NGF and Parkinson disease: The rationale was based on the action of NGF on NGF-responsive cells, therefore on BFCN in AD patients (Olson et al., 1992; Eriksdotter-Jönhagen et al., 1998, 2012; Tuszynski et al., 2005; Bishop et al., 2008; Rafii et al., 2014; Karami et al., 2015; Eyjolfsdottir et al., 2016; Machado et al., 2020) or on catecholaminergic cells of adrenal origin transplanted into the brain of Parkinson’s patients (Olson et al., 1991).