Activity-Dependent Control Of Inhibitory Interneuron Number In The Mammalian Cortex

Cortical networks are composed of excitatory projection neurons and inhibitory interneurons. Although fewer in number relative to projection neurons, interneurons have essential roles in brain activity and behavior since they adjust cortical excitation and control network dynamics. Therefore, the number of cortical interneurons (CIs) must be tightly controlled during development to meet the functional requirements of emerging neuronal circuits. CIs are generated in excess from basal forebrain progenitors and it has been proposed recently that their final number is adjusted via intrinsically determined apoptosis occurring during an early postnatal window. Here we provide evidence that the extent of CI apoptosis during this critical period is plastic, cell type specific and can be reduced in a cell autonomous manner by acute increases in neuronal activity. We further show that hyperactive networks promote the survival of transplanted CIs. We propose that the level of activity in emerging neural networks controls in a homeostatic manner the number of CIs.