PACAP-38 Signaling in Tetrahymena thermophila Involves NO and cGMP

Summary. Chemorepellents are signaling molecules, which have been shown to be important for mammalian neuronal development, and are presumed to have a role in protozoan defense. Tetrahymena thermophila represent a good model system in which to study repellents because of their ease of use in biochemical, behavioral, electrophysiological, and genetic analyses. In this study, we have used Tetrahymena as a model in which to study the chemorepellent, PACAP. Using behavioral and biochemical (EIA) assays, we have found that the NO/cGMP pathway plays an important role in PACAP signaling. An increase in intracellular calcium is also critical for PACAP avoidance, which appears to be mediated through a pertussis toxin-sensitive G-protein.