Dulbecco’s modified eagle medium (DMEM), F-12 nutrient mixture, fetal bovine serum (FBS), HEPES-buffer, amphotericin B, gentamicin, and dispase II, were purchased from Gibco-BRL (Grand Island, NY). All other reagents and chemicals including mouse-derived epidermal growth factor, cholera-toxin (subunit A), dimethyl sulfoxide (DMSO), hydrocortisone, and insulin-transferrin-sodium selenite media supplement were purchased from Sigma Chemical Co. (St. Louis, MO). Plastic cell culture dishes (35 and 60 mm) and 15- and 50-mL sterile centrifuge tubes were obtained from BD Biosciences (Lincoln Park, NJ). Thirty 0.4-μm culture plate inserts (Millicell-PC) and polycarbonate filters were from Millipore (Bedford, MA). Optimal cutting temperature (OCT) compound and cryomolds were from Sakura Finetek (Torrance, CA). Affinity-purified rabbit polyclonal antibody against TrkA full-length form (1:200), TrkB (1:200), and TrkC (1:200) were purchased from Santa Cruz Biotechnology (Santa Cruz, CA). Affinity-purified rabbit polyclonal antibody against p75NTR (1:100), rat monoclonal antibody against NGF (1:100), and chicken polyclonal antibody against BDNF (1:100), NT3 (1:100), and NT4 (1:100) were all purchased from Promega (Madison, WI). The specificity of each of these antibodies has been verified by the manufacturers and other reports. The secondary biotin-conjugated antibody goat anti-rabbit (1:100) for TrkA, TrkB, TrkC, and p75NTR was from Santa Cruz Biotechnology. The biotin-conjugated mouse anti-rat antibody (1:600) was from Sigma Chemical Co., and the biotin-conjugated rabbit anti-chicken antibody was from Promega. An avidin-biotin complex immunoperoxidase staining kit (Elite ABC) was purchased from Vector Laboratories (Burlingame, CA), a bicinchoninic acid (BCA) protein assay kit from Pierce (Rockford, IL), and an NGF immunoassay system (Emax) from Promega. The tyrosine kinase inhibitor K252a was purchased from Calbiochem-Novabiochem (San Diego, CA).