Modulation of the Sensitivity to Systemic Dizocilpine (MK-801; 0.15 mg/kg, Intraperitoneally) Challenge by Periadolescent Antipsychotic and Antidepressant Drug Treatment in Offspring Born to PolyI:C-Treated and Control (CON) Mothers. The graph illustrates the distance traveled in the open field after nontreatment (bins 1–4), saline (SAL) treatment (bins 5–8), and MK-801 treatment (bins 9–24) for CON (a) and PolyI:C offspring (b); the mean distance traveled after MK-801 challenge is shown in (c). Periadolescent exposure to haloperidol (HAL) significantly increased basal locomotor activity (ie, after nontreatment and SAL treatment) compared with periadolescent vehicle (VEH) treatment regardless of the prenatal treatment histories. #P < .05 between HAL-exposed and VEH-treated subjects, based on Fisher post hoc tests. Prenatal PolyI:C exposure led to a significant increase in the locomotor reaction to acute MK-801 challenge compared with prenatal CON treatment, ie, VEH-treated PolyI:C offspring displayed a significant increase in mean distance traveled in the open field compared with VEH-treated CON offspring following MK-801 administration. The prenatal PolyI:C-induced potentiation of MK-801 sensitivity was blocked by chronic HAL treatment during periadolescence but not by periadolescent exposure to CLZ or FLX. On the other hand, HAL and FLX (but not CLZ) treatment significantly increased the sensitivity to acute MK-801 challenge in CON offspring. *P < .05 between VEH-treated CON offspring and VEH- or CLZ-treated PolyI:C offspring; +P < .05 between VEH-treated CON offspring and HAL or FLX-treated CON offspring; #P < .05 between CLZ-treated CON offspring and HAL- or FLX-treated CON offspring; and §P < .05 between HAL-treated PolyI:C offspring and VEH- or CLZ-treated PolyI:C offspring. The number of subjects in each group is listed in table 1. SED in (a) and (b) refers to twice the standard error of difference derived from the error variance associated with the prenatal treatment × periadolescent treatment × 5-min bins interaction term from the overall ANOVA. All values in (c) are means ± standard error of the mean.