Q. Thai Dinh

Capsaicin-sensitive and -insensitive vagal bronchopulmonary C-fibres in the mouse

We developed an isolated tracheally perfused (35‐37 °C) nerve‐lung preparation for the study of bronchopulmonary afferent nerve activity in the mouse. Extracellular recordings were made from the vagal sensory neurons located in the jugular‐nodose ganglia complex (JNC) with identified receptive fields in the lungs. Analysis of the vagal compound action potential revealed that the mouse vagal C‐fibre conduction velocities range from 0.3 to 1.5 m s−1. A total of 83 bronchopulmonary C‐fibres were studied. The sensitivity of the bronchopulmonary C‐fibres to the vanilloid receptor 1 (VR1) agonist capsaicin was dependent on conduction velocity. Thus C‐fibres with conduction velocities between 0.3 and 0.7 m s−1 responded to capsaicin (1 μM) while C‐fibres with conduction velocities between 0.7 and 1.5 m s−1 were capsaicin insensitive. Similarly, bradykinin (1 μM) excited only those C‐fibres with conduction velocities < 0.7 m s−1. The response to bradykinin was not mimicked by the B1 receptor agonist [des‐Arg9]bradykinin (1 μM) and was abolished by the bradykinin B2 receptor antagonist HOE 140 (1 μM). Adenosine 5′‐triphosphate (ATP, 30 μM) activated the C‐fibres irrespective of the conduction velocities. This response was mimicked by the selective P2X agonist α,β‐methylene‐adenosine 5′‐triphosphate (30 μM). Consistent with the electrophysiology, morphological analysis revealed that only ˜40 % of the lung‐specific small diameter (< 20 μm) JNC neurons consistent with the C‐fibre cell bodies display VR1 immunoreactivity. This study describes a convenient in vitro method for the study of mouse bronchopulmonary C‐fibres. The results indicate that C‐fibres in the mouse lungs are not homogeneous, but can be subclassified into capsaicin‐sensitive and capsaicin‐insensitive phenotypes.

Expression and Distribution of Vasoactive Intestinal Polypeptide Receptor VPAC 2 mRNA in Human Airways

Vasoactive intestinal polypeptide (VIP) is a putative neurotransmitter of the inhibitory non-adrenergic non-cholinergic nervous system and influences many aspects of mammalian airway function. VIP binds to two G-protein-coupled VPAC receptors that are highly homologous structurally but distinguished by their different affinities for peptide analogues of VIP. As VIP binding sites in the respiratory tract have only been examined by ligand binding and cytochemical techniques, we studied the distribution of the mRNA that encodes the inducible receptor subtype VPAC2 in the human respiratory tract. Northern blots demonstrated the expression of VPAC2 mRNA in human airways and other tissues. A human-specific VPAC2 cRNA probe was used to detect VPAC2 mRNA expression in human lung by nonradioactive in situ hybridization. In larger airways, positive VPAC2 mRNA signals were localized to tracheal and bronchial ciliated epithelial cells. There was also marked staining of mucous and serous cells of submucosal glands. No signals were obtained in airway and vascular smooth muscle myocytes and endothelial cells. In peripheral lung tissues, VPAC2 mRNA expression was localized to epithelial cells of the bronchioles. Specific staining was detected in immune cells and alveolar macrophages. In summary, VPAC2 is localized in airway epithelial, glandular, and immune cells of the lung but not in airway and vascular smooth muscle. The absence of VPAC2 mRNA in vascular and airway smooth muscle myocytes may indicate that the effects of VIP on vasodilation and bronchodilation are mediated by VPAC1 or undefined receptors. However, a paracrine modulation of the two most prominent effects of VIP in the respiratory tract by VPAC2 cannot be excluded.

Substance P expression in TRPV1 and trkA-positive dorsal root ganglion neurons innervating the mouse lung.

