Perineuronal nets in HVC and plasticity in male canary song

Songbirds learn their vocalizations during developmental sensitive periods
of song memorization and sensorimotor learning. Some seasonal songbirds,
called open-ended learners, recapitulate transitions from sensorimotor
learning and song crystallization on a seasonal basis during adulthood. In
adult male canaries, sensorimotor learning occurs each year in autumn and
leads to modifications of the syllable repertoire during successive
breeding seasons. We previously showed that perineuronal nets (PNN)
expression in song control nuclei decreases during this sensorimotor
learning period. Here we explored the causal link between PNN expression
in adult canaries and song modification by enzymatically degrading PNN in
HVC, a key song control system nucleus. Three independent experiments
identified limited effects of the PNN degradation in HVC on the song
structure of male canaries. They clearly establish that presence of PNN in
HVC is not required to maintain general features of crystallized song.
Some suggestion was collected that PNN are implicated in the stability of
song repertoires but this evidence is too preliminary to draw firm
conclusions and additional investigations should consider producing PNN
degradations at specified time points of the seasonal cycle. It also
remains possible that once song has been crystallized at the beginning of
the first breeding season, PNN no longer play a key role in determining
song structure; this could be tested by treatments with chondroitinase ABC
at key steps in ontogeny. It would in this context be important to develop
multiple stereotaxic procedures allowing the simultaneous bilateral
degradation of PNN in several song control nuclei for extended periods.