Cortical reorganization during adolescence: What the rat can tell us about the cellular basis.

The human cortex, particularly the prefrontal cortex, decreases in volume during adolescence which indicates considerable pruning. There is consistent evidence from human, monkey and rat tissue that synapses, dendritic spines and dendrites are pruned during this time. However, our work with a rat model of adolescence shows that other cellular components are remodeling at this time as well. Neurons are also pruned and we have found that in female rats, puberty is a key signal for this process. Other critical developmental events occur that are not detectable in gross size changes including the growth of dopaminergic inputs. The changes in the inhibitory GABAergic system, especially the parvalbumin-expressing neuronal subtype, are an essential part of the maturation of the prefrontal cortex. This involves the formation of perineuronal nets around parvalbumin interneurons that allow mature fast spiking. We have found a large increase in perineuronal nets from early adolescence to adulthood in both sexes. We also have seen a temporary pause in this increase at the time of puberty in females. These complicated events cannot be deduced from MRI. The cellular reorganization that is indicated by size changes in the human cortex during adolescence can be informed by work from rodent models.