Timing of perineuronal net development in the zebra finch song control system correlates with developmental song learning.

The appearance of perineuronal nets (PNNs) represents one of the mechanisms that contribute to the closing of sensitive periods for neural plasticity. This relationship has mostly been studied in the ocular dominance model in rodents. Previous studies also indicated that PNN might control neural plasticity in the song control system of songbirds. To further elucidate this relationship, we quantified PNN expression and their localization around parvalbumin interneurons at key time-points during ontogeny in both male and female zebra finches, and correlated these data with the well-described development of song in this species. We also extended these analyses to the auditory system. The development of PNN during ontogeny correlated with song crystallization although the timing of PNN appearance in the four main telencephalic song control nuclei slightly varied between nuclei in agreement with the established role these nuclei play during song learning. Our data also indicate that very few PNN develop in the secondary auditory forebrain areas even in adult birds, which may allow constant adaptation to a changing acoustic environment by allowing synaptic reorganization during adulthood.