Fig. 3.

Chronic selenate treatment improves the phenotype of P301L mutant tau transgenic pR5 mice. (A) Amygdala-dependent CTA is impaired in untreated (control) 12-month-old pR5 mice, as indicated by equal saccharine and water consumption; WT mice remember the nausea associated with saccharine consumption during conditioning and hence, consume less saccharine. Treatment of pR5 mice with selenate for 4 mo reverts CTA to WT levels (*P < 0.05 vs. pR5 control/WT). (B) Immunohistochemistry (IHC) for human tau (HT7, red) and phospho-tau (pS422, green) shows pS422 staining only in pR5 control CA1 neurons (yellow merge), although HT7 staining is similar in control and selenate-treated pR5. (Scale bar, 50 μm.) (C) Extraction of brain tissue with buffers of increasing stringency shows reduction of both tau phosphorylation (pS422) and levels of insoluble human tau (HT7, FA fraction) in selenate-treated compared with control pR5 mice. Total levels of soluble human tau, extracted in salt- (RAB), and detergent-containing (RIPA) buffers, are similar in control and selenate-treated pR5 brains. Gapdh and actin show loading. Quantified band intensities are presented as fold of control (*P < 0.05; **P < 0.001). (D) Similarly, extraction of sarkosyl-soluble (sol) and -insoluble (insol) proteins shows a significant reduction in tau phosphorylation at multiple sites (pS422, AT8, AT270) and levels of insoluble human tau (HT7). Gapdh shows loading. Quantified band intensities are presented as fold-changes of control (*P < 0.05; ***P < 0.0001). (E) IHC with pS422 stains numerous neurons in control pR5 amygdala, but rarely in selenate-treated pR5 brains. (Scale bar, 50 μm.) (F) Accordingly, numbers of Gallyas-silver positive NFTs are 6.04-fold reduced in selenate-treated compared with control pR5 brains (*, P < 0.001). (Scale bar, 50 μm.)