Glutamic acid
Glutamate is also a neurotransmitter (see below), which makes it one of the most abundant molecules in the brain. Malignant brain tumors known as glioma or glioblastoma exploit this phenomenon by using glutamate as an energy source, especially when these tumors become more dependent on glutamate due to mutations in the gene "IDH1".
Perineuronal net
PNNs appear to be mainly present in the cortex, hippocampus, thalamus, brainstem, and the spinal cord. Studies of the rat brain have shown that the cortex contains high numbers of PNNs in the motor and primary sensory areas and relatively fewer in the association and limbic cortices. In the cortex, PNNs are associated mostly with inhibitory interneurons and are thought to be responsible for maintaining the excitatory/inhibitory balance in the adult brain.