Methods in laboratory investigation. Identification and evaluation of histopathology at microelectrode puncture sites.

Tissue puncture techniques using microelectrodes for various measurements have been criticized for producing undetermined degrees of tissue damage. Therefore, a method permitting routine identification of puncture tracks was developed to determine local microelectrode-induced injury. Rabbits were anesthetized and the femoral arteries surgically exposed. A 3-ml mixture of saline-India ink suspension was introduced through an ear vein. Oxygen-sensitive (pO2) microcathodes were advanced into and through the arterial wall at 10- or 20-micron intervals using a stepping microdrive to 150 to 450 micron and then withdrawn. The arteries were fixed in 10% formalin and gelatin embedded, and serial frozen sections (less than or equal to 15 micron) of the microelectrode puncture area were made. We observed within 5 minutes of microcathode withdrawal a dark, punctate, microscopic discoloration within the arterial wall. Histologically, ink distribution within the arterial wall demonstrated an acute permeability change: puncture depths generally less than 300 micron showed ink-lined microelectrode tracks (generally less than 2 micron wide) in the media, and greater puncture depths showed local hemorrhage and focal laminar accumulation of ink which extended from the track. The immediate adjacent area to microelectrode puncture depths less than 300 micron showed an apparent intact internal elastic lamina and media. Therefore, microelectrode damage has been shown to be primarily limited to microelectrode tissue tracks.