Association between the degree of MAPK /ERK activity in the prefrontal cortex and social behavioral score was observed in F2 mice. Western blot analysis of extracted proteins from the prefrontal cortex of eight mice with the lowest scores and eight mice with the highest scores of five different social behaviors were using the p-ERK antibody. A) Quantitative fold-changes of bands were assessed, after being normalized by actin levels. Mean p-ERK levels were increased significantly in F2 mice that performed poorly in the ‘juvenile approach front’ social assay using the non-parametric Mann-Whitney U test. B) Other Mapk/Erk signaling pathway proteins including Ras, t-Mek, p-Mek, and t-Erk were compared in mice with low scores on ‘juvenile approach front’ social assay versus mice with high scores, using Western blot analysis. p-Mek levels were also significantly amplified in mice with low juvenile approach front scores. (*P <0.05, bars represent mean values, whiskers show standard deviations). (Erk, Extracellular signal-regulated kinase; p-Erk, phosphorylated extracellular signal-regulated kinase; Mapk, Mitogen-activated protein kinase; Mek, Mitogen-activated protein kinase kinase; p-Mek, phosphorylated Mitogen-activated protein kinase kinase).