Fig 1: Decreased insulin does not alter OSN proliferation but increases apoptotic cell death in immature neurons. A, Representative coronal sections of nasal septa stained with anti-Ki67 antibody for control and STZ mice 3, 7, 14, and 28 d after methimazole-induced injury. Arrowheads indicate Ki67-positive cells. Scale bar: 50 µm. B, Density of Ki67-positive cells in the nasal septa of control and STZ mice 3, 7, 14, and 28 d after methimazole-induced injury. Two-way RM ANOVA with Bonferroni’s post hoc correction, day: F(1,15) = 33.87, p < 0.001; STZ treatment: F(1,15) = 14.25, p = 0.002; interaction: F(1,15) = 0.15, p = 0.858. No significant differences in the numbers of Ki67-positive cells were observed between control and STZ mice [d3: p = 1.000, 3 mice (control) vs 3 mice (STZ); d7: p = 1.000, 2 mice (control) vs 3 mice (STZ); d14: p = 1.000, 3 mice (control) vs 3 mice (STZ); d28: p = 1.000, 3 mice (control) vs 3 mice (STZ); n.s., not significant; Bonferroni’s post hoc test]. Data points represent the value in the analyzed areas of OE (8 areas/mouse). C, Representative coronal sections of nasal septa stained with anti-activated caspase-3 antibody for control and STZ mice 7, 14, and 28 d after methimazole-induced injury. Arrowheads indicate activated caspase-3-positive cells. Scale bars: 50 µm. D, Density of activated caspase-3-positive cells in the nasal septa of control and STZ mice 7, 14, and 28 d after methimazole-induced injury. Two-way RM ANOVA with Bonferroni’s post hoc correction, day: F(2,34) = 154.62, p < 0.001; STZ treatment: F(1,17) = 316.92, p < 0.001; interaction: F(1,17) = 148.56, p < 0.001. The susceptibility to apoptosis of new OSNs in STZ mice was greatest on day 14 (n = 3 mice; ***p < 0.001; Bonferroni’s post hoc test). On days 14 and 28, the total numbers of caspase-3-positive cells in STZ mice were significantly higher than those in control mice (n = 3 mice; ***p < 0.001; Bonferroni’s post hoc test). Data points represent the value in the analyzed areas of OE (8 areas/mouse). E, Representative coronal sections of nasal septa stained with anti-activated caspase-3 (red) and anti-OMP (green) or anti-GAP43 (green) antibodies 14 d after methimazole-induced injury in STZ mice. The majority of activated caspase-3-positive cells (white arrowheads) were costained not by the anti-OMP but by the anti-GAP43 antibody. Scale bar: 20 µm.