TPH2, Mash1, and 5-HT were mainly expressed in neurons but rarely expressed in astrocytes or microglia in the piriform cortex (Pir), while they were not overlapping in the other cerebral regions, implying that the neurons in Pir might be involved in the role of 5-HT in ALS. This evidence concerns the gene TPH2 and amyotrophic lateral sclerosis.