.08 nM (n = 3) and Bmax of 2.38 +/- 0.19 fmol/mg wet tissue. Specific [125I]GAL binding was found in cellular regions, in fiber tracts, and in neuropil areas throughout the brain, except for in the olfactory bulb, pineal organ, and cerebellum. Autoradiographic microdensitometric measurements revealed high total [125I]GAL binding in the ventral hypothalamus (inferior lobes; around 7-12 fmol/mg tissue), the dorsal spinal cord (between 6 and 12 fmol/mg tissue), sublayers of the optic tectum (around 8 fmol/mg), torus semicircularis (around 7 fmol/mg), and glomerular complex (around 6 fmol/mg). Intermediate densities of [125I]GAL binding (3-5 fmol/mg tissue) were found in the pituitary, telencephalon, dorsolateral thalamic nucleus, and raphe nuclei and in association with the forebrain bundles. Except for in the optic tectum, there is a good concordance of [125I]GAL binding sites and GAL-immunoreactive fiber projections in most brain areas of the salmon. The wide distribution of GAL binding sites provides further evidence that a GAL-like substance might be involved in a diversity of brain functions of teleosts. The topographic distribution of target sites in the hypothalamo-hypophyseal axis indicates that GAL-like substances may have both direct and indirect effect on pituitary functions while in extrahypothalamic areas, functional implications by GAL may include involvement in somatosensory, central gustatory, olfactory, and visual functions. This study provides evidence for the presence of a specific GAL receptor in the brain of the Atlantic salmon. Together the distribution of GAL binding and GAL-like molecules provide a covering delineation of the GAL neuronal system in the brain of the Atlantic salmon. Comparisons with mammals suggest that the GAL receptor molecule has been well preserved during evolution and that GAL-like substances may be present, and even possess similar functional properties, throughout the vertebrate phylogeny.

Galanin is more common than NPY in vascular sympathetic neurons of the brush-tailed possum

The distribution of galanin (Gal) in sympathetic vascular neurons of adult and juvenile brush-tailed possums (Trichosurus vulpecula), was examined using double-labelling immunohistochemistry. This was compared with the distribution of neuropeptide Y (NPY) in the same tissues. Immunoreactivity (IR) to galanin was present in the majority (64-99%) of nerve cell bodies in paravertebral sympathetic ganglia, where it mostly co-existed with IR to the catecholamine-synthesizing enzyme, tyrosine hydroxylase (TH). Gal-IR also was present in most, if not all, TH-IR perivascular axons supplying systemic arteries and veins. NPY-IR was less common than Gal-IR in all sympathetic ganglia and perivascular axons examined. Some sympathetic, TH-IR axons supplying the abdominal aorta and renal artery contained both Gal-IR and NPY-IR, while TH-IR axons supplying cephalic and thoracic vessels contained Gal-IR but not NPY-IR. Limited observations on sympathetic neurons in two species of wallabies indicated that Gal-IR also was more common than NPY-IR in other marsupial species, but the incidence of NPY-IR was higher in these wallabies than in the brush-tailed possum. Together with previous studies, this work suggests that the coexistence of galanin and NPY may be the primitive condition for sympathetic neurons in tetrapods. The differential expression of these peptides in specific populations of sympathetic neurons may have important functional consequences in the autonomic control of the circulation.

The influence of neuropeptide Y and norepinephrine on ovulation in the rat ovary

Neuropeptide Y (NPY) was measured in tissue extracts from ovaries of rats treated with pregnant mare serum gonadotropin (PMSG). The extracted NPY-immunoreactive material was identical to synthetic human NPY with regard to size and hydrophobicity as evaluated by gel filtration and high performance liquid chromatography. The concentration of NPY was related to the estrous cycle and a maximum was observed in relation to the endogenous luteinizing hormone (LH) peak. NPY immunoreactivity was demonstrated by immunohistochemistry to be localized within nerve fibers supplying blood vessels and follicles. The increase in the NPY content could not be related to accumulation around specific ovarian structures. Employing an in vitro set-up, NPY (10(-7) M) was unable to induce ovulation and did not increase the ovulation rate in LH-stimulated ovaries. The combination of NPY (10(-7) M) and NE (10(-7) M) did not significantly increase the number of ovulations compared to that induced by NE (10(-7) M) alone. In conclusion, NPY content in the ovary is related to the estrous cycle, but NPY does not seem to have any direct effect on the ovulatory process.

Studies on colocalization of neuropeptide Y, vasoactive intestinal polypeptide, catecholamine-synthesizing enzymes and acetylcholinesterase in the larynx of the rat

In the present immunohistochemical study, the distribution of nerve fibers containing neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) in the larynx was examined and compared with that of fibers containing tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH), and with that of acetylcholinesterase (AChE)-positive nerve fibers, in intact and vagotomized rats and in rats subjected to removal of the superior cervical ganglion (SCG). Fibers showing TH/DBH-like immunoreactivity (LI) were only found in the walls of arteries and arterioles, whereas AChE-positive nerve fibers were located close to the acini and ducts of the glands, in blood vessel walls, in the perichondrium and in the lamina propria. NPY-LI and VIP-LI coexisted in local AChE-positive ganglionic cells and in a subpopulation of the AChE-positive fibers, NPY-LI also being present in some periarterial fibers showing TH/DBH-LI. Unilateral removal of the SCG eliminated the TH/DBH-innervation in the upper but not the lower parts of the larynx ipsilaterally, whereas the NPY-innervation of the arteries in the upper parts only partly disappeared and the NPY-innervation of the other structures remained unchanged. The distribution of VIP-innervation was unchanged after vagotomy and removal of the SCG. The results suggest that VIP is present in the postganglionic parasympathetic innervation, whereas NPY is present in both the postganglionic parasympathetic and sympathetic innervation of the rat larynx.

