Glutamate

What it isThe principal excitatory neurotransmitter, acting at NMDA, AMPA, kainate and metabotropic receptors.

Why this oneEvery glutamatergic drug — ketamine, memantine, perampanel, lamotrigine — is positioned by which part of this system it touches.

What limits itExcitotoxicity from excess glutamate underlies seizure and ischemic injury, which is why blockade is neuroprotective in theory and disappointing in practice.