Song isolation is associated with maintaining high spine frequencies on zebra finch 1MAN neurons

Male zebra finches normally learn much of their song during the second month after hatching. This is a period of rapid change throughout the brain. We studied anatomical consequences of manipulating exposure to song. We investigated neurons of lateral MAN (1MAN), a nucleus implicated in song learning (Bottjer et al., 1984), in male and female zebra finches (Taeniopygia guttata) at 55 days posthatch. Birds were raised either under normal colony conditions (social) or in colonies in which adult males were removed when the young hatched (song deprived). Brains were stained with the Golgi-Cox method. Fine morphological details of spiny 1MAN neurons were recorded with a 3D semiautomated computer system. Several features of the spiny 1MAN neurons differ between sexes. Males have neurons with larger somata, more primary dendrites and thicker dendrites, than neurons from females. These features as well as dendritic length and other branching characteristics do not differ between treatment groups. There is a large difference in dendritic spine frequencies between the social and the song-deprived groups. Social, song-experienced males have spine frequencies 41% lower than song-deprived males. In females, spine frequencies are as high as in the song-deprived males and do not differ between the song-deprived and social conditions. Developmental overproduction and subsequent pruning of neural connections have been observed in many areas of the central nervous system. We suggest that apparent pruning in 1MAN is modulated by experience: It takes place if the social experiences associated with auditory song learning have occurred. This finding is consistent with the synapse selection hypothesis of Changeux and Danchin Brain Research, 309, (1976) and with data found using an acoustic filial imprinting paradigm in the domestic chicken.