http://onlinelibrary.wiley.com/doi/10.1002/wdev.88/full
INTRODUCTION
A
prominent trait of the neocortex is its complex yet well-organized
cellular architecture, the formation of which relies on the production
and positioning of its diverse neuronal populations. There are two major
groups of neurons in the neocortex—glutamatergic excitatory neurons and
γ-aminobutyric acid (GABA)-ergic inhibitory interneurons,
which are responsible for generating excitation and inhibition,
respectively. Excitatory neurons constitute the vast majority (∼70–80%)
of neocortical circuit neurons and are responsible for generating the
output. On the other hand, inhibitory interneurons provide a rich
variety of inhibitions that shape the output of functional circuits.
Proper neocortex function critically depends on the production and
positioning of a correct number of excitatory and inhibitory neurons,
which largely occur during the embryonic stages.
With
the advent of improved fate-mapping tools, including genetically
engineered mice, excitatory and inhibitory neurons in the neocortex were
found to arise from different developmental lineages. In rodents, the
progenitor cells of these two neuronal populations are fully segregated
in space (Figure 1).
Excitatory neurons are generated in the proliferative zone of the
dorsal telencephalon and then migrate radially to constitute the future
neocortex. In contrast, inhibitory interneurons are produced in the
proliferative zone of the ventral telencephalon and migrate tangentially
to reach the neocortex, where they coassemble with excitatory neurons
into functional circuits. This spatial segregation in the excitatory and
inhibitory neuron progenitors no doubt further complicates the
coordinated production and positioning of these neurons.
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