An overview of the physiology of pain for the veterinarian.

The degree of depolarisation in a nociceptor created by a painful stimulus is influenced by numerous substances, including nerve growth factor, prostanoids, substance P and a range of inflammatory mediators. In the dorsal horn of the spinal cord, the frequency of an action potential may be increased or decreased by neurotransmitters, including substance P, calcitonin gene-related peptide, galanin, γ-amino butyric acid and glycine, as well as pro-inflammatory substances. The perception of pain can also be altered in the brain, where the sensation of pain is cognitively integrated. A range of analgesic drugs with different mechanisms of action are available for selection by veterinarians for pain relief.