Preadolescent Phthalate (DEHP) Exposure Is Associated With Elevated Locomotor Activity and Reward-Related Behavior and a Reduced Number of Tyrosine Hydroxylase Positive Neurons in Post-Adolescent Male and Female Rats.

Abstract

Phthalate administration to male rats has been shown to negatively impact neural development while development of the female rat brain is less affected. Because a number of exogenous agents have been shown to interfere with dopamine function, we evaluated post-adolescent behavioral (operant conditioning for food reward and locomotor activity), histological (tyrosine hydroxylase; TH), and genetic (mRNA levels) outcomes of preadolescent (postnatal days [PND] 16-22) phthalate exposure. Male and female Long-Evans rats were administered 4 doses (0, 1, 10, or 20 mg/kg) of di-(2-ethylhexyl)phthalate (DEHP) i.p. from PND16 to 22. Rats were trained on an operant task to bar press for chocolate-flavored pellets from PND55-63 then euthanized on PND78. The 10 mg/kg DEHP dose was associated with elevated bar pressing for food reward during acquisition and extinction while the 20 mg/kg dose was associated with elevated locomotor activity in both males and females. Stereological analysis revealed reduced TH+ densities in the SNc in DEHP- (10 and 20 mg/kg) treated male and female rats. In the VTA, TH+ staining was reduced in male rats treated with 10 or 20 mg/kg DEHP while in females, the TH: CV ratio was higher at the 10 mg/kg dose compared with controls. An examination of Th mRNA showed a main effect of sex with females showing increased Th expression at all DEHP doses. The present results show that preadolescent phthalate exposure results in detrimental dopaminergic system development impacting neurobehavioral function in post-adolescent rats.