AQP1 and Hydrocephalus: To further explore connections between the pathogenesis of hydrocephalus and CP in Ptpn20−/− mice, we compared aquaporin 1 (AQP1), sodium–potassium adenosine triphosphatase (Na+/K+-ATPase), and Na-K-Cl cotransporter (NKCC1) expressions in the CP, as proteins involved in the secretion or absorption of CSF.