Developmental changes in cerebrospinal fluid pressure and resistance to absorption in rats

Abstract

Cerebrospinal fluid (c.s.f.) pressure and resistance to absorption have been studied in exteriorised fetuses (18 to 21 days gestation) from pregnant rats anaesthetised with pentobarbitone and in similarly anaesthetised postnatal rats at 1, 5, 10 and 30 days after birth and in adults. The resting c.s.f. pressure was low in fetuses (17–21 mm H 2O) and it rose to 26–27 mm H 2O at 1 and 5 days after birth. By 10 days after birth the pressure was 34 mm H 2O after which time there was no further change. The plateau pressure response to different infusion rates was linear, but only up to pressures around 7-fold higher than the resting c.s.f. pressure. Hence, resistance to absorption was calculated for plateau pressures up to 140 mm H 2O in fetuses, to 200 mm H 2O in 1- and 5-day rats and to 240 mm H 2O for 10-day, 30-day and adult rats. Resistance to absorption was not significantly different for the two measurement sites (lateral ventricle and subarachnoid space) at any age studied, showing that fluid can move freely through the ventricular system in young rats. The resistance to absorption was low in the fetuses, 10.8 and 16.3 mm H 2O min/μl at 18–19 and 20–21 days gestation, respectively. There was a sharp increase in resistance to 39.2 mm H 2O min/μl at 1 day after birth and thereafter there was a decrease to 6.8 mm H 2O min/μl at 30 days and this was similar to adult values. This decrease in outflow resistance from the first day after birth may be related to the increase in c.s.f. pressure and secretion rate that occur after birth in the rat.