Early postnatal exposure of mice to side-steam tobacco smoke increases neuropeptide Y in lung.

Our recent study showed that prenatal and early postnatal exposure of mice to side-steam tobacco smoke (SS), a surrogate to environmental tobacco smoke (ETS), leads to increased airway responsiveness and sensory innervation later in life. However, the underlying mechanism initiated in early life that affects airway responses later in life remains undefined. The concomitant increase in nerve growth factor (NGF) after exposures suggests that NGF may be involved the regulation of airway innervation. Since NGF regulates sympathetic nerve responses, as well as sensory nerves, we extended previous studies by examining neuropeptide Y (NPY), a neuropeptide associated with sympathetic nerves. Different age groups of mice, postnatal day (PD) 2 and PD21, were exposed to either SS or filtered air (FA) for 10 consecutive days. The level of NPY protein in lung and the density of NPY nerve fibers in tracheal smooth muscle were significantly increased in the PD2-11SS exposure group compared with PD2-11FA exposure. At the same time, the level of NGF in lung tissue was significantly elevated in the PD2-11SS exposure groups. However, neither NPY (protein or nerves) nor NGF levels were significantly altered in PD21-30SS exposure group compared with the PD21-30FA exposure group. Furthermore, pretreatment with NGF antibody or K252a, which inhibits a key enzyme (tyrosine kinase) in the transduction pathway for NGF receptor binding, significantly diminished SS-enhanced NPY tracheal smooth muscle innervation and the increase in methacholine-induced airway resistance. These findings show that SS exposure in early life increases NPY tracheal innervation and alters pulmonary function and that these changes are mediated through the NGF.

A2A adenosine receptor deficiency leads to impaired tracheal relaxation via NADPH oxidase pathway in allergic mice.

A(2A) adenosine receptor (A(2A)AR) has been shown to suppress superoxide generation in leukocytes via the cAMP-protein kinase A (PKA) pathway. However, no study has yet explored the role of A(2A)AR in relation to NADPH oxidase in murine tracheas in vitro, which may lead to altered smooth muscle relaxation in asthma. Therefore, the present study evaluated the effects of A(2A)AR deficiency on the NADPH oxidase pathway in tracheas of A(2A) wild-type (WT) and A(2A) knockout (KO) mice. A(2A)WT mice were sensitized with ovalbumin (30 microg i.p.) on days 1 and 6, followed by 5% ovalbumin aerosol challenge on days 11, 12, and 13. A(2A)AR (gene and protein expression), cAMP, and phosphorylated PKA (p-PKA) levels were decreased in A(2A)WT sensitized mice compared with controls. A(2A)KO mice also showed decreased cAMP and p-PKA levels. A(2A)WT sensitized and A(2A)KO control mice had increased gene and protein expression of NADPH oxidase subunits (p47phox and gp91phox) compared with the controls. Tracheal relaxation to specific A(2A)AR agonist, 4-[2-[[6-amino-9-(N-ethyl-beta-d-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid hydrochloride (CGS 21680), decreased in A(2A)WT sensitized mice compared with the controls, although it was absent in A(2A)KO mice. Pretreatment with NADPH oxidase inhibitors apocyanin/diphenyliodonium reversed the attenuated relaxation to CGS 21680 in A(2A)WT sensitized tracheas, whereas specific PKA inhibitor (9S,10S,12R)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i] [1,6]benzodiazocine-10-carboxylic acid hexyl ester (KT 5720) blocked CGS 21680-induced relaxation. Tracheal reactive oxygen species (ROS) generation was also increased in A(2A)WT sensitized and A(2A)KO control mice compared with the controls. In conclusion, this study shows that A(2A)AR deficiency causes increased NADPH oxidase activation leading to decreased tracheal relaxation via altered cAMP-PKA signaling and ROS generation.

Deficient vasoactive intestinal peptide innervation in the sweat glands of cystic fibrosis patients.

The innervation of acini and ducts of eccrine sweat glands by immunoreactive, vasoactive intestinal peptide-containing nerve fibers was sharply reduced in seven patients with cystic fibrosis compared to eight normal subjects. The decrease in innervation by this neuropeptide, which has been shown to promote blood flow and the movement of water and chloride across epithelial surfaces in other systems, may be a basic mechanism for the decreased water content and relative impermeability of the epithelium to chloride and other ions that characterize cystic fibrosis.

