In order to investigate the neuroprotective effect of APα, as well as to clarify its possible molecular mechanisms, SH-SY5Y neuronal cell lines were incubated with 6-hydroxydopamine (6-OHDA), which has been widely used as an in vitro model for PD, along with APα alone or in combination with GABAAR antagonist (bicuculline, Bic), intracellular Ca2+ chelator (EGTA) and voltage-gated L-type Ca2+ channel blocker (Nifedipine). Here, ENPEP is linked to Parkinson disease.