Effectivity of Two Cell Proliferation Markers in Brain of a Songbird Zebra Finch.

There are two most heavily used markers of cell proliferation, thymidine analogues 5-bromo-2'-deoxyuridine (BrdU) and 5-ethynyl-2'-deoxyuridine (EdU) that are incorporated into the DNA during its synthesis. In neurosciences, they are often used consecutively in the same animal to detect neuronal populations arising at multiple time points, their migration and incorporation. The effectivity of these markers, however, is not well established. Here, we studied the effectivity of equimolar doses of BrdU and EdU to label new cells and looked for the dose that will label the highest number of proliferating cells in the neurogenic ventricular zone (VZ) of adult songbirds. We found that, in male zebra finches (Taeniopygia guttata), the equimolar doses of BrdU and EdU did not label the same number of cells, with BrdU being more effective than EdU. Similarly, in liver, BrdU was more effective. The saturation of the detected brain cells occurred at 50 mg/kg BrdU and above 41 mg/kg EdU. Higher dose of 225 mg/kg BrdU or the equimolar dose of EdU did not result in any further significant increases. These results show that both markers are reliable for the detection of proliferating cells in birds, but the numbers obtained with BrdU and EdU should not be compared.

Is neurogenesis in two songbird species related to their song sequence variability?

Neurogenesis takes part in the adult songbird brain and new neurons are integrated into the forebrain including defined areas involved in the control of song learning and production. It has been suggested that the new neurons in the song system might enable vocal variability. Here, we examined the basal levels of neurogenesis in two songbird species, zebra finch ( Taeniopygia guttata) and Bengalese finch ( Lonchura striata var. domestica), which do not learn new song elements as adults but differ in the level of song sequence variability. We found that Bengalese finches had less linear and stereotyped song sequence and a higher number of newborn cells in the neurogenic subventricular zone (SVZ) as well as the number of newly born neurons incorporated into the vocal nucleus HVC (used as a proper name) in comparison to zebra finches. Importantly, this vocal sequence variability in Bengalese finches correlated with the number of new neurons in the vocal nucleus HVC and more plastic song was associated with higher neuronal incorporation. In summary, our data support the hypothesis that newly generated neurons facilitate behavioural variability.