Airway neural plasticity contributes to the process of airway remodeling in response to airway irritants. However, the mechanisms of neural remodeling in the airways during the early postnatal period, when responses to airway irritation may be most sensitive, have not been characterized. This study used a rat model to examine a possible mechanism of ozone (O 3 )-induced neural hyperresponsiveness during a critical period of developmental, postnatal day (PD) 6, that may be mediated by the neurotrophin nerve growth factor (NGF), resulting in an enhanced release of inflammatory neuropeptide substance P (SP) from airway nerves. Rat pups between PD6-PD28 were killed 24 hours after exposure to O 3 (2 ppm, 3 hours) or filtered air (FA), to establish a timeline of NGF synthesis, or else they were exposed to O 3 or NGF on PD6 or PD21 and re-exposed to O 3 on PD28, and killed on PD29. Measurement endpoints included NGF mRNA in tracheal epithelial cells, NGF protein in bronchoalveolar lavage fluid, airway SP-nerve fiber density (NFD), and SP-positive airway neurons in vagal ganglia. Acute exposure to O 3 increased NGF in bronchoalveolar lavage fluid on PD10 and PD15, and mRNA expression in epithelial cells on PD6, compared with FA controls. NGF protein and mRNA expression in the O 3 -PD6/O 3 -PD28 groups were significantly higher than in the O 3 -PD21/O 3 -PD28 and O 3 -PD6/FA-PD28 groups. NGF-PD6/O 3 -PD28 increased the SP innervation of airway smooth muscle and SP-positive sensory neurons, compared with the NGF-PD21/O 3 -PD28 or NGF-PD6/FA-PD28 groups. NGF enhanced sensory innervation, which may mediate acute responses or prolong sensitivity to O 3 during early life. The model may be relevant in O 3 responses during early childhood.

Nerve growth factor (NGF) is produced in the airway epithelium. The purpose of this study was to determine if ozone, a chemical irritant associated with air pollution, alters NGF message levels specifically in tracheal airway epithelial cells at early postnatal ages. Fisher‐344 rat pups were exposed to 2ppm ozone or filtered air for 3 hours on postnatal days (PD) 6, 15 or 21. Twelve hours after exposure, tracheal epithelial cells were isolated and treated in culture with IgG, resulting in an enriched population containing 96.04%±0.60% (n=3) epithelial cells and 3.97%±0.60% (n=3) immune cells. Total RNA was extracted and transcribed into cDNA. NGF mRNA expression was amplified using the real‐time PCR system and analyzed via the comparative threshold method and expressed relative to endogenous β‐actin. At PD 6, the relative NGF mRNA expression in ozone treated rats showed a significant 2‐fold increase in comparison to the air treated animals (p≤0.05, n=3 per group). At PD 15 (n=7 per group) and 21 (n=3 per group), there were no significant changes in NGF mRNA expression between ozone and air treated animals. Thus, the increase in NGF mRNA levels in response to ozone exposure seen at PD 6 was specifically from the tracheal epithelial cells and not immune cells in this cell population. The increase in NGF expression at PD 6 suggests increased sensitivity to ozone exposure compared to PD15 and 21.

Nerve growth factor (NGF) is produced in the airway epithelium. The purpose of this study was to determine if ozone, a chemical irritant associated with air pollution, alters NGF message levels specifically in tracheal airway epithelial cells at early postnatal ages. Fisher‐344 rat pups were exposed to 2ppm ozone or filtered air for 3 hours on postnatal days (PD) 6, 15 or 21. Twelve hours after exposure, tracheal epithelial cells were isolated and treated in culture with IgG, resulting in an enriched population containing 96.04%±0.60% (n=3) epithelial cells and 3.97%±0.60% (n=3) immune cells. Total RNA was extracted and transcribed into cDNA. NGF mRNA expression was amplified using the real‐time PCR system and analyzed via the comparative threshold method and expressed relative to endogenous β‐actin. At PD 6, the relative NGF mRNA expression in ozone treated rats showed a significant 2‐fold increase in comparison to the air treated animals (p≤0.05, n=3 per group). At PD 15 (n=7 per group) and 21 (n=3 per group), there were no significant changes in NGF mRNA expression between ozone and air treated animals. Thus, the increase in NGF mRNA levels in response to ozone exposure seen at PD 6 was specifically from the tracheal epithelial cells and not immune cells in this cell population. The increase in NGF expression at PD 6 suggests increased sensitivity to ozone exposure compared to PD15 and 21.

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Ozone Induces Nerve Growth Factor Release from Rat Tracheal Epithelial Cells during an Early Postnatal Critical Period Lynnsey A. Carrell-Jacks Ozone, one of the major air pollutants in urban areas, produces epithelial cell injury and inflammation in the airways upon exposure. Previous studies have shown that ozone exposure leads to increased substance P (SP) expression in nerves innervating the smooth muscle in the extrapulmonary airway. Nerve growth factor (NGF), a neurotrophin, is known to increase SP expression. To determine the effect of ozone exposure on the release of NGF, a cell culture technique was developed for studying a homogenous rat tracheal epithelial cell population for analysis of NGF mRNA and protein expression. Furthermore, to determine if this effect is age-dependent, a critical period exposure paradigm was used. Rat pups exposed to ozone at postnatal day (PD) 6 showed an increase in the level of NGF mRNA while pups exposed after PD 6 showed no change in NGF expression. When rat pups exposed to ozone on PD 6 were reexposed at a later date, an increase in NGF mRNA was observed. These data suggest that exposure to ozone has an effect on NGF expression in early postnatal life and that this exposure might play a role in ozone sensitivity later in life