P2RX4 and amyotrophic lateral sclerosis: In various pathological conditions, such as ischemia, chronic pain, MS and neurodegenerative disorders including ALS or AD, de novo P2X4 expression and/or increased surface P2X4 density by mobilization of intracellular pools were observed in microglia and/or in neurons [13, 14, 28, 30, 38, 43–46].