Reagents used were as follows: medium and reagent (Neurobasal/B27 medium; TRIzol reagent; Gibco-Life Technologies, Rockville, MD); trypsin inhibitor (Roche Applied Science, Indianapolis, IN); papain (Worthington Biochemical, Lakewood, NJ); brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), and basic fibroblast growth factor (bFGF; PeproTech, Rocky Hill, NJ); goat anti-rabbit IgG and goat anti-rat IgG (both H+L; Affinipure; Jackson ImmunoResearch Laboratories, West Grove, PA); goat anti-mouse IgG-horseradish peroxidase (HRP), goat anti-rabbit IgG-HRP (Santa Cruz Biotechnology, Santa Cruz, CA); enhanced chemiluminescence (ECL) detection kit (Pierce Biotechnology, Rockford, IL); RNA PCR kit (GeneAmp; Applied Biosystems, Branchburg, NJ); Taq PCR kit (TaKaRa; Takara Bio Inc., Otsu, Shiga, Japan); sense and antisense primers for σR1 (Integrated DNA Technologies, Coralville, IA); viability assay (Live/Dead Assay; Molecular Probes, Eugene, OR); apoptosis detection kit (ApopTag Fluorescein In Situ Apoptosis Detection Kit; Chemicon International, Temecula, CA); D,L-homocysteine thiolactone hydrochloride (MP Biomedical, Inc., Solon, OH); L-glutamate, (+)-pentazocine, (−)-pentazocine, monoclonal antibodies to β-actin and neurofilament 160 (NF-160), and all other chemicals (Sigma-Aldrich Chemical, St. Louis, MO).