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 (CSF) 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, whereas slower waves were detected by thresholding, characterized with principal component analysis, and modeled to estimate amplitude and duration. In five 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 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, whereas 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.NEW & NOTEWORTHY This study demonstrates that intracranial pressure (ICP) in healthy rats contains reproducible slow oscillations resembling human B-waves, with timing differences indicating ventricular origin and outward propagation through CSF spaces. These findings provide direct physiological evidence that B-like waves are intrinsic features of normal CSF dynamics rather than purely pathological signals, supporting a neurogenic contribution to ICP regulation and establishing rats as a tractable model for studying their underlying mechanisms.