Clusters of coupled neuroblasts in embryonic neocortex.

The neocortex of the brain develops from a simple germinal layer into a complex multilayer structure. To investigate cellular interactions during early neocortical development, whole-cell patch clamp recordings were made from neuroblasts in the ventricular zone of fetal rats. During early corticogenesis, neuroblasts are physiologically coupled by gap junctions into clusters of 15 to 90 cells. The coupled cells form columns within the ventricular zone and, by virtue of their membership in clusters, have low apparent membrane resistances and generate large responses to the inhibitory neurotransmitter gamma-aminobutyric acid. As neuronal migration out of the ventricular zone progresses, the number of cells within the clusters decreases. These clusters allow direct cell to cell interaction at the earliest stages of corticogenesis.