Autism spectrum disorders (ASD) are complex developmental disorders that cause problems with social interaction and communication. In addition to the classical idiopathic autism, Rett syndrome (RTT) and several other genetic disorders including Down's syndrome, fragile X, and mental retardation are frequently associated with autism. Altered regulation of brain derived neurotrophic factor (BDNF) has been found in autistic patients. Similarly, in Rett syndrome (RTT) mouse models, BDNF expression is substantially reduced and genetic elevation of BDNF attenuates behavioral deficits. The application of BDNF recombinant protein in therapeutic intervention has not been successful, because BDNF binds to extracellular cholesterol with high affinity preventing its distribution to different tissues. However, novel small molecule compounds (TrkB agonists) that mimic the function of BDNF in the brain have been recently identified. In this study, investigators will assess whether activation of BDNF signaling through small molecule TrkB agonist(s) can lessen the severity of behavioral deficits in RTT mouse models. In this preclinical mouse study, researchers hope to identify a novel treatment for ASDs.