The development of an animal model of autism is one approach researchers use to study potential causes of autism. Given the complexity of autism and its etiology, researchers often focus only on single features of autism when using animal models.
Rodent model
One of the more common rodent models is the Norway rat (Rattus norvegicus). More recent research has used the house mouse (Mus musculus) to model autism because it is a social species. Other strains of mice used include mu opioid receptor knockout mice, as well as Fmr1 knockout mice; the latter are also used as animal models of Fragile X syndrome.
The Norway rat has been used, for example, by Mady Hornig to implicate thiomersal in autism. The current scientific consensus is that no convincing scientific evidence supports these claims, and major scientific and medical bodies such as the Institute of Medicine and World Health Organization (WHO) as well as governmental agencies such as the U.S. Food and Drug Administration (FDA) and Centers for Disease Control and Prevention (CDC) reject any role for thiomersal in autism or other neurodevelopmental disorders.
Behaviors measured in these models include approach to olfactory pheromones emitted by other mice, approach to familiar and new conspecifics, reciprocal social interactions, ultrasonic vocalizations, communal nesting, sexual and parenting behaviors, territorial scent marking, and aggressive behaviors, as well as motor behaviors such as gait. Social interaction is measured by how the mouse interacts with a stranger mouse introduced in the opposite side of a test box.
Researchers from the University of Florida have used deer mice to study restricted and repetitive behavior such as compulsive grooming, and how these behaviors may be caused by specific gene mutations. In addition, Craig Powell of the University of Texas Southwestern Medical Center, with a grant from Autism Speaks, is currently using mice to examine the potential role of neuroligin gene mutations in causing autism. Much research has been done into the use of a rat model to show how Borna virus infection, exposure to valproic acid in utero, and maternal immune activation may cause autism.
Another goal of the use of rodent models to study autism is to identify the mechanism by which autism develops in humans. Other researchers have developed an autism severity score to measure the degree of severity of the mice's autism, as well as the use of scent marking behavior and vocalization distress as models for communication.
It has been observed that mice lacking the gene for oxytocin exhibit deficits in social interaction, and that it may be possible to develop treatments for autism based on abnormalities in this and other neuropeptides.
Environmental Factors of ASD
Looking at the environmental factors of autistic spectrum disorder in rodents helps us to understand the neuropathology of the disorder which can be compared to humans. Environmental factors have been studied in animal rodent models and have been seen to influence brain development and play a role in CNS neuropathology. For example, one study found that a possible environmental contributor to autism may be agents like prenatal exposure to air pollution or any birth difficulty leading to periods of oxygen deprivation to the brain, which alter serotonin levels in early development of the rodent1. This study also found that if the parent exhibits autism, the offspring are more likely to be autistic as well and that since older men have a higher number of DNA mutations in their sperm, these mutations are usually found in the offspring of older men. The last major result that this study observed was that environmental factors during and after pregnancy may have an impact on the immune system as well as the developing nervous system and plays a part in creating neurodevelopmental disorders like autism1. Since environmental factors can occur at any time during the developmental process, there is much variability in the neural and behavioral phenotype of autism. The environment can cause unknown changes in brain development of rodents because they don't all live in the same habitat and therefore might develop different changes to their brain than what is expected.