In the present study, the co-localisation of substance P (SP) with the vanilloid receptor TRPV1 and the neurotrophin receptor tyrosine kinase trkA was analysed in airway-specific murine dorsal root ganglion (DRG) neurons. DRG neurons labelled with Fast Blue were predominantly found at the segmental levels T2-T5. Immunoreactivity for the receptor TRPV1 was localized to 12% of Fast Blue labelled DRG neurons. Double-labelling immunohistochemistry revealed that a substantial number of them also co-express SP (7.6 +/- 1.1% (mean +/- S.E.M.)), whereas neurons with immunoreactivity for TRPV1 only were found in 4.4 +/- 1.3% of the retrogradely labelled neuronal population. Further analysis of retrogradely labelled neurons showed that their majority expressed trkA (62.8 +/- 1.4%), neurofilament protein 68-kDa (64.8 +/- 1.5%) or glutamate alone (19.5 +/- 1.9%). SP was always expressed in trkA-positive neurons. Based on the extent of co-localization of SP with the receptors TRPV1 and trkA in DRG airway neurons, the present study indicates that the DRG pathway may have effects on the magnitude of neurogenic inflammation in airway diseases such as asthma.

Neurokinin-1 receptor mediates stress-exacerbated allergic airway inflammation and airway hyperresponsiveness in mice.

Background: A wealth of clinical observation has suggested that stress and asthma morbidity are associated. We have previously established a mouse model of stress-exacerbated allergic airway inflammation, which reflects major clinical findings. Objective: The aim of the current study was to investigate the role of the neurokinin- (NK-)1 receptor in the mediation of stress effects in allergic airway inflammation. Methods: BALB/c mice were systemically sensitized with ovalbumin (OVA) on assay days 1, 14, and 21 and repeatedly challenged with OVA aerosol on days 26 and 27. Sound stress was applied to the animals for 24 hours, starting with the first airway challenge. Additionally, one group of stressed and one group of nonstressed mice received the highly specific NK-1 receptor antagonist RP 67580. Bronchoalveolar lavage fluid was obtained, and cell numbers and differentiation were determined. Airway hyperreactivity was measured in vitro by electrical field stimulation of tracheal smooth-muscle elements. Results: Application of stress in sensitized and challenged animals resulted in a significant increase in leukocyte number in the bronchoalveolar lavage fluid. Furthermore, stressed animals showed enhanced airway reactivity. The increase of inflammatory cells and airway reactivity was blocked by treatment of animals with the NK-1 receptor antagonist. Conclusion: These data indicate that the NK-1 receptor plays an important role in mediating stress effects in allergen-induced airway inflammation.

Innervation of human nasal mucosa in environmentally triggered hyperreflectoric rhinitis

Hyperreflectoric rhinitis is related to an unspecific hyperreactivity probably caused by chemical irritants. As a major modulatory role may be attributed to the mucosal innervation, the present study was carried out to examine possible changes in the nasal mucosa innervation. Immunohistochemistry for the neuropeptides vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), substance P (SP) and neuropeptide tyrosine (NPY) revealed abundant staining of nerve fibers. Neuropeptide-contents in mucosal nerves was then quantitatively assessed and significant increases were found for SP (3.00 ± 0.37 vs. 1.64 ± 0.34 control group staining intensity) and VIP (2.33 ± 0.42 vs. 0.82 ± 0.33). In conclusion, these findings demonstrated differences in human nasal mucosa innervation between nonrhinitic and hyperreflectoric rhinitic subjects and provide evidence for a modulatory participation of neuropeptide-specific subpopulations of nerve fibers in hyperreflectoric rhinitis.

Is TRPV1 a useful target in respiratory diseases

This review focuses on the transient receptor potential vanilloid 1 (TRPV1). TRPV1 is a non-selective cation channel predominantly expressed in the cell membranes of sensory afferent fibers, which are activated multi-modally. In the mammalian respiratory system, immunohistochemical and electrophysiological studies have revealed heterogeneous localizations of TRPV1 channels in the airways and their presence in pleural afferents. TRPV1 channels in afferents are not only involved with sensory inputs, but also release several neuropeptides upon stimulation. These processes trigger pathophysiological effects (e.g. reflex bronchoconstriction, hypersecretion, cough, etc.) that cause various symptoms of airway diseases. Recent studies have identified several endogenous and exogenous substances that can activate TRPV1 in the lung. Because of its key role in initiating inflammatory processes, TRPV1 receptor antagonists have been proposed as therapeutic candidates. Therefore, a critical update of recent therapeutic results is also given in this review.

