A pictorial representation of endogenous brain ATP by a bioluminescent method.

The layering of a luciferin-luciferase solution on brain slices makes endogenous ATP visible. Rat brains, frozen in situ and sliced at 16 micrometer thickness at a temperature of--15 degrees C, were fixed by a ternary mixture of ethanol, formalin and dioxane at--20 degrees C for 15 min, and dried at 40 degrees C for 12 h. Luciferin, luciferase and a small quantity of magnesium sulfate were dissolved into an arsenate buffer solution containing 1% polyvinylpyrrolidone, 2% gelatin and 1% glycerol. The solution was then frozen into a column, sliced at 40 micrometer thickness at--15 degrees C and placed on the precooled brain slice. A luminiferous luciferin-ATP reaction begins when the brain slice reaches room temperature and persists for more than 10 min. This technique therefore makes possible the optical and/or photographic determination of the endogenous concentration of brain ATP. Capability of the technique is also demonstrated.