An improved Percoll density gradient for measurements of experimental brain edema. Addition of sucrose to an isotonic gradient in an attempt to balance osmotic conditions during density determinations.

Microgravimetric methods are very useful for quantitative studies on brain edema. One of the techniques available is based on a gradient made up by NaCl and polyvinyl pyrrolidone-coated silica particles (Percoll). The present study was performed to find a way of minimizing fluid shifts between the gradient and the samples. For this purpose, five Percoll density gradients containing various concentrations of sucrose in isotonic saline were prepared. Equivalent samples of normal mouse brain were then added and their second slow movement (drift) indicating interactions between the tissue and the gradient was followed. A concentration of 0.125 M sucrose eliminated the drift of the samples almost entirely. The capacity of this sucrose-containing gradient to reveal brain edema was then evaluated by comparing the density values obtained with those measured in the traditional bromobenzene-kerosene gradient as described by Nelson et al. (1971). For this purpose, we produced in the mouse an acute cytotoxic edema by triethyltin intoxication and a vasogenic edema by a cortical cryogenic injury. The two gradients showed almost identical results. We conclude, therefore, that the 0.125 M sucrose-containing Percoll gradient is a very good alternative to bromobenzene-kerosene gradients used for brain density determinations. Furthermore, Percoll gradients are very stable and contain only non-toxic ingredients.