In addition, intranasal injection of LPS could activate microglia in the olfactory bulb and substantia nigra through IL-1β/IL-1R1 signaling, increasing α-synuclein-positive cells, and reducing the number of dopaminergic cells in animal experiments [260], highlighting the role of peripheral inflammation in the pathogenesis of PD. The gene discussed is SNCA; the disease is Parkinson disease.