Experiment 1: VV was measured 30 minutes and 24 hours following acute intraventricular injection of 10kD dextran solution yielding a range of CSF osmolarities spanning an order of magnitude. Results are expressed as a percentage relative to normalized VVs measured prior to ventricular injection. VVs were significantly increased for all groups at 30 minutes post-injection (P < 0.037), with highly significant increases for Groups III (977 mOsm/L), IV (2000 mOsm/L) and V (3347 mOsm/L) (P < 0.007). These increases in VV were completely resolved by 24 hours post-injection. Significant differences in VV between groups were not observed either pre-injection or 24 hours post-injection. At 30 minutes post-injection, there is a positive correlation (R2 = 0.8349) between increased CSF osmolarity and VV. (* P < 0.05, ** P < 0.01).