Factors Affecting Performance of the Push-Pull Cannula in Brain.

摘要

Experiments were performed to study collection of material in vivo from brain tissue by the push-pull technique. Urea(-14)C was injected into the caudal thalamus of rats and local push-pull perfusions were carried out with concentric 20-gauge Gaddum perfusion cannulas. Signs of acute cellular destruction following perfusion were limited to the immediate region within 0.5 mm of the site. Uptake of urea per unit time from brain tissue was constant with perfusion rates up to around 80 microliters/min, after which the amount of urea collected fell. Increasing the distance that the inner cannula protruded beyond the outer up to around 0.75 mm resulted in an increased collection of urea. Beyond this distance no further increase was observed. The ratio of urea(-14)C in tissue to that in sequential perfusate samples in a given experiment remained constant over time in spite of the diffusion-dependent reduction of local tissue levels of urea(-14)C. This indicated that the levels of urea observed in the perfusate paralleled closely the amount known to be in the tissue, substantiating the ability of the push-pull cannula to reflect ongoing changes in the local concentration of a nonspecific marker in brain. (Author)