ENERGY METABOLISM IN THE BRAIN

ENERGY METABOLISM IN THE BRAIN

by Abhishek

COURSE REVIEWS


COURSE DETAILS

Studies of glucose metabolism in the brain reflect a dichotomy due to the fact that the complex, integrating functions of the brain can only be stud- ied in the intact, functioning brain in the conscious individual (human or animal), whereas properties of brain cells, cell-cell interactions, and mech- anisms are most readily evaluated in vitro under controlled conditions us- ing brain slices, subcellular fractions or purified, isolated cells of different types. In viuo studies have most commonly been done in studies with labeled [email protected] (DG) or 2-fluorodeoxyglucose (FDG). “1maging”with DG revolutionized investigations of correlations between brain function and brain metabolism (Sokoloff et aZ., 1977)) because this glucose analog enables local functional analysis of hexokinase activity in viva, from which local rates of glucose utilization can be calculated under steady-state conditions. On the other side, it is becoming overwhelmingly clear that such studies repre- sent only one aspect of brain function, i.e., the “big picture,” identifying the pathways and magnitude of functional metabolic activities; the underlying contributions of different cells and cell types in the brain are not identified and quantified, and the character of the energy-requiring processes are not determined. Brain cells can behave metabolically in very different manners in response to various stimuli and interact so that one cell type may gener- ate a glucose metabolite (e.g., glutamate or lactate), which then undergoes “metabolic trafficking” to sustain function, to be further metabolized in a different cell type, or even to leave the activated area. These heterogeneous interactions have the consequence that imaging of overall brain metabolism cannot provide a picture of glucose metabolism at the cellular level. A variety of in vitro methods have been used to assess metabolic activities