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.
Neuroligin
Expression of neuroligins may differ between species. Neuroligin 1 is expressed specifically in the CNS at excitatory synapses. In humans, expression of neuroligin 1 is low before birth and increases between postnatal days 1-8 and remains high through adulthood. This postnatal increase during active synaptogenesis corresponds to increased expression of postsynaptic density protein-95 (PSD-95). Neuroligin 2 is mainly concentrated at inhibitory synapses in the CNS, but in mice and humans it may also be expressed in tissues such as the pancreas, lung, endothelia, uterus and colon. Neuroligin 3 is expressed in CNS neurons, as well as a variety of glial cells in mice and rats and the brain, heart, skeletal muscle, placenta and pancreas in humans. Neuroligin 4X, found only in humans, is expressed in the heart, liver, skeletal muscle, pancreas and low levels in the brain. Neuroligin 5 (or 4Y), located on the Y chromosome, is only 19 amino acids different from neuroligin 4X. Neuroligin mRNA are present in human endothelial cells from large blood vessels and in Dorsal Root Ganglions.