Sexually dimorphic distribution of a galanin-like peptide in the central nervous system of the teleost fish Poecilia latipinna

Immunohistochemical techniques were used to visualize areas of the brain and spinal cord containing a galanin-like peptide in the teleost fish, the sailfin molly. Galanin-like immunoreactivity (GAL-LI) in both males and females was identified in neurons in the nucleus preopticus periventricularis, nucleus lateralis tuberis, and nucleus commissuralis. GAL-LI fibers had a comparable distribution in the forebrain, preoptic, hypothalamic, and visceral sensory areas of both sexes. In striking contrast to these areas, the optic tectum, torus semicircularis, brainstem tegmentum, and spinal cord of the male contained much higher levels of GAL-LI than the female. GAL-LI in these dimorphic areas in the female was limited to single fiber bundles in the ventromedial tegmentum and in the trigeminal system. Additionally, a population of neurons in the preoptic nucleus was found to contain GAL-LI in the male only. Sexual dimorphism was especially prominent in the spinal cord, where extensive GAL-LI fibers were found in the male only. These fibers were oriented in the longitudinal plane and confined largely to the gray matter. Comparative studies were performed on the goldfish spinal cord, in which GAL-LI was localized solely in the dorsal horn and exhibited no sexual dimorphism. Further, examination of spinal cord material from neonatal mollies revealed a lack of spinal GAL-LI at this developmental stage. As the extent of GAL-LI in the male molly spinal cord differs from both the goldfish and from that reported for the mammalian spinal cord, and a prominent sexual dimorphism in GAL-LI extends from the diencephalon to the caudal spinal cord, it is suggested that a galanin-like peptide may play a unique, sex-specific role in this species.

Enkephalin-like immunoreactivity in ganglionic cells in the larynx and superior cervical ganglion of the rat

The distribution of enkephalin-like immunoreactivity (ENK-LI) in the larynx, the superior cervical ganglion (SCG) and the nodose ganglion of adult rats was examined in the present study. A substantial number of the local acetylcholinesterase (AChE)-positive, presumably parasympathetic, ganglionic cells in the larynx displayed ENK-LI. These cells also exhibited neuropeptide Y (NPY)- and vasoactive intestinal polypeptide (VIP)-LI. Varicose nerve fibers showing ENK-LI were observed close to the acini and ducts of the glands, in the perichondrium and in the lamina propria. The varicosities exhibiting ENK-LI frequently displayed NPY- and VIP-LI. The ENK-LI was detected in a subpopulation of AChE-positive nerve fibers in the laryngeal tissue. In the SCG, only a small number of the ganglionic cells displayed ENK-LI. These cells, in contrast to other ganglionic cells of the SCG, did not show NPY-LI. None of the ganglionic cells of the nodose ganglion exhibited ENK-LI. Sympathectomy and vagotomy affected neither the number nor the distribution of fibers showing ENK-LI in the larynx. In conclusion, ENK appears to be present together with NPY and VIP in the parasympathetic innervation of the larynx and in a very limited number of the ganglionic cells of a sympathetic ganglion, the SCG, of the adult rat.

Peptide-containing nerve fibers in the fungiform papillae of pigs and rats

The occurrence and distribution of an array of neuropeptides and dopamine-beta-hydroxylase in the fungiform papillae of pigs and rats were studied by immunocytochemistry. Structural differences between the fungiform papillae of the two species were correlated to differences in the occurrence and distribution of neuropeptides. Calcitonin gene-related peptide-, substance P- and neurokinin A-containing fibers were numerous in the fungiform papillae of both species, although their distribution within the papilla differed. In the pig, the majority of these fibers ended within the taste buds, while in the rat numerous fibers also penetrated the adjacent epithelium. Galanin- and bombesin-immunoreactive nerve fibers could not be detected in the rat fungiform papillae, while in the pig many, but not all, of the fungiform papillae contained bombesin- and galanin-positive nerve fibers. Vasoactive intestinal peptide- and peptide histidine isoleucine-immunoreactive fibers occurred in the fungiform papillae of both species. A few neuropeptide Y-containing fibers and dopamine-beta-hydroxylase-positive (presumably adrenergic) fibers could be observed in the porcine papillae only.

Differential occurrence and distribution of galanin in adrenal nerve fibres and medullary cells in rodent and avian species

The presence and distribution of galanin (GAL) in adrenal glands of rodent and avian species was investigated by light microscopic immunohistochemistry. GAL immunoreactivity was found in all medullary cells of guinea pig, duck and chicken adrenals. In contrast, only a subpopulation of medullary cells stained for GAL in Phodopus (Djungarian hamster) while the neuropeptide was completely missing in chromaffin cells of rat and pigeon. In rat, guinea pig and pigeon, GAL-immunoreactive nerve fibres were frequent in subcapsular regions and sparse in deeper cortical layers and in the chromaffin tissue. In contrast, only very few GAL fibres were found in Phodopus and no GAL fibres were observed in the adrenal glands of duck. In the chicken adrenal gland, fibres containing GAL were numerous throughout the organ and occurred in close vicinity to both steroidogenic as well as catecholaminogenic cells. The striking differences in the presence of GAL-positive cells and fibres are more pronounced between species within the rodent or avian group, respectively, than between the different vertebrate orders. The hitherto unknown and surprising variability of GAL expression and distribution in adrenal glands of various species suggests species-dependent functional (autocrine, paracrine and/or endocrine) roles of GAL in the neuroadrenal axis.