TuJ1+ and GABA+ neurons derived from postnatal CA1 and CA3 subfield neurospheres are indeed derived from cells that proliferated in neurosphere cultures, which was evidenced through incorporation of BrdU by these cells when grown in a proliferation medium containing 0.5 μM BrdU. Figures A1-A4 illustrate BrdU labeling in Tuj1+ neurons derived from CA1 subfield neurosphere cells of PND4 (A1, A2) and PND12 (A3, A4) hippocampi. Figures B1-B4 show BrdU labeling in Tuj1+ neurons derived from CA3 subfield neurosphere cells of PND4 (B1, B2) and PND12 (B3, B4) hippocampi. Figures C1-D3 illustrate BrdU labeling in GABA-ergic interneurons derived from CA1 subfield neurosphere cells of PND4 hippocampus (C1-C3) and CA3 subfield neurosphere cells of PND12 hippocampus (D1-D3). Scale bars, A1-B4 = 200μm; C1-D3 = 50μm.