Sensory inputs control the integration of neurogliaform interneurons into cortical circuits

Neurogliaform interneurons constitute an essential component of cortical circuits. This paper provides evidence that, during early development, superficial neurogliaform cells of the primary somatosensory barrel field cortex receive prominent innervation from the thalamus. These afferents also activate postsynaptic NR2B-containing NMDA receptors, which are essential for the neurons' proper cortical integration. Neuronal microcircuits in the superficial layers of the mammalian cortex provide the substrate for associative cortical computation. Inhibitory interneurons constitute an essential component of the circuitry and are fundamental to the integration of local and long-range information. Here we report that, during early development, superficially positioned Reelin-expressing neurogliaform interneurons in the mouse somatosensory cortex receive afferent innervation from both cortical and thalamic excitatory sources. Attenuation of ascending sensory, but not intracortical, excitation leads to axo-dendritic morphological defects in these interneurons. Moreover, abrogation of the NMDA receptors through which the thalamic inputs signal results in a similar phenotype, as well as in the selective loss of thalamic and a concomitant increase in intracortical connectivity. These results suggest that thalamic inputs are critical in determining the balance between local and long-range connectivity and are fundamental to the proper integration of Reelin-expressing interneurons into nascent cortical circuits.