Interleukin (IL)-1 regulates ozone-enhanced tracheal smooth muscle responsiveness by increasing substance P (SP) production in intrinsic airway neurons of ferret.

Exposure to ozone induces airway hyperresponsiveness (AHR) mediated partly by substance P (SP) released from nerve terminals of intrinsic airway neurons. Our recent studies showed that interleukin (IL)-1, an important multifunctional proinflammatory cytokine, increases synthesis and release of SP from intrinsic airway neurons. The purpose of this study is to investigate the possible involvement of endogenous IL-1 in modulating neural responses associated with ozone-enhanced airway responsiveness. Ferrets were exposed to 2ppm ozone or filtered air for 3h. IL-1 in the bronchoalveolar lavage (BAL) fluid was significantly increased in ozone-exposed animals and responses of tracheal smooth muscle to methacholine (MCh) and electrical field stimulation (EFS) were elevated significantly. Both the SP nerve fiber density in tracheal smooth muscle and the number of SP-containing neurons in airway ganglia were significantly increased following ozone exposure. Pretreatment with IL-1 receptor antagonist (IL-1 Ra) significantly diminished ozone-enhanced airway responses to EFS as well as ozone-increased SP in the airway. To selectively investigate intrinsic airway neurons, segments of ferret trachea were maintained in culture conditions for 24h to eliminate extrinsic contributions from sensory nerves. The segments were then exposed to 2ppm ozone in vitro for 3h. The changes of ozone-induced airway responses to MCh and EFS, and the SP levels in airway neurons paralleled those observed with in vivo ozone exposure. The ozone-enhanced airway responses and neuronal SP levels were inhibited by pretreatment with IL-1 Ra. These findings show that IL-1 is released during ozone exposure enhances airway responsiveness by modulating SP expression in airway neurons.

Side-stream tobacco smoke-induced airway hyperresponsiveness in early postnatal period is involved nerve growth factor.

Epidemiological studies have shown that children are more susceptible to adverse respiratory effects of passive smoking than adults. The goal of this study is to elucidate the possible neural mechanism induced by exposure to passive smoking during early life. Postnatal day (PD) 2 and PD 21 mice were exposed to side-stream tobacco smoke (SS), a surrogate to secondhand smoke, or filtered air (FA) for 10 consecutive days. Pulmonary function, substance P (SP) airway innervation, neurotrophin gene expression in lung and nerve growth factor (NGF) release in bronchoalveolar lavage (BAL) fluid were measured at different times after the last SS or FA exposure. Exposure to SS significantly altered pulmonary function in PD2, accompanied with an enhanced SP innervation in airway. However, exposure to SS during the later developmental period (PD21) did not appear to affect pulmonary function and SP innervation of the airways. Interestingly, SS exposure in PD2 group significantly induced an increased gene expression on NGF, and decreased NGF receptor P75 in lung; parallel with high levels of NGF protein in BAL. Furthermore, pretreatment with NGF antibody significantly diminished SS-induced airway hyperresponsivenss and the increased SP airway innervation in the PD2 group. These findings suggest that enhanced NGF released in the lung contributes to SS-enhanced SP tracheal innervation and airway responsiveness in early life.

Thyroid vascular conductance: differential effects of elevated plasma thyrotropin (TSH) induced by treatment with thioamides or TSH-releasing hormone.

