Prenatal immune activation induces enhancement of the behavioral sensitivity to acute amphetamine treatment regardless of the offspring's postnatal age. The behavioral sensitivity of prenatally Poly-I:C- or vehicle-treated offspring to a low dose of AMPH (2.5 mg/kg, i.p.) was assessed in an open field arena when they reached the peripubertal (PND35) or adult (PND70) stage of development. The line plots show locomotor activity as indexed by the total distance traveled in the entire open field across bins of 5 min during the initial acclimatization period as well as following saline (SAL) and AMPH administration; the bar plots represent the mean distance moved across the entire 80 min period following AMPH administration. A, No significant differences in basal locomotor activity (as measured during the initial acclimatization period and following SAL administration) were noticeable between Poly-I:C and control offspring at peripubertal age. Acute treatment with the low dose of AMPH led to a modest increase in locomotor activity in peripubertal offspring born to control mothers. The locomotor-enhancing effects of AMPH were significantly increased in peripubertal offspring born to Poly-I:C-treated mothers. *p < 0.05 represents the significant main effect of prenatal treatment in the 2 × 16 (prenatal treatment × bins) repeated-measures ANOVA of distance moved following AMPH treatment (F(1,25) = 4.27). The numbers of offspring included were N(vehicle) = 14, N(Poly-I:C) = 13. B, There were also no significant differences in basal locomotor activity between Poly-I:C and control offspring at the adult stage of life. Acute treatment with the low dose of AMPH led to marked increase in locomotor activity in peripubertal offspring born to control mothers. Again, the locomotor-stimulating effects of AMPH were significantly enhanced in adult offspring born to Poly-I:C-treated mothers. *p < 0.05 represents the significant main effect of prenatal treatment in the 2 × 16 (prenatal treatment × bins) repeated-measures ANOVA of distance moved following AMPH treatment (F(1,20) = 5.36). The numbers of offspring included were N(vehicle) = 10, N(Poly-I:C) = 12. All values in A and B are means ± SEM.