Physiological Fluctuations in Brain Temperature as a Factor Affecting Electrochemical Evaluations of Extracellular Glutamate and Glucose in Behavioral Experiments

The rate of any chemical reaction or process occurring in the brain depends on temperature. While it is commonly believed that brain temperature is a stable, tightly regulated homeostatic parameter, it fluctuates within 1-4 degrees C following exposure to salient arousing stimuli and neuroactive drugs, and during different behaviors. These temperature fluctuations should affect neural activity and neural functions, but the extent of this influence on neurochemical measurements in brain tissue of freely moving animals remains unclear. In this Review, we present the results of amperometric evaluations of extracellular glutamate and glucose in awake, behaving rats and discuss how naturally occurring fluctuations in brain temperature affect these measurements. While this temperature contribution appears to be insignificant for glucose because its extracellular concentrations are large, it is a serious factor for electrochemical evaluations of glutamate, which is present in brain tissue at much lower levels, showing smaller phasic fluctuations. We further discuss experimental strategies for controlling the nonspecific chemical and physical contributions to electrochemical currents detected by enzyme-based biosensors to provide greater selectivity and reliability of neurochemical measurements in behaving animals.