The tail flick test is a test of the pain response in animals, similar to the

hot plate test The hot plate test is a test of the pain response in animals, similar to the tail flick test. Both hot plate and tail-flick methods are used generally for centrally acting analgesic, while peripherally acting drugs are ineffective in these tests ...

. It is used in basic

pain Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, ...

research and to measure the effectiveness of

analgesics An analgesic drug, also called simply an analgesic (American English), analgaesic (British English), pain reliever, or painkiller, is any member of the group of Pharmaceutical drug, drugs used to achieve relief from pain (that is, analgesia or p ...

, by observing the reaction to heat. It was first described by D'Amour and Smith in 1941.

Procedure

Most commonly, an intense light beam is focused on the animal's tail and a timer starts. When the animal flicks its tail, the timer stops and the recorded time (latency) is a measure of the

pain threshold The threshold of pain or pain threshold is the point along a curve of increasing perception of a stimulus at which pain begins to be felt. It is an entirely subjective phenomenon. A distinction must be maintained between the stimulus (an externa ...

. Alternate methods can be used to apply

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

, such as immersion in hot water. Alternately, a dolorimeter with a resistance wire with a constant heat flow may be used. For the tail flick test, the wire is attached to the tail of the organism, and the wire applies heat to the tail. The researcher then records the latency to tail flick.

Applications

Researchers testing the effectiveness of drugs on the pain threshold often use the tail flick test to measure the extent to which the drug being tested has reduced the amount of pain felt by the model organism. Both laboratory mice and rats are a common model organism for these tests. These

rodents Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...

are usually given

, which are responsible for weakening the response to pain. Under these weakened responses to pain, with effectiveness often peaking about 30 minutes after ingestion, researchers test the effectiveness of the drugs by exposing the tail to constant heat and measuring how long it takes to flick, signaling its response to the pain.

Naloxone Naloxone, sold under the brand names Narcan (4 mg) and Kloxxado (8 mg) among others, is a medication used to reverse or reduce the effects of opioids. It is commonly used to counter decreased breathing in opioid overdose. Effects begin withi ...

and

naltrexone Naltrexone, sold under the brand name Revia among others, is a medication primarily used to manage alcohol or opioid use disorder by reducing cravings and feelings of euphoria associated with substance use disorder. It has also been found to ...

, two opioid antagonists, have been used to study pain sensitivity in relation to exercise in mice. Experimental tests of the tail flick testing method showed that the temperature of the skin of the tail plays a major role in the critical temperature, i.e., the temperature at which the tail flicks in response to pain. Researchers found that if the tail has been exposed to a cooler temperatures before the test, then the critical temperature decreases. Through use of the tail flick test, researchers have found that genetics play a role in pain sensation and the effectiveness of analgesics. A mouse of one genetic line may be more or less tolerant of pain than a mouse of another genetic line. Also, a mouse of one genetic line may experience a higher or lower effectiveness of an analgesic than a mouse of another genetic line. Using this test, researchers can also begin to identify genes that play a role in pain sensation. For example, the ''Calca'' gene (se
WikiGenes CALCA
is primarily responsible for the variability in thermal (heat)

nociception Nociception (also nocioception, from Latin ''nocere'' 'to harm or hurt') is the sensory nervous system's process of encoding noxious stimuli. It deals with a series of events and processes required for an organism to receive a painful stimulus, ...

. The ''Sprawling'' mutation (se
WikiGenes Swl
resulted in a moderate sensory

neuropathy Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or or ...

but the mutation did not affect nociceptive modality or motor function in the mice. The mice with the Sprawling mutation were unable to sense the pain, but their other sensory functions were unaffected.

Limitations

The tail flick test is one test to measure heat-induced pain in animals. This reflexive response is an indicator of pain sensitivity in an organism and reduction of pain sensitivity produced by analgesics. Limitations of this test include: the need for more research with

murine The Old World rats and mice, part of the subfamily Murinae in the family Muridae, comprise at least 519 species. Members of this subfamily are called murines. In terms of species richness, this subfamily is larger than all mammal families ex ...

subjects, and determining the validity of applying observed pain responses from animals to humans. Also, researchers have found that skin temperature can significantly affect the results of the tail flick test and it is important to consider this effect when performing the test. Lastly, many thermal tests do not distinguish between opioid agonists and mixed agonist-antagonists, and consequently a tail flick test for mice using cold water in place of heat has been developed to allow that distinction.

References

External links

Tail flick test demonstration

Institutional Animal Care and Use Committee

{{pain Pain scales Animal testing techniques Laboratory techniques