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

Parasympathetic control of airway submucosal glands: central reflexes and the airway intrinsic nervous system

Airway submucosal glands produce the mucus that lines the upper airways to protect them against insults. This review summarizes evidence for two forms of gland secretion, and hypothesizes that each is mediated by different but partially overlapping neural pathways. Airway innate defense comprises low level gland secretion, mucociliary clearance and surveillance by airway-resident phagocytes to keep the airways sterile in spite of nearly continuous inhalation of low levels of pathogens. Gland secretion serving innate defense is hypothesized to be under the control of intrinsic (peripheral) airway neurons and local reflexes, and these may depend disproportionately on non-cholinergic mechanisms, with most secretion being produced by VIP and tachykinins. In the genetic disease cystic fibrosis, airway glands no longer secrete in response to VIP alone and fail to show the synergy between VIP, tachykinins and ACh that is observed in normal glands. The consequent crippling of the submucosal gland contribution to innate defense may be one reason that cystic fibrosis airways are infected by mucus-resident bacteria and fungi that are routinely cleared from normal airways. By contrast, the acute (emergency) airway defense reflex is centrally mediated by vagal pathways, is primarily cholinergic, and stimulates copious volumes of gland mucus in response to acute, intense challenges to the airways, such as those produced by very vigorous exercise or aspiration of foreign material. In cystic fibrosis, the acute airway defense reflex can still stimulate the glands to secrete large amounts of mucus, although its properties are altered. Importantly, treatments that recruit components of the acute reflex, such as inhalation of hypertonic saline, are beneficial in treating cystic fibrosis airway disease. The situation for recipients of lung transplants is the reverse; transplanted airways retain the airway intrinsic nervous system but lose centrally mediated reflexes. The consequences of this for gland secretion and airway defense are poorly understood, but it is possible that interventions to modify submucosal gland secretion in transplanted lungs might have therapeutic consequences.

Human galanin expresses amphipathic properties that modulate its vasoreactivity in vivo

The purpose of this study was to determine whether human galanin, a pleiotropic 30-amino acid neuropeptide, expresses amphipathic properties in vitro and, if so, whether these properties modulate its vasoactive effects in the intact peripheral microcirculation. We found that human galanin aggregates in an aqueous solution and forms micelles with a critical micellar concentration (CMC) of 0.4 microM. In addition, the peptide interacted with model membrane as indicated by long and significant increase of the surface pressure of the biomimetic monolayer membrane in vitro. Interactions of human galanin with sterically stabilized phospholipid micelles (SMM) were not associated with a significant change in peptide conformation. Using intravital microscopy, we found that suffusion of human galanin alone elicited significant concentration-dependent vasoconstriction in the intact hamster cheek pouch. This response was amplified when human galanin in SSM was suffused onto the cheek pouch. The effects of human galanin alone and in SSM were mediated by galanin receptors because galantide, a galanin receptor antagonist, abrogated galanin-induced vasoconstriction. Collectively, these data show that human galanin expresses amphipathic properties in the presence of phospholipids which in turn amplifies its vasoactive effects in the intact peripheral microcirculation.

Innervation of tracheal epithelium and smooth muscle by neurons in airway ganglia

The neurochemical profiles of neurons in ferret tracheal ganglia has been characterized, but their projections to smooth muscle and epithelium in ferret trachea has not been examined. The purpose of this study is to determine the location of cell bodies that project VIP-, SP-, and NPY-containing fibers to the ferret tracheal smooth muscle and epithelium. Segments of ferret trachea were cultured for 0, 1, 3, or 7 days, some in the presence of 3 microm capsaicin. VIP, SP, or NPY nerve fiber density was measured using morphometric procedures. A retrograde tracer, rhodamine-labeled microspheres, identified neurons projecting to the epithelium. The density of SP fibers in the epithelium was reduced after culture, but VIP innervation was not different. In tracheal smooth muscle, the density of VIP- and SP-IR fibers was not different during the culture period, but NPY fiber density was reduced at all culture times. Capsaicin treatment did not affect nerve fiber density in the tracheal smooth muscle but produced a significant reduction in the density of epithelial VIP- and SP-IR nerve fibers after 1 day. Rhodamine-labeled microspheres were identified in VIP-containing nerve cell bodies of the ferret tracheal plexus. VIP innervation to the airway epithelium in ferret originates both from cell bodies in airway ganglia and cell bodies in sensory ganglia. The pathway from airway ganglia suggest the existence of a local reflex mechanisms initiated by epithelial irritation.

