Effect of prenatal exposure to acetaminophen during critical period of brain growth spurt on exploratory and cognitive behavior: Guinea pig model

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ABSTRACT Recommended doses of the analgesic acetaminophen (N-acetyl-p-aminophenol; Tylenol®, APAP) were presumed to be safe for pregnant women until epidemiological studies reported that children prenatally exposed to APAP are at high risk of developing a number of neurological disorders, including attention- deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). It is important to note, however, that these studies did not establish a cause-consequence relationship between prenatal APAP exposure and childhood neurological disorders. Preclinical studies, on the other hand, have shown that exposure of mice and rats to APAP during their neonatal period of brain growth spurt causes cognitive deficits among other neurobehavioral impairments in early adulthood. Unfortunately, the temporal development of the human brain does not parallel that of the mouse or the rat brain. Therefore, the question as to whether gestational exposure to APAP causes disruption of fetal brain development and, thereby, compromises neurobehavioral functions later in life remains unanswered. Here, we propose to use the guinea pig as the animal model of choice to test the central hypothesis that prenatal exposure to APAP during the period of brain growth spurt has long-term, sex-dependent effects on emotional and cognitive behavior that correlate with disruption of the electrical activity and/or structural integrity of the brain. The guinea pig is a unique animal model, because its placental structure, the temporal course of its brain development, and APAP metabolism during pregnancy closely resemble those of humans. A multidisciplinary approach involving behavioral assays, electroencephalography (EEG), and immunohistochemistry (IHC), and a placebo-controlled, randomized, blind design that minimizes experimental bias and maximizes scientific rigor will be used to address two specific aims. In Aim 1, experiments will determine whether male and female offspring born from guinea pigs orally treated with APAP (50-100 mg/kg twice a day for 10 days) during the gestational critical period of fetal brain growth spurt present impaired exploratory, social, and/or cognitive behavior. These are behavioral domains impaired in neurological disorders associated with prenatal APAP exposure of children. At the end of the behavioral test, animals will be used in the experiments designed in Aim 2 to determine whether the prenatal exposure to APAP causes significant alterations of the electrical brain activity, measured in telemetric EEG, and/or disruption of the structural integrity of the hippocampus, a brain region critical known to be structurally disrupted in ADHD and ASD. This approach will enable us to identify functional and structural correlates of the behavioral outcomes in APAP-exposed offspring. Successful completion of this study will fill in the knowledge gap regarding the safety of gestational use of APAP. It will also lay the groundwork for future studies aimed at identifying the effects of developmental effects of APAP exposure at different stages of pregnancy and the molecular mechanisms underlying these effects.