PDE4A and Anxiety: In zebrafish, PDE4 inhibitors promote anxiety-like behaviors, including decreased habituation to the startle response, increased activity, and thigmotaxis (wall-hugging) in larvae and adult fish (Best et al., 2008, Maximino et al., 2011, Richendrfer et al., 2012, Schnorr et al., 2012, Stewart et al., 2011).