Characterization of intracranial pressure variations in ventricular and subarachnoid spaces of the rat brain

Intracranial pressure (ICP) is a dynamic physiological signal shaped by cerebrospinal fluid flow, vascular pulsations, and brain tissue compliance, yet most knowledge of CSF (cerebrospinal fluid) hydrodynamics comes from pathological states in humans. To better understand physiological ICP variability, dual recordings were obtained in 15 healthy anesthetized Brown-Norway rats using pressure sensors connected to cannulas in the lateral ventricle (vICP) and subarachnoid space (sICP). Spectral analysis quantified cardiac and respiratory oscillations, while slower waves were detected by thresholding, characterized with principal component analysis, and modeled to estimate amplitude and duration. In 5 animals, intracranial hypertension was induced via ventricular fluid infusion. Mean pressures differed slightly, but not significantly, between compartments (vICP 6.05 ± 0.90 mmHg vs. sICP 5.90 ± 0.90 mmHg, p = 0.06). Both sites showed rapid cardiac and respiratory fluctuations without measurable delay. Slower B-like waves were also present but peaked earlier in vICP than sICP (1.2 ± 0.7 s). These waves had a larger amplitude and shorter duration in vICP (0.51 ± 0.22 mmHg; 7.5 ± 2.1 s) than in sICP (0.29 ± 0.09 mmHg; 10.7 ± 3.4 s). During ICP elevation, B-like waves increased in amplitude in both compartments and shortened in duration in vICP, while their occurrence rate remained unchanged. These findings demonstrate compartment-specific ICP dynamics in rats and indicate that B-like waves originate in the ventricles before propagating outward, supporting a localized neurogenic mechanism and establishing the rat as a useful model for studying the physiological basis and function of B-waves in CSF homeostasis.