Neuroregulation by vasoactive intestinal peptide (VIP) of mucus secretion in ferret trachea: activation of BK(Ca) channels and inhibition of neurotransmitter release

1. The aims of this study were to determine: (1) whether vasoactive intestinal peptide (VIP) regulates cholinergic and 'sensory-efferent' (tachykininergic) 35SO4 labelled mucus output in ferret trachea in vitro, using a VIP antibody, (2) the class of potassium (K+) channel involved in VIP-regulation of cholinergic neural secretion using glibenclamide (an ATP-sensitive K+ (K(ATP)) channel inhibitor), iberiotoxin (a large conductance calcium activated K+ (BK(ca)) channel blocker), and apamin (a small conductance K(ca) (SK(ca)) channel blocker), and (3) the effect of VIP on cholinergic neurotransmission using [3H]-choline overflow as a marker for acetylcholine (ACh) release. 2. Exogenous VIP (1 and 10 microM) alone increased 35SO4 output by up to 53% above baseline, but suppressed (by up to 80% at 1 microM) cholinergic and tachykininergic neural secretion without altering secretion induced by ACh or substance P (1 microM each). Endogenous VIP accounted for the minor increase in non-adrenergic, non-cholinergic (NANC), non-tachykininergic neural secretion, which was compatible with the secretory response of exogenous VIP. 3. Iberiotoxin (3 microM), but not apamin (1 microM) or glibenclamide (0.1 microM), reversed the inhibition by VIP (10 nM) of cholinergic neural secretion. 4. Both endogenous VIP (by use of the VIP antibody; 1:500 dilution) and exogenous VIP (0.1 microM), the latter by 34%, inhibited ACh release from cholinergic nerve terminals and this suppression was completely reversed by iberiotoxin (0.1 microM). 5. We conclude that, in ferret trachea in vitro, endogenous VIP has dual activity whereby its small direct stimulatory action on mucus secretion is secondary to its marked regulation of cholinergic and tachykininergic neurogenic mucus secretion. Regulation is via inhibition of neurotransmitter release, consequent upon opening of BK(Ca) channels. In the context of neurogenic mucus secretion, we propose that VIP joins NO as a neurotransmitter of i-NANC nerves in ferret trachea.

N-methyl-D-aspartate receptors are expressed by intrinsic neurons of rat larynx and esophagus

Overactivation of N-methyl-D-aspartate receptors (NMDAR), a mechanism of central neurotoxicity, has recently been shown to increase airway responsiveness in rat lungs. NMDAR have not been localized in the airways, but neurons of the myenteric plexus in the rat express mRNA for NMDAR. Furthermore, a population of glutamate-containing cell bodies in the nucleus ambiguus projects to the rat larynx. On this basis, we hypothesized that some postganglionic parasympathetic neurons of the larynx, trachea and esophagus may express NMDAR. Sections of rat larynx, trachea and esophagus were immunocytochemically labeled for NMDAR subtype 2B using a specific antibody. NMDAR immunoreactivity was observed in cell bodies of individual neurons located in the submucosa and on the external surface of skeletal muscle in the larynx and also in neurons of the esophageal plexus. All NMDAR-positive nerve cell bodies also contained immunoreactivity for vasoactive intestinal peptide (VIP) and some were immunoreactive for nitric oxide synthase (NOS). None of the cell bodies of the tracheal plexus contained NMDAR immunoreactivity. The findings demonstrate that NMDAR are expressed in neurons of the rat larynx and esophagus and their activation may be associate with VIP or NO release.

Immunohistochemical localization of galanin in bovine reproductive organs

The vagina, uterus and oviduct were shown to receive galanin immunoreactive (GAL-IR) nerve fibres, the number of which varied between particular organs. In the ovary, GAL-IR nerves were absent. A small number of these nerves were located in the layers of the oviduct. A moderate number of GAL-IR nerves were situated in the body and uterine horns, whereas the uterine cervix and vagina wall contained a large number of GAL-IR nerve fibres, evenly distributed throughout particular membranes of the organs. GAL-IR nerves were found to contain, simultaneously, either vasoactive intestinal polypeptide (VIP), substance P (SP) or Leu5-enkephalin (ENK). Many of the GAL-IR nerves contained tyrosine hydroxylase (TH). A group of GAL-IR nerves that did not possess immunoreactivity to VIP, SP, ENK or TH was also observed.