Oxytocin Signaling in the Early Life of Mammals: Link to Neurodevelopmental Disorders Associated with ASD

Social behaviors in species as diverse as honey bees and humans promote group survival but often come at some cost to the individual. Although reinforcement of adaptive social interactions is ostensibly required for the evolutionary persistence of these behaviors, the neural mechanisms by which social reward is encoded by the brain are largely unknown. Here we demonstrate that in mice oxytocin (OT) acts as a social reinforcement signal within the nucleus accumbens (NAc) core, where it elicits a presynaptically expressed long-term depression of excitatory synaptic transmission in medium spiny neurons. Although the NAc receives OT receptor-containing inputs from several brain regions, genetic deletion of these receptors specifically from dorsal raphe nucleus, which provides serotonergic (5-HT) innervation to the NAc, abolishes the reinforcing properties of social interaction. Furthermore, OT-induced synaptic plasticity requires activation of NAc 5-HT1b receptors, the blockade of which prevents social reward. These results demonstrate that the rewarding properties of social interaction in mice require the coordinated activity of OT and 5-HT in the NAc, a mechanistic insight with implications for understanding the pathogenesis of social dysfunction in neuropsychiatric disorders such as autism.

Atypical sensory-based behaviors are a ubiquitous feature of autism spectrum disorders (ASDs). In this article, we review the neural underpinnings of sensory processing in autism by reviewing the literature on neurophysiological responses to auditory, tactile, and visual stimuli in autistic individuals. We review studies of unimodal sensory processing and multisensory integration that use a variety of neuroimaging techniques, including electroencephalography (EEG), magnetoencephalography (MEG), and functional MRI. We then explore the impact of covert and overt attention on sensory processing. With additional characterization, neurophysiologic profiles of sensory processing in ASD may serve as valuable biomarkers for diagnosis and monitoring of therapeutic interventions for autism and reveal potential strategies and target brain regions for therapeutic interventions.

Autism spectrum disorders (ASD) are diagnosed on the basis of three behavioral features namely deficits in social communication, absence or delay in language, and stereotypy. The susceptibility genes to ASD remain largely unknown, but two major pathways are emerging. Mutations in TSC1/TSC2, NF1, or PTEN activate the mTOR/PI3K pathway and lead to syndromic ASD with tuberous sclerosis, neurofibromatosis, or macrocephaly. Mutations in NLGN3/4, SHANK3, or NRXN1 alter synaptic function and lead to mental retardation, typical autism, or Asperger syndrome. The mTOR/PI3K pathway is associated with abnormal cellular/synaptic growth rate, whereas the NRXN-NLGN-SHANK pathway is associated with synaptogenesis and imbalance between excitatory and inhibitory currents. Taken together, these data strongly suggest that abnormal synaptic homeostasis represent a risk factor to ASD.