NMDA (N-methyl-D-aspartate) antagonists have an antihyperalgesic rather than an analgesic effect in the spinal cord. AMPA = α-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid; CGRP = calcitonin gene-related peptide; NK = neurokinin; NMDA = N-methyl-D-aspartate.