Monitoring Extracellular Glutamate in the Brain by Microdialysis and Microsensors

Recording basal levels of extracellular glutamate by microdialysis in the brain of freely moving animals is of limited value as the result does not fulfill the criteria of synaptic origin (TTX or calcium dependency). In this chapter we discuss whether the recently developed microsensor technique provides an alternative for sampling glutamate by microdialysis. Although glutamate microsensors show advantages in dimensional and temporal resolution, the properties of the detected glutamate do not differ basically from glutamate in microdialysate. The results suggest that glutamate detected by both microdialysis and microsensoring methods is closely regulated by non-neuronal cells. However, there is some evidence that evoked glutamate release recorded by microsensors (e.g., by elevated potassium or behavioral simulation), in the time frame of seconds, might reflect neuronal release.