Staining of PO2 measuring points demonstrated for the rat brain cortex.

A combined physiological and histological technique was developed in order to determine the exact position of the tip of a microelectrode used for PO2 measurements within the rat brain cortex. Using this method it was possible both to identify the tissue layer where PO2 measurements had been performed as well as obtain information about the blood capillaries within the surrounding tissue. After the PO2 had been measured small quantities of dye (Alcian Blue 8 GX) were injected through a micropipette attached to the PO2 microelectrode (tip-tip distance 2-5 micron). Subsequently the tissue was fixed by perfusion, 5 micron sections were cut and stained with Cresylviolet. The points where measurements had been made could be seen under a light microscope as green coloured spots of about 100 micron in diameter. The capillary pattern could be demonstrated by silver nitrate perfusion. Information about the capillaries, such as length, distance and the gas exchange surface were obtained via computer analysis of a television image. This method was used to analyse the O2 supply of the optical cortex of the rat. Correlation of the local PO2 distribution with the capillary data revealed differences between the archi- and the neocortex of the rat brain.