Neural mechanisms in asthma: new developments

Psychiatric symptoms in patients with asthma causality, comorbidity, or shared genetic etiology

Despite the range of diverse studies that attempt to understand the comorbidity of asthma and psychiatric diagnoses, it is still not possible to provide a reliable quantitative estimate of the increased risk for anxiety and mood disorders in children with asthma. A new hypothesis for this comorbidity has evolved, however. It is likely that the stress of having a chronic illness increases the likelihood of the development of anxiety and depressive symptoms. If this were a sufficient etiologic explanation, however, increased comorbidities of psychiatric illnesses would be found in all chronic pediatric illnesses. More precise prevalence estimates of these comorbidities require the completion of large studies that use a longitudinal design and reliable and well-validated assessment instruments. The most promising direction for future research is the definition of underlying genetic vulnerabilities that reflect autonomic regulation, may contribute to the onset of some forms of asthma, and are associated with increased risk for anxiety and mood disorders.

Historical perspective on airway smooth muscle: the saga of a frustrated cell

Despite the lack of a clearly defined physiological function, airway smooth muscle receives substantial attention because of its involvement in the pathogenesis of asthma. Recent investigations have turned to the ways in which the muscle is influenced by its dynamic microenvironment. Ordinarily, airway smooth muscle presents little problem, even when maximally activated, because unending mechanical perturbations provided by spontaneous tidal breathing put airway smooth muscle in a perpetual state of "limbo," keeping its contractile machinery off balance and unable to achieve its force-generating potential. The dynamic microenvironment affects airway smooth muscle in at least two ways: by acute changes associated with disruption of myosin binding and by chronic changes associated with plastic restructuring of contractile and cytoskeletal filament organization. Plastic restructuring can occur when dynamic length changes occur between sequential contractile events or within a single contractile event. Impairment of these normal responses of airway smooth muscle to its dynamic environment may be implicated in airway hyperresponsiveness in asthma.

Animal models of asthma: potential usefulness for studying health effects of inhaled particles

Asthma is now recognized to be a chronic inflammatory disease that affects the whole lung. Incidence appears to be increasing despite improved treatment regimens. There is substantial epidemiological evidence suggesting a relationship between the incidence and severity of asthma (e.g., hospitalizations) and exposure to increased levels of air pollution, especially fine and ultrafine particulate material, in susceptible individuals. There have been a few studies in animal models that support this concept, but additional animal studies to test this hypothesis are needed. However, such studies must be performed with awareness of the strengths and weaknesses of the currently available animal models. For studies in mice, the most commonly used animal, a broad spectrum of molecular and immunological tools is available, particularly to study the balance between Th1 and Th2 responses, and inbred strains may be useful for genetic dissection of susceptibility to the disease. However, the mouse is a poor model for bronchoconstriction or localized immune responses that characterize the human disease. In contrast, allergic lung diseases in dogs and cats may more accurately model the human condition, but fewer tools are available for characterization of the mechanisms. Finally, economic issues as well as reagent availability limit the utility of horses, sheep, and primates.