VIP and Parkinson disease: Second, PACAP and VIP act as anti-inflammatory cytokines and neuroprotective molecules, and the levels may be slightly elevated at the early stage of the disease to protect dopaminergic neurons from degeneration, but when the endogenesis of anti-inflammatory cytokines and neuropeptides such as PACAP or VIP is overwhelmed by an excessive inflammatory response, microglia initiate neuronal death and drive the progressive nature of PD (Wu et al., 2014).