IGF1 and Parkinson disease: Several studies have shown neuroanatomical and pathophysiological associations of IGF-1 and PD: (1) high densities of IGF-1 receptors in the substantia nigra (SN), (2) IGF-1 level-dependent increase of survival of embryonic dopaminergic and SN neurons [14,15], and (3) protection of neuronal cells in vitro from dopamine-induced toxicity [16,17].