In animals, the lack of verbal communication not only confounds the diagnosis and
characterisation of the experience of pain, but also challenges the evaluation of the
analgesic therapy. As animals possess the same neuronal pathways and neurotrans-
mitter receptors as humans, it seems reasonable to expect that their perceptions of
painful stimuli will be similar, and this is a basis for the use of laboratory animals
for screening of analgesics for human use. However, as the evaluation in the
laboratory animal tests is based mainly on behavioural responses, and although
some physiological responses do occur, it is often difficult to separate these from
stress responses.
The use of behavioural responses to evaluate analgesics in a range of species is
complicated by the fact that different species show different behaviours to a similar
pain stimulus, and different pain stimuli produce different pain responses in the
same species. Thus behaviours may be species- and pain-specific and this can
complicate analgesic evaluation. As most animals possess similar neuronal
mechanisms to humans for pain perception, it is not surprising that the standard
human pain control strategies can be applied to animals. For instance, local
anaesthetics, opioids, non-steroidal anti-inflammatory drugs (NSAIDs), as well as
other analgesics used in humans are all found to be effective for animal use.
Differences in metabolism and distribution between various species, as well as
financial considerations in larger animals can affect efficacy and thus limit their use.
In addition, the use of any drug in a species that may be intended for human
consumption will be limited by residue considerations.
The treatment of pain in animals presents many challenges, but the increasing
public concerns regarding animal welfare will ensure that studies into the nature
and control of animal pain will continue to have a high profile.
KeywordsPainPain evaluationPain perceptionPain recognitionAnalgesic
agents
1 Introduction
The concept of pain in animals has long been a source of discussion and debate. The
views of Descartes (Haldane and Ross 1989 ) and Bentham (Bowring 1962 ) repre-
sent the philosophical approaches to pain, and it may be argued that this is one area
in which philosophy and science most significantly overlap. As pain is a totally
subjective experience, and it is not even possible to accurately establish if two
human beings are experiencing a common level or depth of pain, the extrapolation
to animal species is clearly a much greater challenge. What is clear is that animals
consider some experiences to be noxious and they exhibit an aversive response;
thus the concept of “nocioception” was developed (Sherrington 1906 ) to allow that
animals may develop an aversive response to a noxious stimulus, without getting
into the vexatious question of the nature of the experience of pain as applied to
human understanding.
160 A. Livingston