Intracranial hypertension after cerebroventricular infusions in conscious rats.

Cerebrospinal fluid (CSF) pressure (PCSF) was recorded in conscious, relatively unrestrained, and freely behaving rats during a 24-h infusion of artificial CSF (25% synthesis rate) into one lateral ventricle or divided equally into both lateral ventricles. Fourier analysis of PCSF of uninfused rats showed a circadian rhythm; nighttime PCSF was higher (P less than 0.01) than daytime. Unilateral and bilateral infusions did not affect PCSF during the first 2 h, but it then increased in an exponential manner, doubling (P less than 0.01) in both groups by 4 h. The induced intracranial hypertension stabilized at 4 h in unilaterally infused rats, but the PCSF increased further in the bilateral group, so that the overall pressure for 24 h was higher (P less than 0.01. No symptoms emerged in uninfused or unilateral infused rats after 24 h, however, 5 of 13 bilaterally infused rats displayed neurological symptoms (P = 2.4%). These low-volume, long-term infusions may be a model of intracranial hypertension. One explanation for the PCSF increase is that artificial CSF diluted neurochemical control systems beyond autoregulatory capacity. This hypothesis accommodates the exacerbated PCSF rise in bilaterally infused rats, since the same volume bathed a larger ependymal-choroidal surface area.