VIP and Anxiety: Additionally, further research into the coexpression of various neuropeptides and other identified markers such as pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide, cholecystokinin, neuropeptide Y, dynorphin, enkephalin, and substance P (all of which have also been shown to also play important roles in fear and anxiety behaviors) will, in the future, be necessary to identify the extent to which additional populations colocalize within the CeA.