Exposure to O3 is frequently associated with AHR. Release of substance P (SP) from sensory C-fibers may contribute to AHR, but SP levels are increased in intrinsic airway ganglia after O3 exposure. The aim of this study is to examine the role of intrinsic neurons in AHR. Ferrets were exposed to 2ppm O3 or air for 1 h. Tracheas were removed and maintained in organotypic culture for 24 h (+/- 10 microM capsacin). Previous studies have shown that sensory nerves degenerate during culture, but that innervation of smooth muscle by intrinsic airway neurons maintains intact. Responses of tracheal smooth muscle to acetylcholine (ACh), methacholine (MCh) and electrical field stimulation (EFS) were measured in isolated strips. Reactivity to ACh and MCh were elevated significantly after O3-exposure (respective EC50's: for ACh, from 1.69 to 0.65 microM for air and O3; for MCh, from 1.41 to 0.59 microM for air and O3), as were contractions to EFS at 10 and 30 Hz. Capsacin-treatment partially abolished the O3-induced increase in reactivity to ACh, MCh, and EFS. In contrast, capsacin had no effect on these responses after air-treatment. These results suggest that sensory nerves and intrinsic airway neurons may contribute to O3-induced AHR by enhanced neuropeptide release.