الفهرس 
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Abstract
Autism is a pervasive developmental disorder that is characterized by the behavioral traits of impaired social cognition and communication, and repetitive and/or obsessive behavior and interests. The core symptoms are frequently accompanied by a spectrum of neurobehavioral derangements, including: hyperactivity, aberrant sensitivity to sensory stimulation and anxiety.
The number of reported cases of autism increased dramatically in the 1990s and early 2000s. This increase is largely attributable to changes in diagnostic practices, referral patterns, availability of services, age at diagnosis, and public awareness. Autism occurs more often in boys than girls.
The exact cause of autism is unknown. It is a complex disease involving genetic, epigenetic and environmental factors (e.g. exposure to certain teratogens during first and second trimester of preganancy as valproate (VPA)). Family studies have shown that the genetic factors remain important. Added to this, early prenatal and postnatal exposure to environmental toxins causes release of ROS which induce the pathological changes of autism.
Brain of autistic children show several neuropathological abnormalities like: reduced number of Purkinje cells in the cerebellum, abnormal maturation of the forebrain limbic system, brainstem abnormalities and neocortical malformations. Also there are signs of active ongoing inflammation and elevation of inflammatory markers in brain tissue, serum, plasma and CSF of autistic children.
Neurochemically, the most consistent finding in autism is an increase in blood serotonin. Interestingly, serotonin is known to play an active role in brain development, before it acts as a neurotransmitter in the mature brain. Thus, it may be the high levels of serotonin in autistic children which lead to the observed behavioral and brain changes , as the serotonin can enter the brain of a developing fetus, and cause loss of serotonin terminals through negative feedback.
There are several ways to model autism in animals. The greater number of parameters this model hav, the closer it is to mimic human autism. In our study we have chosen the VPA induced rat model because exposure to VPA before the neural tube is closed, was related to a higher incidence of neurodevelopmental disorders including autism.