GDNF and amyotrophic lateral sclerosis: Because IL-19 deficiency increased the expression of TNF-α and GDNF in lumbar spinal cord of SOD1G93A Tg mice (Fig. 5d, f), and in light of a previous observation that TNF-α induces GDNF release from astrocytes [25], we investigated the interaction between TNF-α and GDNF in microglia and astrocytes from ALS mice.