Dendritic pattern formation involves both oriented regression and oriented growth in the barrels of mouse somatosensory cortex.

The dendritic structure of neurons in the inner one-third of the wall of the barrels of somatosensory cortex was examined in animals at 10, 15, 20, 25, and 30 days of age. In adults, dendrites of these neurons project largely towards the barrel hollow. The amount of dendrite in the hemifield towards the barrel hollow, in which thalamic afferents terminate, increased with age, while the amount in the hemifield away from the hollow decreased, as measured by dendritic intersections with concentric rings. Loss of primary dendritic branches across these ages occurred both for dendrites arising on the side of the soma oriented away from the barrel hollow and for dendrites on the side of the soma nearest to the hollow. The loss of primary branches was much greater on the side away from the hollow. The amount of dendrite per primary branch increased for branches oriented towards the hollow, whereas it did not change or was somewhat reduced for those branches that remained on the side of the soma opposite the hollow. Thus both the selective loss of entire branches and the selective embellishment of others occur during the development of these somatosensory cortical structures.