OPTICAL SPECTROSCOPY AND CEREBRAL VASCULAR EFFECTS OF ALCOHOL IN THE INTACT BRAIN - EFFECTS ON TISSUE DEOXYHEMOGLOBIN, BLOOD CONTENT, AND REDUCED CYTOCHROME-OXIDASE
Rl. Barbour et al., OPTICAL SPECTROSCOPY AND CEREBRAL VASCULAR EFFECTS OF ALCOHOL IN THE INTACT BRAIN - EFFECTS ON TISSUE DEOXYHEMOGLOBIN, BLOOD CONTENT, AND REDUCED CYTOCHROME-OXIDASE, Alcoholism, clinical and experimental research, 17(6), 1993, pp. 1319-1324
Dose-response effects of acute ethanol infusions were studied, noninva
sively, in the unopened brain to examine the hypothesis that ethanol c
an induce stroke-like events as a consequence of cerebral vasospasm an
d tissue ischemia. By using a single sending and receiving fiber, an o
ptical backscatter measurement (500-800 nm) was used to monitor the le
vels of deoxyhemoglobin (DH), reduced cytochrome oxidase (rCO), and re
lative tissue blood content in a closed cranium preparation. Anestheti
zed rats were prepared by cannulating a branch of the internal carotid
artery and subjected to either bolus infusions (1.25 or 2.5 mu M etha
nol in Ringers/g tissue) or to constant infusions of 5 or 10% ethanol
at various rates (0.30-2.92 mu M/g/min). To facilitate optical penetra
tion, a portion of the left parietal cranium was shaved to a transluce
nt appearance. Results showed that low, bolus doses of ethanol typical
ly produced a slight increase (5-10%) in the oxyhemoglobin signal, ind
icating that vasodilation had probably occurred. Higher doses, however
, produced a prompt and significant reduction in the hemoglobin signal
, increased levers of DH, and a rise in rCO suggesting a vasoconstrict
or response leading to ischemia had occurred, followed by recovery wit
hin 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 5
0-90%). Control experiments using identical volumes/flow rates of Ring
ers solution produced no significant alterations in the optical spectr
um. Overall, these data indicate that, depending on dose: (a) ethanol
can induce vasodilatory or vasoconstricter effects in the intact brain
; (b) the more pronounced effects involve vasospasm in the cortical mi
crocirculation leading to global ischemia; and (c) optical measurement
s permit direct noninvasive assessment of the cerebral vascular effect
s of alcohol and, potentially, other substances of abuse.