Expansion
Glutamate excites, GABA inhibits, and the monoamines modulate
Expansion
Fast transmission
- Glutamate: the main excitatory transmitter. Acts on AMPA and NMDA receptors; excess causes excitotoxicity in stroke. Ketamine and memantine are NMDA antagonists
- GABA: the main inhibitory transmitter. GABA-A is a chloride channel, the target of benzodiazepines, barbiturates, alcohol and propofol
- Glycine: inhibitory, mainly in the spinal cord; blocked by strychnine and by tetanus toxin
Modulatory monoamines
- Dopamine: reward, movement, prolactin inhibition. Four pathways, which is why antipsychotics cause extrapyramidal effects and hyperprolactinaemia
- Noradrenaline: arousal, attention, mood
- Serotonin: mood, sleep, appetite, pain modulation
- Acetylcholine: arousal, memory. Lost in Alzheimer disease, hence anticholinesterases
Others: histamine (arousal, hence sedation with antihistamines), endogenous opioids, substance P and nitric oxide.
Most psychiatric and anaesthetic drugs act by shifting the balance between glutamate and GABA or by modulating monoamine availability.