Visceral pain in humans: lessons from animals.

Acute and persistent neuropathic and inflammatory injuries of healthy animals have contributed importantly to our current understanding of nociception and pain. Studies have differentiated somatic from visceral nociceptive input, and elucidated the pathways of transduction, transmission, perception, and modulation of the input. Other animal studies have identified important genetic and environmental influences on responses to nociception. Studies of naturally occurring visceral pain syndromes in animals also have added to our understanding of comparable syndromes in humans. Because of the aversive nature of pain, use of healthy animals to study pain in the service of other animals and humans is a decision to be taken carefully, and carries with it the responsibility of treating the animals as humanely as possible.