Postpubertal emergence of altered behavioral sensitivity to acute apomorphine treatment following prenatal immune activation. Locomotor activity was assessed in peripubertal (PND35) and adult (PND70) Poly-I:C and control offspring following acute treatment with a low dose of APO (0.75 mg/kg, s.c.) or vehicle (vitamin C solution, VitC) in a sawdust embedded wire-mesh cylinder. The line plots show horizontal locomotor activity as indexed by the total distance traveled in the test apparatus across bins of 5 min; the bar plots represent the mean distance moved across the entire 60 min period. A, APO treatment similarly depressed horizontal locomotor activity in peripubertal (PND35) Poly-I:C and control offspring relative to corresponding vehicle (VitC) treatment. **p < 0.01 represents the significant main effect of drug treatment in the 2 × 2 × 12 (prenatal treatment × drug treatment × bins) repeated-measures ANOVA of horizontal distance moved (F(1,29) = 8.82). The numbers of offspring included were N(VitC-treated vehicle offspring) = 7, N(APO-treated vehicle offspring) = 10, N(VitC-treated Poly-I:C offspring) = 7, N(APO-treated Poly-I:C offspring) = 9. B, In contrast to the persistent decrease in locomotor activity revealed in adult control (vehicle) offspring following acute APO treatment, horizontal locomotor activity in APO-treated adult Poly-I:C offspring was characterized by an initial decrease and a subsequent increase. The secondary increase in locomotor activity observed in APO-treated adult Poly-I:C offspring was most pronounced between 15 and 30 min following APO treatment and led to a significant attenuation of the APO-induced depression of locomotor activity typically seen in APO-treated adult control offspring. **p < 0.01, based on Fisher's LSD post hoc group comparisons following the presence of a significant (F(1,37) = 6.25, p < 0.05) prenatal treatment × drug treatment interaction in the initial 2 × 2 × 12 (prenatal treatment × drug treatment × bins) repeated-measures ANOVA of horizontal distance moved. The numbers of offspring included were N(VitC-treated vehicle offspring) = 9, N(APO-treated vehicle offspring) = 12, N(VitC-treated Poly-I:C offspring) = 8, N(APO-treated Poly-I:C offspring) = 12. All values in A and B are means ± SEM.