On the Regulation of Arterial Blood Pressure by an Intracranial Baroreceptor
Authors: Chapman Pippa , Korsak Alla , Kellett Daniel , Marina Nephtali , Gourine Alexander 
Published: May 2024

Introduction: There is significant evidence for the existence of an intracranial baroreceptor mechanism(s) capable of sensing physiological changes in cerebral blood flow (Marina et al., 2020). However, little is known about the sensitivity of this mechanism to changes in brain perfusion and its interaction with inputs from the peripheral (arterial) baroreceptors. The aim of this study was to characterise the cardiovascular responses to physiological changes in cerebral perfusion induced by experimental manipulations of intracranial pressure (ICP). Methods: The experiments were performed in adult Sprague-Dawley rats (250–300 g), anesthetized with urethane (induction: 1.3 g kg−1, i.p.; maintenance: 10–25 mg kg−1 h−1, i.v.). The femoral artery and vein were cannulated for measurement of arterial blood pressure (ABP) and administration of anaesthetic. The trachea was cannulated, and the animal was mechanically ventilated. The lateral cerebral ventricles were cannulated and connected via saline-filled catheters to a pressure transducer to record ICP and to a “water column” to allow controlled manipulation of ICP. The experiments included the denervation of the arterial baroceptors, stimulation of the aortic depressor nerve and recording of renal sympathetic nerve activity. Results: The resting ICP in rats anesthetized with urethane was 6.2 ± 0.7 mmHg (n=8). Following a small craniotomy that reduced ICP to 0 mmHg, ABP decreased by 11.2 mmHg (n=6) within 30 min. Restoring the integrity of the intracranial space increased ABP to the baseline level. Progressive increases in ABP were observed in response to experimentally-induced increases in ICP by 5, 10, 15 and 20 mmHg, revealing a linear relationship between ICP and systemic arterial pressure within the physiological range of ICP changes. In the absence of inputs from the arterial baroceptors (bilateral sino-aortic denervation and vagotomy) the ABP responses to ICP increases were preserved. Analysis of the ABP and heart rate responses to the electrical stimulation of the aortic depressor nerve suggested baroreflex re-setting at raised ICP. Renal nerve recordings demonstrated increased sympathetic activity at raised ICP (172 ± 34.91 % at 20 mmHg ICP (p=0.003; n=7) with markedly enhanced bursts of activity during the inspiratory phase of the respiratory cycle. Conclusion: These data demonstrate that the intracranial baroceptor mechanism is highly sensitive to changes in cerebral perfusion within the physiological range and suggest that cerebral blood flow is an important determinant of systemic ABP. The data suggest that at raised ICP the baroreflex control of sympathetic vasomotor activity is reset and provides effective control of arterial blood pressure at a higher level required to compensate for reduced brain perfusion. Marina, N., Christie, I.N., Korsak, A., Doronin, M., Brazhe, A., Hosford, P.S., Wells, J.A., Sheikhbahaei, S., Humoud, I., Paton, J.F. and Lythgoe, M.F., 2020. Astrocytes monitor cerebral perfusion and control systemic circulation to maintain brain blood flow. Nature Communications, 11(1), 131. This PhD Studentship is funded by the British Heart Foundation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.