DARPP-32 Distinguishes a Subset of Adult-Born Neurons in Zebra Finch HVC

Adult male zebra finches ( Taeniopygia guttata ) continually incorporate adult-born neurons into HVC, a telencephalic brain region necessary for the production of learned song. These neurons express immediate early genes during song production, suggesting a role for neurogenesis in song production throughout the lifespan. Half of these adult-born HVC neurons (HVC NNs) can be backfilled from the robust nucleus of the arcopallium (RA) and are a part of the vocal motor pathway underlying learned song production, but the other half do not backfill from RA, and they remain to be characterized. Here we used cell birth-dating, retrograde tract tracing, and immunofluorescence to demonstrate that half of all HVC NNs express thephosphoprotein DARPP-32, a protein associated with dopamine (DA) receptor expression. We also demonstrate that DARPP-32+ HVC NNs are contacted by tyrosine hydroxylase immunoreactive fibers suggesting that they receive catecholaminergic input, have transiently larger nuclei than DARPP-32− HVC NNs, and do not backfill from RA. Taken together, these findings help characterize a group of HVC NNs that have no apparent projections to RA and so far have eluded any positive identification other than HVC NN status.