Research Tools for the Measurement of Pain and Nociception

Abstract

Simple SummaryPain is an integral aspect of many diseases and it is important to be able to measure it in the clinic so that the progression of disease and the animal’s response to treatment can be monitored. When research into pain is undertaken, it is also important to be able to measure the pain, but this time the aim is to provide meaningful results that will further our understanding of the mechanisms of pain or how it can be better treated. This change in emphasis between clinical and research measurement of pain means that the advantages and disadvantages of the many ways in which pain can be measured influence the choice of the most suitable technique and the way in which it is used. It is important to carefully select the most appropriate methodologies so that the data generated are relevant to the hypotheses being tested.AbstractThere are many ways in which pain in animals can be measured and these are based on a variety of phenomena that are related to either the perception of pain or alterations in physical or behavioural features of the animal that are caused by that pain. The features of pain that are most useful for assessment in clinical environments are not always the best to use in a research environment. This is because the aims and objectives of the two settings are different and so whilst particular techniques will have the same advantages and disadvantages in clinical and research environments, these considerations may become more or less of a drawback when moving from one environment to the other. For example, a simple descriptive pain scale has a number of advantages and disadvantages. In a clinical setting the advantages are very useful and the disadvantages are less relevant, but in a research environment the advantages are less important and the disadvantages can become more problematic. This paper will focus on pain in the research environment and after a brief revision of the pathophysiological systems involved will attempt to outline the major advantages and disadvantages of the more commonly used measurement techniques that have been used for studies in the area of pain perception and analgesia. This paper is expanded from a conference proceedings paper presented at the International Veterinary Emergency and Critical Care Conference in San Diego, USA.

Castration of Dogs Using Local Anesthesia After Sedating With Xylazine and Subanesthetic Doses of Ketamine

“…Heart and respiratory rates and blood pressure did not increase during surgical manipulations in this study. These autonomic responses are modulated in the brain stem in response to noxious stimulation and are not necessarily evidence of pain, because nociception does not become interpreted as pain until noxious signals reach the cerebral cortex (13). Lack of an autonomic response to noxious stimulation is evidence that nociceptive inputs never reached the spinal tracts that carry nociceptive signals to the brain, where they could be interpreted as pain.…”

Effects of noxious stimuli on the electroencephalogram of anaesthetised chickens (Gallus gallus domesticus)

“…For example, transient increases in both heart rate and blood pressure were observed in chickens following feather removal; however, there was considerable individual variation in heart rate responses [ 3 ]. Despite their relative ease of use, a significant limitation of these measures is that they are not specific to nociception [ 18 ] and may also be influenced by non-painful stressors such as exercise, anxiety, handling and restraint [ 18 , 19 ].…”

The Neuroimmune Interface and Chronic Pain Through the Lens of Production Animals

“…Quantitative sensory testing (QST) is commonly used in pain research and involves testing an animal’s response to a ramped mechanical, thermal, or electrical stimulus and recording the intensity of the stimulus applied ( Johnson, 2016 ; Taylor, 2020 ). Quantitative sensory testing is useful for assessing the development of hyperalgesia and allodynia in response to a noxious stimulus, and it is also used to investigate resolution or reduction in nociceptive thresholds over time or with interventions, such as analgesic agents.…”

“…Ideally, the research environment should be strictly controlled to obtain the most reliable and repeatable results from QST. This involves minimizing distractions such as noise and unfamiliar smells, animals or people, allowing subjects time to acclimatize to their environment, and maintaining a regular ambient temperature ( Johnson, 2016 ). Distraction or external threat, particularly in prey animals, can alter response to stimuli; generally leading to reduced focal pain sensitivity which equates to increased nociceptive thresholds ( Johnson, 2016 ; Taylor, 2020 ).…”

“…This involves minimizing distractions such as noise and unfamiliar smells, animals or people, allowing subjects time to acclimatize to their environment, and maintaining a regular ambient temperature ( Johnson, 2016 ). Distraction or external threat, particularly in prey animals, can alter response to stimuli; generally leading to reduced focal pain sensitivity which equates to increased nociceptive thresholds ( Johnson, 2016 ; Taylor, 2020 ). When testing livestock, it is often necessary to restrain them in unfamiliar environments and it is usually not economically feasible or ethical to manage them in stringently controlled research environments, as is possible with rodents.…”