Micropipette

IVP measurements were performed as previously described [5 (link),19 (link)]. Briefly, mice were anesthetized with 100 mg/kg ketamine (Pfizer, New York, NY, USA) and 10 mg/kg xylazine (Bayer, Leverkusen, Germany) and immobilized, in prone position, in a stereotaxic device (Stoelting, St. Louis, MO, USA). A 34-gauge micropipette (Hamilton, Reno, NV, USA) filled with artificial CSF (aCSF) was placed in the parietal cortex above the lateral ventricle (from bregma in mm: anteroposterior, −0.2; lateral, +1.0; and ventral, −1.0). Then, the micropipette was inserted into the lateral ventricle through the cerebral cortex and a syringe pump (KD Scientific, Holliston, MI, USA) was used to perfuse the aCSF into the ventricles at an infusion rate of 0.3 μL/min. The micropipette was connected to a pressure transducer (TSD104A; Biopac Systems, Goleta, CA, USA) using noncompliant tubing interfaced to a recording system (model MP150; Biopac Systems, Goleta, CA, USA). Once the pipette entered the brain parenchyma, the pressure gradually increased; when the pressure was >40 cm H₂O, the infusion was stopped and the pipette was slowly advanced. The pressure dropped promptly when the pipette tip reached the lateral ventricle. Then, IVP was continuously monitored and recorded.

IVP was measured using a 34-gauge micropipette (Hamilton, Reno, NV, USA) filled with artificial CSF (aCSF), which was inserted into the lateral ventricle through the cerebral cortex (see Figure 3A) as previously shown [13 (link),19 (link)]. The micropipette was coupled to a pressure transducer and communicated with a recording system (Biopac Systems, Goleta, CA, USA). Briefly, animals were anesthetized and immobilized in a stereotaxic device (Stoelting, Wood Dale, IL, USA). The micropipette, with an aCSF (120 mM NaCl, 3 mM KCl, 0.6 mM NaH₂PO₄, 0.8 mM MgSO₄, 18 mM NaHCO₃, 10mM glucose, 1.1 mM CaCl₂; 7.4 pH) infusion rate of 0.3 μL/min [by a syringe pump (KD Scientific, Holliston, MA, USA)], was placed in the parietal cortex above the lateral ventricle (from bregma in mm: anteroposterior, −0.2; lateral, +1.0; and ventral, −1.0). When the pipette reached the parietal cortex, the pressure gradually rose. Once the pressure was >50 cm H₂O, the infusion was stopped and the pipette was slowly advanced. The pressure fell promptly when the micropipette reached the lateral ventricle. Henceforth, IVP was recorded. A detailed example of an in vivo record of IVP, and the procedure used to infer the CSF outflow and ventricular compliance (see Section 2.5) is shown in Figure S2. IVP values were analyzed using Matlab software (Mathworks, Natic, MA, USA).