We have reported previously that thyroid gland blood flow, expressed as vascular conductance (C) per mass, is decreased at very low and increased at very high chronic plasma TSH concentrations, but is apparently unchanged over a broad range of plasma TSH concentrations encompassing normal levels. The aim of the present study was to examine the apparently very steep dose-response relationship between elevated plasma TSH and thyroid vascular C/mass. In the first series of experiments, endogenous plasma TSH concentrations were manipulated by treating male Sprague-Dawley rats (250-280 g) for 6 days as follows: 1) controls (0.5 ml saline/day, ip), 2) propylthiouracil injections (2.0 mg PTU/day, ip), 3) PTU plus partial thyroid hormone replacement (2.0 mg PTU/day and 0.3-0.9 microgram T4 plus 0.075-0.225 microgram T3/100 g.day via continuous sc infusion), or 4) TRH (9-1200 micrograms TRH/100 g.day via continuous iv infusion). The vascular C values of the thyroid gland, salivary gland, kidney, and pancreas were determined using the reference sample version of the radioactive microsphere technique. PTU treatment led to the expected hypothyroidism, increased plasma TSH concentrations (959 +/- 66 vs. 154 +/- 22 ng/dl), increased thyroid weight (9.19 +/- 0.36 vs. 4.60 +/- 0.15 mg/100 g), and increased thyroid vascular C/mass (495 +/- 51 vs. 127 +/- 20 microliters/mm Hg.g/min). PTU-treated rats receiving partial thyroid hormone replacement demonstrated a dose-related suppression of plasma TSH, thyroid weight, and thyroid vascular C. Although, TRH treatments resulted in increased plasma TSH concentrations (e.g. 1200 micrograms TRH, 706 +/- 46 ng/dl) and thyroid weight (e.g. 1200 micrograms TRH, 7.45 +/- 0.41 mg/100 g), thyroid vascular C per tissue mass was not significantly increased after any TRH treatment (e.g. 1200 micrograms TRH, 166 +/- 19 microliters/mm Hg.g/min). Thus, at similarly elevated plasma TSH concentrations, the thyroid vascular C/mass of PTU- and TRH-treated rats constituted separate populations. Both PTU- and TRH-induced thyroid growth were accompanied by similar alterations in thyroid gland morphology (i.e. increased cellular mass with little change in the total amount of colloid). To investigate the mechanisms involved, groups of rats were treated for 6 days as follows: 1) control, 2) PTU or methimazole (25 mg MMI/day, ip), 3) PTU or MMI plus thyroid hormone replacement (1.2 micrograms T4 plus 0.3 microgram T3/d.100 g), 4) TRH (12 micrograms/100 g.day), and 5) PTU or MMI, thyroid hormones, and TRH.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of vasoactive intestinal peptide- and substance P-containing nerves originating from neurons of airway ganglia in cat bronchi.

This study examined the possibility that vasoactive intestinal peptide (VIP)- and substance P (SP)-containing nerve fibers in bronchial smooth muscle, glands, epithelium, and blood vessels originate from neurons of airway ganglia. Explants of airway walls were maintained in culture with the expectation that nerve fibers from neurons of airway ganglia would remain viable, whereas fibers originating from neurons not present in the airway walls would degenerate. Airways were dissected and placed into culture dishes containing CMRL 1066 medium for 3, 5, and 7 days. In controls (noncultured), VIP- and SP-like immunoreactivity was observed in nerve fibers associated with bronchial smooth muscle, glands, and blood vessel walls and in nerve cell bodies of airway ganglia. Nerve fibers containing SP were also observed within the bronchial epithelium. After 3, 5, and 7 days in culture, VIP- and SP-containing fibers were identified in all of the same locations except in the airway epithelium where SP-containing fibers could not be demonstrated. VIP and SP were frequently colocalized in the same nerve fibers of bronchial smooth muscle and glands in controls and cultured airways. There were no statistically significant differences in nerve fiber density for either VIP- or SP-containing fibers in bronchial smooth muscle between controlled and cultured airways. VIP concentrations in cultured airways were significantly less than in controls. The results suggest that a large proportion of VIP- and SP-containing nerve fibers supplying bronchial smooth muscle, glands, and blood vessels in the airways originate from neurons of airway ganglia.

Identification and neuropeptide content of trigeminal neurons innervating the rat nasal epithelium.

Trigeminal ganglia provides sensory innervation to the rat nasal cavity. The purpose of this study was to identify the location and characterize the neuropeptide content of trigeminal neurons that project specifically to the rat nasal epithelium. The right nasal cavity was instilled with 4 microliters of rhodamine-labelled latex microspheres. Seven, 10 or 14 days after tracer instillation, both trigeminal ganglia were removed and prepared for substance P and calcitonin gene-related peptide immunocyto-chemistry. neurons labelled with microspheres were located in the trigeminal ganglia at the division of the ophthalmic and maxillary nerves and were only found on the side ipsilateral to the instillation. The percentage of labelled cell body profiles in the right trigeminal ganglia averaged 1.61 +/- .04% at seven days. 1.54 +/- .01% at 10 days, and 1.65 +/- .02% at 14 days after instillation. These values were not statistically different, but the fluorescence intensity in labelled neurons was increased after 14 days. The right trigeminal ganglia contained a mean of 166 +/- 13.81 labelled cell body profiles representing 1.60 +/- .09% of the total. Of the labelled profiles, 81.6 +/- 3.27% were immunoreactive for substance P and 35.2 +/- 4.00% for calcitonin gene-related peptide. Sections of nasal mucosa showed that the microspheres were localized only in the epithelial layer and did not enter the lamina propria indicating that the microsphere transport was confined to nerve fibres present in the epithelial layer. These studies have identified specific neurons in the trigeminal ganglia that project to the nasal epithelium. Most of the neurons retrogradely labelled from the nasal cavity contained substance P but some contained calcitonin gene-related peptide, suggesting that the nasal epithelium is predominantly targeted by substance P-containing neurons.

