Glutamate

Control of the CNS can be thought of in terms of a balance between ‘go’ (excitatory) and ‘stop’ (inhibitory) signals.^[1,2] If the sum of the ‘go’ signals that a neurone receives outweighs the sum of the ‘stop’ signals, then that neurone will exist in an active state, and will continue to signal to the downstream neurone.^[1,2] The main excitatory neurotransmitter in the CNS is glutamate; the main inhibitory neurotransmitter is gamma-aminobutyric acid (GABA).^[1]

Glutamate is arguably the most important neurochemical for normal brain function.^[1] Nearly all excitatory neurones in the CNS are glutamatergic – more than half of the neurones in the brain.^[1] It is noteworthy, though, that high concentrations of glutamate are neurotoxic.^[1] There are three types of receptor to which glutamate can bind (named after the agonists that activate them), each of which has slightly different properties:^[1]

• NMDA (N-methyl-d-aspartate)
• AMPA (α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate)
• kainate (kainic acid).

References:
[1] Purves D, Augustine GJ, Fitzpatrick D, et al. (eds). Neuroscience. 4th edition. Sinauer Associates ,2008.

[2] Stahl SM. Stahl’s Essential Psychopharmacology. Neuroscientific Basis and Practical Applications. 4th edition. © Cambridge University Press, 2013.