Since these IRs are not significantly altered by DT treatment in the dorsal or ventral hilus in controls (Figure S2B), and there is no difference among control genotypes in number of hilar GluA2/3-, CR-, and neuropeptide Y (NPY)-positive cells (Figure S2C),
we combined data from our three control genotypes (Cre, fDTR, and B6 wild-type) to form our combined control (control) group. In mutants 1 week after DT treatment, the number of GluA2/3-positive cells in the hilus of the dorsal hippocampus decreases to 26.1%, and by 4 weeks after Selleck LDN193189 treatment to 9.5% compared to numbers in DT-treated controls (Figures 3B to 3D). Similarly, the number of GluA2/3-positive cells in the ventral hilar region in mutants decreases selleck compound to 27.9% of that in controls by week one and to
10.5% by week four following DT treatment. The number of CR-positive hilar cells in mutants decreases by week one to 79.9% and by week four to 6.7% compared to levels found in controls. By contrast, 4 weeks after DT treatment mutants show no obvious effect on the interneuron marker NPY-IR in the dorsal or ventral hilus (Figures 3C and 3D). Different rates of reduction in GluA2/3- and CR-positive hilar cells following DT treatment may arise from variability in protein degradation. While GluA2/3- and CR-positive mossy cells mostly overlap (Figure S2A; see Fujise et al., 1998), 1 week after DT treatment the number of GluA2/3- and CR-positive ventral
hilar cells originating from the same mutant out brain tissues varies widely (Figure 3B). In contrast, DT treatment does not obviously affect the interneuron marker NPY-IR in the dorsal or ventral hilus in mutants (Figures 3C and 3D). Since hilar neurodegeneration is already prominent one week after DT treatment (Figures 2 and 3A), loss of GluA2/3 mossy-cell-marker labeling is likely to be a signature of mossy cell neurodegeneration. If so, our results show that in mutants, ∼75% of mossy cells are selectively degenerated 7 days after DT treatment and ∼90% by 4 weeks post-DT. To assess the acute effects of functional mossy cell loss, we performed experiments at 4–11 days (acute phase), and to assess the chronic effects, at 4–6 weeks (chronic phase) after DT treatment. Cre-recombination also occurs in CA3c pyramidal neurons (Figures 1A and S1A), whose axons may project, either directly or via mossy cells, to dentate granule cells (Scharfman, 2007; Wittner et al., 2007).