Peg 4

In vivo microdialysis sampling of brain interstitial fluid (ISF) tau was performed as described previously^{7 ,21 (link),22 (link)}. The microdialysis probe had a 4 mm shaft with a 3.0 mm, 1000 kDa molecular weight cutoff (MWCO) polyethylene membrane (PEP-4-03, Eicom, Japan). Before use, the probe was conditioned by briefly dipping it in ethanol, and then washed with an artificial cerebrospinal fluid (aCSF) perfusion buffer (in mM: 122 NaCl, 1.3 CaCl₂, 1.2 MgCl₂, 3.0 KH₂PO₄, 25.0 NaHCO₃) that was filtered through a 0.2 μm pore-size membrane. The preconditioned probe's outlet and inlet were connected to a peristaltic pump (ERP-10, Eicom) and a microsyringe pump (ESP-32, Eicom), respectively, using fluorinated ethylene propylene (FEP) tubing (φ 250 μm i.d.).
Probe implantation was performed as previously described^{22 (link)}, with slight modifications. Briefly, the animals were anesthetized with isoflurane, while a guide cannula (PEG-4, Eicom) was stereotactically implanted in the hippocampus (bregma -3.1 mm, -2.5 mm lateral to midline, -1.0 mm ventral to dura at a 12° angle). Three days after the implantation of the guide cannula, the mice were placed in a standard microdialysis cage and a probe was inserted through the guide. ISF samples were collected at a flow rate of 0.5 μl/min.