Reagents used were as follows: Trizol, phenol-chloroform, chloroform, Superscript II, DNase I, oligo d(T), and random hexamers (Invitrogen, Carlsbad, CA); RNase H; isopropanol, sucrose, EDTA, Tris, NaCl (Fisher Scientific, Hanover Park, IL); GABA antibody, staurosporine, paraformaldehyde, Tris, 199 culture medium with HEPES, high glucose DMEM, bovine serum albumin, 10× HBSS, 10× calcium and magnesium-free HBSS, bromodeoxyuridine, Triton X-100, linoleic acid, ethidium bromide (Sigma, St. Louis, MO); RQ1 DNase I (Promega, Madison, WI); iScript Reverse Transcription Kit (Bio-Rad, Hercules, CA); culture dishes and other plastics (Dot Scientific, Burton, MI); CNTF, BMP2, BMP4, BMP5, BMP6, Activin A (R&D Systems, Minneapolis, MN); fetal bovine serum, 0.25% Trypsin (1:250) without Mg2+, Ca2+, or sodium bicarbonate (Irvine Scientific, Santa Ana, CA). BrDU antibody was developed by Stephen J. Kaufman and obtained from the Developmental Studies Hybridoma Bank developed under the auspices of the National Institute of Child Health and Human Development and maintained by the Department of Biological Sciences, University of Iowa (Iowa City, IA).