Neurogenesis in conventional neurogenic niches (SVZ and SGZ) also depends on insulin and insulin-like growth factors (IGF) [233]; thus, cerebral insulin resistance evident in chronic neurodegeneration (Alzheimer’s disease, Parkinson’s disease) negatively affects neurogenesis [234], whereas peptides facilitating insulin effects promote the development of new dopaminergic neurons in SN in a model of PD [235]. The gene discussed is IGF1; the disease is Parkinson disease.