Can prenatal methamphetamine exposure be considered a good animal model for ADHD?

Attention-deficit/hyperactivity disorder (ADHD) is a mental disorder with a heterogeneous origin with a global incidence that continues to grow. Its causes and pathophysiological mechanisms are not fully understood. It includes a combination of persistent symptoms such as difficulty in concentration, hyperactivity and impulsive behavior. Maternal methamphetamine (MA) abuse is a serious problem worldwide, it can lead to behavioral changes in their offspring that have similarities with behavioral changes seen in children with ADHD. There are several types of ADHD animal models, e.g. genetic models, pharmacologically, chemically and exogenously induced models. One of the exogenously induced ADHD models is the hypoxia-induced model. Our studies, as well as those of others, have demonstrated that maternal MA exposure can lead to abnormalities in the placenta and umbilical cord that result in prenatal hypoxia as well as fetal malnutrition that can result in irreversible changes to experimental animals. Therefore, the aim the present study was to compare the cognitive impairments in MA exposure model with those in established model of ADHD - prenatal hypoxia model, to test whether MA exposure is a valid model of ADHD. Pregnant Wistar rats were divided into four groups based on their gestational exposure to MA: (1) daily subcutaneous injections of MA (5 mg/kg), (2) saline injections at the same time and volume, (3) daily 1-hr hypoxia (10 % O2), and (4) no gestational exposure (controls). Male rat offspring were tested for short-term memory in the Novel Object Recognition Test and the Object Location Test between postnatal days 35 and 40. Also their locomotor activity in both tests was measured. Based on the present results, it seems that prenatal MA exposure is not the best animal model for ADHD since it shows corresponding symptoms only in certain measures. Given our previous results supporting our hypothesis, more experiments are needed to further test possible use of prenatal MA exposure as an animal model of the ADHD.