CSF pressure in fetal mice in utero: External factors pressurize the intraventricular space

Previous experiments inducing leakage of embryonic cerebrospinal fluid (CSF) suggest the necessity of intraventricular CSF pressure (PCSF) for brain morphogenesis. Nevertheless, how embryonic PCSF occurs is unclear, especially in utero. Using a Landis water manometer, we measured PCSF in fetal mice isolated from the amniotic cavity (PCSF-ISO). At embryonic day (E) 13, PCSF-ISO was 82.7 Pa. Intraventricular injections of [≥]2 l of saline elevated PCSF-ISO by [~]30%. Intraventricularly injecting inhibitors of CSF secretion decreased PCSF-ISO by [~]30%. Shh-mediated cerebral-wall expansion and the resulting ventricular narrowing did not significantly increase PCSF-ISO. Removal of the brain-surrounding contractile tissues decreased PCSF-ISO by 80-90%. The intraamniotic pressure measured in utero (PAF-IU) was 1030.7 Pa. Our direct measurement revealed that the PCSF in utero (PCSF-IU) was 1076.4 Pa, confirming the susceptibility of PCSF to external factors. Subsequent PCSF measurements under hydrostatic pressure loading suggested that PCSF-IU = PCSF-ISO + PAF-IU, a relationship further used to estimate PCSF-IU at other ages when direct measurement was not possible. The estimated PCSF-IU decreased almost constantly from E10 to E16 (2000 500 Pa).