This study describes a closed cranial window technique that allows the observation and measurement of rat pial arterioles and venules in situ. The resolving power of this system is 1–2 μm. Using this sensitive technique, we characterized the responses to 7% carbon dioxide inhalation and adenosine in arterioles (10–70 μm) and venules (15–100 μm). During carbon dioxide inhalation, larger arterioles (>40μm) dilated more than smaller arterioles (<20 μm). There was limited vasoreac-tivity of pial venules during CO2 inhalation. Dilation of arterioles was initially observed with an adenosine concentration of 10−8 M. Almost a twofold increase in diameter was noted at 10−3 M. In contrast to the effect of CO2 inhalation, the degree of dilation with topical application of adenosine was not size dependent. Pial venules did not respond to adenosine. The technique for observation of pial vessels using the closed cranial window and for measurement of vessel diameter by video camera system microscopy is a powerful tool for studying in vivo the cerebral circulation in the rat.

Summary:We compared the effect of the acute applica tion of ethanol, methanol, I-propanol, I-butanol, urea, and mannitol (1-100 mM) on the basal tone of isolated cannulated rat intracerebral arterioles to determine if the response of these arterioles to ethanol could be attributed to alteration of membrane fluidity or changes in osmolal ity. These arterioles spontaneously developed tone to 62.0 ± 8.4% of passive diameter (44.2 ± 11.9 vs. 70.9 ± 14.7 fJ-m). Ethanol caused a dose-dependent reduction in arteriolar diameter starting at 3 mM (p = 0.03), reaching a diameter of 81.4 ± 3.0% of basal tone at 100 mM. In comparison, all other agents tested caused the arterioles to dilate, with the exception of I-propanol, which pro duced inconsistent vessel responses. At 100 mM concen tration, methanol, I-butanol, urea, and mannitol dilated