Control of the CNS can be thought of in terms of a balance between ‘go’ (excitatory) and ‘stop’ (inhibitory) signals.[Purves et al., 2008; Stahl, 2013] 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.[Purves et al., 2008; Stahl, 2013] The main excitatory neurotransmitter in the CNS is glutamate; the main inhibitory neurotransmitter is gamma-aminobutyric acid (GABA).[Purves et al., 2008]
Glutamate is arguably the most important neurochemical for normal brain function.[Purves et al., 2008] Nearly all excitatory neurones in the CNS are glutamatergic – more than half of the neurones in the brain.[Purves et al., 2008] It is noteworthy, though, that high concentrations of glutamate are neurotoxic.[Purves et al., 2008] 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:[Purves et al., 2008]
- NMDA (N-methyl-d-aspartate)
- AMPA (α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate)
- kainate (kainic acid).
References:
Purves D, Augustine GJ, Fitzpatrick D, et al. (eds). Neuroscience. 4th edition. Sinauer Associates, 2008.
Stahl SM. Stahl’s Essential Psychopharmacology. Neuroscientific Basis and Practical Applications. 4th edition. © Cambridge University Press, 2013.