Colocalization of vasoactive intestinal peptide and nitric oxide synthase in neurons of the ferret trachea.

Neurally-mediated relaxation of smooth muscle in human, guinea-pig, cat, and pig airways is largely attributed to a nonadrenergic, noncholinergic mechanism. While the specific transmitter(s) of this relaxant system have not been conclusively identified, vasoactive intestinal peptide and nitric oxide have emerged as likely mediators in airway smooth muscle. Both vasoactive intestinal peptide and nitric oxide relax guinea-pig, pig and human smooth muscle. Vasoactive intestinal peptide is present in nerve fibers associated with airway smooth muscle in humans and several animal species. In guinea-pigs, vasoactive intestinal peptide is released during electrical field stimulation of airway strips and the release correlates with the nonadrenergic relaxation. This relaxation is markedly reduced after incubation of tracheal tissue with a specific VIP antibody and by immunization to vasoactive intestinal peptide. Similarly, nonadrenergic relaxations induced by electrical field stimulation are reduced in human, pig, guinea-pig and bovine airways by nitric oxide synthesis inhibitors. Vasoactive intestinal peptide is present in nerve cell bodies of airway ganglia, suggesting that these nerves in airway smooth muscle originate from intrinsic neurons. It is stored in dense-core vesicles of nerve terminals near airway smooth muscle, suggesting that preformed vasoactive intestinal peptide is released by fusion of the vesicles with the cell membrane of the nerve terminal. Nitric oxide is probably generated by a novel mechanism involving de novo synthesis at the nerve terminal during neural activation by the action of the enzyme nitric oxide synthase.(ABSTRACT TRUNCATED AT 250 WORDS)

Co-localization of vasoactive intestinal peptide- and substance P-containing nerves in cat bronchi.

The occurrence of vasoactive intestinal peptide (VIP) and substance P in nerve fibers within the lung is well established, and both VIP- and substance P-containing nerve fibers are known to supply pulmonary vascular and bronchial smooth muscle and submucosal glands. In the present study, we have investigated the co-localization of these two peptides in cat lung. The co-localization procedure follows a standard immunocytochemical protocol except that the primary and labeled secondary antisera each contain a combination of two antisera allowing the simultaneous detection of two antigens in a single tissue section. Using fluorescence microscopy, VIP- and substance P-containing nerve fibers were co-localized in bronchial smooth muscle, in the walls of pulmonary and bronchial arteries, and around submucosal glands. VIP and substance P were also co-localized in nerve cell bodies that comprised the intrinsic airway ganglia. Substance P-containing nerve fibers were observed within the bronchial epithelium, but VIP was not present at this location. The co-localization of VIP and substance P in the same nerve fibers suggests that airway and pulmonary vascular function may be partially regulated by the simultaneous or sequential release of VIP and substance P from the same nerve fibers. The results also suggest that, in addition to extrinsic nerve fibers that contain substance P, the airways of cats are supplied by substance P-containing nerve fibers that originate from intrinsic nerve cell bodies.

Ultrastructural immunocytochemical localization of 5-hydroxytryptamine in gastric enterochromaffin cells.

Enterochromaffin (EC) cells in the gastrointestinal tract are known to contain 5-hydroxytryptamine (5HT). The probable ultrastructural localization of 5HT in the dense core vesicles ( DCVs ) of EC cells is based on the use of histochemical techniques, such as argentaffinity and the potassium dichromate reaction. In the present paper we describe an immunocytochemical method for specifically localizing 5HT in EC cells by electron microscopy. Pieces of mucosa from the pyloric region of the rabbit stomach were prepared for electron microscopy by fixation in 0.5% glutaraldehyde-picric acid-formaldehyde without osmication , and then embedded in LX-112. Thick sections (1 micron) were mounted on glass slides and processed for the fluorescence immunocytochemical localization of 5HT. Thin sections (60-90 nm) were mounted on formvar-coated slot grids and processed for the ultrastructural immunocytochemical localization of 5HT. Both the thick and thin sections were processed by an identical procedure, beginning with a 30-min incubation in anti-5HT antiserum diluted 1:1400, followed by an IgG-FITC-gold-labeled second antibody. Fluorescent EC cells were consistently observed in the thick sections of gastric mucosa. By carefully trimming and sectioning the adjacent block face, the identical EC cell could be identified by electron microscopy. A quantitative analysis revealed the number of gold particles in EC cells to be significantly greater over the cores of DCVs than over the non-core cytoplasm or over the nucleus. Absorption of the primary antiserum with 5HT abolished all labeling, while absorption with a 5HT precursor, 5-hydroxytryptophan, did not significantly reduce core labeling. Non-EC epithelial cells were not labeled. These results demonstrate that immunoreactive 5HT in EC cells is stored in the cores of DCVs .

