Reactivity of Rat Pial Arterioles and Venules to Adenosine and Carbon Dioxide: With Detailed Description of the Closed Cranial Window Technique in Rats

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.