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Autism spectrum disorder (ASD) is increasingly thought to result from low-level deficits in synaptic development and neural circuit formation that cascade into more complex cognitive symptoms. However, the link between synaptic dysfunction and behavior is not well understood. By comparing the effects of abnormal circuit formation and behavioral outcomes across different species, it should be possible to pinpoint the conserved fundamental processes that result in disease. Here we use a novel model for neurodevelopmental disorders in which we expose Xenopus laevis tadpoles to valproic acid (VPA) during a critical time point in brain development at which neurogenesis and neural circuit formation required for sensory processing are occurring. VPA is a commonly prescribed antiepileptic drug with known teratogenic effects. In utero exposure to VPA in humans or rodents results in a higher incidence of ASD or ASD-like behavior later in life. We find that tadpoles exposed to VPA have abnormal sensorimotor and schooling behavior that is accompanied by hyperconnected neural networks in the optic tectum, increased excitatory and inhibitory synaptic drive, elevated levels of spontaneous synaptic activity, and decreased neuronal intrinsic excitability. Consistent with these findings, VPA-treated tadpoles also have increased seizure susceptibility and decreased acoustic startle habituation. These findings indicate that the effects of VPA are remarkably conserved across vertebrate species and that changes in neural circuitry resulting from abnormal developmental pruning can cascade into higher-level behavioral deficits. [ABSTRACT FROM AUTHOR]

Thefunctional properties of neural circuits become increasingly robust over development. This allows circuitsto optimizetheir output in response to a variety of input. However, it is not clear whether this optimization is a function of hardwired circuit elements, or whether it requires neural experience to develop. We performed rapid in vivo imaging of calcium signals from bulk-labeled neurons in the Xenopus laevis optic tectum to resolve the rapid spatiotemporal response properties of populations of developing tectal neurons in response to visual stimuli. Wefoundthat during a criticaltime intectal development, network activity becomes increasingly robust, more correlated, and more synchronous. These developmental changes require normal visual input during development and are disrupted by NMDAR blockade. Our data show that visual activity and NMDAR activation are critical for the maturation of tectal network dynamics during visual system development. [ABSTRACT FROM AUTHOR]

The functional properties of neural circuits become increasingly robust over development. This allows circuits to optimize their output in response to a variety of input. However, it is not clear whether this optimization is a function of hardwired circuit elements, or whether it requires neural experience to develop. We performed rapid in vivo imaging of calcium signals from bulk-labeled neurons in the Xenopus laevis optic tectum to resolve the rapid spatiotemporal response properties of populations of developing tectal neurons in response to visual stimuli. We found that during a critical time in tectal development, network activity becomes increasingly robust, more correlated, and more synchronous. These developmental changes require normal visual input during development and are disrupted by NMDAR blockade. Our data show that visual activity and NMDAR activation are critical for the maturation of tectal network dynamics during visual system development.