At present, several studies have highlighted the relation between changes in the gut microbiota/microbiome and a few pathologies of the CNS, including autism and other disorders of social behavior. We have checked out a hypothesis that gut microbiome-produced neurotoxins might participate in the development of these disorders. As was found, intraperitoneal injections of a gut toxin, p-cresol, induced changes in social behavior of rats, which could be interpreted as autism-like ones. Intranasal administration of oxytocin rescued the behavioral impairments in p-cresol-treated rats in the three-chambered social approach test and neutralized the respective modifications of locomotor activity, research activity, and emotion-related indices in the open-field test. The effects of oxytocin were eliminated by administration of an opioid antagonist, naltrexone. These data suggest that there are functional interactions between the oxytocinergic and opioidergic systems in p-cresol-induced changes of social behavior under condtions of the animal model used.