Cerebral Blood Flow Regulation Assays

CBF recordings were started after arterial pressure and blood gases were stable. To test functional hyperemia, the CBF response evoked by gently stroking the whiskers with a cotton-tipped applicator for 60 sec was recorded. To test endothelium-dependent vasodilatation, acetylcholine (10 µM, Sigma), the Ca²⁺ ionophore A23187 (3 µM; Sigma) or bradykinin (50 µM; Sigma) was topically superfused for 3–5 min and the evoked CBF increases recorded. To test smooth muscle function, the CBF responses to adenosine (400 µM, Sigma) or to the NO donor S-Nitroso-N-acetyl-DL-penicillamine (SNAP; 50 µM, Sigma) were examined [25 (link), 30 (link), 36 (link)]. All pharmacological agents were dissolved in a modified Ringer’s solution [35 (link)]. The increase in CBF produced by hypercapnia was tested by introducing 5% CO₂ in the ventilator to increase arterial pCO₂ up to 50–60 mmHg. Once a stable increase in CBF was obtained for 3–5 min, pCO₂ was returned to normocapnia.