 In addition, glutamate plays important roles in the regulation of growth cones and synaptogenesis during brain development as originally described by Mark Mattson.Extracellular glutamate in "Drosophila" brains has been found to regulate postsynaptic glutamate receptor clustering, via a process involving receptor desensitization.A gene expressed in glial cells actively transports glutamate into the extracellular space, while, in the nucleus accumbens-stimulating group II metabotropic glutamate receptors, this gene was found to reduce extracellular glutamate levels.