As astrocytes, we used rat C6 glioma cells (rat glial tumor cell line), which have been frequently and extensively used as an alternative to astrocytes in primary culture [9,10,11,12,13], because these cells have similarities with primary astrocytes in culture [14,15] and have ability to synthesize/secrete high levels of GDNF [9,10,11]. Here, GDNF is linked to central nervous system cancer.