Determination of Cerebral Glucose Use in Rats Using [14C]Glucose

The postulate that useful information about the activity of cerebral tissue can be deduced from a measure of energy metabolism, as reflected by the cerebral metabolic rate of glucose (CMRglc), is supported by a considerable body of data. Because there are adequate reviews of this subject (e.g., Sokoloff, 1981), it will not be further considered. The purpose of this chapter is to explain how CMRglc may be measured in the laboratory rat with a natural isotope, [6-¹⁴ C]glucose. The reasons for using [6-¹⁴ C] glucose are that the experimental period may be as brief as 5 min (enabling the study of short-lived states), the isotope behaves kinetically exactly as glucose and no correction factors are necessary, and label from [6-¹⁴ C] glucose is almost completely trapped in brain tissue in short experimental periods (i.e., 10 min or less). Whereas [6-¹⁴ C]glucose measures total CMRglc, the use of [l-¹⁴ C]glucose instead enables determination of only energy metabolism, without the contribution of the hexose monophosphate shunt, as explained below.