Central acute pain mechanisms.

This account will consider the events occurring in the spinal cord that give rise to acute pain. The transmission and control of acute pain is not immutable but subject to plasticity so that the dividing line between acute and chronic pain is difficult to draw. Very brief acute pain is transmitted in a simple way and rarely produces difficulties in treatment. The situation within the spinal cord changes if the stimulus continues. After only seconds of C-fibre stimulation, additional peptides are released from C fibres, and spinal N-methyl-D-aspartate (NMDA) receptor activation and nitric oxide production occur. Soon after, genes are induced in central neurones, and increases and decreases in diverse pharmacological systems involved in pain transmission and modulation occur over periods of only a few hours. This rapid plasticity has important implications for the pharmacological treatment of acute because both the level of pain transmission and pain modulation will be altering over time.