Air Pollutant Impacts on the Brain and Neuroendocrine System with Implications for Peripheral Organs: A Perspective
Air pollutants are increasingly linked to extrapulmonary multi-organ effects. Specifically, recent studies associate air pollutants with brain disorders including psychiatric conditions, neuroinflammation and chronic diseases. Current evidence of linkage between neuropsychiatric conditions and chronic peripheral immune and metabolic diseases, provides insights on the potential role of the neuroendocrine system in mediating neural and systemic effects of inhaled pollutants (reactive particulates and gases). Autonomically-driven stress response, involving sympathetic-adrenal-medullary (SAM) and hypothalamus-pituitary-adrenal (HPA) axes regulate cellular physiological processes through adrenal-derived hormones and diversified receptor systems. Recent experimental evidence demonstrates the contribution of the very stress system responding to non-chemical stressors, in mediating systemic and neural effects of reactive air pollutants. The assessment of how respiratory encounter of air pollutants induce lung and peripheral responses through brain and neuroendocrine system, and how the impairment of these stress pathways could be linked to chronic diseases might help us understand the causes of individual variations in susceptibility and the contribution of habituation/learning and resiliency. This review emphasizes effects of air pollution in the respiratory tract that impact the brain and neuroendocrine system, including the discussion of the role of the potential contribution of autonomic sensory nervous system in triggering neural stress response, the likely contribution of translocated nano particles or metal components, and biological mediators released systemically in causing effects remote to the respiratory tract. The perspective on the use of systems approaches that encompass multiple chemical and non-chemical stressors, including climate-related temperature extremes, with assessment of interactive neural mechanisms and peripheral networks, are emphasized.