Histochemical and ultrastructural characterization of serotonin-containing cells in rabbit tracheal epithelium.

Tracheal endocrine cells (TECs) that contain serotonin have been characterized previously by staining with ferric ferricyanide. In the present article, the ferric ferricyanide staining reaction has been used to locate the TECs in deplasticized thick sections of Epon-embedded rabbit tracheas. Adjacent thin sections of the same cell were subsequently observed by electron microscopy. The TECs were filled with dense-core vesicles (DCVs) located in the cytoplasm between the nucleus and the lumen and also lateral to the nucleus. In a separate experiment, pieces of rabbit trachea were treated with a solution of glutaraldehyde-dichromate to demonstrate the presence of amines. High levels of chromium were detected in the DCVs by energy-dispersive X-ray analysis. The results from these studies have correlated the ultrastructure of a serotonin-containing endocrine cell present in rabbit tracheal epithelium with a cell type previously characterized only by light and fluorescence histochemical methods. The results also indicate that serotonin in these cells is stored in the DCVs.

Enhancement of nitric oxide production by pulmonary cells following silica exposure.

In vivo exposure of rat lungs to crystalline silica either by intratracheal instillation or by inhalation results in an increase in mRNA levels for inducible nitric oxide synthase (iNOS) in bronchoalveolar lavage cells (BALC), elevated nitric oxide (.NO) production by BALC, and an increase in .NO-dependent chemiluminescence (CL) from alveolar macrophages (AM). Induction of iNOS message occurs in both AM and polymorphonuclear leukocytes (PMN) harvested from silica-exposed lungs but is not significantly elevated in lavaged lung tissue. In vitro exposure of AM to silica does not stimulate .NO production or enhance iNOS message. However, treatment of naive AM with conditioned media from BALC harvested from silica-exposed rats does increase iNOS message and .NO production by these AM. The potency of this conditioned medium is dependent on interaction between AM and PMN. In the rat model, a relationship exists between the ability of various dusts to cause PMN recruitment or protein leakage into the alveolar space and the induction of iNOS message in BALC, i.e., silica > coal mine dust > carbonyl iron > titanium dioxide. Similarly, a comparison of BALC from a healthy volunteer, a silica-exposed coal miner with a normal chest radiograph, and a silica-exposed coal miner with an abnormal chest radiograph shows a correlation between pathology and both the level of iNOS message in BALC and the magnitude of .NO-dependent CL from AM. These data suggest that .NO may play a role in silicosis and that human pulmonary phagocytes exhibit enhanced .NO production in response to an inflammatory insult.

Glutamate toxicity in the lung and neuronal cells: prevention or attenuation by VIP and PACAP.

VIP, which has been demonstrated to reduce or prevent oxidant injury in the lungs and other organs, is shown here to protect against excitotoxic injury of the lung and excitotoxic death of cortical neuronal cells in primary culture. Glutamate killing of neuron-like PC-12 cells, attributable to oxidant stress rather that to excitotoxicity, is also reduced or prevented by VIP and by the closely related peptide PACAP. The exact mechanisms of this protection remain to be determined, but appear to include antioxidant and anti-apoptotic actions, and suppression of glutamate-induced upregulation of its own receptor. Both VIP and PACAP offer the promise of novel and nontoxic means of defending against NMDA and glutamate toxicity.

Origin and colocalization of CGRP- and SP-reactive nerves in cat airway epithelium.

