A Subtype of Adult-Born Neuron in Male Zebra Finch HVC Expresses DARPP-32 and Does Not Project to RA as part of the Vocal Motor Pathway

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 following song production, suggesting a role for neurogenesis in song production throughout the lifespan. Half of these adult-born HVC neurons (HVC NNs) send their axons to RA as part of the vocal motor pathway underlying learned song production, but the other half do not, and their identity remains unknown. Here we used cell birth-dating, retrograde tract tracing, and immunofluorescence to demonstrate that half of all HVC NNs express the neuron-specific phosphoprotein DARPP-32, a protein associated with DA receptor expression. We also demonstrate that DARPP-32+ HVC NNs are contacted by tyrosine hydroxylase immunoreactive fibers suggesting that they receive catecholaminergic input, are transiently larger than DARPP-32-negative HVC NNs, and do not send axons to RA as part of the vocal motor pathway. Taken together, these findings indicate the existence of a class of HVC NNs that do not project to RA and may constitute the aforementioned unknown half of all HVC NNs.

Horizontal transmission of the father's song in the zebra finch ( Taeniopygia guttata )

As is the case for human speech, birdsong is transmitted across generations by imitative learning. Although transfer of song patterns from adults to juveniles typically occurs via vertical or oblique transmission, there is also evidence of horizontal transmission between juveniles of the same generation. Here, we show that a young male zebra finch ( Taeniopygia guttata ) that has been exposed to its father during the sensitive period for song learning can lead a brother, that has never heard the paternal song, to imitate some sounds of the father. Moreover, song similarity between the two brothers was higher than the similarity measured between the paternal song and the song of the brother that had a week-long exposure to the father. We speculate that the phenomenon of within-generation song learning among juveniles may be more widespread than previously thought and that when a juvenile evaluates potential models for imitative learning, a sibling may be as salient as an adult.