Mechanism of delayed intracranial hypertension after cerebroventricular infusions in conscious rats

Prior studies showed that cerebroventricular infusions of artificial cerebrospinal fluid, 8 μl/min for 10 min, followed by a 10 min rest and a 24 h infusion of 0.5 μl/min, raised cerebrospinal fluid pressure (CSFp) of conscious, unrestrained rats after about 2 h. Here, we report that the 10 min infusion alone evoked a delayed, prolonged rise in CSFp. Pressure during the infusion itself rose and recovered quickly, as is usually reported. Pressure/volume tests, used to calculate resistance to outflow (R_o) and compliance (C), revealed that infusions increasedR_o and decreasedC, after a delay (P < 0.05). The rise in CSFp after infusion was blocked by pretreatment with acetazolamide + ouabain (P < 0.05), but the delayed changes in R_o andC were unaffected. We suggest that the 10 min infusion of a sterile, balanced salt solution has a primary effect that increasesR_o; as CSF synthesis continues, C is exhausted and the delayed rise in CSFp ensues. This non-traumatic method of raising CSFp may be a useful method to study intracranial fluid dynamics.