Proliferation of guinea pig tracheal epithelial cells in coculture with rat dorsal root ganglion neural cells

Developmental expression of neurokinin A and functional neurokinin-2 receptors in lung

Peribronchial smooth muscle constriction causes airway stretch, an important mechanical force in developing lung. Little is known about factors influencing these spontaneously active muscle elements. We measured contractile activity of neurokinin (NK) receptors on fetal intrapulmonary smooth muscle by tracheal perfusion assay ( n = 11). Injecting either capsaicin or the NK2 receptor agonist [NLE10]NKA resulted in significant ( P < 0.05) bronchoconstriction. A specific NK2 receptor antagonist inhibited constriction caused by endogenous tachykinins released by capsaicin. We then examined NK2 receptor ( n = 44) and NKA ( n = 23) ontogeny in human lung. NKA immunostaining was identified in peribronchial nerves in samples with gestational age >12 wk. NK2 receptor protein was identified in peribronchial and perivascular smooth muscle. These results indicate that endogenous tachykinins released by the developing lung act via NK2receptors to cause smooth muscle constriction. We speculate that tachykinins could modulate lung development.

Hints of a functional connection between the neuropeptidergic innervation of arteriovenous anastomoses and the appearance of epithelioid cells in the rabbit ear

Peripheral blood flow can be regulated by specialized vessel segments, the arteriovenous anastomoses. Their wall consists of a relatively thick layer of smooth muscle cells and so-called epithelioid cells. The epithelioid cell is a specialized myogenic cell phenotype expressing nitric oxide synthase. We studied the innervation of the different segments of arteriovenous anastomoses in the rabbit ear using antisera against neuropeptide Y, tyrosine hydroxylase, calcitonin gene-related peptide and substance P, as well as neuron-specific enolase, calbindin D and neurotubulin. The participation was especially examined of neuropeptidergic innervation and a possible morphological connection to the occurrence of epithelioid cells and a paracrine function. The NADPH diaphorase reaction and alpha-smooth muscle actin immunoelectron microscopy served to distinguish epithelioid cells from smooth muscle cells. Using conventional fluorescence microscopy and confocal laser scanning microscopy, we found the most dense innervation pattern of pan-neuronal markers (neurotubulin, neuron-specific enolase), tyrosine hydroxylase-immunoreactive nerve fibres and neuropeptidergic nerve fibres (neuropeptide Y, calcitonin gene-related peptide, substance P) around the intermediate segment in arteriovenous anastomoses, whereas the venous segment was barely marked. Single nerve fibres penetrated into the medial layer and reached the epithelioid cells. Using immunoelectron microscopy, we found intercellular contacts between epithelioid cells, but not the gap junction protein connexin 43. Here, we report for the first time a correlation of the innervation pattern with epithelioid cell type in arteriovenous anastomoses. Our findings suggest that epithelioid cells of the arteriovenous anastomoses are controlled by a dense network of neuropeptidergic nerve fibres in functional connection to their paracrine role as a nitric oxide producer.

Localization of leukaemia inhibitory factor to airway epithelium and its amplification of contractile responses to tachykinins

1. In neural tissue, leukaemia inhibitory factor (LIF) is an important trophic cytokine. In this investigation, we determined if LIF was present in human and guinea-pig airways and examined the role of this cytokine in modulating airway responses to endogenous and exogenous tachykinins as well as muscarinic receptor and beta-adrenoceptor stimulation. 2. The presence of LIF in both human and guinea-pig airways was determined by immunohistochemistry. Guinea-pig tracheal explants were incubated in CRML-1066 media containing LIF (0.5, 5 or 50 ng ml-1) for periods of 3, 6, 24 and 48 h. Tracheal rings were then transferred to organ baths for measurement of isometric force in response to carbachol, capsaicin, the neurokinin1 (NK1) receptor agonist [Sar9,Met(O2)11]-substance P (SP), the NK2 receptor agonist neurokinin A (NKA) and isoprenaline. 3. LIF immunoreactivity was observed primarily in basally situated cells in the airway epithelium of both large and small airways. Less intense immunoreactivity was observed in vascular endothelium and glandular epithelium. 4. Treatment with LIF (0.5 ng ml-1) for 3 and 6 h significantly increased contractile responses to capsaicin by 42% and 43%, respectively, compared to time controls, whereas higher concentrations of LIF (5 and 50 ng ml-1) enhanced capsaicin-induced contractions only after 6 h. After 24 h, responses to capsaicin were not significantly different from 0 h control. Contractile responses to capsaicin following exposure to LIF at any concentration for 24 h were not significantly different from relative time control values. 5. Responses to [Sar9,Met(O2)11]-SP, carbachol and isoprenaline were not influenced by time in culture or by exposure to LIF for up to 48 h. Contractile responses induced by NKA were not influenced by 3 or 6 h exposure to LIF, but at 24 and 48 h the mean maximum contractile responses to NKA were significantly increased by 33% and 35%, respectively, compared to control. 6. These results demonstrate that LIF is present in guinea-pig and human airway epithelium, and modulates airway responses to tachykinins. In the acute setting LIF augments the capsaicin-induced release of endogenous tachykinins, whilst in the longer term (> 24 h), LIF increases airway smooth muscle responses to tachykinins via an NK2 receptor selective mechanism. We conclude that LIF may be an important effector molecule in the response of airways to injury or inflammation.