Figure 2.

Apoptosis in HVC occurs rapidly after transition from breeding to nonbreeding conditions. A, Number of Hu positive neurons in one hemisphere of HVC across the time course of regression. HVC neuron number drops by 7 d following transition to nonbreeding conditions. B, Number of apoptotic cells in HVC on one side of the brain over the time course of regression. Number of AC-3-positive cells peaks at 2 d following transition from breeding to nonbreeding conditions. Letters above bars indicate significant differences among groups (one-way ANOVA, Tukey post hoc pairwise comparisons). All data plotted as mean ± SEM. C, Representative image of AC-3 immunohistochemistry in fresh frozen tissue counter-stained for Nissl (cytoplasm stains light purple, nuclei stain dark purple) illustrating apoptotic cells in HVC. The arrow indicates an AC-3-positive cell (brown). Note the condensed chromatin (a distinctive feature of apoptotic cells; shown in dark purple) contained within the AC-3-positive cell.