Pain in animals
[3] Therefore, this concept is often excluded in definitions of pain in animals, such as that provided by Zimmerman: "an aversive sensory experience caused by actual or potential injury that elicits protective motor and vegetative reactions, results in learned avoidance and may modify species-specific behaviour, including social behaviour.
[5] Overview of anatomy of the nervous system across animal kingdom indicates that, not only vertebrates, but also most invertebrates have the capacity to feel pain.
[7] This is the ability to detect noxious stimuli which evoke a reflex response that rapidly moves the entire animal, or the affected part of its body, away from the source of the stimulus.
Nociception usually involves the transmission of a signal along nerve fibers from the site of a noxious stimulus at the periphery to the spinal cord.
[7] Nerve impulses from nociceptors may reach the brain, where information about the stimulus (e.g. quality, location, and intensity), and effect (unpleasantness) are registered.
The authors claim this study is the first experimental evidence to support the argument that nociceptive sensitisation is actually an adaptive response to injuries.
If we stick a pin in a chimpanzee's finger and she rapidly withdraws her hand, we use argument-by-analogy and infer that like us, she felt pain.
It might be argued that consistency requires us to infer, also, that a cockroach experiences conscious pain when it writhes after being stuck with a pin.
The usual counter-argument is that although the physiology of consciousness is not understood, it clearly involves complex brain processes not present in relatively simple organisms.
[17] In his interactions with scientists and other veterinarians, Bernard Rollin was regularly asked to "prove" that animals are conscious, and to provide "scientifically acceptable" grounds for claiming that they feel pain.
[15][19] The ability to experience pain in an animal, or another human for that matter, cannot be determined directly but it may be inferred through analogous physiological and behavioral reactions.
[21] Nociceptive nerves, which preferentially detect (potential) injury-causing stimuli, have been identified in a variety of animals, including invertebrates.
The medicinal leech, Hirudo medicinalis, and sea slug are classic model systems for studying nociception.
[41][42] The presence of opioids in crustaceans has been interpreted as an indication that lobsters may be able to experience pain, although it has been claimed "at present no certain conclusion can be drawn".
It is practiced occasionally in medicine, as a diagnostic tool, and is regularly used in research into the basic science of pain, and in testing the efficacy of analgesics.
These physiological proxies are valued because their assessments are carried out by machines and do not rely on humans to determine the magnitude of the variable under study.
[72] Marian Stamp Dawkins defines "suffering" in laboratory animals as the experience of one of "a wide range of extremely unpleasant subjective (mental) states.
"[73] The U.S. National Research Council has published guidelines on the care and use of laboratory animals,[74] as well as a report on recognizing and alleviating pain in vertebrates.
In the U.S., researchers are not required to provide laboratory animals with pain relief if the administration of such drugs would interfere with their experiment.
The AWA, the Guide for the Care and Use of Laboratory Animals, and current Public Health Service policy all allow for the conduct of what are often called 'Category E' studies – experiments in which animals are expected to undergo significant pain or distress that will be left untreated because treatments for pain would be expected to interfere with the experiment.
"[79] Eleven countries have national classification systems of pain and suffering experienced by animals used in research: Australia, Canada, Finland, Germany, The Republic of Ireland, The Netherlands, New Zealand, Poland, Sweden, Switzerland, and the UK.
The US also has a mandated national scientific animal-use classification system, but it is markedly different from other countries in that it reports on whether pain-relieving drugs were required and/or used.
It should be remembered that in the UK system, many research projects (e.g. transgenic breeding, feeding distasteful food) will require a license under the Animals (Scientific Procedures) Act 1986, but may cause little or no pain or suffering.
"[83] The Guide states that the ability to recognize the symptoms of pain in different species is essential for the people caring for and using animals.
