Glutamate (neurotransmitter)
In neuroscience, glutamate refers to the anion of glutamic acid in its role as a neurotransmitter: a chemical that nerve cells use to send signals to other cells. It is by a wide margin the most abundant excitatory neurotransmitter in the vertebrate nervous system. It is used by every major excitatory function in the vertebrate brain, accounting in total for well over 90% of the synaptic connections in the human brain. It also serves as the primary neurotransmitter for some localized brain regions, such as cerebellum granule cells.
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.