The cerebral cortex contains multiple areas with distinctive cytoarchitectonic patterns, but the cellular mechanisms underlying the emergence of this diversity remain unclear. Here, we have investigated the neuronal output of individual progenitor cells in the developing mouse neocortex using a combination of methods that together circumvent the biases and limitations of individual approaches. Our experimental results indicate that progenitor cells generate pyramidal cell lineages with a wide range of sizes and laminar configurations. Mathematical modeling indicates that these outcomes are compatible with a stochastic model of cortical neurogenesis in which progenitor cells undergo a series of probabilistic decisions that lead to the specification of very heterogeneous progenies. Our findings support a mechanism for cortical neurogenesis whose flexibility would make it capable to generate the diverse cytoarchitectures that characterize distinct neocortical areas.

Background and Purpose: Dravet syndrome is a severe, genetic form of paediatric epilepsy associated with premature mortality and co-morbidities such as anxiety, depression, autism, motor dysfunction and memory deficits. Cannabidiol is an approved anticonvulsive drug in the United States and Europe for seizures associated with Dravet syndrome in patients 2 years of age and older. We investigated its potential to prevent premature mortality and improve associated co-morbidities. Experimental Approach:The efficacy of sub-chronic cannabidiol administration in two mouse models of Dravet syndrome was investigated. The effect of cannabidiol on neonatal welfare and survival was studied using Scn1a −/− mice. We then used a hybrid, heterozygote Scn1a +/− mouse model to study the effect of cannabidiol on survival and behavioural co-morbidities: motor deficits (rotarod and static-beam test), gait abnormality (gait test), social anxiety (social interaction test), anxiety-like (elevated plus maze) and depressive-like behaviours (sucrose preference test) and cognitive impairment (radial arm maze test). Key Results:In Scn1a −/− mice, cannabidiol increased survival and delayed worsening of neonatal welfare. In Scn1a +/− mice, chronic cannabidiol administration did not show any adverse effect on motor function and gait, reduced premature mortality, improved social behaviour and memory function, and reduced anxiety-like and depressive-like behaviours. Conclusion and Implications:We are the first to demonstrate a potential diseasemodifying effect of cannabidiol in animal models of Dravet syndrome. Cannabidiol treatment reduced premature mortality and improved several behavioural comorbidities in Dravet syndrome mice. These crucial findings may be translated into human therapy to address behavioural co-morbidities associated with Dravet syndrome.

Significance Brain function requires appropriate numbers of different neuronal subtypes, but how these numbers are established remains poorly understood. Here, we identified a key role for the cerebral cortex in remotely controlling interneuron survival and thus establishing appropriate numbers of the two main types of interneurons in another brain region, the striatum. While cortical pyramidal cells directly control the survival of parvalbumin-expressing GABAergic neurons, the survival of cholinergic interneurons is indirectly controlled through the activity of the striatal medium spiny neurons. Our results demonstrate that the input-specific modulation of neuronal activity is universally required to control the survival of interneurons across very different brain circuits. This is important for the assembly of balanced neural networks.

No abstract