Optical Spectroscopy and Cerebral Vascular Effects of Alcohol in the Intact Brain: Effects on Tissue Deoxyhemoglobin, Blood Content, and Reduced Cytochrome Oxidase

Dose‐response effects of acute ethanol infusions were studied, noninvasively, in the unopened brain to examine the hypothesis that ethanol can induce stroke‐like events as a consequence of cerebral vasospasm and tissue ischemia. By using a single sending and receiving fiber, an optical backscatter measurement (500–800 nm) was used to monitor the levels of deoxyhemoglobin (DH), reduced cytochrome oxidase (rCO), and relative tissue blood content in a closed cranium preparation. Anesthetized rats were prepared by cannulating a branch of the internal carotid artery and subjected to either bolus infusions (1.25 or 2.5 μm ethanol in Ringers/g tissue) or to constant infusions of 5 or 10% ethanol at various rates (0.30–2.92 μm/g/min). To facilitate optical penetration, a portion of the left parietal cranium was shaved to a translucent appearance. Results showed that low, bolus doses of ethanol typically produced a slight increase (5–10%) in the oxyhemoglobin signal, indicating that vasodilation had probably occurred. Higher doses, however, produced a prompt and significant reduction in the hemoglobin signal, increased levels of DH, and a rise in rCO suggesting a vasoconstrictor response leading to ischemia had occurred, followed by recovery within 3–5 min. Constant infusions of ethanol produced a similar cerebral vascular response, in a dose‐related manner, but of a more sustained nature. At levels of 50–60% of the maximum bolus dose, the effect was more pronounced, accompanied by an increase in the levels of rCO (by 50–90%). Control experiments using identical volumes/flow rates of Ringers solution produced no significant alterations in the optical spectrum. Overall, these data indicate that, depending on dose: (a) ethanol can induce vasodilatory or vasoconstrictor effects in the intact brain; (b) the more pronounced effects involve vasospasm in the cortical microcirculation leading to global ischemia; and (c) optical measurements permit direct noninvasive assessment of the cerebral vascular effects of alcohol and, potentially, other substances of abuse