NMDA is
an excitatory amino acid. It can potentiate the neuronal
firing at lower levels of stimulus. Long-term or permanent
changes may occur in the pain receptor as
a result of ongoing noxious stimuli. One of the effects
of continual NMDA receptor activation is long-term potentiation.
This is usually a product of long-term pain
input from more than one pain afferent exceeding
a certain threshold