Figure 6.

Effect of NGF tracheal instillation on substance P (SP) nerve fiber density in extrapulmonary airway smooth muscle during a critical period of development. The percent area of SP-immunoreactive (IR) nerve fibers was measured in the extrapulmonary smooth muscle to determine if NGF tracheal instillation during a critical period (PD6) would increase sensory innervation upon exposure to O₃ (2 ppm, 3 hours) on PD28, compared with control samples and NGF treatment outside the critical period (PD21). Values are means ± SE, n = 5 for all groups. *P < 0.05, significant in all groups.