neuronal phenotype (Figure 5a). Also, a slight but significant increase was observed in the percentage of cells that did not colabel for either NeuN or GFAP, labeled as “other.” Two recent reports in adults suggest that these cells could be either microglia (Nixon et al., 2008) or undifferentiated cells (He et al., 2009). The cell phenotype percentages observed are similar to that reported in adolescent and juvenile rodents (Crews et al., 2006b; Ibi et al., 2008; Qiu et al., 2007) but remain consistently higher than that typically reported in adult rats (Nixon and Crews, 2004). The slightly lower percentage of glial differentiation observed in the current study may be due to GFAP and BrdU labeling different aspects of the cell (filaments versus nucleus) and therefore our conservative approach to analyzing colabeling could have biased the percentage of GFAP-labeled BrdU+ cells downward. Regardless, the majority of newborn cells become new neurons regardless of treatment.
