Effects of (R,S)-ketamine (Ket, 1 μM), (R,S)-norketamine (NK, 10 nM), (2S,6S)-hydroxynorketamine (HNK, 0.1 nM), and methyllycaconitine (MLA, 50 nM) with or without nicotine (2 μM) on the levels of monomeric serine racemase (m-SR) protein in PC-12 cells. (A) Representative immunoblots of m-SR and β-actin. (B) Scatter plot illustrating the relative m-SR levels after quantification and normalization with β-actin (n = 3 independent experiments). *P < 0.05 (ANOVA) compared with control cells.