Developmental expression of ΔFosB and DAT. A, ΔFosB (35–37 kDa) immunoreactivity in the caudate putamen and nucleus accumbens of naive CD-1 mice as a function of age. Representative immunoblots are shown in the top panels.Bottom panels show means ± SEM of three mice per group. *p < 0.05, adult versus P24; #p < 0.05, adult versus P36 (Tukey's multiple comparison test after ANOVA). B, Densitometric values of DAT immunoreactivity in the caudate putamen and nucleus accumbens for naive CD-1 mice as a function of age. Levels of DAT did not differ among the three age groups.