Neurocalcin protein labeling reveals a dimorphism within the developing zebra finch brain

The exact mechanism(s) responsible for sexual differentiation of the zebra finch song system remains unknown but likely involve a combination of hormonal and genetic factors. One product that may play a role is the calcium binding protein, neurocalcin. A previous study indicated that neurocalcin mRNA was widely distributed throughout the zebra finch telencephalon, overlapping with song control regions. Because it was not clear how much of that expression was functionally relevant, we labeled tissue with a specific antibody. At the three age ranges that were examined, there were region-specific fluctuations in the number of neurocalcin immunoreactive cells. During post-hatching developmental ages (P) 18–23, quantitative analyses indicated that females had significantly more neurons containing neurocalcin protein in HVC and RA than males. This difference was not detected at P10 or in adults. Labeling in LMAN did not reveal a sex difference at any of the ages. In other areas of the brain, semi-quantitative analyses of the relative number of cells immunopositive for neurocalcin varied across specific regions, but with the possible exception of the lateral striatum, no obvious sex differences were apparent. Taken together, these data are consistent with the idea that neurocalcin may be important for regulating sexual dimorphisms within the neural song system at a specific developmental period. In addition, because of variations in events related to post-transcriptional modification, a thorough study of a gene's role in development and/or behavior should include investigations of its transcription as well as translation.