Subplate neurons regulate maturation of cortical inhibition and outcome of ocular dominance plasticity

Refining the roles of GABAergic signaling during neural circuit formation

Our understanding of the role of GABA signaling in circuit development is rapidly expanding. Here, we review three recent refinements in our understanding of the diverse roles that GABA plays at different stages of neural circuit formation. First, we discuss recent evidence that depolarizing GABA plays at least a permissive role in promoting both excitatory and inhibitory synaptogenesis in developing neurons (including newly generated neurons in the adult). Next, we discuss recent evidence that GABAergic circuits sculpt the temporal and spatial aspects of synaptic integration. Consequently, early developmental events affecting the establishment of GABAergic circuits will control subsequent activity-dependent refinements of information processing and circuit function. In the third section, we review recent evidence of molecular mechanisms by which GABAergic signaling plays a role in the regulation of the balance between GABAergic and glutamatergic transmission in developing circuits. Throughout the review, we concentrate on the effects of the signaling by GABA(A) receptors, as told from the point of view of the GABA-responsive cells, and do not discuss mechanisms that govern GABA release or activity of GABAergic neurons per se.

Autism spectrum disorders: developmental disconnection syndromes

Autism is a common and heterogeneous childhood neurodevelopmental disorder. Analogous to broad syndromes such as mental retardation, autism has many etiologies and should be considered not as a single disorder but, rather, as 'the autisms'. However, recent genetic findings, coupled with emerging anatomical and functional imaging studies, suggest a potential unifying model in which higher-order association areas of the brain that normally connect to the frontal lobe are partially disconnected during development. This concept of developmental disconnection can accommodate the specific neurobehavioral features that are observed in autism, their emergence during development, and the heterogeneity of autism etiology, behaviors and cognition.

Mechanisms of eye-specific visual circuit development

Eye-specific visual connections are a prominent model system for exploring how precise circuits develop in the CNS and, in particular, for addressing the role of neural activity in synapse elimination and axon refinement. Recent experiments have identified the features of spontaneous retinal activity that mediate eye-specific retinogeniculate segregation, the synaptic events associated with this process, and the importance of axon guidance cues for organizing the overall layout of eye-specific maps. The classic model of ocular dominance column development, in which spontaneous retinal activity plays a crucial role, has also gained new support. Although many outstanding questions remain, the mechanisms that instruct eye-specific circuit development are becoming clear.

Early retinal activity and visual circuit development

Does spontaneous retinal activity prior to vision play a role in the establishment of visual maps? In this issue of Neuron, two separate papers by Huberman et al. and Hooks and Chen demonstrate a role for early spontaneous retinal activity in the establishment of ocular dominance columns and synaptic refinement at retinogeniculate synapses.

Subplate neurons foster inhibition

Previous work demonstrates an essential role of subplate neurons during ocular dominance (OD) column formation in the developing visual cortex. While inhibitory circuitry has also been shown to play an essential role in OD plasticity, the relationship between subplate neurons and the development of inhibitory circuits has been unclear. In this issue of Neuron, Kanold and Shatz provide evidence that maturation of inhibitory circuitry requires subplate neurons in the developing cortex.