A history of ES potentiated the DOI-induced increase in Arc mRNA levels within the PFC. Shown are representative autoradiograms of PFC sections and graphical representation of the densitometric analysis from control (C), ES, DOI, and ES plus DOI groups. Results are expressed as a percentage of control and are the mean ± SEM. Two-way ANOVA revealed a significant ES × DOI interaction (F(1,15) = 11.39, p = 0.004). *p < 0.05, significantly different from control; #p < 0.05, significantly different from ES; δp < 0.05, significantly different from DOI (ANOVA and Bonferroni post hoc test); n = 4–5 per group.