A combination of neuroanatomic techniques was used to examine the origin and neuropeptide content of nerve fibers in the airway epithelium of adult cats. By the use of immunocytochemical methods, the peptides substance P (SP) and calcitonin gene-related peptide (CGRP) were colocalized in airway epithelial nerve fibers. Two days after wheat germ agglutinin (WGA) was injected into the nodose ganglion, fibers containing WGA immunoreactivity (IR) were detected in the airway epithelium. SP-like immunoreactivity (LI) and CGRP-LI were demonstrated separately in the WGA-IR fibers, establishing their origin from nerve cell bodies of nodose ganglion. Vagal transection inferior to the nodose ganglion reduced the number of SP- and CGRP-IR fibers by greater than 90% in ipsilateral airways. In contralateral airways, SP-IR fibers were substantially reduced, whereas the effect on CGRP-IR fibers was not statistically significant. Vagotomy superior to the nodose ganglion did not alter the density of peptide-IR fibers. The results prove that SP- and CGRP-IR nerve fibers of cat airway epithelium originate from nerve cell bodies in the nodose ganglion and that SP- and CGRP-like peptides may be stored together in some nerve fibers of the airway epithelium.

Role of intrinsic airway neurons in ozone-induced airway hyperresponsiveness in ferret trachea.

Exposure to ozone (O(3)) enhances airway responsiveness, which is mediated partly by the release of substance P (SP) from airway neurons. In this study, the role of intrinsic airway neurons in O(3)-induced airway responses was examined. Ferrets were exposed to 2 ppm O(3) or air for 1 h. Reactivity of isolated tracheal smooth muscle to cholinergic agonists was significantly increased after O(3) exposure, as were contractions to electrical field stimulation at 10 Hz. Pretreatment with CP-99994, a neurokinin type 1 receptor antagonist, partially abolished the O(3)-induced reactivity to cholinergic agonists and electrical field stimulation. The O(3)-enhanced airway responses were present in tracheal segments cultured for 24 h, a procedure shown to deplete sensory nerves while maintaining viability of intrinsic airway neurons, and all the enhanced smooth muscle responses were also diminished by CP-99994. Immunocytochemistry showed that the percentage of SP-containing neurons in longitudinal trunk and the percentage of neurons innervated by SP-positive nerve fibers in superficial muscular plexus were significantly increased at 1 h after exposure to O(3). These results suggest that enhanced SP levels in airway ganglia contribute to O(3)-induced airway hyperresponsiveness.

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.

Pulmonary alterations associated with inhalation of occupational and environmental irritants.

Many gases, vapors, or particles found in occupational and/or environmental settings can act as irritants. In the present study, sensory irritants are characterized by the stimulation of neuropeptide release from sensory nerves in the nasal mucosa, while pulmonary irritants are characterized by recruitment of PMN into bronchoalveolar airspaces, elevation of breathing frequency, and neuropeptide release from sensory fibers innervating the epithelium of the conducting airways. A review of data from our laboratory as well as results from others indicate that asphalt fume is a sensory irritant; toluene diisocyanate (TDI), methyl isocyanate, and machining fluid act as both sensory and pulmonary irritants; while cotton dust, agricultural dusts, microbial products, leather conditioner, and ozone exhibit responses characteristic of pulmonary irritants.

Effects of silica exposure on substance P immunoreactivity and preprotachykinin mRNA expression in trigeminal sensory neurons in Fischer 344 rats.

Trigeminal sensory neurons innervate the nasal cavity and may release substance P (SP) upon exposure to inhaled irritants. The purpose of this study was to determine if silica dust, an occupational irritant causing inflammation, activates sensory neurons supplying the nasal cavity. Male Fischer 344 rats were placed in inhalation chambers and exposed daily to 2 mg/m3 of fresh silica (average diameter 1 microm) for 6 mo. Following exposure, the trigeminal ganglia (TG) were removed and prepared for SP immunocytochemistry and for preprotachykinin (PPT) autoradiographic in situ hybridization. The SP-like immunofluorescence in TG neurons was subjectively categorized as high, moderate, or low (background) intensity. In situ hybridization autoradiographs were quantified on the basis of grain density using digital imaging analysis. The SP immunoreactivity and PPT mRNA expression in the TG neurons were significantly increased after silica inhalation. The proportion of highly positive SP-immunoreactive neurons shifted from 1.30 +/- 0.58% in controls to 11.30 +/- 1.15% after silica treatment. The neurons exhibiting high grain density for PPT mRNA increased from 1.50 +/- 0.87% in controls to 11.67 +/- 0.58% in the silica group. Thus, inhalation of silica causes upper airway irritation resulting in increased levels of immunoreactive neuronal SP and PPT mRNA. These findings suggest that silica activates sensory pathways that may be involved in nasal inflammation.