Abstract
Taking the “initial dip” into cellular mechanisms of neurovascular coupling
Highlights
Neuronal activation and regional cerebral blood flow are tightly linked by physiological mechanisms that are still not fully understood
Functional hyperemia, or the increased regional cerebral blood flow (CBF) that occurs on neuronal activation, serves as the basis of functional brain imaging techniques [1,6], for example, positron emission tomography (PET) and functional magnetic resonance imaging, that detect signal changes related to various aspects of brain hemodynamic response (HDR): changes in CBF, cerebral blood volume (CBV), and blood oxygenation level
At the risk of oversimplification, the hypothesis can be summarized through the following sequence of events: 1) Neuronal activation intensifies the uptake of potassium and glutamate into astrocytes
Summary
“One is forced to conclude that a more likely explanation will emerge from future research that examines the manner in which a change in blood flow may regulate an effect of the activity change [1]”. Cessation of neuronal activation is hypothesized to be associated with the return of perivascular tone to baseline due to the capacity of astrocytes to homeostasis This suggests that activated capillaries will further distend under present ILP in response to restored relaxed compliance of the vessel wall, and their resistance to flow will drop. The capillaries of activated neurovascular units are considered as the system “plant” which is perturbed by the functional modulation of perivascular tone, while the upstream arterial vasculature is regarded as the controller that responds to the error signal (vasoactive mediators) “measured” by interactions of the flowing red cells with capillary endothelium (sensors) in the “plant.” It must be remembered that the diagram is oversimplified, whereas the hypothesized “real control system” is heterogeneous and distributed, its settled states and responses are determined by the intricate interplay of various system parts and compartments. To flow in capillaries increases because they become less distended by a decreased transmural pressure gradient (ILP-ICP), and, from this point, the cerebral autoregulatory response and the functional hyperemic response develop further along the same basic scenario, notwithstanding the difference in systemic/regional CBF involved
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