Changes in cerebrospinal fluid pressure and outflow from the lateral ventricles during development of congenital hydrocephalus in the H-Tx rat.

Rats from the H-Tx strain develop hydrocephalus at 19 or 21 days gestation, and were used to measure cerebrospinal fluid pressure and resistance to absorption at different ages between 19 days gestation and 21 days after birth. The results were compared with earlier experiments on normal rats from a different strain. The resting pressure of cerebrospinal fluid in the lateral ventricles of hydrocephalic rats was not elevated above normal up to 10 days after birth, but by 21 days the pressure was nearly twice that of normal rats. Resting pressure measured from the cisterna magna was not significantly different from lateral ventricle pressure. In hydrocephalic rats the resistance to outflow from the lateral ventricles measured by constant-rate infusion, was the same as for normal rats at 19 days gestation but subsequently increased to a value above normal at 1 day after birth. This high resistance was maintained throughout the postnatal period without the postnatal decline seen in normal rats. Resistance to absorption from the cisterna magna, on the other hand, was similar to that in normal rats of the same age. Thus the results of these experiments showed that in the H-Tx strain, cerebrospinal fluid pressure increased only in the late stages of hydrocephalus and that the condition is associated with a reduction in outflow from the ventricular system.