NPY and Anxiety: Interneurons also use neuropeptides, such as cholecystokinin (CCK) and neuropeptide Y (NPY), as co-transmitters that exert profound effects on fear, anxiety, learned helplessness behavior and stress response (Ishida et al., 2007; Sherrin et al., 2009; Lach and de Lima, 2013; Serova et al., 2014), and stress was found to affect their expression as well (Hadad-Ophir et al., 2014).