Overview of neural mechanisms in asthma.

There is much evidence that neural mechanisms are involved in the mechanisms and symptoms of asthma. Afferent nerves may be activated and sensitized by inflammatory mechanisms, resulting in symptoms such as cough and chest tightness, in activation of cholinergic reflexes and in the release of inflammatory neuropeptides. Cholinergic mechanisms are the predominant bronchoconstrictor neural pathway and may be enhanced in asthma, particularly during exacerbations, through several mechanisms, including impaired function of muscarinic autoreceptors on cholinergic nerve terminals. There may also be abnormalities in adrenergic control and in the function of beta-adrenoceptors, particularly in severe asthma. The neurotransmitter of bronchodilator nerves is now identified as nitric oxide and this mechanism may be impaired during asthma exacerbations. Finally, neurogenic inflammation, due to release of neuropeptides from sensory nerves, may contribute and amplify the inflammation in asthmatic airways.