Tachykinins in the respiratory tract.

Tachykinins as substance P and neurokinin A belong to a family of peptides, which are released from airway nerves after noxious stimulation. They influence numerous respiratory functions under both normal and pathological conditions including the regulation of airway smooth muscle tone, vascular tone, mucus secretion and immune functions. For the most part the synthesis/release of tachykinins is associated with neuronal cells; nevertheless, inflammatory and immune cells can synthesize and release tachykinins under certain physiological conditions. Moreover, this second cellular source of tachykinins may play an important role in inflammatory airway diseases such as bronchial asthma or chronic obstructive pulmonary disease (COPD). Dual tachykinin (NK1 and NK2) receptor antagonists demonstrate a significant bronchoprotection and a possible future role in the development of novel therapeutic approaches. In addition, NK3 receptors could also possess a bronchoprotective action, however, their presence in the human respiratory tract still needs to be confirmed. The family of tachykinins has recently been extended by the discovery of a third tachykinin gene that encodes the previously unknown NK1 receptor selective tachykinins hemokinin 1, endokinin A and B. Together with other novel tachykinin peptides such as C14TKL-1 and virokinin further research is required to define their respiratory biological role in health and disease.

Neuronal plasticity in persistent perennial allergic rhinitis.

Objective:Persistent perennial allergic rhinitis belongs to the most frequent diseases in occupational and environmental medicine. Because the innervation may play a role in the pathogenesis of the disease, the present study analyzed nasal mucosal nerve profiles. Methods:Neuropeptide-containing nerve fibers were examined using immunohistochemistry and related to eosinophil and mast cell numbers. Results:In contrast to constant numbers of mast cells, there was a significant increase in the number of eosinophils. Immunohistochemistry for calcitonin gene-related peptide (CGRP), substance P (SP), vasoactive intestinal peptide (VIP), and neuropeptide tyrosine (NPY) revealed abundant staining of mucosal nerves. Semiquantitative assessment of nerve fiber neuropeptide density demonstrated a significant increase of VIP-positive fibers in rhinitis tissues. Conclusions:The present data indicate a differential regulation of neuropeptide-containing nerve fibers with increased numbers of VIPergic fibers suggesting a modulatory role of the upper airway innervation in perennial allergic rhinitis.

Simultaneous detection of receptor mRNA and ligand protein in human skin tissues

Background:  In situ hybridization techniques allow a cell‐type‐specific messenger RNA (mRNA) analysis in complex tissues such as human skin.

Toxic Rhinitis-Induced Changes of Human Nasal Mucosa Innervation

Irritative toxic rhinitis is a nasal disorder induced by chemical compounds like ozone, formaldehyde, nickel, chrome, solvents and tobacco smoke. These noxious stimuli may have effects on the nasal innervation leading to a cascade of neuro-immune interactions and an augmentation of the symptoms. Here we examined changes in the neuropeptide content of mucosal parasympathetic, sympathetic and sensory nerves of patients with toxic rhinitis caused by chronic cigarette smoke exposure. Semiquantitative immunohistochemistry using antibodies against calcitonin gene-related peptide (CGRP), substance P (SP), neuropeptide tyrosine (NPY), and vasoactive intestinal peptide (VIP) was carried out on cryostat sections of human nasal mucosa obtained from normal subjects and patients with toxic rhinitis and revealed significant differences between both groups. Toxic rhinitis patients had significantly elevated expression scores for VIP (2.83 ± 0.31 vs 1.27 ± 0.47 control group) and NPY (3.17 ± 0.31 vs 0.91 ± 0.37 control group) revealing an increase of mediators in distinct subpopulations of airway nerves. In summary, the present studies indicate a differential participation of subclasses of mucosal nerves in the pathophysiology of toxic rhinitis. Airway innervation may have a major role in the pathophysiology of toxic rhinitis associated with chronic cigarette smoke exposure.